HEAVY METAL REMOVAL USING MINERALS BEING FUNCTIONALIZED WITH ADSORPTION ENHANCERS

Abstract

The present invention relates to the use of a particulate mineral material being functionalized with one or more adsorption enhancing agents for scavenging and removing ionic metal contaminants from an aqueous medium. Furthermore, the present invention relates to a corresponding process for scavenging and removing ionic metal contaminants from an aqueous medium as well as to a functionalized particulate mineral material and a process for making such material.

Claims

1. Use of a particulate mineral material being functionalized with one or more adsorption enhancing agents for scavenging and removing ionic metal contaminants from an aqueous medium, wherein the particulate mineral material is selected from particulate magnesium carbonate and/or calcium carbonate containing mineral material having a specific surface area prior to functionalization with said one or more adsorption enhancing agents of 10 to 200 m.sup.2/g, wherein the adsorption enhancing agent is selected from elemental iron, iron oxide species and mixtures thereof and wherein the ionic metal contaminant comprises at least one metal selected from the group consisting of Pb, Zn, Mn, Cd, Cu, Mo, Co and Ni, wherein the ionic metal contaminant preferably is cationic.

2. 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.

3. Use according to claim 1 or 2, wherein the adsorption enhancing agent is elemental iron or magnetite or a mixture of the foregoing and preferably is elemental iron.

4. Use according to claim 1, wherein the functionalized particulate mineral material comprises the adsorption enhancing agent in an amount of 0.1 to 40 wt.-%, based on the dry weight of the particulate mineral material, preferably 1 to 30 wt.-% and more preferably 5 to 25 wt.-%.

5. Use according to claim 1, wherein the particulate magnesium carbonate containing material is hydromagnesite and/or the calcium carbonate containing particulate material is selected from surface-reacted calcium carbonate (SRCC), ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC) and mixtures of the foregoing, and preferably is surface-reacted calcium carbonate (SRCC).

6. Use according to claim 1, wherein the specific surface area of the particulate mineral material prior to functionalization with said one or more adsorption enhancing agents is more than 20 m.sup.2/g, preferably more than 40 m.sup.2/g, more preferably more than 50 m.sup.2/g and most preferably more than 60 m.sup.2/g.

7. Use according to claim 1, wherein the ionic metal contaminant is water-soluble and/or the metal of the ionic metal contaminant is selected from the group consisting of Pb, Zn, Cd, and Ni and preferably is Cd and most preferably the ionic metal contaminant is Cd.sup.2+.

8. Process for scavenging and removing ionic metal contaminants from an aqueous medium comprising the steps: a) Providing an aqueous medium containing one or more ionic metal contaminants selected from the group consisting of Pb, Zn, Mn, Cd, Cu, Mo, Co and Ni, wherein the ionic metal contaminant preferably is cationic; b) Functionalizing a particulate mineral material with one or more adsorption enhancing agents selected from elemental iron, iron oxide species and mixtures thereof; wherein the mineral material is selected from particulate magnesium carbonate and/or calcium carbonate containing mineral material having a specific surface area prior to functionalization with said one or more adsorption enhancing agents of 10 to 200 m.sup.2/g; c) Adding the functionalized particulate mineral material of step b) to the aqueous medium for scavenging the one or more of the ionic metal contaminants selected from the group consisting of Pb, Zn, Mn, Cd, Cu, Mo, Co and Ni; d) Removing the functionalized particulate mineral material from the aqueous medium after step c).

9. The process according to claim 8, wherein removing step d) is performed by filtration, centrifugation, sedimentation, flotation or magnetism, and preferably is performed by applying magnetism, preferably using a neodymium or electro magnet.

10. The process according to claim 8, 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 5 to 10, preferably 6 to 9 and most preferably 7 to 8.

11. The process according to claim 8, wherein the functionalization of the particulate mineral material of step b) is performed by immobilizing an iron salt on the particulate mineral material, preferably an iron salt selected from iron sulphate, iron (II) chloride, iron (III) chloride and mixtures thereof, and optionally reducing the immobilized iron salt present on the surface of the particulate mineral material with a reducing agent.

12. A functionalized particulate mineral material comprising at least one adsorption enhancing agent, which covers at least partially the surface of the particulate mineral material, wherein the particulate mineral material is selected from particulate magnesium carbonate and/or calcium carbonate containing mineral material having a specific surface area prior to functionalization with said one or more adsorption enhancing agents of 10 to 200 m.sup.2/g, and wherein said at least one adsorption enhancing agent is elemental iron.

13. Process for preparing a functionalized particulate mineral material according to claim 12 comprising the steps of i) Providing a particulate mineral material selected from particulate magnesium carbonate and/or calcium carbonate containing mineral material having a specific surface area prior to functionalization with said one or more adsorption enhancing agents of 10 to 200 m.sup.2/g; ii) Providing an iron salt; iii) Contacting the at least one particulate mineral material of step (i) with the at least one iron salt of step (ii), and optionally water, in one or several steps to form a mixture; iv) Providing a reducing agent; v) Contacting the mixture of step iii) with the reducing agent of step iv).

14. The process according to claim 13, wherein the mixture formed in step iii) is an aqueous suspension, and the process further comprises a step vi) of separating the functionalized particulate mineral material from the aqueous suspension after step (v).

15. The process according to claim 13, wherein the contacting step iii) and/or contacting step v) is carried out under inert gas atmosphere, preferably under a nitrogen or argon atmosphere.

Description

EXAMPLES

[0134] 1. Measuring Methods

[0135] In the following, measuring methods implemented in the examples are described. Reference is also made to the methods already described above.

[0136] 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).

[0137] The Cd-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) on .sup.111Cd and .sup.113Cd. The calibration was conducted using standard reference material (Instrument Calibration Standard 2). The samples were diluted directly with the prepFAST system prior to analysis wherever possible. Samples which had to be diluted prior to this step were diluted with HNO.sub.3 1% (e.g. 1 ml sample+9 ml acidified H2O). Standard additions were conducted as follows: 10 l standard/10 ml measuring solution. Further details are provided in the report.

[0138] 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.

[0139] 2. Manufacture of the SRCC-Materials

[0140] A surface-reacted calcium carbonate material was prepared as described in the following:

[0141] 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 m, 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.

[0142] 3. Manufacture of the Functionalized Mineral Materials

[0143] Functionalized SRCC-based materials were prepared as described in the following:

[0144] 5 g of the above obtained SRCC was dried at 100 C. overnight. The resulting powder was stirred in water (100 ml for samples 1 and 2; 50 ml for sample 3) at 30 C. for 30 minutes. FeSO4.7H2O was mixed with 20 mL of water in order to obtain a Fe(II)-salt solution. The corresponding iron salt solution was added dropwise to the SRCC (wet impregnation). The resulting mixture was mixed and kept under nitrogen for 1 hour. A NaBH4 solution was prepared in 20 (sample 1) or 30 (samples 2 and 3) mL of water and was then added dropwise to the particulate material which was treated with the salt solution. After two hours, the solid was finally filtered (Whatman Art. No. 9060202, 090 mm, 589/2) and washed with a 2:1-water/ethanol mixture (100 ml/50 ml mixture). Finally, the functionalized SRCC-material was dried at 100 C. under vacuum (50 mbar) for 3 hours. Finally, a manual de-agglomeration step was applied.

[0145] The amounts of the respective adsorption enhancing agent, the type of adsorption enhancing agent as well as the amount of particulate mineral material and reducing agent (amount and type) is given in table 1 below.

TABLE-US-00001 TABLE 1 Amount Weight Adsorp. Adsorp. Weight enh. enh. Amount Weight Mineral agent agent NaBH.sub.4 NaBH.sub.4 No Mineral [g] Metal salt [wt.-%] [g] [wt.-%] [g] 1 SRCC 10 FeSO.sub.47H.sub.2O 5 2.48 10 3.6 2 SRCC 10 FeSO.sub.47H.sub.2O 10 5.0 10 7.1 3 SRCC 5 FeSO.sub.47H.sub.2O 20 5 10 7.16

[0146] 4. Scavenging and Removal-Tests

[0147] In order to investigate the scavenging and removal capabilities and especially the efficiency of the inventive materials and processes for removing heavy metal ions, the functionalized SRCC-based materials described above were tested in relation to an aqueous medium containing cadmium(II)nitrate.

[0148] Test Solution

[0149] A Cd.sup.2+-containing stock solution (15 ppm) was prepared by dilution of a commercial 1000 ppm standard (Sigma Aldrich, 36379-100ML-F) with Milli-Q filtered, deionized water.

[0150] Treatment Procedure (Contacting and Removal)

[0151] For each experiment, 95 g of this stock solution was transferred into a glass flask and 100 mg of the respective mineral material was added at room temperature. The solids were suspended by using magnetic stirring bars (800 rpm, 1 hour). The suspensions were left for settling (10 min), the turbid supernatant (50 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 m). To these solutions (ca. 30 g), nitric acid (0.5 mL, 37%, SigmaAldrich) was added to prevent the precipitation of any material before analysis. A blank experiment (#1) was conducted and the resulting concentration was taken as reference. Statements regarding the Cd removal are made with respect to the concentration of this reference sample. The Cd-content or concentration was determined as explained above by using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). Furthermore, the SRCC material was tested without functionalization (experiment #2).

[0152] In the set of experiments (#3-5) SRCC functionalized with elemental iron as adsorption enhancing agent was tested (materials No. 1-3 in table 1).

[0153] The corresponding results of the scavenging and removal test are reported in Table 2.

TABLE-US-00002 TABLE 2 Final Amount concentration Removal Adsorp. enh. cadmium cadmium # Mineral material No. agent [wt.-%] [mg/l] [%] #1 Reference 15 0 #2 SRCC (no func.) 4 73 #3 SRCC/elemental iron 1 5 1.9 87 #4 SRCC/elemental iron 2 10 1.3 90.6 #5 SRCC/elemental iron 3 20 0.31 97.9

[0154] 5. Results

[0155] As can be gathered from table 2, the functionalization of the mineral material with an adsorption-enhancing agents being elemental iron significantly improved the Cd removal efficiency over a corresponding SRCC material without functionalization. Already small amounts of 5 wt.-% of the adsorption enhancing agent led to excellent performance, which is much better than that of the SRCC without functionalization. By increasing the amount of adsorption enhancing agent, also the efficacy could be increased to a level of 97.9% removal.