BARITE FOR HEAVY METAL REMOVAL

Abstract

The present invention relates to the use of particulate mineral material comprising barite for scavenging heavy metal anions from a liquid medium, wherein the heavy metal anions form water-insoluble barium salts with barium cations of the barite, and wherein the particulate mineral material has a specific surface area of from 0.1 m.sup.2/g to 100 m.sup.2/g, measured using nitrogen sorption and the BET method.

Claims

1. A method of using a particulate mineral material comprising barite for scavenging heavy metal anions from a liquid medium comprising the steps of, providing a particulate mineral material comprising barite and providing a liquid medium, wherein heavy metal anions form water-insoluble barium salts with barium cations of the barite, and wherein the particulate mineral material has a specific surface area of from 0.1 m.sup.2/g to 100 m.sup.2/g, measured using nitrogen sorption and the BET method.

2. The method according to claim 1, wherein the liquid medium is an aqueous medium, preferably the aqueous medium is selected from process water, sewage water, waste water, preferably waste water from the paper industry, waste water from the colour-, paints-, or coatings industry, waste water from breweries, waste water from the leather industry, agricultural waste water, slaughterhouse waste water, process or waste water from power plants, waste water from waste incineration, waste water from mercury recycling, waste water from cement production, waste water from concrete handling and production, waste water from shotcrete handling and production, waste water from steel production, waste water from production of fossil fuels, from sludge, preferably sewage sludge, harbour sludge, river sludge, coastal sludge, digested sludge, mining sludge, municipal sludge, civil engineering sludge, jet grouting sludge, sludge from oil drilling or the effluents the aforementioned dewatered sludges, or aqueous compositions comprising cement, preferably a cement paste or an aqueous building material comprising cement, or an aqueous system comprising hardened cement, preferably recycled concrete, or an aqueous system comprising wood ash.

3. The method according to claim 1, wherein the particulate mineral material comprises at least 60 wt.-% barite, based on the total weight of the particulate mineral material, preferably at least 80 wt.-%, more preferably at least 90 wt.-%, even more preferably at least 95 wt.-%, and most preferably the particulate mineral material consists of barite.

4. The method according to claim 1, wherein the particulate mineral material has a volume median particle size d.sub.50 from 0.05 to 20 μm, preferably from 0.1 to 2 μm, more preferably from 0.2 to 0.8 μm, and most preferably from 0.3 to 0.5 μm, and/or a volume top cut particle size d.sub.98 from 0.15 to 200 μm, preferably from 0.5 to 50 μm, more preferably from 0.8 to 25 μm, and most preferably from 0.8 to 10 μm.

5. The method according to claim 1, wherein the particulate mineral material has a specific surface area of from 0.5 m.sup.2/g to 80 m.sup.2/g, preferably from 1 m.sup.2/g to 60 m.sup.2/g, more preferably from 3 m.sup.2/g to 50 m.sup.2/g, even more preferably from 4 m.sup.2/g to 35 m.sup.2/g, and most preferably from 10 m.sup.2/g to 30 m.sup.2/g, measured using nitrogen sorption and the BET method.

6. The method according to claim 1, wherein the particulate mineral material is used in combination with a pH modifying agent, preferably selected from the group consisting of slaked lime, calcium carbonate, sodium hydroxide, potassium hydroxide, dolomite, half-burned dolomite, lime, brucite, magnesium oxide, and any combination thereof.

7. The method according to claim 1, wherein the heavy metal anions are selected from the group consisting of chromate, arsenate, manganate, molybdate, selenate, ferrocyanide, and mixtures thereof.

8. (canceled)

9. The method according to claim 1, wherein the liquid medium contains the heavy metal anions, and comprising the further step of: contacting the particulate mineral material and the liquid medium to scavenge heavy metal anions from the liquid medium by forming a heavy metal loaded particulate mineral material.

10. A method according to claim 1 comprising the further steps of: providing a material composition that releases heavy metal anions on contact with said liquid medium, wherein the heavy metal anions form water-insoluble barium salts with barium cations of the barite, and contacting the particulate mineral material, the liquid medium, and the material composition in any order to form a liquid medium containing said heavy metal anions and to scavenge said heavy metal anions from the liquid medium by forming a heavy metal loaded particulate mineral material.

11. The method of claim 9, wherein the particulate mineral material comprising barite is provided in a weight ratio of from 1:20000 to 1:30, preferably from 1:10000 to 1:35, more preferably from 1:1000 to 1:40 and most preferably from 1:850 to 1:45, relative to the weight of the heavy metal anions in the liquid medium.

12. The method of claim 9, wherein the method further comprises a subsequent step of removing the heavy metal loaded particulate mineral material from the liquid medium, preferably said step is performed by filtration, centrifugation, sedimentation, or flotation.

13. A building material composition comprising cement and a particulate mineral material comprising barite as scavenger for heavy metal anions, wherein the heavy metal anions form water-insoluble barium salts with barium cations of the barite, and wherein the particulate mineral material has a specific surface area of from 0.1 m.sup.2/g to 100 m.sup.2/g, measured using nitrogen sorption and the BET method.

14. The building material composition of claim 13, wherein the building material composition is Portland cement, Pozzolan-lime cement, slag-lime cement, supersulfated cement, calcium sulfoaluminate cement, concrete, mortar, or hardened concrete.

15. A method of using a particulate mineral material comprising barite as a scavenger for heavy metal anions in a building material composition comprising cement comprising the steps of, mixing the particulate mineral material with a dry building material to form the building material composition; and adding a liquid medium to the building material composition; wherein the heavy metal anions form water-insoluble barium salts with barium cations of the barite, and wherein the particulate mineral material has a specific surface area of from 0.1 m.sup.2/g to 100 m.sup.2/g, measured using nitrogen sorption and the BET method.

16. The method of claim 10, wherein the particulate mineral material comprising barite is provided in a weight ratio of from 1:20000 to 1:30, preferably from 1:10000 to 1:35, more preferably from 1:1000 to 1:40 and most preferably from 1:850 to 1:45, relative to the weight of the heavy metal anions in the liquid medium.

17. The method of claim 10, wherein the method further comprises a subsequent step of removing the heavy metal loaded particulate mineral material from the liquid medium, preferably said step is performed by filtration, centrifugation, sedimentation, or flotation.

18. The composition of claim 13, wherein the particulate mineral material comprises at least 60 wt.-% barite, based on the total weight of the particulate mineral material, preferably at least 80 wt.-%, more preferably at least 90 wt.-%, even more preferably at least 95 wt.-%, and most preferably the particulate mineral material consists of barite.

19. The composition of claim 13, wherein the particulate mineral material has a volume median particle size d.sub.50 from 0.05 to 20 μm, preferably from 0.1 to 2 μm, more preferably from 0.2 to 0.8 μm, and most preferably from 0.3 to 0.5 μm, and/or a volume top cut particle size d.sub.98 from 0.15 to 200 μm, preferably from 0.5 to 50 μm, more preferably from 0.8 to 25 μm, and most preferably from 0.8 to 10 μm.

20. The composition of claim 13, wherein the particulate mineral material has a specific surface area of from 0.5 m.sup.2/g to 80 m.sup.2/g, preferably from 1 m.sup.2/g to 60 m.sup.2/g, more preferably from 3 m.sup.2/g to 50 m.sup.2/g, even more preferably from 4 m.sup.2/g to 35 m.sup.2/g, and most preferably from 10 m.sup.2/g to 30 m.sup.2/g, measured using nitrogen sorption and the BET method.

21. The composition of claim 13, wherein the heavy metal anions are selected from the group consisting of chromate, arsenate, manganate, molybdate, selenate, ferrocyanide, and mixtures thereof.

Description

EXAMPLES

1. Methods

Specific Surface Area (BET)

[0151] The specific surface area (in m.sup.2/g) is determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:2010). The total surface area (in m.sup.2) of the filler material is then obtained by multiplication of the specific surface area and the mass (in g) of the corresponding sample.

Particle Size

[0152] Volume median particle size d50 (vol) and volume top cut particle size d98 (vol) are evaluated using a Malvern Mastersizer 3000 Laser Diffraction System equipped with an Aero S dry dispersing unit. The d50 or d98 value, measured using a Malvern Mastersizer 3000 Laser Diffraction System, indicates a diameter value such that 50% or 98% by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement are analysed using the Fraunhofer theory.

[0153] The processes and instruments are known to the skilled person and are commonly used to determine the particle size of fillers and pigments.

2. Materials

[0154]

TABLE-US-00001 TABLE 1 List of particular mineral materials and their physical characteristics. SSA(BET) d.sub.50 d.sub.98 Mineral Description [m.sup.2/g] [μm] [μm] B1 Natural white barite, 5.6 1.0 6.9 dry-ground on a jet mill B2 Natural white barite, 1.3 4.3 12 dry-ground on a pin mill (intermediate fraction) B3 Natural white barite, 0.7 9.6 78 dry-ground on a pin mill (coarse fraction) B4 Natural barite, 2.2 18 410 API grade, commercial product B5 White natural barite, 38.2 n/a n/a wet-milled in a ball mill and dried B6 White natural barite, 32.2 n/a n/a wet-milled in a ball mill and dried B7 White natural barite, 10.1 n/a n/a wet-milled in a ball mill and dried B8 White natural barite, 8.0 n/a n/a wet-milled in a ball mill and dried B9 White natural barite, 9.8 n/a n/a wet-milled in a (nano) ball mill and dried B10 White natural barite, 12.4 n/a n/a wet-milled in a (nano) ball mill and dried B11 White natural barite, 14.9 n/a n/a wet-milled in a (nano) ball mill and dried B12 Natural white barite, dry-ground on a 0.6 22 320 pin mill B13 Natural white barite, dry-ground on a 0.8 10 115 pin mill B14 Natural white barite, dry-ground on a 1.4 3.8 11 pin mill B15 Natural white barite, dry-ground on a 3.1 1.4 5.4 pin mill B16 Omyacarb ® 1-AV, 3.7 2.2 10.2 commercial natural calcium carbonate

3. Examples

Example 1—Chromate Scavenging Experiments with Calcium Carbonate as pH Modifier

[0155] A chromate (Cr(VI)) stock solution was prepared by dilution of a commercial 1000 ppm standard (TraceCERT®, 1000 mg/L Cr in nitric acid, prepared with (NH4)2Cr2O7, Sigma Aldrich, 68131-100ML-F) with Milli-Q filtered, deionized water to 1 ppm. For each experiment, 100-200 g of this stock solution was transferred into a glass flask and the barite-containing particulate mineral material and optionally calcium carbonate were added according to the indicated quantities. The solids were suspended by magnetic stirring with 25 mm stirring bars (800 rpm, 1 h). Subsequently, the suspensions filtered through a syringe filter (Chromafil Xtra, RC-20/25 0.2 μm). The content of Cr(VI) c(CrVI) was analysed using LCK 313 cuvette tests (EN ISO 11083) evaluated in a Hach Lange DR6000 spectral photometer.

TABLE-US-00002 TABLE 2 Removal experiments with 95 g of a 1 ppm Cr(VI) stock solution. Mineral m.sub.Mineral 1 Mineral m.sub.Mineral 2 c(Cr.sub.VI) Removal Test 1 [mg] 2 [mg] [ppm] [%] C0 — — — — 0.998 — (com- parative) C1 B1 1000 B16 100 0.03 97 C2 B1 500 B16 100 0.052 95 C3 B1 250 B16 100 0.099 90 C4 B1 500 — — 0.042 96 C5 B2 500 B16 100 0.268 73 C6 B3 500 B16 100 0.622 38 C7 B4 500 B16 100 0.696 30

[0156] From tests C1-C3, it is evident that the addition of a barite-containing particulate mineral material in combination with calcium carbonate leads to a reduced concentration of chromate in the solutions. The addition of larger quantities of barite leads to higher chromate removal. Test C4 demonstrates that a similar effect is attained also in the absence of calcium carbonate. Furthermore, tests C5-C7 demonstrate that the removal efficiency can be controlled by the particle size and the specific surface area.

Example 2—Chromate Scavenging Under High pH Conditions

[0157] A chromate (Cr(VI)) stock solution was prepared by dilution of a commercial 10000 ppm standard (Sigma Aldrich) with Milli-Q filtered, deionized water to 10 ppm, 4 ppm, 2 ppm, and 0.5 ppm. 90 g of the stock solutions were transferred into a glass flask. Subsequently, 1 mL milk of lime (10 wt.-% Tagger Lime from Golling, Austria) was added to each glass flask to simulate the pH conditions in aqueous compositions comprising cement. Then, 0.5 g of the barite-containing mineral particulate mineral material was added. The solids were suspended by magnetic stirring (800 rpm, 1 h) and subsequently filtered through a syringe filter (Chromafil Xtra, RC-20/25 0.2 μm). The pH of the filtered solution were measured using a Mettler Toledo SevenMulti™ pH meter. The concentrations of Cr(IV) c(CrIV) in the filtered solutions was determined on a Hach Lange DR6000 spectral photometer using LCK 313 (Cr). Samples were diluted as necessary to match the target range of the cuvette tests.

TABLE-US-00003 TABLE 3 Experimental details and results of chromate removal experiments. Test Mineral m.sub.mineral [mg] m.sub.Cr, solution [g] C.sub.Cr, start [mg/L] C.sub.Cr, end [mg/L] Cr.sub.removed [%] pH C8 B5 499.8 90.0 9.25 1.38 85.1 12.38 C9 B5 499.6 90.0 3.48 0.323 90.7 12.39 C10 B5 500.2 90.0 1.71 0.121 92.9 12.36 C11 B5 499.5 90.0 0.445 0.053 88.1 12.37 C12 B6 499.2 90.0 9.25 1.51 83.7 12.37 C13 B6 499.2 90.0 3.48 0.347 90.0 12.38 C14 B6 500.8 90.0 1.71 0.13 92.4 12.37 C15 B6 499.8 90.0 0.445 0.054 87.9 12.37 C16 B7 500.6 90.0 9.25 3.76 59.4 12.36 C17 B7 499.2 90.0 3.48 0.814 76.6 12.39 C18 B7 499.9 90.0 1.71 0.29 83.0 12.39 C19 B7 499.8 90.0 0.445 0.075 83.1 12.37 C20 B8 500.3 90.0 9.25 4.75 48.6 12.37 C21 B8 500.5 90.0 3.48 1.11 68.1 12.38 C22 B8 499.6 90.0 1.71 0.387 77.4 12.37 C23 B8 499.6 90.0 0.445 0.093 79.1 12.36 C24 B9 500.4 90.0 8.72 3.59 58.8 12.43 C25 B9 500.2 90.0 3.47 0.748 78.4 12.45 C26 B9 500.1 90.0 1.74 0.252 85.5 12.43 C27 B9 500.1 90.0 0.429 0.053 87.6 12.46 C28  B10 500.2 90.0 8.72 3.02 65.4 12.45 C29  B10 500.0 90.0 3.47 0.605 82.6 12.45 C30  B10 500.3 90.0 1.74 0.224 87.1 12.46 C31  B10 500.3 90.0 0.429 0.049 88.6 12.44 C32  B11 500.1 90.0 8.72 2.69 69.2 12.39 C33  B11 499.8 90.0 3.47 0.534 84.6 12.35 C34  B11 500.5 90.0 1.74 0.195 88.8 12.40 C35  B11 499.9 90.0 0.429 0.047 89.0 12.44

[0158] From tests C8-C35, it is evident that the addition of a barite-containing particulate mineral material at high pH conditions leads to a reduced concentration of chromate in the solutions. Furthermore, it can be gathered that with a given barite-containing particulate mineral material, the removal tends to be more efficient at higher chromate concentration. Furthermore, under otherwise identical conditions, barite-containing particulate mineral materials with higher surface areas tend to perform better than their counterparts with lower BET surfaces.

Example 3—Chromate Removal from Cement Mixtures

[0159] 4.5 g of cement (Cement CEM I 42.5N) was mixed with different barite quantities (2.25, 4.5, and 9 g), as indicated in Table 4 below. 6.75 g of Milli-Q water was added and mixed with a spatula during 30 sec. Then 13.5 g of sand (CEN-Normsand EN 196-1) was added to the mixture before mixing with a spatula for 1 min. The mixture was left for 10-20 min (as indicated), and then filtered through a Whatman Grade 42 filter paper using a Buchner funnel. The concentrations of Cr(IV) c(CrIV) in the filtrate was determined on a Hach Lange DR6000 spectral photometer using LCK 313 (Cr). Samples were diluted as necessary to match the target range of the cuvette tests.

TABLE-US-00004 TABLE 4 Experimental details and results of Example 3. Test Mineral m.sub.mineral [g] C.sub.Cr, end [mg/L] Cr.sub.removed [%] Treatment time [min] C36 (comparative) — — 2.3 0 10 C37 B5 9 0.371 84 10 C38 B5 4.5 0.97 58 10 C39 B5 2.25 1.42 38 10 C40 B5 4.5 0.85 63 20 C41 B6 2.25 1.49 35 10 C42 B6 4.5 1.04 55 10 C43 B7 4.5 1.72 25 10 C44 B8 4.5 1.92 17 10

[0160] From test C36, it can be gathered that the concentration of chromate in the filtrate in absence of barite is 2.3 mg/L. Tests C37 to C39 illustrate that the addition of barite results in a reduced concentration of chromate in the filtrate. The utilization of a higher quantity of barite leads to a higher chromate removal. As illustrated by comparison of tests C38 and C40, the utilization of a longer contact time also improves the removal. Furthermore, tests C41 to C44 demonstrate that the removal efficiency can be controlled by the specific surface area.

Example 4—Chromate Leaching from Hardened Cement

[0161] Concrete slabs were prepared from 1050 g of sand (CEN-Normsand EN 196-1), 380 g of cement (Cement CEM I 42.5N), 400 g of calcium carbonate (Betocarb HP OG), 190 g water, and 2.8 g of a polycarboxylate superplasticizer. In some of the samples, 200 g of the calcium carbonate was replaced by 200 g of different barite materials. After 7 days, the hardened slabs were transferred into ca. 1300 mL of demineralized water and extracted for 102 days. Subsequently, the concentration of Cr(IV) c(Criv) in the solutions was analyzed by ICP-MS.

TABLE-US-00005 TABLE 5 Experimental details and results of Example 4. Test Mineral m.sub.mineral [g] C.sub.Cr, end [μg/L] Cr.sub.removed [%] C45 — — 42 — (comparative) C46 B12 200 39 7 C47 B13 200 35 17 C48 B14 200 30 29 C49 B15 200 17 60

[0162] From test C45, it can be gathered that the concentration of chromate in the eluate in absence of barite is 42 μg/L. Tests C46 to C49 illustrate that the addition of barite results in a reduced concentration of chromate in the eluate. If materials with higher BET surface are utilized, the chromate removal is correspondingly improved.

Example 5—Arsenate Scavenging Experiments

[0163] An As stock solution was prepared by dilution of a commercial standard solution (Arsenic Standard for ICP, TraceCERT®, 1000 mg/L As in nitric acid, Sigma Aldrich 01969-100ML-F) with Milli-Q filtered, deionized water to 4 ppm, 2 ppm and 0.5 ppm. 90 g of the stock solution was transferred into a glass flask. Then, 0.5 g of the barite-containing particulate mineral material was added. The solids were suspended by magnetic stirring (800 rpm, 1 h) and subsequently filtered through a syringe filter (Chromafil Xtra, RC-20/25 0.2 μm). The pH of the filtered solution were measured using a Mettler Toledo SevenMulti™ pH meter. The overall concentration of As in the samples were determined using ICP-MS a on NexION 350D instrument. Samples were diluted as necessary for the analysis.

TABLE-US-00006 TABLE 6 Experimental details and results of Example 5. Test Mineral m.sub.mineral [mg] m.sub.As, solution [g] c.sub.As, start [mg/L] c.sub.As, end [mg/L] As.sub.removed [%] pH A1 B5 500.2 90.4 2.013 1.938 3.75 3.71 A2 B5 499.6 90.7 0.497 0.250 49.61 6.27 A3 B6 501.7 90.5 2.013 1.881 6.60 3.52 A4 B6 499.8 89.8 0.497 0.291 41.48 6.50 A5 B7 499.9 90.3 2.013 1.883 6.47 3.66 A6 B7 499.9 91.3 0.497 0.422 14.95 7.04 A7 B8 500.4 91.8 2.013 1.841 8.55 4.03 A8 B8 503.9 91.7 0.497 0.357 28.10 7.70

[0164] From tests A1 to A8, it is evident that the addition of a barite-containing particulate mineral material leads to a reduced As concentration in the solutions. Furthermore, it can be gathered that with a given barite-containing particulate mineral material, the removal tends to be more efficient at lower As concentration. Furthermore, under otherwise identical conditions, barite-containing particulate mineral materials with higher surface areas tend to perform better than their counterparts with lower BET surfaces.