OPALINE BIOGENIC SILICA/EXPANDED PERLITE COMPOSITE PRODUCTS
20170368486 · 2017-12-28
Assignee
Inventors
Cpc classification
C02F1/286
CHEMISTRY; METALLURGY
B01D37/02
PERFORMING OPERATIONS; TRANSPORTING
B01D39/2075
PERFORMING OPERATIONS; TRANSPORTING
B01D39/06
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
A powdered composite filtration medium includes composite particles that include at least one diatomite particle and at least one expanded perlite particle sintered together. The composite powdered filtration medium may include from about 7 wt % to about 90 wt % diatomite, from about 93 wt % to about 10 wt % expanded perlite. Less than about 1% total crystalline silica may be present in the medium. The medium may have a permeability of at least 0.25 darcy. The diatomite and expanded perlite may be sintered or calcined with or without a fluxing agent.
Claims
1: A powdered composite filtration medium comprising: from about 7 wt % to about 90 wt % diatomite, and from about 93 wt % to about 10 wt % expanded perlite, wherein less than about 1 wt % total crystalline silica is present in the powdered composite filtration medium and the powdered composite filtration medium has a permeability from 0.25 darcy to about 20 darcy, wherein at least a portion of the powdered composite filtration medium is in the form of composite particles, each composite particle including at least one diatomite particle and at least one expanded perlite particle sintered together.
2: The powdered composite filtration medium of claim 1, wherein less than about 0.3 wt % boron, less than about 0.1 wt % quartz and less than about 0.1 wt % cristobalite are present in the powdered composite filtration medium.
3-5. (canceled)
6: The powdered composite filtration medium of claim 1, wherein the composite particles are formed by flux-calcination with at least one fluxing agent, wherein the at least one fluxing agent is a salt of an alkali metal and is added at a dosage level equal to about 0.1 wt % to 10 wt % of the combined weight of the diatomite and the expanded perlite, wherein the alkali metal salt is an alkali metal halide, an alkali metal carbonate, an alkali metal silicate or an alkali metal borate.
7-8. (canceled)
9: The powdered composite filtration medium of claim 1, wherein the powdered composite filtration medium has less than about 5 ppm of soluble arsenic, or less than about 180 ppm of soluble aluminum, or less than about 500 ppm of soluble calcium, or less than about 80 ppm of soluble iron, or less than about 150 ppm of soluble boron, each as measured by the EBC method.
10-13. (canceled)
14: The powdered composite filtration medium of claim 1, wherein the filtration medium has a total floater content of less than about 1 ml/g and a persistent floater content of less than about 0.5 ml/g.
15: A method of manufacturing a powdered composite filtration medium, the method comprising: selecting a diatomite powder and an expanded perlite powder for a combined feed and selecting a diatomite content and an expanded perlite content of the combined feed so that the combined feed has a diatomite content from about 7 wt % to about 90 wt % and a crystalline silica content of less than 0.1 wt %, and sintering the combined feed at a temperature ranging from about 704° C. to about 1038° C. to form the powdered composite filtration medium.
16: The method of claim 15 further comprising adding at least one fluxing agent to the combined feed prior to the sintering at about 0.1 wt % to about 10 wt % of the combined feed, wherein the at least one fluxing agent is a salt of an alkali metal, wherein the salt of an alkali metal is an alkali metal halide, an alkali metal carbonate, an alkali metal borate or an alkali metal silicate.
17-18. (canceled)
19: The method of claim 15, wherein the combined feed is free of boric acid fluxing agents.
20-23. (canceled)
24: The method of claim 15 further including acid-washing the powdered composite filtration medium.
25: A powdered composite filtration medium comprising: from about 7 wt % to about 90 wt % diatomite, and from about 93 wt % to about 10 wt % expanded perlite, wherein less than about 0.1 wt % cristobalite, less than about 0.1 wt % quartz, and from about 0.1 wt % to about 17.5 wt % combined opal C and opal CT are present in the powdered composite filtration medium, wherein at least a portion of the powdered composite filtration medium is in the form of composite particles, each composite particle including at least one diatomite particle and at least one expanded perlite particle sintered together.
26: The powdered composite filtration medium of claim 25, wherein less than 0.1 wt % total crystalline silica is present in the powdered composite filtration medium.
27: The powdered composite filtration medium of claim 25, wherein the powdered composite filtration medium has a permeability from 0.25 darcy to about 20 darcy.
28: The powdered composite filtration medium of claim 25, wherein the powdered composite filtration medium has less than about 5 ppm of soluble arsenic, less than about 180 ppm of soluble aluminum, less than about 500 ppm of soluble calcium, and less than about 80 ppm of soluble iron as measured by the EBC method.
29-30. (canceled)
31: The powdered composite filtration medium of claim 1, wherein the powdered composite filtration medium is a regenerated powdered composite filtration medium previously used in clarification or other processing of a liquid, wherein further the powdered composite filtration medium was regenerated by physical, chemical or thermal processes.
32: A method for regenerating the powdered composite filtration medium of claim 1 following use in a liquid processing application, the method comprising regenerating the powdered composite filtration medium, wherein the regenerating does not increase the total crystalline silica wt % present in the powdered composite filtration medium.
33. (canceled)
34: The powdered composite filtration medium of claim 1 further comprising an adsorbent, wherein the adsorbent is selected from the group consisting of silica gel, precipitated silica, fumed silica, activated alumina, activated bleach clay, natural zeolite, synthetic zeolite and activated carbon, wherein the adsorbent is intimately bound to the composite particles of the powdered composite filtration medium.
35: The powdered composite filtration medium of claim 1, wherein less than 0.1 wt % cristobalite, and from about 0.1 wt % to about 17.5 wt % combined opal C and opal CT are present in the powdered composite filtration medium.
36: The powdered composite filtration medium of claim 1 wherein less than 0.1 wt % crystalline silica, and from about 0.1 wt % to about 17.5 wt % combined opal C and Opal CT are present in the powdered composite filtration medium.
37: The powdered composite filtration medium of claim 25, wherein the powdered composite filtration medium is a regenerated powdered composite filtration medium previously used in clarification or other processing of a liquid, wherein further the powdered composite filtration medium was regenerated by physical, chemical or thermal processes.
38: The powdered composite filtration medium of claim 31, wherein less than 0.1 wt % crystalline silica is present in the regenerated powdered composite filtration medium.
39: The powdered composite filtration medium of claim 37, wherein less than 0.1 wt % crystalline silica is present in the regenerated powdered composite filtration medium.
40: A method for regenerating the powdered composite filtration medium of claim 25 following use in a liquid processing application, the method comprising regenerating the powdered composite filtration medium, wherein the regenerating does not increase the total crystalline silica wt % of the powdered composite filtration medium.
41: The powdered composite filtration medium of claim 25 further comprising an adsorbent, wherein the adsorbent is selected from the group consisting of silica gel, precipitated silica, fumed silica, activated alumina, activated bleach clay, natural zeolite, synthetic zeolite and activated carbon, wherein the adsorbent is intimately bound to the composite particles of the powdered composite filtration medium.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] For a more complete understanding of the disclosed methods and filtration media, reference should be made to the embodiments illustrated in greater detail on the accompanying drawings, wherein:
[0061]
[0062]
[0063]
[0064]
[0065]
[0066]
[0067]
DETAILED DESCRIPTION
[0068] In the examples of this disclosure, feed materials used for making powdered diatomite/expanded perlite composite filtration media include diatomite from ores mined in Nevada and Oregon and expanded perlite products available from EP Minerals (Celatom® CP-600P, CP-1400P and CP-4000P), which were obtained from ores mined in northern Nevada. Table I shows the major element compositions of the diatomite feed materials as analyzed by the x-ray fluorescence (XRF) method and normalized to the ignited basis. Also included in Table I are the loss of ignition (LOI) results and the quartz contents by the x-ray diffraction (XRD) method. Each feed diatomite contained 0.2 wt % or less quartz. XRD scans of the diatomite feed materials show non-detectable level of cristobalite and also show the presence of a small amount of feldspars. The major element compositions of the three expanded perlite products are also listed in Table I. Among the diatomite feed materials, Diatomite A, A1 and B were all of so-called “natural”. i.e., uncalcined. Among those, Diatomite A1 was prepared from Diatomite A by wet gravity separation to remove a portion of heavier particles at a yield of 84 wt %. Diatomite C was a flux-calcined diatomite containing no cristobalite but 21.5 wt % opal-C. Samples of the expanded perlite products used in this disclosure. Celatom® CP-600P. CP-1400P and CP-4000P, had permeabilities of 0.84, 1.9 and 2.7 darcy and wet bulk densities of 12.7, 9.1 and 8.2 lbs/ft.sup.3 (0.20, 0.15 and 0.13 g/cm.sup.3), respectively. Any fluxing agents used were all milled and passed through a 325-mesh sieve. The boron content in selected feed materials (Table I) was analyzed by dissolving a powder sample in a mixture of hydrofluoric acid (HF) and nitric acid (HNO.sub.3) and analyzing by the inductively-coupled plasma optical emission spectroscopy (ICP-OES).
TABLE-US-00001 TABLE I Compositions of Diatomite and Perlite Feed Materials Opal SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O Fe.sub.2O.sub.3 As S B LOI Qz.sup.1 Crist.sup.2 TCS.sup.3 C/CT Sample wt % wt % wt % wt % wt % wt % wt % ppm ppm ppm wt % wt % wt % wt % wt % DEA 92.7 3.2 0.87 0.35 0.46 0.36 1.73 14 123 66 7.4 0.15 ND 0.15 ND DE A1 94.1 2.7 0.65 0.32 0.32 0.22 1.51 10 59 N/A 5.4 <0.1 ND <0.1 ND DE B 87.4 6.9 0.95 0.64 0.30 0.21 3.05 12 157 N/A 4.7 0.2 ND 0.2 ND DE C 88.3 4.8 0.5 0.3 2.5 0.2 2.9 6 117 N/A 0.1 <0.1 ND <0.1 21.5 Perlite 76.1 13.4 0.64 0.13 4.3 4.5 0.59 20 6 49 ND <0.1 ND <0.1 ND DE-Diatomite; N/A-Not analyzed; .sup.1Quartz; .sup.2Cristobalite; .sup.3Total crystalline silica; ND-non-detectable.
[0069] Calcination or sintering took place in an electrical muffle furnace. Each feed was prepared by mixing a diatomite (powder) and an expanded perlite (powder), according to the desired feed ratio, with or without a fluxing agent, in a plastic container placed in a paint shaker. The mixed feed was calcined at the desired temperature (for example, between about 704° C. to about 1038° C.) for about 30 to about 40 minutes in a ceramic crucible. The calcined product, upon cooling to ambient temperature, was dispersed by sifting through 40- and 70-mesh sieves and shaking with several small ceramic balls. In the cases of high-permeability composite samples made from Diatomite C, the dispersion was done by hand brushing through a 30-mesh sieve. The dispersed product (powdered composite filtration medium) comprises composite particles, each composite particle including at least one diatomite particle and at least one expanded perlite particle sintered together. In an embodiment, the product may contain opaline biogenic silica (e.g., opal-A, opal-CT or opal-C) intimately and directly bound to expanded perlite (wherein the opaline biogenic silica and the particles of expanded perlite are a coherent mass (i.e., are intimately bound)). The dispersed product was analyzed for permeability and wet bulk density (WBD), crystallinity by XRD scan, floater content, and for soluble metal contents according to the methods to be described below. As mentioned above, the inventors made use of the method of Lenz, et al. in distinguishing between the opal-CT/opal-C and cristobalite contents of the samples.
[0070] As disclosed in Lenz et al., to determine whether a diatomite sample contains cristobalite or opal-C/CT involves a number of steps. First, a determination is made as to whether the sample contains water of hydration via high temperature loss on ignition (LOI) testing. Opals always contain some water existing as internal or attached silane groups, while cristobalite is anhydrous. Thus, the sample (or a portion of the sample) may be analyzed for the presence of residual hydration water (and the potential presence of opaline silica) by an LOI test. During the LOI test, the sample (or portion of) is calcined at a high temperature (for example, 982° C., 1000° C., or the like) for a sufficient time (at least 1 hour) so that chemically-bound water has a chance to disassociate and volatilize. Precise measurement of the tested sample mass (or tested portion mass) before and after this treatment allows quantification of the water of hydration. Tested samples that are determined to have contained over 0.1% residual hydration water via the LOI test have the potential to contain opal-C/CT.
[0071] Second, bulk powder x-ray diffraction is performed on composite samples, and the resulting diffraction pattern is used to detect the potential presence of quartz, cristobalite and opaline silica of opal-C and opal-CT phases. All of the bulk powder XRD work detailed herein was performed using a Siemens D5000 diffractometer controlled with MDI Datascan5 software, with CuKα radiation (λ=1.54056 Å), sample spinning, graphite monochromator, and scintillation detector. Power settings were at 50 KV and 36 mA, with step size at 0.04° and 4 seconds per step. JADE (2010) software was used for analyses of XRD scans. Sample preparation included SPEX® milling in zirconia vials. Selected samples showing a detectable peak near 220 2θ are examined against the full pattern of cristobalite to determine whether it is cristobalite or opaline silica of opal-C or CT based on the peak centroid location and FWHM and the development of secondary peaks, especially the peak near 28.5° 2θ. Differentiation between opal-C and opal-CT is not attempted in this disclosure due to the low concentrations in the products of this disclosure and transitional natural of these two phases. When the following conditions are all met the phase presented by the 22° 2θ peak (4-Å phase) is determined as opal-C/CT: a) calculated d-spacing from 220 2θ peak centroid location (according to Bragg law, λ=2d sin θ) is 4.05 Å or higher, b) FWHM of the 22° 2θ peak is higher than 0.2° 2θ, and c) peak(s) near 28.50 and 31.50 2θ are missing or poorly developed. Lower d-spacing, lower FWHM and well developed cristobalite secondary peaks are indicators of potential presence of cristobalite.
[0072] If the pattern is obviously indicative of opal-C (or opal-CT), then further analysis is not required. If the diffraction pattern is questionable, then a second XRD analysis is needed, this time on a split of the sample with a known amount of cristobalite standard reference material (i.e. National Institute of Standards and Technology (NIST) Standard Reference Material 1879A) added to it (a “spiked sample”). To confirm the absence of cristobalite within the spiked sample, an XRD analysis is run on the spiked sample. The original un-spiked sample diffraction pattern is compared with the spiked sample pattern. If the spiked sample pattern simply increases the intensity of the primary and secondary peaks but does not show a position shift or show additional peaks, then the original sample most likely contains cristobalite. If the primary peak shifts and becomes sharper (or resolves into two separate peaks), and secondary peaks appear or become much better defined, then opal-C/CT, and not cristobalite, is present in the original sample. As described above, the cristobalite spike significantly modifies the diffraction pattern if the sample comprises opal-C/CT but only results in increased peak intensity if the sample comprises cristobalite.
[0073] It has been demonstrated that calcination of the expanded perlite materials used to produce the samples disclosed in this patent application, with or without a fluxing agent, does not form any phase with an x-ray diffraction peak near 220 2θ or 4-Å phase. The formation of the 220 2θ peaks in a diatomite-perlite composite relates to the presence of diatomite. Factors promoting the 4-Å phase formation in the composite filter media are diatomite to perlite ratio, fluxing agent and dosage and calcination temperature. Products produced under the combinations of extreme conditions (highest diatomite to perlite ratios, highest dosages of fluxing agent and highest calcination temperatures) have shown highest contents of 4-Å phases among the respective groups of similar formulation. These products are selected for detailed XRD pattern analysis to determine the nature of the 4-Å phases. A determination confirming the presence of opal-C/CT and excluding cristobalite is also applied to other composite samples made with the same or lower diatomite-to-perlite ratios with the same fluxing agent of the same or lower dosages at the same or lower temperatures.
[0074] To quantify the opal-C/CT content of a diatomite sample can be complicated as its diffraction pattern is a combination of broad peaks and amorphous background, and diatomite products often contain other x-ray amorphous phases in addition to opal. After either cristobalite or opal-C/CT is identified for a sample, the respective quantification is determined from the area of the near 22° 2θ peak of the XRD scan, based on calibration by cristobalite standard reference material (NIST 1879A) in a natural diatomite (opal-A) matrix. For opal-C/CT, it may not be the exact mass quantification but an equivalent mass concentration referenced to cristobalite. An estimate of the quantity can be obtained by treating the opal-C/CT peaks of the XRD scan as if they are cristobalite and quantifying against the cristobalite standards. This method, called the XRD Method in Lenz et al., will usually underestimate the opal-C/CT content but is effective for a number of purposes, such as manufacturing quality control. A more exact measure can be obtained by heating the sample at very high temperature (1050° C.) for an extended period (24 hours). This converts opaline phases to cristobalite (reduces amorphous background component), and then the cristobalite can be quantified against the standards to give a more absolute estimate of original opal-C/CT content.
[0075] In addition, it is well known that feldspars have secondary peaks in their XRD scan patterns that are very close to the 22.02° 2θ primary peak of cristobalite, which interferes with cristobalite or opal-C/CT quantification. For diatomite products made from an ore containing a small amount of feldspars, this interference becomes significant when the nominal content of cristobalite or opal-C/CT is low, i.e., <1 wt %. To correct for this interference, a diatomite used in composite preparation was also used to prepare a blank sample with no cristobalite (˜0 wt %) and a 0.1 wt % cristobalite standard sample. Multiple XRD scans were performed on the blank and standard samples. Using the XRD scan patterns of the blank sample, the x-ray diffraction counts in both primary (N.sub.fp-b) and secondary peaks (N.sub.fs-b) of feldspars were taken from which a count ratio between the peaks are calculated (R=N.sub.fs-b/N.sub.fp-b). An average ratio (R.sub.avg) is produced from multiple scans of the same blank sample. This is easily done without interference from cristobalite, which is absent in the blank sample. From the XRD scans on the standard sample (0.1 wt % cristobalite), the counts at both the primary peak for feldspars (N.sub.fp-std) and the overlapping primary peak for cristobalite/secondary peak for feldspars (N.sub.overlap-std) were collected. Because the average ratio for feldspars (R.sub.avg) applies to both the blank and standard samples, the counts at the secondary peak (N.sub.fs-std) for feldspars in the standard sample contributing to the overlapping peak may be calculated by multiplying the average ratio (R.sub.avg) by the primary counts (N.sub.fp-std) for feldspars in the standard sample (N.sub.fs-std=R.sub.avg.Math.N.sub.fp-std). The net cristobalite primary counts (N.sub.cp-std) in the standard sample are calculated by deducting those attributable to the secondary counts of the feldspars (N.sub.fs-std) in the standard sample from the total counts for the overlapping primary cristobalite peak/secondary feldspar peak (N.sub.cp-std=N.sub.overlap-std−N.sub.fs-std). Thus, average ratio (R.sub.avg) can be used to calculate the corrected or net cristobalite or opal-C/CT content of the composite samples from the XRD scans:
C.sub.sample wt %=C.sub.std(wt %).Math.(N.sub.overlap-sample−R.sub.avg.Math.N.sub.fp-sample)/N.sub.cp-std
or,
C.sub.sample wt %=C.sub.std(wt %).Math.(N.sub.overlap-sample−R.sub.avg.Math.N.sub.fp-sample)/(N.sub.overlap-std−R.sub.avg.Math.N.sub.fp-std)
[0076] In this disclosure, the permeabilities of the powdered filtration media disclosed below were determined using an automated permeability meter developed by EP Minerals and described in principle in U.S. Pat. No. 5,878,374. The wet bulk densities of powdered filtration media disclosed below were determined at the same time as permeability during the permeability meter as described above.
[0077] In this disclosure, the EBC extraction method for soluble iron is used to determine the contents of soluble substances including, in addition to iron, calcium, aluminum, arsenic, and boron and the solubility of each substance is described as EBC soluble iron, calcium, aluminum, arsenic, and boron, respectively. The EBC soluble metal test consists of suspending a sample (2.5% slurry concentration) for two hours at ambient temperature in a 1% solution of potassium hydrogen phthalate (pH of 4), filtering the suspension, and then analyzing the filtrate for metal contents using the atomic absorption (AA) or the inductively-coupled plasma (ICP) spectrophotometers. In this disclosure, the extracted arsenic was analyzed by the graphite furnace atomic absorption spectroscopy (GFAA) and iron, calcium, aluminum and boron by the inductively-coupled plasma optical emission spectroscopy (ICP-OES).
[0078] In this disclosure, the floater content of an expanded perlite or a composite of diatomite and expanded perlite is expressed in two ways: volume fraction or volume per unit mass of a powder. A 5-g powder sample may be mixed in 250-ml water in a 250-ml graduated cylinder by inverting several times, followed by standing to allow floaters to rise to water surface and non-floaters to settle to the bottom of the cylinder. After sixty minutes, the volumes of both floaters and the “sinkers” are read from the graduation, and the “total floater” volume fraction is calculated from the floater volume divided by the total volume of floaters and sinkers. Then, the floater layer is gently stirred and the graduated cylinder is let stand for another 30 minutes. A second set of floater and sinker volumes are read from the graduation, from which a second floater volume fraction is calculated. Those initial floaters that fall or drop to the bottom after a gentle stirring are weak floaters, meaning that these are not fully sealed perlite bubbles and can be easily incorporated into slurry with mild agitation. The remaining floaters are “persistent” floaters, which are harder to incorporate into a slurry, may accumulate in process vessels and may not participate in the filtration process.
Examples
[0079] Examples of composite filter media made under various conditions according to this disclosure are listed in the Tables II to XI, and Tables XIII to XIV. All the products contain less than 0.1 wt % or no-detectable amount of quartz. Products made under combined high levels of diatomite-to-perlite ratios, dosages of fluxing agents and calcination temperatures were selected for detailed XRD pattern analysis, and the results are listed in Table II. The XRD pattern of the product of Example 10, showing the most pronounced 22° 2θ peak among the composite samples listed in Tables II to VII, is presented in
TABLE-US-00002 TABLE II XRD Analysis on Selected Composite Samples 22° 2θ Peak 28.5° Fluxing agent Temp. d FWHM 2θ LOI 4-Å phase Ex. No. DE* wt % Type wt % ° C. Å ° 2θ Peak wt % Phase wt % 74 75 None 0 982 4.08 0.33 no 0.43 Opal-C/CT <0.1 48 50 Na.sub.2CO.sub.3 1.0 982 4.06 0.30 no 0.80 Opal-C/CT 0.5 21 50 Na.sub.2CO.sub.3 2.0 927 4.03 0.34 poor 1.1 Cristobalite 1.2 29 25 Na.sub.2CO.sub.3 2.0 927 4.05 0.29 poor 1.2 Opal-C/CT 0.5 10 75 Na.sub.2CO.sub.3 5.0 871 4.06 0.42 poor 0.17 Opal-C/CT 17.5 13 50 Na.sub.2CO.sub.3 5.0 871 4.06 0.40 poor 0.19 Opal-C/CT 13.3 16 25 Na.sub.2CO.sub.3 5.0 871 4.08 0.40 poor 0.29 Opal-C/CT 5.8 38 50 Na.sub.2CO.sub.3 7.0 760 4.02 0.35 poor 0.63 Cristobalite 2.9 37 50 Na.sub.2CO.sub.3 7.0 704 4.06 0.31 poor 1.2 Opal-C/CT 2.3 41 25 Na.sub.2CO.sub.3 7.0 760 4.06 0.34 no 0.64 Opal-C/CT 1.3 1 50 H.sub.3BO.sub.3 3.0 816 4.06 0.29 no 0.99 Opal-C/CT 0.1 76 50 K.sub.2CO.sub.3 5.0 816 4.05 0.33 no 1.4 Opal-C/CT 1.2 79 50 K.sub.2SiO.sub.3 5.0 816 4.06 0.29 poor 1.5 Opal-C/CT 1.3 82 25 K.sub.2SiO.sub.3 6.8 816 4.06 0.27 poor 1.2 Opal-C/CT 1.4 *Percent of diatomite in the feed blend of diatomite and perlite, excluding fluxing agent, if any, the same below.
[0080] Example 74 demonstrates a composite filter medium made with 75 wt % diatomite without using a fluxing agent by calcination at a temperature of about 982° C. Analysis on the XRD scan pattern of the product shows that the weak near 22° 2θ peak has a 4.08 Å peak centroid and 0.330 2θ FWHM and the 28.50 2θ peak of cristobalite is missing (Table II). Combination of all these indicates the presence of opal-C/CT instead of cristobalite. Therefore, the product contains no cristobalite and is determined to have less than 0.1 wt % opal-C/CT. Composite filter media made with less content of diatomite of similar properties without the use of a fluxing agent at the same or lower temperature should contain no cristobalite and less than about 0.1 wt % or no opal-C/CT.
[0081] Example 48 presents a composite filter medium made with 50 wt % diatomite and 1 wt % soda ash fluxing agent by calcination at 982° C. Analysis on its XRD scan pattern produces a centroid of 4.06 Å and 0.30° 2θ FWHM for the 22° 2θ peak and the 28.5° 2θ peak of cristobalite is absent (Table II). Therefore the product contains no cristobalite, and about 0.5 wt % opal-C/CT is determined.
[0082] Examples 21 and 29 present composite filter media made with 50 or 25 wt % diatomite and 2 wt % soda ash dosage and calcination at 927° C. XRD scan patterns for both samples show wide FWHMs for the 22° 2θ peaks and poor near 28.5° 2θ peaks (Table II). However, Example 21, made with 50 wt % diatomite, has a centroid of 4.03 Å, and that of Example 29, made with 25 wt % diatomite, is 4.05 Å. Therefore the former is determined to contain 1.2 wt % cristobalite and latter 0.6 wt % opal-C/CT.
[0083] Higher soda ash dosages may lead to higher amounts of 4-Å phase formation, however they may not necessarily be cristobalite. In Examples 10, 13 and 16, composites of 75, 50 and 25 wt % diatomite were made with 5 wt % soda ash and calcination at 871° C. Analysis on their XRD scan patterns show high 22° 2θ peak centroids (4.06-4.08 Å), high FWHMs (0.40-0.42° 2θ) and poorly developed 28.50 2θ peaks (Table II).
[0084] Examples 37, 38 and 41 in Table II are composite media made with 7 wt % soda ash with 25 or 50 wt % diatomite calcined at temperatures of 704 or 760° C. Example 38 demonstrates that the combination of 50 wt % diatomite, 7 wt % soda ash and 1400° F. (760° C.) temperature produced a composite product containing 2.9 wt % cristobalite. However, either a lower temperature (Example 37) or a lower content of diatomite in feed (Example 41) produced a composite containing about 2.3 or 1.3 wt % opal-C/CT and cristobalite was absent.
[0085] Selected composite filter media samples made with other fluxing agents were also analyzed for their silica crystallinity. Example 1 presents a composite medium made with 50 wt % diatomite and 3 wt % boric acid (H.sub.3BO.sub.3) and calcination at 816° C. Analysis on its XRD scan pattern produces a 220 2θ peak centroid of 4.06 Å and an FWHM of 0.29° 2θ and an absent 28.5° 2θ peak (Table II). These lead to a determination of about 0.1 wt % opal-C/CT in the product and cristobalite is absent.
[0086] Examples 76 and 79 present composite media made with 50 wt % diatomite and 5 wt % potassium carbonate (K.sub.2CO.sub.3) or potassium silicate (K.sub.2SiO.sub.3), respectively, by calcination at 816° C. Analysis on their XRD scan patterns produce 22° 2θ peak centroids of 4.05 and 4.06 Å and FWHMs of 0.33 and 0.29° 2θ, respectively, and the 28.5° 2θ peaks are either absent or poorly developed (Table II). These lead to a determination of opal-C/CT instead of cristobalite in the products at levels of about 1.2 and 1.3 wt %, respectively. Example 82 presents a composite made with a feed of 25 wt % diatomite and 6.8 wt % potassium silicate by calcination at 816° C. It is analyzed to contain 1.4 wt % opal-C/CT according to its XRD scan pattern (Table II).
[0087] Composite filtration media made with diatomite and perlite using boron fluxing agents are shown in Table III. The product of Example 1 contains the highest (0.1 wt %) 4-Å phase which is determined as opal-C/CT (Table II). Therefore, this group of composite filter media contains no detectable amount of crystalline silica and about 0.1 wt % opal-C/CT or less. Referring to Examples 1-2, using a Diatomite A to CP-1400P perlite weight ratio of 50/50, 3-5 wt % boric acid and calcination at 816° C. the products had permeabilities of 0.85-1.4 darcy and WBDs of 0.20-0.22 g/cm.sup.3. Referring to Examples 5-7, by using a coarser perlite, CP-4000P, at 50-75 wt % (corresponding diatomite content at 50-25 wt %), 5-7 wt % boric acid and with a lower calcination temperature of 760° C., composites of 1.2-4.0 darcy were made. In Examples 3-4, non-crystalline silica diatomite-perlite composite filtration media were made using borax or sodium borate (Na.sub.2B.sub.4O.sub.7.10H.sub.2O) as the fluxing agent. Prepared with a weight ratio of Diatomite A to CP-1400P perlite of 50/50, 3-5.6 wt % borax and calcination at 816° C., the products had permeabilities of 0.84-2.2 darcy and WBDs of 0.19-0.22 g/cm.sup.3. It is worth noting that borax is different from boric acid in the presence of sodium ions and the use of this sodium fluxing agent does not lead to the formation of cristobalite in a diatomite-perlite composite under the conditions of this disclosure. As shown by Examples 1-7 (Table III), the use of boron-containing fluxes leads to an increase in the soluble aluminum (Al) and calcium (Ca) content of the composites. The high levels of aluminum and calcium shown in Table III render the products of Examples 1-7 as unacceptable in some filtration applications.
[0088] Table III. Examples of Composites Made with Diatomite A and Boron Fluxing Agents
TABLE-US-00003 TABLE III Examples of Composites Made with Diatomite A and Boron Fluxing Agents Opal- EBC Solubility, Ex. DE Flux Temp. Perm. WBD C/CT ppm No. wt % wt % ° C. darcy g/cm.sup.3 wt % As Al Ca Fe CP-1400P and boric acid 1 50 3.0 816 0.85 0.22 0.1 1.2 137 675 45 2 50 5.0 816 1.4 0.20 <0.1 1.1 122 620 39 CP-1400P and borax 3 50 3.0 816 0.84 0.22 <0.1 1.6 130 652 73 4 50 5.6 816 2.2 0.19 <0.1 1.7 96 613 86 CP-4000P and boric acid 5 25 7.0 760 4.0 0.14 <0.1 0.4 244 406 64 6 50 5.0 760 1.2 0.17 <0.1 0.7 271 866 91 7 25 5.0 760 2.5 0.14 <0.1 0.4 230 450 109
[0089] Listed in Table IV are examples of composites made from Diatomite A and expanded perlite CP-1400P in weight ratios of 25/75 to 75/25 with soda ash as the fluxing agent. The products have permeabilities from 0.2 to 2.8 darcy and wet bulk densities of 0.19 to 0.75 g/cm.sup.3. As an important property of powdered filtration media, wet bulk density of a composite of certain diatomite-to-perlite ratio is significantly impacted by soda ash dosage and temperature. An over-calcined product is demonstrated by a high wet bulk density which reflects a low porosity and poor filtration performance. A lower diatomite-to-perlite feed blend tends to soften more easily and be over-calcined at a lower temperature and/or with a lower dosage of soda ash. This is also demonstrated by the permeabilities of the composites of certain formulations which increase and then decrease with an increasing calcination temperature (see Examples 31-34). Without being bound by theory, it is believed that the reversal of the permeability trend reflects an over-softening of the expanded perlite at higher temperatures and is accompanied by a dramatic increase in wet bulk density (see Example 34). The over-calcination and the resulting increase in product density are generally undesired for powdered filtration media.
[0090] The composite products listed in Table IV contain no detectable level of quartz and most of the samples contain no detectable level of cristobalite. The only exception is Example 21 in which a feed of 50/50 diatomite-to-perlite weight ratio was calcined with 2% soda ash at 927° C. and contained 1.2 wt % cristobalite. The other products made at lower temperatures or at the same temperature but with a lower soda ash dosage and/or a lower diatomite-to-perlite weight ratio contain no cristobalite. In general, at the same soda ash dosage, the opal-C/CT content drops with increasing perlite content but increases with increasing calcination temperature.
[0091] Examples 17-35 of Table IV demonstrate that diatomite-perlite composites may be made with a lower dosage of soda ash, but a higher calcination temperature is needed for a suitable permeability. The contents of opal-C/CT in these lower soda ash composites are also generally lower than those of higher soda ash dosages but similar permeability. For instance, from a feed consisting of Diatomite A and CP-1400P in the weight ratio of 25/75, Example 28 is a composite of 1.8 darcy and 0.7 wt % opal-C/CT made with 2 wt % soda ash and calcination at 871° C. Example 33 is a composite of 1.6 darcy and 0.3 wt % opal-C/CT made with 1 wt % soda ash and calcination at 927° C. Examples 28 and 33 may be compared to Example 15, which is a 1.4 darcy composite containing 1.4 wt % opal-C/CT and was made from the same feed blend with 5 wt % soda ash and calcination at 816° C.
TABLE-US-00004 TABLE IV Examples of Composites Made from Diatomite A, CP-1400P and Soda Ash Soda ash Temp. Perm. WBD Crist-obalite Opal-C/CT EBC Solubility, ppm Ex. No. DE wt % wt % ° C. darcy g/cm.sup.3 wt % wt % As Al Ca Fe 8 75 5.0 760 0.51 0.27 3.1 1.8 231 730 99 9 75 5.0 816 0.78 0.28 5.2 1.5 71 668 50 10 75 5.0 871 1.3 0.30 17.5 2.3 43 545 71 11 50 5.0 760 1.4 0.21 2.0 1.1 156 532 61 12 50 5.0 816 1.8 0.26 3.9 0.9 52 483 34 13 50 5.0 871 1.4 0.38 13.3 1.1 32 370 37 14 25 5.0 760 2.8 0.19 1.2 0.4 99 323 39 15 25 5.0 816 1.4 0.35 1.4 0.8 44 267 23 16 25 5.0 871 0.20 0.75 5.8 0.7 37 210 34 17 50 3.0 760 0.67 0.23 1.5 1.5 285 628 183 18 50 3.0 816 0.96 0.22 1.4 1.3 84 491 106 19 50 3.0 871 1.4 0.26 2.7 1.8 53 504 65 20 50 2.0 871 0.75 0.24 1.3 1.2 59 442 135 21 50 2.0 927 0.94 0.27 1.2 1.5 50 344 90 22 50 1.0 760 0.33 0.24 0.6 2.0 195 653 144 23 50 1.0 816 0.38 0.24 0.6 2.3 154 614 96 24 50 1.0 871 0.49 0.23 0.4 2.7 115 443 81 25 50 1.0 927 0.65 0.26 0.7 1.9 68 336 70 26 25 3.0 760 1.5 0.19 0.8 0.4 144 375 87 27 25 3.0 816 2.0 0.19 1.1 0.5 68 302 53 28 25 2.0 871 1.8 0.19 0.7 0.6 77 272 82 29 25 2.0 927 1.6 0.31 0.6 0.8 38 208 47 30 25 1.0 760 1.0 0.19 0.3 0.5 165 375 103 31 25 1.0 816 1.0 0.18 0.3 0.7 104 313 74 32 25 1.0 871 1.1 0.19 0.2 1.0 91 269 59 33 25 1.0 927 1.6 0.20 0.3 0.9 63 188 47 34 25 1.0 982 1.1 0.33 0.3 2.5 34 170 34 35 25 0.5 982 1.3 0.27 0.2 2.0 50 139 31
[0092] Products of higher permeabilities may be made with a coarser or higher permeability expanded perlite, a lower diatomite to perlite ratio, and/or a higher soda ash dosage. Examples 36-50 of Table V are composites made from Diatomite A and CP-4000P perlite in weight ratios ranging from 50/50 to 5/95, with 1 wt % to 7 wt % soda ash and calcined at temperatures ranging from 704-982° C. The resulting products had permeabilities of about 0.7-4.8 darcy and contained from less than 0.1 wt % to 2.9 wt % 4-Å phase, among which only the product made with 50 wt % diatomite with 7 wt % soda ash and calcined at 760° C. contained cristobalite. Less diatomite and/or less soda ash in the feed blend in combination with a lower calcination temperature prevent the formation of cristobalite and led to lower opal-C/CT formation. Example 39 is a composite made from Diatomite A and CP-4000P, in a weight ratio of 25/75 and 5 wt % soda ash, calcined at 760° C. and having a permeability of 3.9 darcy and 1.2 wt % opal-C/CT. Alternatively, similar permeability composites having lower opal-C/CT content may be made from a feed blend of less diatomite, a lower soda ash dosage but calcined at a higher temperature. Example 47 is a composite made from a feed of 5/95 weight ratio of Diatomite A and CP-4000P, 1 wt % soda ash, calcined at 927° C. and exhibits a permeability of 3.9 darcy and <0.1 wt % opal-C/CT.
TABLE-US-00005 TABLE V Examples of Composites Made from Diatomite A, CP-4000P and Soda Ash DE Soda WBD Crist- Opal- EBC Ex. wt Ash Temp. Perm. g/ obalite C/CT Solubility, ppm No. % wt % ° C. darcy cm.sup.3 wt % wt % As Al Ca Fe 36 50 5.0 760 1.7 0.17 1.6 1.0 168 532 65 37 50 7.0 704 1.9 0.18 2.3 1.1 336 530 118 38 50 7.0 760 2.6 0.22 2.9 0.9 162 430 83 39 25 5.0 760 3.9 0.15 1.2 0.6 94 314 38 40 25 7.0 704 4.0 0.15 1.1 0.8 215 346 87 41 25 7.0 760 2.1 0.28 1.3 0.6 78 248 38 42 5 5.0 760 4.5 0.15 0.2 0.4 66 126 29 43 5 7.0 704 4.8 0.14 0.2 0.4 94 166 52 44 5 7.0 760 1.3 0.39 0.4 0.3 48 78 26 45 50 1.0 927 0.74 0.20 0.6 3.6 76 368 59 46 25 1.0 927 2.0 0.16 0.4 2.1 63 206 44 47 5 1.0 927 3.9 0.14 <0.1 0.8 66 66 23 48 50 1.0 982 1.0 0.27 0.5 4.4 45 273 50 49 25 1.0 982 2.0 0.26 0.4 3.0 39 150 39 50 5 1.0 982 4.0 0.24 0.2 1.6 67 56 24
[0093] Non- or low crystalline silica composites of a wide permeability range can also be made without a fluxing agent, as demonstrated in Examples 51-74 of Table VI. The products of these examples contain less than detectable amount of quartz and cristobalite, and the vast majority of the group contain 0.1 wt % or less opal-C/CT. This is especially valuable for making composites of relatively higher diatomite to perlite ratios. Diatomite is considered to be the primary filtration functioning component in the composites because of its ability to filter finer particles as compared to expanded perlite. Thus, a higher diatomite to perlite ratio is desired for composite filtration media for filtration of fine or small particles, or in other words, for applications requiring a size exclusion of finer particles and/or where fine particles must be removed from a liquid.
TABLE-US-00006 TABLE VI Examples of Diatomite A Based Composites Made without a Fluxing Agent DE Opal- EBC Ex. wt Temp. Perm. WBD C Solubility, ppm No. % ° C. darcy g/cm.sup.3 wt % As Al Ca Fe CP-4000P based composites 51 25 927 1.5 0.14 0.1 2.2 101 265 37 52 50 954 0.70 0.21 <0.1 5.3 94 351 46 53 25 954 1.7 0.16 <0.1 3.0 91 197 37 54 5 954 3.4 0.13 <0.1 1.7 106 108 29 55 25 982 1.9 0.18 <0.1 3.0 62 160 27 CP-1400P based composites 56 50 760 0.25 0.25 0.2 2.5 139 720 78 57 25 760 0.84 0.20 <0.1 0.7 108 372 50 58 50 816 0.29 0.25 <0.1 2.6 165 642 57 59 25 816 0.91 0.19 <0.1 1.0 129 350 36 60 50 871 0.33 0.24 0.1 3.6 137 516 46 61 25 871 0.93 0.19 <0.1 0.8 115 271 34 62 50 927 0.42 0.26 <0.1 2.9 114 338 48 63 25 927 1.1 0.20 <0.1 1.1 86 189 32 64 5 927 1.9 0.16 <0.1 0.7 79 104 23 65 50 982 0.65 0.27 <0.1 4.2 82 285 39 66 25 982 1.2 0.23 <0.1 2.6 58 149 29 67 25 1038 0.91 0.41 <0.1 2.2 35 82 27 CP-600P based composites 68 50 927 0.25 0.31 0.1 3.8 101 308 46 69 25 927 0.79 0.26 <0.1 1.7 75 146 27 70 5 927 1.1 0.24 <0.1 1.2 76 51 58 71 50 982 0.40 0.33 <0.1 4.3 73 222 38 72 25 982 1.1 0.28 <0.1 2.1 55 58 50 73 5 982 1.7 0.27 <0.1 0.8 60 43 25 74 75 982 0.19 0.32 <0.1 5.6 78 399 47
[0094] Applicants also tested potassium carbonate and potassium silicate as fluxing agents as shown in Examples 75-82 in Table VII. None of the composite products contains cristobalite. A 50/50 blend of Diatomite A and CP-1400P perlite, 5 wt % potassium carbonate and calcination at 816° C. resulted in a composite of 1.3 darcy and 1.2 wt % opal-C/CT (Example 76). This product made with potassium carbonate is slightly less permeable and has a lower content of opal-C/CT than that made under the same conditions but instead using 5 wt % soda ash, which resulted in 1.8-darcy permeability and 3.9 wt % opal-C/CT (Example 12). Similarly, a 25/75 blend of diatomite and CP-4000P perlite, 5 wt % potassium carbonate and calcination at 760° C. resulted in a composite of 2.5 darcy and 0.3 wt % opal-C/CT (Example 78), as compared to the composite of 3.9 darcy and 1.2 wt % opal-C/CT made under the same conditions with 5 wt % soda ash (Example 39). Compared to soda ash, potassium carbonate only mildly reduces opal-C/CT formation but its fluxing capability is poorer. At the same dosage, potassium silicate makes products of much lower permeability than soda ash. For instance, calcining a 25/75 blend of Diatomite A and CP-4000P perlite with 5 wt % potassium silicate at 760° C. produced a product of 1.4 darcy and 1.1 wt % opal-C/CT (Example 80). Under the same conditions, 5 wt % soda ash made a product of 3.9-darcy permeability and 1.2 wt % opal-C/CT (Example 39). Further, increasing the dosage of potassium silicate to 6.8 wt % by weight to have the same molar dosage of potassium as the sodium molar dosage at 5 wt % soda ash and, at the same time, increasing the calcination temperature to 816° C. only increased the permeability of the product to 1.8 darcy while opal-C/CT content was increased to 1.4 wt % (Example 82).
TABLE-US-00007 TABLE VII Examples of Composites Made with Diatomite A and a Potassium Fluxing Agent DE Flux WBD Opal- EBC Ex. wt wt Temp. Perm. g/ C/CT Solubility, ppm No. % % ° C. darcy cm.sup.3 wt % As Al Ca Fe CP-1400P and K.sub.2CO.sub.3 based composites 75 50 3.0 816 0.73 0.22 0.7 1.6 120 539 172 76 50 5.0 816 1.3 0.21 1.2 1.2 105 509 66 CP-4000P and K.sub.2CO.sub.3 based composites 77 50 5.0 816 1.5 0.20 1.3 1.4 61 518 50 78 25 5.0 760 2.5 0.17 0.3 0.9 121 362 64 CP-4000P and K.sub.2SiO.sub.3 based composites 79 50 5.0 816 0.52 0.23 1.3 1.9 123 550 203 80 25 5.0 760 1.4 0.17 1.1 1.1 190 406 178 81 25 5.5 816 1.6 0.17 1.4 1.1 94 382 105 82 25 6.8 816 1.8 0.17 1.4 1.0 78 398 84
TABLE-US-00008 TABLE VIII Flux-calcined Diatomite C and Composite Based on Diatomite C 22° 2θ Peak Ex. DE-C EP-1400P Soda ash Temp. Perm. WBD d FWHM 28.5° 2θ Opal-C No. wt % wt % wt % ° C. darcy g/cm.sup.3 Å ° 2θ Peak wt % 83 100 0 5 1104 5.2 18.8 4.06 0.49 no 21.5 84 70 30 5 816 17.2 17.2 4.08 0.44 poor 15.7
[0095] Shown in Table VIII are a flux-calcined diatomite (Diatomite C) and a composite based on Diatomite C. The flux-calcined diatomite (Example 83) has a permeability of about 5.2 darcy and contains <1 wt % quartz, no cristobalite and about 22 wt % opal-C, as evidenced by the centroid location and FWHM of its 220 2θ peak (see
[0096] The inventors of the present disclosure have demonstrated that cristobalite may be formed during preparation of diatomite-perlite composite filtration media under certain conditions: 1) calcining a feed blend of 50 wt % or more diatomite with 2 wt % or more soda ash at a temperature of about 927° C. or higher, or 2) calcining a feed blend of 50 wt % or more diatomite with 7 wt % or more soda ash at a temperature of about 760° C. or higher. Although opal-C/CT was not differentiated from cristobalite in the prior art disclosure (U.S. Pat. Nos. 6,524,489 and 5,776,353), one of ordinary skill in the art understands from such prior art that the soda ash fluxed products disclosed in the prior art clearly contain cristobalite: Example 4 (prior art) was made with 70 wt % diatomite and 2 wt % soda ash at 1700° F. (927° C.), Example 12 (prior art) with 90 wt % diatomite and 7 wt % soda ash at 1562° F. (850° C.), and Example 9 (prior art), as discussed above, was made with 90% of a highly flux-calcined and high cristobalite diatomite. Celite® 560, and 5 wt % soda ash at 1500° F. (816° C.).
[0097] The existing prior art demonstrated that composites of perlite and diatomite could be produced but composites comprising more than about 5% diatomite without the use of a boric acid flux and free of cristobalite were not taught, suggested or disclosed in the prior art. It is therefore surprising and unexpected that, the inventors of the present disclosure have shown that diatomite-perlite composite filter media can be produced without forming cristobalite through not one or two, but through at least seven different approaches, which are: 1) calcining a feed blend of 75 wt % or less diatomite at a temperature of about 982° C. or lower, 2) calcining a feed blend of 75 wt % or less diatomite with 5 wt % or less soda ash at a temperature of about 871° C. or lower; 3) calcining a feed blend of 50 wt % or less diatomite with 7 wt % or less soda ash at a temperature of about 704° C. or lower, 4) calcining a feed blend of 25 wt % or less diatomite with 7 wt % or less soda ash at a temperature of about 760° C. or lower; 5) calcining a feed blend of 50 wt % or less diatomite with 5 wt % or less potassium carbonate at a temperature of about 816° C.; 6) calcining a feed blend of 50 wt % or less diatomite with 6.8 wt % potassium silicate at a temperature of about 816° C.) or lower; and 7) calcining a feed blend of 50 wt % or less diatomite with 5.6 wt % or less borax at a temperature of about 816° C. or lower. The above listed parameters for producing a cristobalite-free diatomite-perlite composite are for demonstration purpose and should not be taken as limitation and/or boundaries.
[0098] In addition, careful selection of the diatomite and perlite components having very low or non-detectable levels of quartz have been shown to contribute to the production of composite products containing very low or non-detectable quartz content and thus a non-detectable or very low level of total crystalline silica content. While not common in nature, diatomite containing very low levels of quartz may also be obtained by beneficiating diatomite ores to remove quartz and other mineral impurities prior to sintering.
[0099] Very low quartz perlite may be obtained by using a perlite ore that is free of quartz or by selecting an expanded perlite in which the quartz has been removed during expansion or post-expansion processes. In an embodiment, crystalline silica content in the expanded perlite powder used for the feed may be reduced by beneficiation prior to sintering. The perlite products used in the examples all contain non-detectable levels of quartz because the perlite ore selected for the manufacture of these products was substantially free of quartz.
[0100] In some embodiments, the combined feed (that contains the diatomite and perlite components) may have a crystalline silica content of less than 1 wt % prior to calcination (sintering). In another embodiment, the combined feed may have a crystalline silica content of less than 0.5 wt % prior to calcination. Most of the examples of the resulting composite products (powdered composite filtration media) listed in this application contain non-detectable or less than 0.1 wt % quartz. Examples 85-86 of Table IX are composites made by calcination at 982° C. from 50/50 blends of CP-1400P and Diatomite A with or without reduced mineral impurities. In both Examples 85 and 86, the composites had <0.1 wt % opal-C/CT and <0.1 wt % quartz.
TABLE-US-00009 TABLE IX Examples of Quartz Contents of Composites Made with 50 wt % CP- 1400P without A Fluxing Agent at 982° C. Ex. Diatomite Perm. WBD Opal-C/CT Quartz No. Type Quartz, wt % darcy g/cm.sup.3 wt % wt % 85 A 0.15 0.56 0.30 <0.1 <0.1 86 A1 <0.1 0.50 0.30 <0.1 <0.1
[0101] As shown in the above examples, by using no flux or a low sodium flux dose and avoiding over-calcination, the amorphous silica content of the diatomite raw materials will not convert to quartz during the formation of the composite, and further, the expanded perlite component will not devitrify to form quartz during the composite formation process.
[0102] Diatomite-perlite composite filtration media made without or with a low dosage of soda ash also have reduced soluble metal content. When the content of the fluxing agent is reduced, a higher calcination temperature is needed to complete the particle agglomeration required to achieve a wide permeability range. Applicants have shown that with a reduced flux content, higher calcination temperatures can be applied without the large increases in product density caused by over-calcination. The higher calcination temperature also reduces the solubility of certain undesirable metals. Example 17 (see Table IV) is a composite made from a 50/50 blend of Diatomite A and CP-1400P expanded perlite with 3 wt % soda ash at 760° C. and possessing a permeability of 0.67 darcy and 1.5 wt % opal-C/CT. In contrast, Example 65 (see Table VI) shows a composite made from the same feed blend without a fluxing agent, calcined at 982° C. possessing a permeability of 0.65 darcy and <0.1 wt % opal-C/CT. Not only is the opal-C/CT level reduced through the reduction of the flux and the increase in calcination temperature, but the solubilities of Al, Ca and Fe, as determined by the EBC method, were reduced from 285, 628 and 183 to 82, 285 and 39 ppm, respectively, which are all extremely attractive levels in many food, chemical and beverage filtration processes.
[0103] The solubilities of impurities may also be controlled by careful selection of raw materials. For instance, Examples 87-89 of Table X show composite filtration media made from Diatomite B and CP-1400P. These composite products contain <0.1 wt % quartz and cristobalite is absent. Without using a fluxing agent, the Diatomite B based products of Table X have lower As, Ca and Fe solubilities as compared to those Diatomite A based composites of otherwise the same formulations (comparing Examples 87-89 of Table X with Examples 71-73 of Table VI).
TABLE-US-00010 TABLE X Examples of Composites of Diatomite B and CP-1400P without A Fluxing Agent DE Opal- EBC Ex. wt Temp. Perm. WBD Quartz C/CT Solubility, ppm No. % ° C. darcy g/cm.sup.3 wt % wt % As Al Ca Fe 87 50 982 0.82 0.27 <0.1 <0.1 2.1 106 164 36 88 25 982 1.8 0.22 ND <0.1 1.6 72 73 26 89 5 982 3.0 0.21 ND <0.1 0.7 58 8 20 ND-non-detectable
[0104] As shown in Table I, the diatomite and perlite feed materials for making composite filter media may contain minute amounts of boron, in the levels of about <100 ppm (<0.01 wt %). Composite filtration media made from these raw materials with different feed ratios and without using a boron-containing fluxing agent will have a total boron content of about <0.01 wt %. Boric acid (H.sub.3BO.sub.3) contains about 17.5 wt % boron. When it is used as a fluxing agent to make the composite filter media, say, at the 2 wt % level, it increases the boron content in the product by about 0.35 wt %. Solubility of boron of a powdered composite filtration medium can be minimized by not using a boron-containing fluxing agent. It can be seen that without using a boron containing fluxing agent, the composite filtration medium (Example 90) had less than 20 ppm soluble boron while the sample made with 2 wt % boric acid (Example 91) had more than 170 ppm soluble boron.
TABLE-US-00011 TABLE XI Examples of Composites of Diatomite A and CP-1400P Made with or without out Boric Acid as Fluxing Agent Ex. DE Boric acid Total B* Temp. Perm. WBD Qz Opal-C/CT EBC Solubility, ppm No. wt % wt % wt % ° C. darcy g/cm.sup.3 wt % wt % B As Al Ca Fe 90 40 0 <0.01 954 0.24 0.30 ND <0.1 17 1.6 72 73 26 91 50 2.0 0.35 927 1.2 0.25 ND <0.1 171 0.7 58 8 20 *Estimated from feed composition and boric acid addition. ND—non-detectable.
[0105] Listed in Tables XII and XIII are measurements on floater contents of selected expanded perlites (Examples 92 through 94 of Table XII) and diatomite-expanded perlite composites of this disclosure (Examples 95-112 of Table XIII). The perlite samples had 0.8-3.9 ml/g total floaters and 0.4-1.0 ml/g persistent floaters. The composites (see Table XIII) containing 50-95 wt % perlite (50-5 wt % diatomite) have much fewer floater particles than the corresponding expanded perlite would have contributed had these floater particles not been altered.
TABLE-US-00012 TABLE XII Examples of Floater Contents of Expanded Perlite Floaters, % v Floaters, ml/g Stirred Stirred Ex. Expanded Perm. WBD (persistent (persistent No. perlite darcy g/cm.sup.3 Total floaters) Total floaters) 92 CP-600P 0.8 0.20 16 8 0.8 0.4 93 CP-1400P 1.9 0.15 29 9 2.0 0.6 94 CP-4000P 2.7 0.13 35 10 3.9 1.0
TABLE-US-00013 TABLE XIII Examples of Floater Contents of Selected Composite Samples Floaters, ml/g Stirred Ex. DE Fluxing Agent Temp. Perm. WBD (persistent No. wt % Type wt % ° C. darcy g/cm.sup.3 Total floaters) Diatomite A & CP-600P based composites 95 5 None 927 1.1 0.24 0.2 0.1 96 25 None 927 0.8 0.26 0.2 0.1 97 50 None 927 0.2 0.31 0.2 0.1 Diatomite A & CP-1400P based composites 98 5 None 927 1.9 0.16 0.6 0.2 99 25 None 927 1.1 0.20 0.6 0.2 100 25 None 982 1.2 0.23 0.2 0.1 101 25 Na.sub.2CO.sub.3 5 760 2.8 0.19 0.2 0.1 102 50 None 927 0.42 0.26 0.2 0.1 103 50 None 982 0.65 0.27 0.2 0.1 104 50 Na.sub.2CO.sub.3 5 760 1.4 0.21 0.2 0.1 105 50 H.sub.3BO.sub.3 5 816 1.4 0.20 0.2 0.1 Diatomite A & CP-4000P based composites 106 5 Na.sub.2CO.sub.3 5 760 4.5 0.15 0.2 0.1 107 25 None 954 1.7 0.16 0.4 0.1 108 25 Na.sub.2CO.sub.3 5 760 3.9 0.15 0.2 0.1 109 25 H.sub.3BO.sub.3 5 760 2.5 0.14 0.2 0.1 110 50 None 954 0.70 0.21 0.2 0.1 111 50 Na.sub.2CO.sub.3 5 760 1.7 0.17 0.2 0.1 112 50 H.sub.3BO.sub.3 5 760 1.2 0.17 0.2 0.1
[0106] The lower floater content of the composites described herein indicates that a large portion of the floater particles are converted to non-floaters during the calcination process taught in this application. For example, expanded perlite CP-600P (Example 92) has 0.8 ml/g total and 0.4 ml/g persistent floaters, and it could have contributed 0.4 ml/g total and 0.2 ml/g persistent floaters to a composite of 50 wt % CP-600P. However, a composite of such formulation has only 0.2 ml/g total and 0.1 ml/g persistent floaters (Example 97). Expanded perlite CP-4000P (Example 94) has 3.9 ml/g total and 1.0 ml/g persistent floaters. However, a composite containing 95 wt % CP-4000P (Example 106) has only 0.2 ml/g total and 0.1 ml/g persistent floaters. Most of the well calcined composites of diatomite-expanded perlite of this invention have 0.2-0.6 ml/g total and 0.1-0.2 ml/g persistent floaters.
[0107] Some of the powdered composite filtration media comprising diatomite and expanded perlite were tested for filtration performance against regular diatomite products. The fluids filtered included an Ovaltine® drink, an apple juice, and a home brew light beer. All the filtration tests were conducted in a small lab pressure filter, having a horizontal filter area of 13.4 cm.sup.2 and a PZ80 septum. A peristaltic pump delivered one of the fluids to the filter at a set flow rate, the pressure inside the filter chamber was monitored by an analogue gauge, and a filtrate sample was measured for turbidity once every 5 minutes using a HACH® Ratio/XR Turbidimeter, as is known how to do by those of ordinary skill in the art. A “precoat” layer of certain thickness of a powdered composite filtration medium was formed on the filter area before starting filtration. The quantity of the powdered composite filtration medium was determined from its wet bulk density and the surface area of the septum (13.4 cm.sup.2). The powdered composite filtration medium was suspended in about 15-ml of deionized (DI) water and pumped to the filter with the filtrate being recirculated. The precoat time was fixed at 6 minutes. For each filtration test, a prescribed amount of powdered composite filtration medium was added to the fluid to be filtered as “body-feed” and the slurry was agitated for 30 minutes before starting filtration.
[0108] Examples 113 through 120 of Table XIV demonstrate the superior filtration performance of the diatomite-expanded perlite composite filtration media in comparison with regular diatomite products. An Ovaltine® chocolate malt powder was used for making up an aqueous Ovaltine® suspension for filtration tests. The particular aqueous suspension used in the testing contained about 14 wt % water insoluble or total suspended solids (TSS), as determined by filtering a suspension through a 0.45-μ membrane filter.
[0109] The fluid used for filtration tests was prepared by dispersing 3.50 g of Ovaltine powder in about 100-ml DI water, followed by sonication for 60 seconds and then dilution to 1.0 liter with DI water, resulting in a suspension containing 0.5 g/L TSS. The apple juice used was prepared by mixing a cloudy apple juice with a clear one, both purchased from a grocery store, and decantation to remove access solids. The mixture contained about 1.3 g/L TSS as determined by the same method described above. The beer was brewed in the lab from a home brewing kit. A supernatant of the brewed beer was obtained by decantation for the filtration tests and was determined to have 0.5 g/L TSS.
[0110] Examples 113 through 116 show the results from filtering the Ovaltine® suspension. The filtration tests were conducted with a fixed precoat thickness of 1.6 mm ( 1/16″), using the same powdered composite filtration medium for both precoat and body-feed, and a fixed peristaltic pump flow rate of 40 ml/min for the precoat. The filtration flow rate was maintained at a constant 20 ml/min for filtration with the products of or similar to the “calcined” grades (<0.5 darcy; Examples 113-114;
[0111] Examples 117 and 118 and
[0112] Examples 119-120 and
TABLE-US-00014 TABLE XIV Examples of Filtration Performance of Diatomite A Based Composites Filtration Perlite Soda Ash, Perm. WBD Precoat Body- flowrate Ex. No. Filter Media Type wt % wt % darcy g/cm.sup.3 mm feed: TSS ml/min Ovaltine (0.5 g/L TSS, >2000 ntu) Filtration Tests 113 FP-4 N/A N/A 0 0.35 0.40 1.6 2:1 20 114 Composite CP-600P 50 0 0.40 0.33 1.6 2:1 20 115 FW-12 N/A N/A N/A 1.0 0.35 1.6 3:1 40 116 Composite CP-1400P 75 0 1.1 0.20 1.6 2:1 40 Apple Juice (1.3 g/L TSS, >2000 ntu) Filtration Tests 117 FW-40 N/A N/A N/A 2.5 0.37 3.2 6.2:1 40 118 Composite CP-4000P 85 0 3.1 0.15 3.2 3.5:1 40 Beer (0.5 g/L TSS, 96 ntu) Filtration Tests 119 FP-3 N/A N/A 0 0.20 0.52 3.2 1:1 30 120 Composite CP-600P 50 0 0.25 0.31 3.2 0.84:1 30
INDUSTRIAL APPLICABILITY
[0113] Mined diatomite is subjected to conventional diatomite pre-calcination processes such as drying and classification to remove non-diatomite impurity minerals to produce a “natural” product. Diatomite of specific properties may be selected to minimize soluble substances and/or quartz content. Diatomite may also be subjected to additional beneficiation to remove mineral impurities including quartz. Perlite ore is subjected to the conventional crushing, sizing, expansion, and post-expansion milling and classification for the removal of minerals and to achieve specific particle size distribution, floater content and permeability.
[0114] The natural diatomite and expanded perlite are blended in a desired ratio, and, optionally, a fluxing agent, preferably finely milled, are mixed with the diatomite-perlite blend, preferably in a pneumatic system and thus the prepared feed material is calcined or flux calcined. With specific formulations, the diatomite feed material may be already calcined or flux-calcined. The optional fluxing agent may also be added dry or in form of a solution, preferably aqueous. The calcination feed may be pre-agglomerated by adding a solvent, preferably water, and/or a binding agent. It may also be pre-formed by balling and/or spraying drying.
[0115] The calcination can be carried out in a conventional directly fired rotary kiln with controlled hot gas draft and temperature profile. This may also be done in other types of industrial calciners. The calcination product can be cooled and dispersed conventionally and classified if necessary.
[0116] The commercially-produced composite filtration media of diatomite and expanded perlite as described above will have a wide range of permeabilities, low or non-detectable level of crystalline silica, low soluble substances and low floater particle content, and these properties can be altered by adjusting feed formulations and process conditions to make desired property combinations. The disclosed composite filtration media can be used in commercial filtration applications where either currently diatomite and/or expanded perlite filtration media are used but with reduced or non-detectable or no crystalline silica content than most commercial diatomite filtration media products and with reduced unit consumption of the filtration media while maintaining attractive clarification and filtration cycle time performance.
[0117] The disclosed composite filtration media may be used in solid-liquid separation where, for example, the composite filtration media can be used to form a precoat on a rotary vacuum filter or used in functions of both precoat and body-feed in a pressure filtration application. The composite filtration media may also be used in solid-gas separation where, for instance, the composite filtration media are used to precoat fabric filtration media in a dust collector to enhance the efficiency of filtration and dust discharge from the fabric media.
[0118] The composite filtration medium/media may also be modified by processes such as acid washing to reduce further the levels of soluble substances. At least one adsorptive agent may be incorporated into the composite medium/media to add the adsorption capability which would allow the removal of certain undesired or desired substances from the liquid being filtered. In an embodiment, the at least one adsorbent may be selected from the group consisting of silica gel, precipitated silica, fumed silica, activated alumina, activated bleach clay, natural zeolite, synthetic zeolite and activated carbon. The adsorbent is intimately bound to the composite particles of the powdered composite filtration medium.
[0119] The composite filtration medium may also be added as a component into filter sheets or other specialty paper products containing cellulose and other additives, such as powdered filtration media and adsorbents.
[0120] In some embodiments, the powdered composite filtration medium/media disclosed above may be used in clarification or processing of other liquids (for example blood plasma processing and fractionation, cellular separation, or the like).
[0121] In some embodiments, the powdered composite filtration medium/media disclosed above spent in clarification or processing of a liquid may be subsequently regenerated through a process comprising physical, chemical, or thermal processing steps as are known in the art (for example, by pyrolysis, solvent extraction, gasification, or the like), and then used again for clarification or processing of liquids. The regeneration does not result in measurable conversion of opaline silica phases (opal-A, opal-CT or opal-C) present in the used medium/media to a form of crystalline silica in the regenerated medium. In other words, the regenerating does not result in an increase in the wt % of total cristobalite, or an increase in the wt % of quartz, or an increase in the wt % of total crystalline silica present in the filter medium/media. Thus, in an embodiment, the regenerated powdered composite filtration medium/media will have substantially the same wt % total crystalline silica as it did prior to regeneration. For example, if there was no detectable wt % crystalline silica present in a powdered composite filtration medium/media prior to regeneration, there will be no detectable wt % crystalline silica present in the powdered composite filtration medium/media after regeneration. Similarly, in an embodiment, the regenerated powdered composite filtration medium/media will have substantially the same wt % of total cristobalite as it did prior to regeneration. In an embodiment, the regenerated powdered composite filtration medium/media will have substantially the same wt % of quartz as it did prior to regeneration.
[0122] In accordance with another aspect of the disclosure, a method of regenerating a powdered composite filtration medium/media is disclosed. The method may comprise treating the used medium/media with a liquid characterized by a pH of more than 7. Another method of regenerating a powdered composite filtration medium/media is disclosed. The method may comprise applying thermal energy to the used medium/media.
[0123] The disclosures of the publication referenced below are hereby incorporated by reference into the present disclosure in its entirety: Elzea and Rice (Clays and Clay Minerals, vol. 44. pp. 492-500, 1996).
[0124] While only certain embodiments have been set forth, alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of the present disclosure.