COLUMN MATERIAL FOR THE CAPTURE OF HEAVY METAL AND PRECIOUS METAL IONS

Abstract

Composite ion-exchange materials for use in an ion-exchange column are provided. Also provided are ion-exchange columns packed with the materials and methods for using the materials to remove metal ions from samples, such as waste water samples. The composite ion-exchange materials comprise a composite material comprising a metal chalcogenide and an alginate, wherein the composite material is mixed with a granular material.

Description

BACKGROUND

Oxide based compounds, such as clays and zeolites, are commonly used inorganic ion-exchange materials. Layered metal chalcogenide based materials also can be used for a variety of ion-exchange applications. However, some ion-exchange applications, such as industrial heavy water and nuclear waste treatment processes, require a continuous bed flow ion-exchange column. Due to their small particle size, layered metal chalcogenide based materials do not allow sufficient flow through a column and therefore, are poorly suited for ion-exchange column applications.

SUMMARY

A composite ion-exchange material for use in an ion-exchange column is provided. Also provided are ion-exchange columns packed with the material and methods for using the materials to remove metal ions from samples, such as waste water samples. The composite ion-exchange materials comprise a composite material comprising a metal chalcogenide and an alginate mixed with a granular material.

Methods of using the materials for the remediation of unwanted metal ions from a sample include the steps of passing a sample comprising the metal ions through a column, such as a fixed bed flow column, containing the material, whereby ion-exchange occurs between the chalcogenide and the metal ions in the sample; and collecting the sample exiting the column.

Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the invention will hereafter be described with reference to the accompanying drawings.

FIG. 1(A) shows the layer framework of KMS-2 viewed down the c-axis. The Mg/Sn and S atoms are represented by black and grey balls respectively.

FIG. 1(B) shows a view of the KMS-2 structure along the c-axis with the disordered K⁺ ions (larger balls) in the interlayer space.

FIG. 2 shows the powder X-ray diffraction patterns of KMS-2 (experimental and calculated) and a KMS-2-alginate composite.

FIG. 3(A) is an SEM image of pristine KMS-2.

FIG. 3(B) is an SEM image of the pristine KMS-2 at a higher magnification.

FIG. 3(C) is an SEM image of a KMS-2-alginate composite.

FIG. 3(D) is an SEM image of the KMS-2-alginate composite at a higher magnification.

FIG. 4 is a plot of the bed volumes treated vs. the percentage removal of Ag⁺ ion for an ion-exchange column loaded with a metal chalcogenide and an alginate mixed with a granular material.

FIG. 5 is a plot of the bed volumes treated vs. the percentage removal of Co²⁺, Ni²⁺, Hg²⁺ and Pb²⁺ ions for an ion-exchange column loaded with a metal chalcogenide and an alginate mixed with a granular material.

DETAILED DESCRIPTION

The present ion-exchange materials include a composite material comprising a layered metal chalcogenide and an alginate. A mixture of this composite material with an inert granular phase provides an ion-exchange material for an ion-exchange column.

The metal chalcogenides are layered structures with loosely bound interlayer cations. Examples include metal chalcogenides of the nominal formula A_2xM_xSn_3-xS₆, where x has a value in the range from about 0.5 to about 1 (including, for example, x values in the range from about 0.5 to about 0.95); A is Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺; and M is Mg²⁺, Ca²⁺, Mn²⁺, Mn³⁺, Zn²⁺, Fe²⁺ or Fe³⁺. The A_2xM_xSn_3-xS₆ materials have a layered structure that is built up by edge-sharing “M,Sn” S₆ octahedra. The M and Sn atoms occupy the same crystallographic position and the sulfur atoms are three-coordinated. The A⁺ ions are positionally disordered and intercalated between the layers. The structure of the A_2xM_xSn_3-xS₆ metal chalcogenides, viewed down the c-axis and along the c-axis is shown in FIGS. 1(A) and 1(B), respectively. Suitable alginates for use in forming the composite materials include sodium alginate.

Granular materials that may be mixed with the metal chalcogenide-alginate composite material include inert granular materials (that is, granular materials that do not interfere with the ion-exchange process), such as activated carbon or sand (silica powder). The grain size and amount of the granular material can be selected to provide an appropriate flow rate for a given application. By way of illustration, in some embodiments, the ratio of metal chalcogenide-alginate composite material to granular material is in the range from about 1:3 to 3:1. This includes embodiments in which the ratio is in the range from about 1:2 to 2:1 and further includes embodiments in which the ratio is in the range from about 1:1.5 to 1.5 to 1. Illustrative mesh sizes for the granular material include those in the range from about 15 to 75.

The ion-exchange materials can be used to remove a variety of metal ions from a fluid sample, including ions of metals that pose an environmental and/or health risk. Thus, examples of fluid samples that can be remediated by the present methods include, drinking water and waste water generated from a nuclear reactor, an industrial plant or from mining processes, such as ore leaching. Examples of metal ions that can be removed from the samples include heavy metal ions and precious metal ions. Metal ions that can be removed using the ion-exchange materials include Co²⁺, Ni²⁺, Ag⁺, Hg²⁺, Cd²⁺, Pb²⁺, Pd²⁺, Pt²⁺, and UO₂²⁺.

EXAMPLE

This example illustrates the use of an ion-exchange material comprising a composite of nominal formula K_2xMg_xSn_3-xS₆ (“KMS-2”) and sodium alginate mixed with activated carbon or sand in the remediation of aqueous solutions containing various metal ions.

In this example, a fixed bed column with packed with the KMS-2-alginate composite and activated carbon (20-40 mesh) in 1:1 ratio. The total mass of the exchanged material is 4 g. The bed volume of the column was about 5.4 mL, which was calculated as follows: Bed volume=[bed height (cm)×cross sectional area (cm²)]; and for the column, cross sectional area=πr², where, r=radius of the column. For the column used here the bed height was 14 cm and r was 0.35 cm, so the bed volume was 5.385 mL.

Experimental

Example of Synthesis of K_2xMg_xSn_3-xS₆ (KMS-2) (x=0.5-1)

Hydrothermal synthesis: Elemental Sn (1.88 mol, 223.0 g), Mg (0.94 mol, 22.8 g), S (6.57 mol, 210.83 g), K₂CO₃ (1.41 mol, 194.72 g), water (500 mL) were mixed in a 1 L beaker. The beaker was kept inside a 1 gallon Parr autoclave and heated slowly to 180° C. and kept for 6 hours. Then, the autoclave was allowed to cool at room temperature. A bright yellow polycrystalline product was isolated by filtration (275 g, yield≈55%), washed several times with water and acetone and dried under vacuum. Electron Dispersive Spectroscopy (EDS) analysis showed the presence of K, Mg, Sn and S and gave the average formula “K_1.3Mg_0.6Sn_2.6S_6.0”.

Example of Synthesis of KMS-2-Alginate Composite

An amount of 0.2 g of sodium alginate was dissolved in 400 mL of warm water, and then the solution was allowed to cool. To the alginate solution 10 g of KMS-2 was added. 10 g of CaCl₂ was dissolved in 200 ml of water and then it was poured into the alginate-KMS-2 with continuous stirring. The product was then isolated by filtration, washed with water and acetone and vacuum dried. Electron Dispersive Spectroscopy (EDS) analysis shows the presence of Mg, Ca, Sn and S and gave a ratio of Mg:Ca:Sn:S=1.8:0.6:2.8:6.

Preparation of the Column.

2 g of KMS-2-alginate composite and 2 g of activated carbon (20-40 mesh) were ground in a mortar and pestle and filled in a glass column. Similarly another column was prepared by using sand (50-70 mesh) instead of activated carbon.

Ion-Exchange Studies.

A typical ion-exchange experiment of KMS-2 with various ions was conducted as follows: Two bed volumes of the solution (10.8 mL) were passed through the column and collected at the bottom in a conical propylene tube. Similarly a number of bed volumes were passed through the column and collected.

Physical Measurements.

Powder patterns were collected by spreading the ground sample on a glass slide using a CPS 120 INEL X-ray powder diffractometer with a graphite monocromated Cu Kα radiation operating at 40 kV and 20 mA. FIG. 2 shows the powder X-ray diffraction pattern of KMS-2 and a KMS-2-alginate composite.

The energy dispersive spectroscopy (EDS) analyses were performed using a Hitachi S-3400N-II scanning electron microscope (SEM) equipped with an ESED II detector for elemental analysis. Data acquisition was performed with an accelerating voltage of 20 kV and 60 s acquisition time. FIG. 3(A) is an SEM image of the pristine KMS-2. FIG. 3(B) is an SEM image of the pristine KMS-2 at a higher magnification. FIG. 3(C) is an SEM image of the KMS-2-alginate composite. FIG. 3(D) is an SEM image of the KMS-2-alginate composite at a higher magnification.

The Ag⁺ ion-exchange samples were analyzed by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) using VISTA MPX CCD SIMULTANEOUS ICP-OES instrument.

The multi ion solution (Co²⁺, Ni²⁺, Hg²⁺ and Pb²⁺) after ion-exchange was analyzed with Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) using a computer-controlled ThermoFisher X Series II Inductively Coupled Plasma Mass Spectrometer with a quadruple setup equipped with Collision Cell Technology.

Results.

The fixed bed column made with the 1:1 KMS-2-alginate and activated carbon ion-exchange material showed exceptional removal of Ag⁺ ions. A solution of 100 PPM of Ag+ passed through the column showed more than 99% by weight removal of the Ag+ ion from the solution (Table 1). FIG. 4 is a plot of the bed volumes treated vs. the percentage removal of Ag⁺ ion for an ion-exchange column loaded with the 1:1 KMS-2-alginate and activated carbon ion-exchange material.

TABLE 1
Ag+ ion-exchange using the fixed bed column with 1:1
KMS-2-alginate and activated carbon ion-exchange material.
			Initial	Final
	Bed volumes		concentration	Concentration	%
ID	Treated	mL	(PPM)	(PPM)	Removal
1	2	10.8	102.59	0.2888	99.718
2	16	10.8	102.59	0.0056	99.995
3	18	10.8	102.59	0.0025	99.998
4	20	10.8	102.59	0.0012	99.999
5	22	10.8	102.59	0.0053	99.995
6	26	10.8	102.59	0.0134	99.987
7	28	10.8	102.59	0.0075	99.993
8	30	10.8	102.59	0.004	99.996
9	32	10.8	102.59	0.0277	99.973
10	34	10.8	102.59	0.0137	99.987
11	36	10.8	102.59	0.0061	99.994
12	38	10.8	102.59	0.0093	99.991
13	40	10.8	102.59	0.0011	99.999
14	42	10.8	102.59	0.0849	99.917
15	46	10.8	102.59	0.0044	99.996
16	50	10.8	102.59	0.0028	99.997
17	52	10.8	102.59	0.0281	99.973
18	54	10.8	102.59	0.0088	99.991
19	80	10.8	102.59	0.0074	99.993

The fixed bed column was also tested with a solution of mixed ions (Co²⁺, Ni²⁺, Hg²⁺ and Pb²⁺) at low concentration (˜2 PPM) to check its efficiency at low concentration level. The result shows that it removed more than 99.9% by weight of all the ions (Table 2). FIG. 5 is a plot of the bed volumes treated vs. the percentage removal of Co²⁺, Ni²⁺, Hg²⁺ and Pb²⁺ ions for an ion-exchange column loaded with the 1:1 KMS-2-alginate and activated carbon ion-exchange material.

TABLE 2
Removal of Co2+, Ni2+, Hg2+ and Pb2+ from
a mixture using the fixed column with 1:1 KMS-2-
alginate and activated carbon ion-exchange material.
			Initial	Final
	Bed volumes		Concentration	Concentration	%
ID	Treated	mL	(PPB)	(PPB)	Removal
Co2+
1	2	10.8	2159.47	0.037	99.998
2	4	10.8	2159.47	0.057	99.997
3	6	10.8	2159.47	0.058	99.997
4	8	10.8	2159.47	0.063	99.997
5	10	10.8	2159.47	0.064	99.997
6	12	10.8	2159.47	0.057	99.997
7	14	10.8	2159.47	0.06	99.997
8	16	10.8	2159.47	0.083	99.996
Ni2+
1	2	10.8	2420.52	0.288	99.988
2	4	10.8	2420.52	0.287	99.988
3	6	10.8	2420.52	0.114	99.995
4	8	10.8	2420.52	0.287	99.988
5	10	10.8	2420.52	0.338	99.986
6	12	10.8	2420.52	0.024	99.999
7	14	10.8	2420.52	0.078	99.996
8	16	10.8	2420.52	0.114	99.995
Hg2+
1	2	10.8	1492.63	<1	>99.9
2	4	10.8	1492.63	<1	>99.9
3	6	10.8	1492.63	<1	>99.9
4	8	10.8	1492.63	<1	>99.9
5	10	10.8	1492.63	<1	>99.9
6	12	10.8	1492.63	<1	>99.9
7	14	10.8	1492.63	<1	>99.9
8	16	10.8	1492.63	<1	>99.9
Pb2+
1	2	10.8	2273.157	0.051	99.997
2	4	10.8	2273.157	0.021	99.999
3	6	10.8	2273.157	0.01	99.999
4	8	10.8	2273.157	0.065	99.997
5	10	10.8	2273.157	0.016	99.999
6	12	10.8	2273.157	0.012	99.999
7	14	10.8	2273.157	0.012	99.999
8	16	10.8	2273.157	0.026	99.998

The word “illustrative” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “illustrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more”.

The foregoing description of illustrative embodiments of the invention has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical applications of the invention to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

1. An ion-exchange column comprising: a column; andan ion-exchange material packing the column, the ion-exchange material comprising: a composite material comprising a metal chalcogenide and an alginate; andan inert granular material mixed with the composite material.

2. The ion-exchange column of claim 1, wherein the metal chalcogenide has the nominal formula A2xMxSn3-xS6, where x has a value in the range from about 0.5 to about 1; A is Li+, Na+, K+, Rb+ or Cs+; and M is Mg2+, Ca2+, Mn2+, Mn3+, Zn2+, Fe2+ or Fe3+.

3. The ion-exchange column of claim 2, wherein the metal chalcogenide has the nominal formula K2xMgxSn3-xS6

4. The ion-exchange column of claim 2, wherein the ratio of composite material to inert granular material is in the range from about 1:3 to 3:1.

5. The ion-exchange column of claim 4, wherein the inert granular material comprises activated carbon, sand or silica powder.

6. The ion-exchange column of claim 1, wherein the ratio of composite material to inert granular material is in the range from about 1:3 to 3:1.

7. The ion-exchange material of claim 1, wherein the inert granular material is activated carbon, sand or silica powder.

8. The ion-exchange material of claim 1, wherein the inert granular material has a mesh size in the range from about 15 to about 75.

9. A method of removing metal ions from a sample comprising the metal ions, the method comprising passing the sample through the ion-exchange column of claim 1, whereby ion-exchange occurs between the metal chalcogenide and the metal ions in the sample; and collecting the sample exiting the column.

10. The method of claim 9, wherein the metal chalcogenide has the nominal formula A2xMxSn3-xS6, where x has a value in the range from about 0.5 to about 1; A is Li+, Na+, K+, Rb+ or Cs+; and M is Mg2+, Ca2+, Mn2+, Mn3+, Zn2+, Fe2+ or Fe3+.

11. The method of claim 9, wherein the sample is waste water from a nuclear reactor, an industrial plant or a mining operation.

12. The method of claim 10, wherein the percentage of the metal ions removed is at least 99.9 wt. %.