CHELATING POLYMERIC MEMBRANES

Abstract

The present application offers a solution to the current problems associated with recovery and recycling of precious metals such as gold and copper from scrap material, discarded articles, and other items. The solution is premised on a microporous chelating polymeric membrane comprising a poly-thiosemicarbazide formed from N,N-diaminopiperazine and a suitable reactant such as diisothiocyanate; the membrane may be formed through the use of a solvent system and non-solvent system. The membrane may be used to separate metal ions from solutions and incorporated in a membrane module.

Claims

1. A membrane module for selective recovery of a metal ion comprising: a casing having flanges which support and sealingly close ends of the casing; an inlet opening configured to couple with an inlet conduit for introducing a feed into the casing; an outlet opening configured to couple with an outlet conduit for removing a filtrate from the casing; and a membrane cell defined by the casing and comprising a microporous polymeric body, wherein the polymer has the following recurring unit: ##STR00007## wherein R is a bivalent hydrocarbon radical.

2. The membrane module of claim 1, wherein R comprises an alkanediyl, oxy-alkanediyl, methylene diphenylene, or phenylene.

3. The membrane module of claim 2, wherein the polymer has a weight average molecular weight of about 10,000 to 500,000.

4. The membrane module of claim 1, wherein the polymer comprises the following recurring unit: ##STR00008##

5. The membrane module of claim 4, wherein the polymer has a weight average molecular weight of 10,000 to 100,000.

6. The membrane module of claim 1, further comprising an evacuation opening configured to couple with an evacuation conduit for the egress of the filtrate from the casing, wherein the portion of filtrate passing through the evacuation opening has passed through the microporous polymeric body from a first surface of the microporous polymeric body to a second surface of the microporous polymeric body.

7. The membrane module of claim 1, wherein the microporous polymeric body is a plurality of beads or particles.

8. The membrane module of claim 7, wherein the beads or particles have a diameter of 50 to 1000 m.

9. The membrane module of claim 1, wherein the microporous polymeric body is in the form of a film, sheet, fiber, or hollow fiber.

10. The membrane module of claim 9, wherein the microporous polymeric body is an asymmetric membrane.

11. The membrane module of claim 9, wherein the microporous polymeric body is a film having a thickness of 20 to 1000 m.

12. The membrane module of claim 11, wherein the film is supported on a non-woven polyester support.

13. The membrane module of claim 9, wherein the membrane cell comprises a plurality of microporous polymeric bodies in the form of hollow fibers bundled longitudinally.

14. The membrane module of claim 13, wherein the hollow fibers extend along the direction of flow.

15. The membrane module of claim 9, wherein the microporous polymeric body is the form of a spirally-rolled sheet having a first spiral end and a second spiral end.

16. The membrane module of claim 15, wherein the first spiral end faces the inlet opening and the second spiral end faces the outlet opening.

17. The membrane module of claim 1, wherein the casing is a pressure vessel.

18. The membrane module of claim 17, wherein the membrane cell is adapted for a pressure difference within the range of 0.5 to 4 bar.

19. The membrane module of claim 1, wherein the casing is a tubular conduit with ends that sealingly close to prevent or minimize leaking of the feed during operation.

20. The membrane module of claim 1, wherein the microporous polymeric body is configured for regeneration and reuse.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The following drawings illustrate by way of example and not limitation. For the sake of brevity and clarity, every feature of a given structure may not be labeled in every figure in which that structure appears. Identical reference numbers do not necessarily indicate an identical structure. Rather, the same reference number may be used to indicate a similar feature or a feature with similar functionality, as may non-identical reference numbers.

[0023] FIGS. 1A-1D illustrate various polymeric body shapes.

[0024] FIG. 2 illustrates an embodiment of a membrane filtration module in accordance with the present disclosure.

[0025] FIG. 3 is an SEM micrograph of a cross-section of the membrane made in accordance with Example 2.

[0026] FIGS. 4A-4B are photographs of a membrane made in accordance with Example 2 before gold absorption (A) and after gold absorption (B).

[0027] FIG. 5 is a table of the data obtained in Example 5.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Various features and advantageous details are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements will become apparent to those of ordinary skill in the art from this disclosure.

[0029] In the following description, numerous specific details are provided to provide a thorough understanding of the disclosed embodiments. One of ordinary skill in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0030] Disclosed herein is a microporous polymeric chelating membrane for the selective recovery of one or more metal ions from a solution and methods of using and making the same. The microporous polymeric membrane comprises, in the polymeric backbone, thiosemicarbazide groups. In various embodiments, the mole fraction of the thiosemicarbazide in the polymer is at least 0.05, 0.08, 0.1, 0.2, or 0.3.

[0031] In various embodiments, the microporous membrane comprises a polymer having the following recurring structural unit:

##STR00004##

wherein R is a bivalent hydrocarbon radical. In various embodiments, R can comprise an alkanediyl, oxy-alkanediyl, methylene diphenylene, phenylene, and/or diphenylene ether. The weight average molecular weight can be in the range of about 10000 to 500000. For a fiber forming polymer, the molecular weight values can range from 20000 to 500000 for weight average MW.

[0032] In a preferred embodiment, the polymer comprises the following recurring structural unit:

##STR00005##

The weight average molecular weight can be in the range of about 10000 to 100000. For a fiber forming polymer, the molecular weight values can range from 20000 to 100000 for weight average MW.

[0033] In general, the polymeric chelating membrane is prepared by polymerizing N,N-diaminopiperazine and a difunctional co-reactant capable of forming with N,Ndiaminopiperazine the following:

##STR00006##

[0034] In some embodiments, the difunctional co-reactant includes various diisothiocyanates such as methylene-bis (4-phenylisothiocyanate), m-phenylene diisothiocyanate, xylene diisocyanate, cyclohexane diisocyanate, and/or diphenylether diisocyanate. The preferred co-reactant is methylene-bis (4-phenylisothiocyanate). The prepared polythiosemicarbazide, dissolved in a solvent system, is then cast into a desired form (i.e., a polymeric body) and simultaneously or subsequently exposed to a non-solvent system, thereby inducing a phase separation. In some embodiments, the phase separation can be induced by immersion of a polymer solution into a vessel of non-solvent or by contacting the cast polymer solution with a vapor of non-solvent. In various embodiments, the polythiosemicarbazide solution can be cast into a sheet, a hollow fiber, a fiber, or a symmetrical or asymmetrical particle. Illustrated embodiments of the various shapes is provided in FIGS. 1A to 1D.

[0035] The above-mentioned solvent system comprises one or more solvents within which the described polythiosemicarbazide is soluble. In various embodiments, the solvent system comprises, consists of, or consists essentially of dimethyl sulfoxide (DMSO). The solvent system can further comprise, consist of, or consist essentially of 1,4-dioxane. For example, polymeric solution can have a weight percentage of DMSO between about 50 wt % to 100 wt % and a weight percentage of 1,4-dioxane between about 1 wt % to 50 wt %, preferably between 3 wt % and 20 wt %; 1,4-dioxane is used as an additive to decrease the formation of macrovoids in the membrane. Other solvents with low affinities for water that are miscible with DMSO and that, in low concentrations, do not promote the precipitation of the polymer in the polymeric solution could be used as well. Other suitable solvents include, but are not limited to tetrahydrofuran and/or cyclohexanone.

[0036] In contrast, the non-solvent system comprises one or more solvents within which the described polythiosemicarbazide is not soluble or has sufficiently limited solubility to induce a phase separation of the prepared polymer. In various embodiments, the non-solvent system comprises, consists essentially of, or consists of water. Other suitable non-solvents include, but are not limited to methanol, ethanol, and/or isopropanol. In a preferred embodiment, the solvent system and the non-solvent system are miscible.

[0037] In various embodiments, the polymeric body is exposed to the non-solvent system for a time of at least 0.1, 0.3, 0.5, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 hours, or more. The time can be adjusted to account for the thickness or diameter of the polymeric body. Before immersion in the non-solvent, the polymeric body can be exposed to air for a time between Is and 30 min. During this time, part of the solvent evaporates leading to smaller pores in the membrane surface after precipitation. Additives can be included in the solvent system or the non-solvent system to affect the membrane properties. For example, DMSO can be added to the non-solvent system to cause larger pores and higher porosity.

[0038] The described membranes can be in any suitable shape. For example, as previously mentioned, the described membranes can include a film, a fiber, a hollow fiber, or a particle. In various embodiments, the thickness of the described membrane, such as a film membrane, can range between 20 to 1000 m. Similarly, the diameter of membrane particles can range between 50 to 1000 m.

[0039] In various embodiments, with reference to FIG. 2, the microporous chelating polymeric membrane 2 can be incorporated into a membrane module 200 for selective recovery of one or more metal ions. Membrane module 200 can comprise a casing 4 defining a membrane cell. In various embodiments, casing 4 is a pressure vessel. Casing 4 can be a tubular conduit with ends that sealingly close to prevent or minimize leaking of the feed during operation. Casing 4 can comprise an inlet opening 6 configured to couple with an inlet conduit for introducing a feed into casing 4 and an outlet opening 8 configured to couple with an outlet conduit for removing a filtrate from casing 4. Casing 4 can define a membrane cell within which the described microporous polymeric body 2 can be located.

[0040] In further embodiments, the membrane module 200 can further comprise an evacuation opening (not shown) configured to couple with an evacuation conduit for the egress of the filtrate from casing 4, wherein the portion of filtrate passing through the evacuation opening has passed through microporous polymeric body 2 from a first surface of microporous polymeric body 2 to a second surface of microporous polymeric body 2. For example, the feed can pass into the lumen of a hollow fiber and through the membrane to the outer surface of the hollow fiber.

[0041] The casing can house any desired shape of a polymeric body, such as a plurality of particles or beads, a plurality of fibers or hollow fibers, or a sheet. The fibers or hollow fibers can be bundled longitudinally and arranged to extend along the direction of flow. The sheet can be spirally rolled, with the ends of the spiral facing the inlet and outlet openings of the membrane module.

[0042] Also disclosed is a method of using the described chelating polymeric membranes. In various embodiments, a method of separating metal ions from a solution can comprise contacting a metal ion-containing solution (e.g., a feed) with a described microporous polymeric body, whereby a fraction of the metal ions are absorbed by the microporous polymeric body.

[0043] The described chelating polythiosemicarbazide membrane can be used to selectively recover a metal ion from a solution containing at least two metal ions. For example, the metal ion-containing solution can comprise a first metal ion and a second metal ion, and upon contact with the microporous polymeric body, the first metal ion will be selectively absorbed but the second metal ion will not be absorbed or will be absorbed to a lesser degree. In various embodiments, the selectively absorbed metal(s), e.g., the first metal ion) is gold, palladium, and/or mercury. In addition, non-absorbing or lower-absorbing metals, e.g., the second metal ion, can include copper, nickel, cobalt, iron, and/or zinc.

[0044] In various embodiments, the described polythiosemicarbazide membrane can selectively absorb gold from a solution containing both gold and copper. For example, as shown in Example 5, less than 20% of the copper in a solution was absorbed by the prepared membrane. In all solutions tested in Example 5, the percentage of gold absorbed by the membrane was at least 6 times greater than that of copper.

[0045] In various embodiments, the membrane can be regenerated and reused. For example, the method of using the membrane to recover a metal can further comprise stripping at least a portion of the absorbed metal ions from the polythiosemicarbazide by contacting a recovery solution with the microporous polymeric body. In various embodiments, the recovery solution can flow in the same or opposite direction of the metal-ion containing solution, where contacting the polymeric body involves flow of a feed past or through the polymeric body. The recovery solution facilitates reuse of the microporous polymeric body to absorb more metal ions. In further embodiments, the metal ion-containing solution can be recycled through the membrane to recover residual metal ions not absorbed in a previous cycle.

[0046] The described membranes are sufficiently stable in a variety of solutions. In addition to the metal ions, the metal ion-containing solution can comprise hydrochloric acid, nitric acid, and/or sulfuric acid. The described membrane is stable at low pHs. For example, the described membrane is stable in a solution of 5-30% HCl, e.g., about 10% HCl. In addition, the described membrane is stable in a variety of solvents. Generally, the membrane is stable in any non-solvent indicated herein. Other solvents that do not degrade the polysemicarbazide membrane include aliphatic and aromatic hydrocarbons like hexane, cyclohexane, benzene, and xylene, and chlorinated hydrocarbons like chloroform, ketones like acetone methylisobutylketone.

[0047] In various embodiments, the recovery solution comprises an aqueous solution of thiourea and sulfuric acid. The concentration of the solution can range from about 0.1M to 5M of thiourea, preferably about 0.5M, and about 0M to 2M of sulfuric acid, preferably about 0.5M.

[0048] Membranes made in accordance with the present disclosure exhibit a high flux. The flux of a microporous polymeric body can be at least 1, 100, 300, 500, 800, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1750, 1800, 1900, 2000, 2100, 2200, 2300, 2400, or 2500 L/m.sup.2h. Even at high fluxes, the desired metal ion can be effectively recovered from the metal ion-containing solution. Loadings of the selectively absorbed metal ion, such as gold, can be at least 0.1, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, or 6 mmol/g.

[0049] In various embodiments, the described membranes are stored in a manner that prevents or mitigates damage. For example, the membranes can be stored in a manner to maintain sufficient wetness with a non-solvent, such as water, until use.

[0050] Metals absorbed by the described membrane can be extracted from a variety of sources. For example, sources of gold and/or other precious metals can include electronics, ores, catalysts, and/or jewelry. In addition, the membranes can be used to extract said metals from contaminate water.

EXAMPLES

[0051] Embodiments of the present disclosure will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

Polythiosemicarbazide (PTSC) Synthesis

[0052] Instructions for synthesizing the PTSC shown in Formula III can be found in Campbell and Tomic, Polythiosemicarbazides 1. Preparation and Properties of Polymers and Some Simple Metallic Chelates, J. Polymer Science, 62(174): 379-386 (1962), which is hereby incorporated by reference in its entirety.

[0053] For example, the PTSC shown in Formula III was made by stirring a solution containing 3.1 wt % 1,4-diaminopiperazine, 7.6 wt % of 4,4-methylenebis (phenyl isothiocyanate) and 89.2 wt % of DMSO at 50 C. for 24 hours. The resulting polymer was precipitated in water, chopped into small pieces, washed again with water and dried.

Example 2

Microporous PTSC Film

[0054] A PTSC polymer was prepared in accordance with Example 1. A polymer solution was prepared comprising 15 wt % PTSC, 75 wt % DMSO, and 10 wt % 1,4-dioxane by mixing the 3 components and stirring for approximately 5 hours at room temperature. The resulting viscous liquid rested for 5 hours to permit the escape of any air bubbles.

[0055] The polymer solution was casted onto a glass plate into a 250 m thick film with the use of a doctor knife. The glass plate was then immersed into a non-solvent bath (tap water) at room temperature for at least 12 hours. The membrane was stored in a water bath until use. FIG. 3 depicts a cross-section of the resulting asymmetric membrane.

Example 3

Gold Recovery with Microporous PTSC Membrane at Flux=101 L/M.SUP.2.H

[0056] A microporous membrane prepared in accordance with Example 2 was tested with the method(s) described below to assess gold loading of the membrane. The membrane was cut into a four circles, each with an approximate diameter of 2.5 cm and an average dry weight of 14.3 mg. Each membrane was placed on a non-woven polyester circular support of approximately the same size.

[0057] Four aqueous solutions containing gold in 10% HCl were prepared at 100 ppm, 200 ppm, 500 ppm, and 1000 ppm. 10 mL of each solution permeated through a membrane with the use of pressurized air. A difference in pressure of 0.5 bar was sufficient to permeate the solutions through the respective membrane with a flux of 101 L/m.sup.2h. FIGS. 4A and 4B depict the membranes before gold absorption (4A) and after gold absorption (4B).

[0058] Prior to gold absorption, the membrane is an off-white color, and afterward, the membrane is a brownish color. The amount of gold absorbed from each solution is provided in Table 1 below.

TABLE-US-00001 TABLE 1 Solution Au Conc. % No. (ppm) Absorbed 1 100 98% 2 200 98% 3 500 90% 4 1000 76%

Example 4

Gold Recovery with Microporous PTSC Membrane at Flux=1800 L/M.SUP.2.H

[0059] Three PTSC membranes were prepared and set up in accordance with Example 3, each with an approximate diameter of 2.5 cm and an average dry weight of 14.3 mg.

[0060] Three gold solutions were prepared in accordance with Example 3 at 100 ppm, 200 ppm, and 500 ppm. 10 mL of each solution permeated through a membrane with the use of pressurized air. A difference in pressure of 4 bar was sufficient to permeate the solutions through the respective membrane with a flux of 1800 L/m.sup.2h. The amount of gold absorbed from each solution is provided in Table 2 below.

TABLE-US-00002 TABLE 2 Solution Au Conc. % No. (ppm) Absorbed 4 100 93% 5 200 78% 6 500 44%

Example 5

Gold Recovery from a Copper and Gold Solution with Microporous PTSC Membrane at Flux=1800 L/M.SUP.2.H

[0061] Three PTSC membranes were prepared and set up in accordance with Example 3, each with an approximate diameter of 2.5 cm and an average dry weight of 14.3 mg.

[0062] Three gold-copper solutions were prepared in accordance with Example 3 at concentrations shown in Table 3. 10 mL of each solution permeated through a membrane with the use of pressurized air. A difference in pressure of 4 bar was sufficient to permeate the solutions through the respective membrane with a flux of 1800 L/m.sup.2h. The amount of gold and copper absorbed from each solution is provided in Table 3 below. The data of which is provided in FIG. 5.

TABLE-US-00003 TABLE 3 Solution Au Conc. Cu Conc. % Au % Cu No. (ppm) (ppm) Absorbed Absorbed 7 100 100 99% 15% 8 100 500 91% 11% 9 500 500 46% 3% 10 100 900 97% 16%

[0063] In actual electronic scrap processing, copper is usually present in much higher concentrations than gold. These experiments show that the gold recovery capacity of the membrane is not affected by higher concentrations of copper. The experiments made with 100 ppm of gold and 100 ppm of copper show that 99% of the gold was absorbed, and increasing the copper to 5 and 9-fold excess show an almost complete absorption of gold at 91%) and 97% respectively. Only a small percentage of copper was absorbed for all three. Moreover, these absorption percentages are comparable to the results in Example 4 at the same flux but without copper in the solution.

Example 6

Gold Recovery from the Microporous PTSC Membranes

[0064] Gold was successfully recovered from the gold-containing membranes of Example 4 by permeating a solution containing 0.5 M thiourea and 0.5 M sulfuric acid. The process was able to recover at least 98% of the gold.

[0065] The above specification and examples provide a complete description of the structure and use of an exemplary embodiment. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the illustrative embodiment of the present chelating microporous membrane is not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the described embodiments. For example, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments.

[0066] The claims are not to be interpreted as including means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) means for or step for, respectively.