SURFACE-TREATED MINERAL MATERIALS AND ITS USE IN WATER PURIFICATION

Abstract

The present invention relates to a process for increasing the solids content of aqueous sludges and/or sediments, to the use of a surface-treated mineral material for increasing the solids content of sludges and/or sediments, and to a composite material comprising a surface-treated mineral material and impurities obtainable by said process.

Claims

1. A process for increasing the solids content of aqueous sludges and/or sediments, comprising the following steps of: a) providing aqueous sludge and/or sediment to be dewatered comprising impurities; b) providing at least one surface-treated mineral material, wherein the mineral material prior to surface-treatment has a tapped bulk density measured according to the standard method ISO 787/11 of the dry powder from 0.05 g/mL to 0.80 g/mL and wherein the mineral material is surface-treated by a material which provides a cationic charge to the mineral material, c) contacting sludge and/or sediment of step a) with the at least one surface-treated mineral material of step b) for obtaining a composite material of surface-treated mineral material and impurities and d) removing water from the sludge and/or sediment comprising the composite material of step c).

2. The process according to claim 1, wherein the sludge and/or sediment of step a) is selected from sludge such as harbour sludge, river sludge, coastal sludge or digested sludge, mining sludge, municipal sludge, civil engineering sludge, drilling mud, sludge from oil drilling, waste water or process water from breweries or other beverage industries, waste water or process water in the paper industry, colour-, paints-, or coatings industry, agricultural waste water, slaughterhouse waste water, leather industry waste water and leather tanning industry.

3. The process according to claim 1, wherein the at least one surface-treated mineral material of step b) comprises magnesium and/or calcium carbonate comprising mineral materials and/or aluminium or aluminosilicate comprising mineral materials and/or phyllosilicates and is preferably selected from the group consisting of pumice, scorea, tuff, MCC, kaolin, bentonite, alumina, bauxite, gypsum, magnesium carbonate, perlite, dolomite, diatomite, huntite, magnesite, boehmite, palygorskite, mica, vermiculite, hydrotalcite, hectorite, halloysite, gibbsite, kaolinite, montmorillonite, illite, attapulgite, laponite, sepiolite, hydromagnesite, zeolite and mixtures thereof, more preferably is selected from the group consisting of MCC, huntite, perlite, hydromagnesite, zeolite, bentonite and mixtures thereof and most preferably is selected from the group consisting of hydromagnesite, zeolite and mixtures thereof.

4. The process according to claim 1, wherein a) the mineral material particles of the at least one surface-treated mineral material prior to surface-treatment have a weight median particle diameter d.sub.50 value of between 1.0 m and 300 m, preferably between 1 m and 200 m, more preferably between 2 m and 50 m, even more preferably between 3 m and 30 m, and most preferably between 4 m and 25 m and/or b) the mineral material of the at least one surface-treated mineral material prior to surface-treatment has a tapped bulk density measured according to the standard method ISO 787/11 of the dry powder from 0.07 g/mL to 0.60 g/mL, preferably from 0.08 g/mL to 0.40 g/mL, and most preferably from 0.10 g/mL to 0.20 g/mL and/or c) the mineral material particles of the at least one surface-treated mineral material prior to surface-treatment have a specific surface area of from 1 to 800 m.sup.2/g, more preferably from 20 to 500 m.sup.2/g, even more preferably from 30 to 300 m.sup.2/g and most preferably from 30 to 150 m.sup.2/g.

5. The process according to claim 1, wherein the surface-treatment of the at least one surface-treated mineral material comprises at least one material which provides a cationic charge to the mineral material selected from the group consisting of mono-, di-, or trivalent cations, cationic polymers and mixtures thereof.

6. The process according to claim 5, wherein the cationic polymers comprise polymers a) having a positive charge density in the range of 1 mEq/g and 15 mEq/g, more preferably in the range of 2.5 mEq/g and 12.5 mEq/g and most preferably in the range of 5 mEq/g and 10 mEq/g and/or b) in which at least 60% of the monomer units have a cationic charge, preferably at least 70%, more preferably at least 80%, even more preferably at least 90% and most preferably equal to 100% and/or c) having a weight average molecular weight M.sub.w of below 1,000,000 g/mole, more preferably from 50,000 to 750,000 g/mole, even more preferably from 50,000 to 650,000 g/mole and most preferably from 100,000 to 300,000 g/mole and/or d) being a homopolymer based on monomer units selected from the group consisting of diallyldialkyl ammonium salts; tertiary and quaternized amines; quaternized imines; acrylamide; methacrylamide; N,N-dimethyl acrylamide; acrylic acid; methacrylic acid; vinylsulfonic acid; vinyl pyrrolidone; hydroxyl ethyl acrylate; styrene; methyl methacrylate and vinyl acetate, preferably diallyldialkyl ammonium salts and acrylic acid, or e) being a copolymer based on monomer units selected from diallyldialkyl ammonium salts and methacrylic acid and comonomer units selected from the group consisting of acrylamide; methacrylamide; N,N-dimethyl acrylamide; acrylic acid; methacrylic acid; vinylsulfonic acid; vinyl pyrrolidone; hydroxyl ethyl acrylate; styrene; methyl methacrylate; vinyl acetate and mixtures thereof, preferably the monomer units are selected from diallyldialkyl ammonium salts and methacrylic acid and comonomer units selected from acrylamide and acrylic acid.

7. The process according to claim 5, wherein the mono-, di-, or trivalent cations are selected from Fe.sup.3+, Al.sup.3+, Mn.sup.2+ Zn.sup.2+ and mixtures thereof.

8. The process according to claim 1, wherein at least 0.1% of the accessible surface area of the mineral material is surface-treated with the at least one material which provides a cationic charge to the mineral material, preferably between 0.2% and 50%, more preferably between 0.5% and 30%, even more preferably between 0.7% and 20% and most preferably between 1.0% and 10%.

9. The process according to claim 1, wherein the process further comprises step e) of contacting the sludge and/or sediment to be dewatered of step a) or c) with at least one polymeric flocculation aid.

10. The process according to claim 9, wherein the polymeric flocculation aid of step e) has a) a weight average molecular weight M.sub.w in the range from 100,000 to 10,000,00 g/mole, preferably in the range from 300,000 to 5,000,000 g/mole, more preferably in the range from 300,000 to 1,000,000 g/mole and most preferably in the range from 300,000 to 800,000 g/mole and/or b) is non-ionic or ionic, preferably a cationic or anionic polymer selected from polyacrylamides, polyacrylates, poly(diallyldimethylammonium chloride), polyethyleneimines, polyamines, starches and mixtures thereof.

11. The process according to claim 1, wherein step d) is performed by filtration, sedimentation and/or centrifugation and preferably by filtration.

12. The process according to claim 1, wherein the process further comprises a step of adding an anionic polymer before step d), preferably after step c).

13. Use of a surface-treated mineral material for increasing the solids content of sludges and/or sediments, wherein the mineral material prior to surface-treatment has a tapped bulk density measured according to the standard method ISO 787/11 of the dry powder from 0.05 g/mL to 0.80 g/mL and wherein the mineral material is surface-treated with a material which provides a cationic charge to the mineral material.

14. A composite material comprising a surface-treated mineral material and impurities obtainable by the process according to claim 1.

15. The composite material according to claim 14 having a water content of less than 90 wt.-%, based on the total weight of the composite material after filtration from the sludges and/or sediments and before drying, preferably below 80 wt.-%, more preferably below 60 wt.-%, even more preferably below 50 wt.-% and most preferably below 30 wt.-%.

Description

EXAMPLES

[0220] The scope and interest of the invention may be better understood on the basis of the following examples which are intended to illustrate embodiments of the present invention. However, they are not to be construed to limit the scope of the claims in any manner whatsoever.

Measurement Processes

[0221] The following measurement processes were used to evaluate the parameters given in the examples and claims.

Tapped Bulk Density of the Mineral Material According to ISO 787/11

[0222] 100 g0.5g of dried mineral material powder is shaken or sieved though a power funnel into a 250 mL glass measuring cylinder (graduation marks at 2 mL). The cylinder is gently tapped until the surface of the sample is roughly levelled. Then the cylinder is placed in a holder of a tapping volumeter (jolting volumeter STAV II, Engelsmann) and tapped in steps of 1250 times until the differences between the last two readings is less than 2 mL. The final value is read off the nearest 1 mL.

Tapped density [g/mL] is evaluated as: weighted sample[g]/tapped volume [mL]

Particle Size Distribution (Mass % Particles with a Diameter<X) and Weight Median Diameter (d.SUB.50.) of a Particulate Material

[0223] Weight median grain diameter and grain diameter mass distribution of a particulate material were determined via the sedimentation process, i.e. an analysis of sedimentation behavior in a gravitational field. The measurement was made with a Sedigraph 5100.

[0224] The process and instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurements were carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and ultrasound.

BET Specific Surface Area of a Material

[0225] The BET specific surface area was measured via the BET process according to ISO 9277 using nitrogen, following conditioning of the sample by heating at 250 C. for a period of 30 minutes. Prior to such measurements, the sample was filtered, rinsed and dried at 110 C. in an oven for at least 12 hours.

pH Measurement

[0226] The pH of the water samples is measured by using a standard pH-meter at approximately 25 C.

Charge Density

[0227] The charge density of a polymer and of a surface-treated mineral material was measured with a particle charge detector (PCD). The used particle charge detector was either a PCD-03 or a PCD-05, both available from Mtek with a measuring cell type 1 (10 to 30 ml).

[0228] The measurement of the charge density of a sample was carried out by weighting the sample in the cell as well as 10.0 g of demineralized water. The electrodes inside the cell have to be covered with liquid.

[0229] The piston was slowly inserted in the measuring cell and the measurement was started.

[0230] The samples were titrated with a 2.5 mmol/l polyvinylsulfate potassium solution. The solution was prepared by weighting 0.234 g polyvinylsulfate potassium salt in a volumetric flask (500 ml) and dissolving it with approximately 250 ml deionized water. 500 l formaldehyde solution 37% and 100 l benzylalcohol 99% were added and the solution was filled up to 500 ml with deionized water.

[0231] The titration solution factor (f) for the 2.5 mmol/l polyvinylsulfate potassium solution was determined by titrating 10.0 g demineralized water with 1000 ml poly-DADMAC 2.5 mmol/l solution. The factor f was calculated by the following equitation:

factor (f)=volume theoretical (ml)/volume used (ml)

[0232] The charge density of the titrated sample was calculated by the following equation:

charge density=titrant consumption (ml)*2.5(mol/ml)*factor f/sample weight of the dry sample (g)

Weight Solids (% by Weight) or Solids Content of a Material in Suspension

[0233] The weight of solids is determined by dividing the weight of the solid material by the total weight of the aqueous suspension. The solids content of a suspension given in wt.-% in the meaning of the present invention can be determined using a Moisture Analyzer HR73 from Mettler-Toledo (T=120 C., automatic switch off 3, standard drying) with a sample size of 5 to 20 g.

Turbidity

[0234] For each sample the turbidity was measured after a settling period of 20 min. The turbidity was measured with a Hach Lange 2100AN IS Laboratory Turbidimeter and the calibration was performed using StabCal turbidity standards (formazin standards) of <0.1, 20, 200, 1000, 4000 and 7500 NTU.

Preparation of the Surface-Treated Mineral Material

[0235] Mineral material is coated with a cationic coating material. The used mineral materials are listed below:

TABLE-US-00001 weight median Sample Mineral bulk density of the particle name material dry powder diameter d.sub.50 A Ground calcium 1.3 g/cm.sup.3 5.0 m carbonate GCC B Hydromagnesite (PHM) 0.15 g/cm.sup.3 8.4 m C Zeolite (clinoptilolite) 0.41 g/cm.sup.3 12 m D Surface modified calcium 0.15 g/cm.sup.3 4.7 m carbonate MCC E Hydromagnesite (PHM) 0.70 g/cm.sup.3 1.68 m F Zeolite X 0.66 g/cm.sup.3 3.57 m G Clinoptilolite 0.68 g/cm.sup.3 2.06 m H Surface modified calcium 0.62 g/cm.sup.3 1.84 m carbonate MCC I Diatomite 0.72 g/cm.sup.3 2.60 m

[0236] The used cationic coating material are [0237] Catiofast BP Liquid commercially available from BASF, a cationic homopolymer based on diallyldimethyl ammonium chloride (polyDADMAC) [0238] Iron (III) chloride commercially available from Sigma-Aldrich, CAS Number 7705-08-0

[0239] The used dispersing agent is ETHACRYL M dispersant available from Coatex.

[0240] A slurry of the mineral material having a solids content of 10 wt.-% is provided. The mineral material is optionally dispersed with 1.8 wt.-% dispersing agent and coated with the cationic coating material as follows: [0241] The mineral material is coated with 1.8 wt.-% of the cationic polymer, based on the total weight of the mineral material. [0242] The mineral material is coated with iron (III) chloride, whereby the iron mass is 10 wt.-%, based on the dry weight of the zeolite.

[0243] The obtained slurry is vigorously agitated to obtain a homogenous slurry and to avoid settling.

[0244] The following surface-treated mineral materials are obtained:

TABLE-US-00002 Mineral Sample number material Dispersing agent Cationic coating material Example 1 A yes Catiofast BP Liquid Example 2 B yes Catiofast BP Liquid Example 3 C yes Iron(III) chloride Example 4 C yes Iron(III) chloride and Catiofast BP Liquid Example 5 D yes Catiofast BP Liquid Example 6 E yes Catiofast BP liquid Example 7 F yes Catiofast BP liquid Example 8 G yes Catiofast BP liquid Example 9 H yes Catiofast BP liquid Example 10 I yes Catiofast BP liquid

Dewatering Tests

[0245] The sediment sample that is treated is obtained from RWE Power AG by Garzweiler (Germany). The location of sampling takes place at the Sandfang LD10 pond. The provided sample is dark brown, nearly black, of very fine and oily consistency and has a total solids content of 13.8 wt.-%, based on the total weight of the provided sample. The provided sediment sample is an organic sediment sample.

The sediment sample is homogenized by mixing and sieving the sample on a 500 m mesh and afterwards diluted with water to a total solids content of 5 wt.-%, based on the total weight of the sample.

[0246] The surface-treated mineral material samples of Example A are added to the diluted sediment sample. 20 kg of the surface-treated mineral material are added per ton sludge (dry/dry) which represents 1000 ppm of the surface-treated mineral material, based on the total weight of the diluted sediment. The mixture is mixed for 2 minutes.

[0247] Afterwards the treated sediment sample is filtered on a Buchner funnel 90 mm with a Whatman filter paper 589/1 (90 mm) having a pore size of 12 to 25 m. The filtration is performed under standard ambient conditions with a diaphragm pump from Vacuubrand Type MZ 2C with a suction capacity of 2.4 m.sup.3/hour for 10 min.

[0248] The filter cake is removed and dried in an oven at 70 C. under normal pressure (100 kPa) for 10 hrs. The mass of the filter cake is measured before and after drying with an analytical balance of Mettler Toledo. The solids content of the samples is calculated based on the mass before and after drying. The values are listed in the table below. Furthermore, the turbidity of the filtrate is measured.

TABLE-US-00003 Solids content Sample Mineral of the filter Turbidity of number material cake the filtrate Sample 1 Example 1 8.6 wt.-% 100 NTU Sample 2 Example 2 40.4 wt.-% 29 NTU Sample 3 Example 3 39.2 wt.-% 11 NTU Sample 4 xample 4 41.0 wt.-% 21 NTU Sample 5 Example 5 42.4 wt.-% 78 NTU Sample 6 Example 6 38.4 wt.-% 36 NTU Sample 7 Example 7 37.5 wt.-% 44 NTU Sample 8 Example 8 34.5 wt.-% 38 NTU Sample 9 Example 9 37.3 wt.-% 46 NTU Sample 10 Example 10 35.4 wt.-% 49 NTU

[0249] This data shows that sediment treatment, especially the increasing of the solids content of an aqueous sediment is possible with the process of the present invention. As can be seen from samples 2 to 10 it is possible by a process according to the present invention, wherein at least one surface-treated mineral material is used, wherein the mineral material prior to coating has a bulk density of the dry powder between 0.05 g/mL and 0.80 g/mL and the mineral material particles prior to coating have a weight median particle diameter d.sub.50 value of from 0.1 m to 50 m and wherein the mineral material is covered by a material which provides a cationic charge it is possible to increase the solids content of the aqueous sediment by filtration. Furthermore, it can be seen that the solids content of the samples of the inventive process (samples 2 to 10) is much higher than the solids content of the comparative process (sample 1), wherein the used surface-treated mineral material is GCC having a tapped bulk density of 1.3 g/mL and a weight median particle diameter of 5.0 m. In sample 1 the filter is blocked and, therefore, most of the water does not flow through the filter but stays in the filter cake and above in the funnel. Thus the solids content of the filter cake is relatively low. Contrary to that the filter cake in samples 2 to 10 is not blocked and, therefore, a huge amount of water flows through the filter. Therefore, the solids content of the filter cake is relatively high.

[0250] In addition, the turbidity values of the filtrate are much lower in samples 2 to 10 (11 to 78 NTU) in comparison to sample 1 (100 NTU). Therefore, the filtration quality and efficiency of the inventive process is increased in comparison to a comparative process.