Dolomite-based heavy metal adsorbent, preparation, and use for adsorbing heavy metal, halogen and metalloid

Abstract

A dolomite-based adsorbent for heavy metal, halogen and metalloid is half-fired dolomite, and a content of a residual CaMg(CO.sub.3).sub.2 phase in the half-fired dolomite, which is analyzed using a Rietveld method by means of powder X-ray diffraction, is 0.4x35.4 (wt %), and preferably, the dolomite-based absorbent for heavy metal, halogen and metalloid further comprises ferrous sulfate.

Claims

1. A dolomite-based adsorbent for heavy metal, halogen and metalloid, wherein the dolomite-based absorbent comprises half-fired dolomite and a ferrous compound, and a content of a residual CaMg(CO.sub.3).sub.2 phase in the half-fired dolomite, which is analyzed using a Rietveld method by means of powder X-ray diffraction, is 0.4x35.4 (wt %).

2. The dolomite-based adsorbent for heavy metal, halogen and metalloid according to claim 1, wherein the ferrous compound is selected from the group consisting of ferrous chloride and ferrous sulfate.

3. A method for preparing a dolomite-based adsorbent for heavy metal, halogen and metalloid, comprising: firing dolomite so that a content of a residual CaMg(CO.sub.3).sub.2 phase in the obtained dolomite material, which is analyzed using a Rietveld method by means of powder X-ray diffraction, is 0.4x35.4 (wt %), and blending ferrous compound in the obtained dolomite material.

4. The method for preparing a dolomite-based adsorbent for heavy metal, halogen and metalloid according to claim 3, wherein the ferrous compound is selected from the group consisting of ferrous chloride and ferrous sulfate.

5. A method for controlling a quality of a dolomite-based adsorbent containing half-fired dolomite and a ferrous compound for heavy metal, halogen and metalloid, comprising: adjusting a residual amount of a residual CaMg(CO.sub.3).sub.2 phase in the obtained dolomite-based material by firing dolomite so that a content of the residual CaMg(CO.sub.3).sub.2 phase in the obtained half-fired dolomite material, which is analyzed using a Rietveld method by means of powder X-ray diffraction, is 0.4x35.4 (wt %), is obtained.

6. A method for adsorbing heavy metal, halogen and metalloid, comprising: using the dolomite-based adsorbent for heavy metal, halogen and metalloid according to claim 1.

7. A method for adsorbing heavy metal, halogen and metalloid, comprising: using the dolomite-based adsorbent for heavy metal, halogen and metalloid according to claim 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a line graph illustrating contents of a residual dolomite phase and an adsorption removal ratio of heavy metal, halogen and metalloid in a fired-dolomite material which is an example of a dolomite-based heavy metal adsorbent.

(2) FIG. 2 is a line graph illustrating contents of a residual dolomite phase and an adsorption removal ratio of heavy metal, halogen and metalloid in a fired-dolomite material which is another example of a dolomite-based heavy metal adsorbent.

(3) FIG. 3 is a line graph illustrating contents of a residual dolomite phase and an adsorption removal ratio of heavy metal, halogen and metalloid in a fired-dolomite material which is still another example of a dolomite-based heavy metal adsorbent.

(4) FIG. 4 is a line graph illustrating contents of a residual dolomite phase and an adsorption removal ratio of heavy metal, halogen and metalloid in a fired-dolomite material which is still another example of a dolomite-based heavy metal adsorbent.

(5) FIG. 5 is a line graph illustrating contents of a residual dolomite phase and an adsorption removal ratio of heavy metal, halogen and metalloid in a fired-dolomite material which is still another example of a dolomite-based heavy metal adsorbent.

(6) FIG. 6 is a line graph illustrating contents of a residual dolomite phase and an adsorption removal ratio of heavy metal, halogen and metalloid in a fired-dolomite material which is still another example of a dolomite-based heavy metal adsorbent.

DETAILED DESCRIPTION OF THE INVENTION

(7) The present invention will be described using the following preferred examples, but is not limited thereto.

(8) A dolomite-based adsorbent for heavy metal halogen and metalloid of the present invention is an adsorbent that is half-fired dolomite, in which the content of a residual CaMg(CO.sub.3).sub.2 phase in the half-fired dolomite, which is analyzed using the Rietveld method by means of powder X-ray diffraction, is 0.4x35.4 (wt %).

(9) Here, the substances that can be adsorbed and removed are heavy metal, halogen, and metalloid. The heavy metal can be exemplified by one or more of chromium, lead, cadmium, and the like, and the halogen can be exemplified by chlorine, fluorine, and the like, and metalloid can be exemplified by one or more of arsenic, boron and the like but the heavy metal, halogen, and metalloid are not limited thereto.

(10) Since there is a close relationship between the content of a residual dolomite phase in fired dolomite and the adsorption removal ratio of heavy metal, halogen and metalloid, the present invention enables dolomite to have most excellent adsorption properties for heavy metal, halogen and metalloid regardless of the difference in composition caused by the difference in localities of a dolomite mineral as a raw material, setting of firing conditions such as the firing temperature, and the like by determining the amount of a CaMg(CO.sub.3).sub.2 phase in the half-fired dolomite and adjusting the amount to be a residual amount in the above specific range.

(11) Any of raw dolomite material can be used as raw dolomite material in the present invention, and the locality or the composition of the raw material dolomite does not matter.

(12) Dolomite has a double salt structure in which the molar ratio between limestone (CaCO.sub.3) and magnesite (MgCO.sub.3) reaches 1:1, Ca.sup.2+ ions and Mg.sup.2+ ions form layers with each other with a CO.sub.3.sup.2 group therebetween, and, generally, the proportion of magnesium carbonate is in a range of 10 wt % to 45 wt %. Since a large amount of dolomite is present in Japan, an absorbent for heavy metal, halogen and metalloid is prepared using the dolomite is also advantageous in views of costs or environmental load.

(13) When dolomite is fired, a decomposition reaction represented by the following formula is caused:
CaMg(CO.sub.3).sub.2.fwdarw.MgO+CaCO.sub.3+CO.sub.2(1)

(14) It is considered that the thermal decomposition of dolomite by means of firing forms fine pores and adsorption properties for heavy metal, halogen and metalloid is exhibited.

(15) In the present invention, half-fired dolomite in which the content of a residual CaMg(CO.sub.3).sub.2 phase in the half-fired dolomite obtained by firing dolomite, which is analyzed using the Rietveld method by means of powder X-ray diffraction, is 0.4x35.4 (wt %) and preferably 1.8x17.4 (wt %), the dolomite can have excellent adsorption properties for heavy metal, halogen and metalloid.

(16) In a case in which the content of the residual CaMg(CO.sub.3).sub.2 phase is smaller than 0.4 wt % or larger than 35.4 wt %, the adsorption properties for heavy metal, halogen and metalloid of the dolomite is small.

(17) Unlike a TG-DSC method, the powder X-ray diffraction method is capable of accurately analyzing the amounts of a CaMg(CO.sub.3).sub.2 phase, a CaCO.sub.3 phase, and a MgO phase in the half-fired dolomite, and thus it becomes possible to accurately determine the amount of the residual CaMg(CO.sub.3).sub.2 phase in the half-fired dolomite.

(18) The present dolomite-based adsorbent invention, preferably, further comprises a ferrous compound, examples of which include ferrous sulfate and ferrous chloride.

(19) Regarding the blended amount of the ferrous composition, the weight ratio between the ferrous composition and half-fired dolomite in which the content of the residual CaMg(CO.sub.3).sub.2 phase is 0.4x35.4 (wt %) is in a range of 5:5 to 9:1 and preferably 9:1.

(20) When the absorbent includes the ferrous composition, high adsorption properties for heavy metal, halogen and metalloid are also obtained. Due to its reduction action, it is possible to more effectively insolubilize heavy metal, halogen and metalloid, and it becomes possible to remove heave metal, halogen and metalloid from contaminated waste water or contaminated soils.

(21) In addition, in the method for preparing a dolomite-based adsorbent for heavy metal, halogen and metalloid of the present invention, dolomite is fired so that the content of the residual CaMg(CO.sub.3).sub.2 phase in the obtained dolomite-based material, which is analyzed using the Rietveld method by means of powder X-ray diffraction, is 0.4x35.4 (wt %).

(22) The temperature at which dolomite is fired is not particularly limited, and dolomite can be fired at an ordinary temperature at which dolomite is fired so as to prepare half-fired dolomite, for example, a temperature in a range of 650 C. to 1000 C. The firing duration is also not limited as long as dolomite is fired so that the content of the residual CaMg(CO.sub.3).sub.2 phase is 0.4x35.4 (wt %).

(23) In a process of firing dolomite, when half-fired dolomite is selected at a point in time at which the content of the residual CaMg(CO.sub.3).sub.2 phase is 0.4x35.4 (wt %), the dolomite-based adsorbent for heavy metal, halogen and metalloid of the present invention can be obtained.

(24) In addition, when the content of the residual CaMg(CO.sub.3).sub.2 phase in the fired-dolomite material analyzed using the Rietveld method by means of powder X-ray diffraction of the fired-dolomite material is adjusted to 0.4x35.4 (wt %), it is possible to facilitate quality control so that dolomite has excellent adsorption properties for heavy metal, halogen and metalloid.

(25) When the dolomite-based heavy metal adsorbent of the present invention is brought into contact with contaminated soils or contaminated waste water, it is possible to adsorb and remove heavy metal, halogen and metalloid in the contaminated soils or the contaminated waste water.

(26) As a contact method, a well-known arbitrary method is applicable, and examples thereof include mixing of the dolomite-based adsorbent for heavy metal, halogen and metalloid of the present invention and soils and a method in which the dolomite-based adsorbent for heavy metal, halogen and metalloid of the present invention is added into and stirred with waste water. In addition, in a case in which the dolomite-based adsorbent for heavy metal, halogen and metalloid of the present invention is added into contaminated waste water, it is also possible to collect heavy metal, halogen and metalloid by adding an agglomerating agent and conducting solid-liquid separation.

EXAMPLES

(27) The present invention will be described by the following examples and comparative examples.

(28) Six kinds of dolomite from different A to F localities were fired at 800 C. in the air for 10 minutes to 120 minutes, and, during that period, a fired-dolomite material was obtained every 10 minutes from the beginning of the firing. For the respective fired-dolomite materials, the contents of a residual CaMg(CO.sub.3).sub.2 phase in the respective fired-dolomite materials were analyzed by the powder X-ray diffraction Rietveld method under the below conditions.

(29) The results are respectively shown in Tables 1 to 6 and FIGS. 1 to 6 (dolomite from the A locality is in Table 1 and FIG. 1; dolomite from the B locality is in Table 2 and FIG. 2; dolomite from the C locality is in Table 3 and FIG. 3; dolomite from the D locality is in Table 4 and FIG. 4; dolomite from the E locality is in Table 5 and FIG. 5; dolomite from the F locality is in Table 6 and FIG. 6).

(30) TABLE-US-00001 TABLE 1 Amount determination results of individual phases by means of Rietveld analysis (wt. %) Firing duration [min] CaMg(CO.sub.3).sub.2 CaCO.sub.3 MgO CaO Ca(OH).sub.2 SiO.sub.2 0 82.5 17.5 0 0 0 0 10 44.6 55.6 0 0 0 0 20 19.4 63.8 16.8 0 0 0 30 2.6 76.5 20.9 0 0 0 40 0.5 77.0 22.5 0 0 0 60 0.1 80.7 17.9 1.1 0.1 0 120 0 66.9 28.2 3.9 1.0 0

(31) TABLE-US-00002 TABLE 2 Amount determination results of individual phases by means of Rietveld analysis (wt. %) Firing duration [min] CaMg(CO.sub.3).sub.2 CaCO.sub.3 MgO CaO SiO.sub.2 0 85.9 11.7 0 0 2.3 10 73.2 24.6 0 0 2.2 20 26.9 64.5 5.0 0 3.7 30 21.5 70.1 5.6 0 2.8 40 4.5 79.6 12.2 0 3.6 50 0.5 81.9 13.1 0 4.6 60 0.3 80.2 15.3 0.3 4.0 70 0 75.0 20.1 1.1 3.8 80 0 71.7 20.4 3.3 4.6 120 0 68.3 20.2 7.9 3.7

(32) TABLE-US-00003 TABLE 3 Amount determination results of individual phases by means of Rietveld analysis (wt. %) Firing duration [min] CaMg(CO.sub.3).sub.2 CaCO.sub.3 MgO CaO SiO.sub.2 0 54.3 44.3 0 0 1.4 10 36.0 55.8 0 0 1.3 20 17.4 74.3 7.2 0 1.0 30 4.4 86.5 7.9 0 1.2 40 0.4 83.5 14.6 0 1.5 50 0 81.6 15.8 0.8 1.8 60 0 83.3 12.3 2.4 2.0 120 0 61.6 12.7 24.0 1.6

(33) TABLE-US-00004 TABLE 4 Amount determination results of individual phases by means of Rietveld analysis (wt. %) Firing duration [min] CaMg(CO.sub.3).sub.2 CaCO.sub.3 MgO CaO SiO.sub.2 0 93.9 5.9 0 0 0.2 10 44.1 48.3 7.4 0 0.2 20 27.5 60.9 11.3 0 0.3 30 5.9 80.3 13.5 0 0.3 40 4.5 81.9 13.3 0 0.3 50 1.1 84.7 13.9 0 0.3 60 0.6 84.2 14.9 0 0.3 70 0 76.5 21.7 1.6 0.1 80 0 76.9 19.5 3.3 0.3 120 0 61.8 21.9 16.1 0.1

(34) TABLE-US-00005 TABLE 5 Amount determination results of individual phases by means of Rietveld analysis (wt. %) Firing duration [min] CaMg(CO.sub.3).sub.2 CaCO.sub.3 MgO CaO SiO.sub.2 0 100 0 0 0 0 10 63.5 32.0 4.4 0 0 20 35.4 54.9 8.7 0 0 30 11.1 77.1 11.8 0 0 40 2.8 83.9 13.3 0 0 50 0 87.7 11.8 0.5 0 60 0 84.4 15.0 0.6 0 120 0 66.6 24.1 9.6 0

(35) TABLE-US-00006 TABLE 6 Amount determination results of individual phases by means of Rietveld analysis (wt. %) Firing duration [min] CaMg(CO.sub.3).sub.2 CaCO.sub.3 MgO CaO SiO.sub.2 0 100 0 0 0 0 10 73.6 22.8 3.6 0 0 20 37.9 54.1 8.0 0 0 30 25.3 65.2 9.6 0 0 40 10.5 76.9 12.7 0 0 50 4.8 79.7 15.6 0 0 60 1.8 81.2 17.1 0 0 70 0 77.4 21.1 1.6 0 80 0 74.0 21.4 4.6 0 90 0 72.5 21.2 6.3 0 100 0 63.5 22.4 14.0 0 110 0 67.6 21.7 10.7 0 120 0 63.7 22.3 14.0 0

(36) The measurement conditions of the powder X-ray diffraction are as described below.

(37) Apparatus name: PANalytical X'Pert Pro MPD

(38) Rietveld analysis software: PANalytical X'Pert HighScore Plus

(39) Measurement Conditions

(40) Bulb: Cu-K

(41) Tube voltage: 45 kV

(42) Current: 40 mA

(43) Divergence slit: variable (12 mm)

(44) Anti-Scatter slit (incidence side): none

(45) Solar slit (incidence side): 0.04 Rad

(46) Receiving slit: none

(47) Anti-Scatter slit (light receiving side): variable (12 mm)

(48) Solar slit (light receiving side): 0.04 Rad

(49) Scanning field: 2=590

(50) Step scanning: 0.008

(51) Continuous scanning time: 0.10/sec

(52) Each of the fired-dolomite material (1 g) was added to 100 mg of respective solutions (100 ml) containing arsenic (As), fluorine (F), or lead (Pb) (5 mg/l, respectively) which were prepared using respective reagents shown in Table 7, uniformly mixing with four-hour vibration is conducted.

(53) TABLE-US-00007 TABLE 7 Element Reagent As(III) NaAsO.sub.2 F NaF Pb Pb(NO.sub.3).sub.2

(54) After that, the adsorption removal ratio of arsenic in the solution and the average removal ratios of the arsenic, fluorine, and lead were calculated from the residual amounts of arsenic, fluorine, and lead remaining in the respective solutions using individual methods shown in Table 8 below, and the results are respectively shown in Tables 9 to 14 and FIGS. 1 to 6 (dolomite from the A locality is in Table 9 and FIG. 1; dolomite from the B locality is in Table 10 and FIG. 2; dolomite from the C locality is in Table 11 and FIG. 3; dolomite from the locality D is in Table 12 and FIG. 4; dolomite from the E locality is in Table 13 and FIG. 5; dolomite from the F locality is in Table 14 and FIG. 6).

(55) Meanwhile, for lead, an ICP emission spectroscopic analysis method in the case of an analysis of an mg/l order is used, and electrothermal atomizer atomic absorption spectrometry in the case of an analysis of a g/l order is used.

(56) In addition, the pH and oxidation reduction potential (ORP) of a filtrate were measured using a desktop pH meter: F-73 manufactured by Horiba, Ltd. (pH electrode: 9615S-10D, ORP electrode: 9300-10D), and the results are also shown in Tables 9 to 14.

(57) TABLE-US-00008 TABLE 8 Subject element Analysis method As JIS K 0102-2008 61.2 Hydride generation atomic absorption spectrometry F JIS K 0170-2011 6 Lanthanum/Alizarin Complexone method Pb JIS K 0102-2008 54.2 Electrothermal atomizer atomic absorption spectrometry JIS K 0102-2008 54.3 ICP emission spectroscopic analysis method

(58) TABLE-US-00009 TABLE 9 Adsorption test Firing Properties of duration Adsorption removal ratio [%] filtrate [min] As(III) F Pb Average pH ORP [mV] 0 5.7 9.8 97.9 37.8 8.0 280 10 83.4 83.1 86.9 84.5 9.4 190 20 95.6 97.9 97.8 97.1 10.8 202 30 96.0 97.9 99.6 97.8 10.8 204 40 95.1 95.8 97.9 96.3 11.2 180 60 76.5 35.1 80.0 63.9 12.0 92 120 72.1 29.5 41.2 47.6 12.3 42

(59) TABLE-US-00010 TABLE 10 Adsorption test Firing Properties of duration Adsorption removal ratio [%] filtrate [min] As(III) F Pb Average pH ORP [mV] 0 7.4 21.3 99.6 42.8 8.8 276 10 56.7 96.0 99.6 84.1 9.1 249 30 95.7 96.2 99.6 97.2 10.5 213 40 95.0 97.2 99.6 97.3 10.7 207 50 95.7 96.4 99.6 97.2 10.9 201 60 89.0 93.2 99.5 93.9 11.4 171 70 81.5 68.5 95.3 81.8 12.0 118 80 78.8 60.9 84.4 74.7 12.3 94 120 77.5 13.7 56.7 49.3 12.6 71

(60) TABLE-US-00011 TABLE 11 Adsorption test Firing Properties of duration Adsorption removal ratio [%] filtrate [min] As(III) F Pb Average pH ORP [mV] 0 5.7 19.0 97.9 40.8 9.2 279 10 83.4 77.6 97.9 86.3 10.8 196 20 95.6 96.9 99.6 97.4 10.9 197 30 96.4 96.6 99.6 97.5 11.0 197 40 95.1 91.4 99.6 95.4 11.3 186 50 87.7 54.9 90.5 77.7 11.9 142 60 76.5 35.1 72.8 61.5 12.6 97 120 72.1 29.5 50.5 50.7 12.1 58

(61) TABLE-US-00012 TABLE 12 Adsorption test Firing Properties of duration Adsorption removal ratio [%] filtrate [min] As(III) F Pb Average pH ORP [mV] 0 4.4 23.5 99.6 42.5 9.3 259 10 50.3 60.4 99.6 70.1 9.8 212 20 94.5 95.5 99.6 96.5 10.6 195 30 94.3 96.0 99.6 96.7 10.8 183 40 94.9 96.8 99.6 97.1 10.8 146 50 94.4 95.5 99.5 96.5 11.0 145 60 81.3 61.5 93.7 78.8 11.9 102 70 76.0 49.2 82.3 69.2 12.0 92 80 77.3 50.4 87.2 71.6 12.1 85 120 68.7 45.4 59.2 57.7 12.6 53

(62) TABLE-US-00013 TABLE 13 Adsorption test Firing Properties of duration Adsorption removal ratio [%] filtrate [min] As(III) F Pb Average pH ORP [mV] 0 24.7 28.4 99.6 50.9 10.1 216 10 92.4 89.7 99.6 93.9 10.8 193 20 95.2 94.1 99.6 96.3 10.9 192 30 96.0 96.4 99.6 97.3 10.9 187 40 95.7 96.4 99.6 97.2 10.9 189 50 84.4 79.4 99.6 87.8 11.4 152 60 77.6 57.9 99.6 78.4 11.6 132 120 42.3 12.9 44.1 33.1 12.6 52

(63) TABLE-US-00014 TABLE 14 Adsorption test Firing Properties of duration Adsorption removal ratio [%] filtrate [min] As(III) F Pb Average pH ORP [mV] 0 0.2 20.3 99.1 39.9 9.4 243 10 40.3 76.7 99.4 72.1 9.7 215 30 96.0 98.4 99.6 98.0 10.6 194 50 98.0 97.3 99.6 98.3 10.4 212 60 98.0 98.9 99.6 98.8 10.6 203 70 73.3 84.9 97.7 85.3 11.7 125 90 73.1 66.9 81.2 73.8 12.3 89 120 70.9 59.4 50.8 60.4 12.5 73

(64) From FIGS. 1 to 6 and the tables, it is found that, in an absorbent in which the adsorption removal ratio of heavy metal, halogen and metalloid is as high as 95% or higher, the content of the residual CaMg(CO.sub.3).sub.2 phase remaining in the half-fired dolomite is 0.4x35.4 (wt %) regardless of the localities of dolomite.

(65) In addition, 100 ml of respective solutions containing 5 mg/l and 100 mg/l of arsenic (As) were prepared using the reagents shown in Table 7. Uniform mixtures obtained by adding 1 g of half-fired dolomite in Table 1 in which the content of the dolomite (CaMg(CO.sub.3).sub.2) phase remaining in the half-fired dolomite is 2.6 wt % to the above solutions respectively by four-hour vibration and uniform mixtures obtained by adding 0.9 g of the half-fired dolomite and 0.1 g of ferrous sulfate to the solutions respectively by four-hour vibration were prepared. After that, the respective solutions were separated into solid and liquid, the amounts of residual arsenic in filtrates were measured by the method shown in Table 8, and respective arsenic adsorption removal ratios (%) were calculated. The results are shown in Table 15.

(66) In addition, the pH and oxidation reduction potential (ORP) of the filtrates were measured using a desktop pH meter: F-73 manufactured by Horiba, Ltd. (pH electrode: 9615S-10D, ORP electrode: 9300-10D), and the results are also shown in Table 15.

(67) TABLE-US-00015 TABLE 15 Properties of filtrate As 5 mg/l As 100 mg/l pH ORP [mv] Half-fired dolomite 95 95.6 11.6 200 10 Half-fired dolomite + 99.4 97.2 10.6 250 10 ferrous sulfate

(68) From the table, it is found that, when ferrous sulfate is added to the half-fired dolomite of the present invention in which the content of the residual dolomite (CaMg(CO.sub.3).sub.2) phase is 0.4x35.4 (wt %), the adsorption removal ratio of heavy metal, halogen and metalloid further increases.

(69) The present invention is capable of easily providing a dolomite-based heavy metal adsorbent having an excellent heavy metal adsorption removal ratio regardless of localities or the composition of raw dolomite material and thus can be applied to efficiently adsorb and remove harmful heavy metal, halogen and metalloid in waste water or soils, and, for example, can be effectively applied to a treatment of a large amount of contaminated soils containing heavy metal, halogen and metalloid generated due to an excavation work and a construction work for tunnels or dams or a treatment of waste water containing heavy metal, halogen and metalloid from plants and factories.