PARTICULATE MINERAL MATERIALS FUNCTIONALIZED WITH REDUCING AGENTS FOR LOWERING THE AMOUNT OF HEAVY METAL CONTAMINANTS FROM AN AQUEOUS MEDIUM

Abstract

The present invention relates to the use of a particulate mineral material being functionalized with one or more reducing agents for lowering the amount of heavy metal contaminants ions from an aqueous medium. Furthermore, the present invention relates to a corresponding process for lowering the amount of heavy metal contaminants from an aqueous medium as well as to a functionalized particulate mineral material. Additionally, the present invention relates to a process for preparing a functionalized particulate mineral material and to a scavenging complex.

Claims

1. Use of a particulate mineral material being functionalized with one or more reducing agents for lowering the amount of heavy metal contaminants from an aqueous medium, wherein the mineral material is selected from the group consisting of hydromagnesite, calcium carbonate containing particulate material, bentonite, brucite, magnesite, dolomite and mixtures thereof, wherein the reducing agent is selected from the group consisting of Fe(II) salts, Mn(II) salts, Co(II) salts, elemental Mg, elemental Ag, elemental Sn, elemental Al, elemental Cu, elemental Fe and mixtures thereof.

2. Use according to claim 1, wherein the heavy metal contaminates are in the form of cationic heavy metal ions and/or in the form of an anionic compound comprising said heavy metal.

3. Use according to claim 1, wherein the aqueous medium is selected from sewage water, preferably industrial 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 or slaughterhouse waste water, from sludge, preferably sewage sludge, harbour sludge, river sludge, coastal sludge, digested sludge, mining sludge, municipal sludge, civil engineering sludge, sludge from oil drilling or the effluents the aforementioned dewatered sludges.

4. Use according to claim 1, wherein the reducing agent is selected from the group consisting of Fe(II) salts, Mn(II) salts, Co(II) salts and mixtures thereof and preferably the group of Fe(II) salts and preferably the anion is selected from SO.sub.4.sup.2−, C.sub.2O.sub.4.sup.2−, (NO.sub.3).sup.−, Cl.sup.−, Br.sup.−, OH.sup.− or mixtures thereof, more preferably the anion is SO.sub.4.sup.2−, and most preferably the salt is FeSO.sub.4.

5. Use according to claim 1, wherein the functionalized particulate mineral material comprises the reducing agent in an amount of 1 to 50 wt.-%, based on the total dry weight of the particulate mineral material, preferably 5 to 30 wt.-% and more preferably 10 to 20 wt.-%.

6. Use according to claim 1, wherein the particulate mineral material is selected from hydromagnesite, calcium carbonate containing particulate material or mixtures thereof, preferably is a calcium carbonate containing particulate material, more preferably is selected from SRCC, GCC, PCC or mixtures thereof and most preferably is GCC.

7. Use according to claim 1, wherein the particulate mineral material prior to functionalization with said one or more reducing agents has a median particle diameter d.sub.50 value of between 0.01 μm and 500 μm, preferably between 0.1 μm and 250 μm, more preferably between 0.5 μm and 150 μm and most preferably between 1 μm and 100 μm and/or the particulate mineral material prior to functionalization with said one or more reducing agents has a specific surface area of from 0.5 to 250 m.sup.2/g, more preferably from 1 to 200 m.sup.2/g, even more preferably from 4 to 150 m.sup.2/g and most preferably from 10 to 80 m.sup.2/g.

8. Use according to claim 1, wherein the heavy metal contaminant is in the form of an anionic compound comprising said heavy metal wherein the heavy metal in the anionic compound is selected from the group consisting of Hg, Cr, As, Se, Mn and mixtures thereof, preferably is Hg(II), Cr(VI), As(V), Mn(VII), Se(VI) or mixtures thereof, even more preferably the anionic compound is CrO.sub.4.sup.2−, Cr.sub.2O.sub.7.sup.2−, Cr.sub.3O.sub.10.sup.2−, Cr.sub.4O.sub.13.sup.2−, AsO.sub.4.sup.3−, MnO.sub.4.sup.2−, SeO.sub.4.sup.2−, mixtures thereof and/or protonated versions thereof and most preferably is CrO.sub.4.sup.2−, AsO.sub.4.sup.3−, and/or protonated versions thereof.

9. Process for lowering the amount of heavy metal contaminants from an aqueous medium comprising the steps: a) Providing an aqueous medium comprising heavy metal contaminants; b) Functionalizing a particulate mineral material with one or more reducing agents selected from the group consisting of Fe(II) salts, Mn(II) salts, Co(II) salts, elemental Mg, elemental Ag, elemental Sn, elemental Al, elemental Cu, elemental Fe and mixtures thereof, wherein the mineral material is selected from the group consisting of hydromagnesite, calcium carbonate containing particulate material, bentonite, brucite, magnesite, dolomite and mixtures thereof, c) Adding the functionalized particulate mineral material of step b) to the aqueous medium for scavenging the heavy metal contaminants and d) Removing the functionalized particulate mineral material from the aqueous medium after step c).

10. The process according to claim 9, wherein the heavy metals in the heavy metal contaminants undergo a reduction reaction during step c)

11. The process according to claim 9, wherein the molar ratio of reducing agent to heavy metal contaminants in step c) is from 1:0.8 to 1:5000, preferably from 1:1 to 1:3000, more preferably from 1:2 to 1:1000, even more preferably from 1:3 to 1:500 and most preferably from 1:5 to 1:50.

12. The process according to claim 9, wherein the pH-value of the aqueous medium has been adjusted prior to the addition of the functionalized particulate mineral material to a value of 4 to 10, preferably 5 to 9 and most preferably 6 to 8.

13. The process according to claim 9, wherein the functionalization of the particulate mineral material of step b) is performed by the addition of Fe(II) salts, Mn(II) salts, Co(II) salts or mixtures thereof and/or by the addition of aluminum salts, magnesium salts, tin salts, silver salts, iron salts, copper salts and/or mixture thereof and reducing the aluminum salt, magnesium salt, tin salt, silver salt, iron salt, copper salts and/or mixture thereof present on the surface of the particulate mineral material with an electron donor agent.

14. A functionalized particulate mineral material comprising at least one reducing agent, which covers at least partially the surface of the particulate mineral material, wherein the particulate mineral material is selected from the group consisting of hydromagnesite, calcium carbonate containing particulate material, bentonite, brucite, magnesite, dolomite and mixtures thereof, and wherein the reducing agent is selected from the group consisting of Fe(II) salts, Mn(II) salts, Co(II) salts, elemental Al, elemental Sn, elemental Mg, elemental Ag, elemental Cu, elemental Fe and mixtures thereof.

15. Process for preparing a functionalized particulate mineral material according to claim 14, wherein the reducing agent is elemental Al, elemental Sn, elemental Mg, elemental Ag, elemental Cu, elemental Fe or mixtures thereof comprising the steps of i) Providing a particulate mineral material selected from the group consisting of hydromagnesite, calcium carbonate containing particulate material, bentonite, brucite, magnesite, dolomite and mixtures thereof; ii) Providing an aluminum salt, magnesium salt, tin salt, silver salt, iron salt, copper salt and/or mixture thereof, iii) Contacting the at least one particulate mineral material of step (i), the at least one aluminum salt, magnesium salt, tin salt, silver salt, iron salt and/or copper salt of step (ii), and optionally water, in one or several steps to form a mixture; iv) Providing an electron donor agent; v) Contacting the mixture of step iii) with the electron donor agent of step iv).

16. Scavenging complex comprising at least one heavy metal contaminant and at least one functionalized particulate mineral material obtained by the process as defined in claim 9.

Description

EXPERIMENTAL SECTION

1. Measuring Methods

[0120] In the following, measuring methods implemented in the examples are described. Reference is also made to the methods already described above.

[0121] Any pH value is measured at 25° C. using a Mettler-Toledo Seven Easy pH meter and a Mettler-Toledo InLab Expert Pro pH electrode. A three point calibration (according to the segment method) of the instrument is first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 25° C. (from Aldrich). The reported pH values are the endpoint values detected by the instrument (signal differs by less than 0.1 mV from the average over the last 6 seconds).

[0122] The Cr-content or concentration was determined by using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). The samples were measured with a NexION 350D ICP-MS system from Perkin Elmer in KED mode (Kinetic Energy Discrimination). The calibration was conducted using standard reference material (Instrument Calibration Standard 2). The samples were diluted when necessary with HNO.sub.3 1% (e.g. 1 ml sample+9 ml acidified H2O). Standard additions were conducted as follows: 10 μl standard/10 ml measuring solution.

[0123] Alternatively, the Cr-content or concentration was determined by using ICP-OES (Inductively Coupled Plasma-Atomic emission spectroscopy) according to EN ISO 11885:2009 using an Agilent 5100 VDV system. The used methods and instruments are known to the skilled person and are commonly used to determine the heavy metal concentrations.

[0124] The specific surface area (in m.sup.2/g) was determined by using the BET method (using nitrogen as adsorbing gas) in accordance with ISO 9277:2010. The total surface area (in m.sup.2) of the filler material was then obtained by multiplication of the specific surface area and the mass (in g) of the corresponding sample.

2. Particulate Mineral Materials

[0125] A surface-reacted calcium carbonate material (SRCC) was prepared as described in the following:

[0126] Surface reacted calcium carbonate (SRCC) was obtained by preparing 10 liters of an aqueous suspension of ground calcium carbonate in a mixing vessel by adjusting the solids content of a ground limestone calcium carbonate from Blaubeuren, Germany having a particle size distribution of 90% less than 2 μm, as determined by sedimentation, such that a solids content of 15 wt %, based on the total weight of the aqueous suspension, is obtained. In addition, concentrated phosphoric acid was diluted in water to prepare a 30 wt % phosphoric acid solution. Whilst mixing the slurry, 2.8 kg of the phosphoric acid solution was added to said suspension over a period of 10 minutes at a temperature of 70° C. Finally, after the addition of the phosphoric acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying. The specific surface area of the SRCC was determined to be 92 m.sup.2/g.

[0127] The GCC 1 used in the present invention is a ground calcium carbonate based on marble from Avenza, Italy which was subjected to wet grinding without dispersant and subsequently spray-dried, resulting in a material with a particle size of do of 1.7 μm, a d.sub.98 of 5 μm and a surface area of 3.5 m.sup.2/g.

[0128] The GCC 2 used in the present invention is a ground calcium carbonate based on marble from Avenza, Italy which was dry-milled to a particle size of do of 1.7 μm, a d.sub.98 of 6.5 μm and a surface area of 3.7 m.sup.2/g.

[0129] The GCC3 used in the present invention is a ground calcium carbonate based on limestone from Orgon, France which was wet-milled and subsequently spray-dried to attain a material with a particle size of do of 0.53 μm, a d.sub.98 of 0.78 μm and a surface area of 7.8 m.sup.2/g. The PCC used in the present invention is an aragonitic PCC which has been received as filter cake and has been spray dried, with a particle size of do of 0.88 μm and a surface area of 14.6 m.sup.2/g

[0130] The PHM used in the present invention is a food grade hydromagnesite. with a particle size of do of 21 μm, a d.sub.98 of 64 μm and a surface area of 38 m.sup.2/g

3. Manufacture of the Functionalized Mineral Materials

[0131] Functionalized mineral materials 1 to 9 were prepared as described in the following:

[0132] 5 g of SRCC/GCC/PCC/PHM was dried at 100° C. overnight. FeCl.sub.2 was used as scavenging agents for functionalizing the dried SRCC/GCC/PCC/PHM. The respective amount of reducing agent was dissolved in water. The corresponding solutions were added dropwise on the SRCC/GCC/PCC/PHM material (dry impregnation). After that, the obtained material was dried at 100° C. under vacuum (50 mbar) for 3 hours. Finally, a manual de-agglomeration step was applied.

[0133] Functionalized mineral materials 10-14 were prepared as described in the following: 20 g of GCC and 2 g of reducing agent were introduced into a Retsch PM 100 planetary ball mill equipped with a 50 mL ZrO.sub.2-coated grinding jar. For grinding, 10 g of 2 mm ZrO.sub.2 grinding beads were added, along with 1 g of EtOH was added to prevent agglomeration during grinding. The samples were milled at 600 rpm for 10 min, the grinding beads removed and the resulting powders dried in an oven at 65° C.

[0134] The amounts of the respective reducing agent, the type of reducing agent as well as the amount of particulate mineral material and solvent is given in table 1 below.

TABLE-US-00001 TABLE 1 Weight Amount Re- Re- Amount ducing ducing. Amount Mineral Reducing Agent Agent Solvent No Mineral [g] agent [wt.-%] [g] Solvent [g]  1 SRCC 5 FeCl.sub.2 15 0.75 H.sub.2O 10  2 GCC 1 10 FeCl.sub.2 15 0.75 H.sub.2O 3.5  3 PCC 5 FeCl.sub.2 15 0.75 H.sub.2O 4.5  4 PHM 5 FeCl.sub.2 15 0.75 H.sub.2O 10  5 SRCC 5 FeCl.sub.2 15 0.75 Ethanol 17  6.sup.a SRCC 10 elemental  5 2.5  H.sub.2O 250 Fe  7.sup.a SRCC 10 elemental 10 5   H.sub.2O 250 Fe  8.sup.a SRCC 5 elemental 20 5   H.sub.2O 250 Fe  9.sup.a GCC3 5 elemental 25 3.15 H.sub.2O 250 Cu 10.sup.b GCC1 20 elemental 10 2   EtOH 1 Mg 11.sup.b GCC1 20 elemental 10 2   EtOH 1 Mn 12.sup.b GCC1 20 elemental 10 2   EtOH 1 Zr 13.sup.b GCC1 20 elemental 10 2   EtOH 1 Ag 14.sup.b GCC1 20 elemental 10 2   EtOH 1 Zn .sup.aSamples prepared by a wet impregnation procedure. .sup.bSamples prepared by a cogrinding procedure.

4. Reducing, Scavenging and Removal-Tests

[0135] In order to investigate the reducing, scavenging and removal capabilities and especially the efficiency of the inventive materials and processes for removing heavy metal ions, the functionalized particulate mineral materials described above were tested in relation to an aqueous medium containing chromium (VI) ions.

Test Solution

[0136] A Cr-containing stock solution (1 ppm Cr as Cr.sub.2O.sub.4.sup.2−) was prepared by dilution of a commercial 1000 ppm standard (Sigma Aldrich, 68131-100ML-F) with Milli-Q filtered, deionized water.

Treatment Procedure (Contacting and Removal)

[0137] For each experiment, 200 g of this stock solution was transferred into a glass flask and 200 mg of the respective mineral material was added at room temperature. The solids were suspended by using magnetic stirring bars (500 to 800 rpm, 1 to 23 hours). The suspensions were left for settling (10 min), the turbid supernatant (100 mL) transferred into centrifugation tubes, centrifuged (4500 rpm, 4 min) and the now clear supernatant filtered through a syringe filter (Chromafil Xtra, RC-20/25 0.2 μm). To these solutions (ca. 87 g), hydrochloric acid (1 mL, 37%, SigmaAldrich) was added to prevent the precipitation of any material before analysis.

[0138] Blank experiments (#1) were conducted and the resulting concentrations were taken as reference. Statements regarding the Cr reduction and removal are made with respect to the concentration of these reference samples. The Cr-content or concentration was determined as explained above by using ICP-OES. Furthermore, some of the particulate mineral materials and the reducing agents were tested without functionalization (#2, #3, #5, #7, #9).

[0139] The corresponding results of the reducing, scavenging and removal test are reported in Table 2.

TABLE-US-00002 TABLE 2 Weight Final Final (function- Weight concen- total Cr alized) reducing. tration concen- Mineral mineral Agent Cr(VI) tration # material No. [ppm] [ppm] [mg/l] [mg/l]  #1 Reference — — 0.91 1.1   #2 SRCC (n. — 1000 — 0.91 1.1  func.)  #3 FeCl.sub.2 — 150 0.0* 1.0   #4 SRCC/FeCl.sub.2 1 1150 — 0.71 0.86  #5 GCC 1 (n. 1000 — 0.93 1.1  func.)  #6 GCC 2 1150 — 0.0* 0.0  1/FeCl.sub.2  #7 PCC (n. 1000 — 0.90 1.1  func.)  #8 PCC/FeCl.sub.2 3 1150 — 0.78 0.89  #9 PHM (n. 1000 — 0.91 1.1  func.) #10 PHM/FeCl.sub.2 4 1150 0.43 0.50 *values of 0.0 lie below the detection limit of 0.002 mg/l

[0140] Blank experiment (#11) was conducted and the resulting concentration was taken as reference. Statements regarding the Cr removal are made with respect to the concentration of these reference samples. The Cr-content or concentration was determined as explained above by using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). Furthermore, some of the particulate mineral materials were tested without functionalization (#12, #13).

[0141] The corresponding results of the reducing, scavenging and removal test are reported in Table 3.

TABLE-US-00003 TABLE 3 Weight Final total (function- Weight concen- alized) reducing. tration Cr mineral Agent Cr removed # Mineral material No. [ppm] [ppm] [ppm] % #11 Reference — —  0.996- — #12 SRCC (n. func.) —  1000 — 1.1   0 #13 GCC 2 (n. func.) —  5200 0.996  0 #14 SRCC/elemental  7  1060 0.926  6 Fe #15 SRCC/elemental  8  1270 0.641 35 Fe #16 SRCC and —  1040 3370 0.980  1 elemental Fe separately #17 GCC/elemental  9  2540 0.743 25 Cu #18 GCC/elemental 10 10700 0.011 99 Mg #19 GCC/elemental 11 10900 0.688 31 Mn #20 GCC/elemental 12 10700 0.950  5 Zr #21 GCC/elemental 13 10400 0.900 10 Ag #22 GCC/elemental 14 10900 0.897 10 Zn

5. Results

[0142] As can be gathered from tables 2 and 3, the functionalization of the mineral material with one or more reducing agents according to the present invention significantly improved the heavy metal contaminants removal efficiency over a corresponding particulate mineral material without functionalization. Furthermore, also reduction of the Cr(VI) ions to lower oxidation states is possible even if the reducing agent is immobilized on the surface of the particulate mineral material. This can especially be seen from examples #1 to #10. Furthermore, as can be seen from examples #11 to #22 the concept works with different Fe(II) salts, Mn(II) salts, Co(II) salts, elemental Cu, elemental Fe, elemental Mg, elemental Mn, elemental Zr, elemental Ag, and elemental Zn.