AP20A

AP20A - High density ion exchange resin for molybdenum recovery.

Info

Publication number: AP20A
Application number: APAP/P/1985/000008A
Authority: AP
Inventors: Melvin J Hatch
Original assignee: Dow Chemical Co
Priority date: 1984-03-05
Filing date: 1985-03-05
Publication date: 1988-05-11
Also published as: ZA851651B; AU3951085A; JPS6128460A; AP8500008A0; PH20935A

Abstract

A macroporous anion exchange resin in the sulfate salt form which resin has barium sulfate precipitate therein and which resin comprises a polymeric matrix which has a treated bulk density of 0.33 to 0.41 prior to the attachment of active ion exchange sites thereto. The resin is suitable for the recovery of metal values from aqueous streams in particular molybdenum.

Description

HIGH DENSITY ION EXCHANGE RESIN FOR MOLYBDENUM RECOVERY

This invention relates to a high density ion exchange resin suitable for absorbing metal ions, particularly molybdenum ions from aqueous solutions.

It is often desirable to remove dissolved metal values from aqueous solution. For example, in the mining processing of molybdenum from molybdenite (MoS₂) or as a by-product of copper production, waste streams are generated containing several parts per million (ppm) of molybdenum values. Such waste streams cannot be discharged into unrestricted waters unless the level of molybdenum values is reduced, typically to less than 0.7 ppm. Accordingly, it is necessary to remove molybdenum values from the waste stream for discharge.

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It is known to remove molybdenum values from waste streams by contacting the waste stream with a weak base ion exchange resin. Unfortunately, due to the presence of suspended solids in such waste streams, bad ORIGINAL

-1-Σit is necessary to employ a so-called fluidized bed of ion exchange resin in treating such streams. Previously known weak base resins are not dense enough to permit a commercially acceptable flow rate in such a fluidized bed system. In addition, previously known weak base ion exchange resins have not exhibited satisfactory loading capacity for molybdenum values, i.e. said resins are not sufficiently selective for molybdenum and/or do not load molybdenum values as rapidly as desired. ·

Accordingly, a high density ion exchange resin which exhibits superior loading characteristics for metal values in general and molybdenum values in particular would be highly desirable.

This invention is such a desirable ion exchange resin. The resin of this invention is a weak base macroporous ion exchange resin in the sulfate salt form having a colloidally dispersed barium sulfate precipitate therein. Said resin is prepared from a macroporous copolymer which, prior to attachment at active ion exchange sites thereto, has a treated bulk density of 0.33 to 0.41 grams per millilter (g/ml). The resin contains sufficient barium sulfate to measurably increase the density thereof.

In another aspect^ this invention is a process for removing metal values from an aqueous stream. This process comprises contacting said stream with a bed of the macroporous weak base ion exchange resin of this invention under conditions such that the level of such metal values in said waste stream is measurably reduced.

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-3The resin of this invention exhibits a higher density than conventional ion exchange resins, thereby permitting the use of higher, more commercially acceptable flow rates in a fluidized bed operation. In addition, said resin has a surprisingly high capacity for loading metals, especially molybdenum, i.e. the selectivity and/or rate of loading of such resin is significantly increased as compared to conventional ion exchange resins.

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The ion exchange resin employed herein is a so-called macroporous resin containing the plurality of active weak base anion exchange sites in the sulfate salt form. Said resin comprises a macroporous copolymer matrix which, prior to the attachment of active ion exchange sites thereto, has a treated bulk density of 0.33 to 0.41 g/ml. The ion exchange resin employed herein comprises a polymeric matrix which may be phenolic, polyethylenic including styrenic or acrylic, or others that can be modified to exchange anions. Preferably, crosslinked styrenic polymers are employed. Especially preferred are addition polymerization products of styrene and divinylbenzene which are polymerized in the presence of an inert organic diluent in which the monomers to be polymerized are soluble, but the polymers formed thereby are not soluble. In the course of such polymerization, the polymer precipitates out of the inert diluent, forming a highly porous polymeric structure. Such pores typically have a volume average pore o * o o diameter of 200 A to 20,000 A, preferably from 200 A to o

5,000 A. In addition, the copolymer matrix is generally crosslinked with from 5 to 20, preferably 6 to 12 weight percent of a crosslinking monomer which is preferably divinylbenzene. Methods for the preparation

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-4of macroporous resins are taught in U.S. Patent Nos. 3,173,842; 3,549,562 and 3,637,535 .

In addition, the resin contains a plurality of active weak base anion exchange sites. Exemplary weak base groups. include pendant amine and phosphine groups. Preferred are amine groups such as amino; alkylamino, especially methylamino; dialkylamino, especially dimethylamino; and similar moieties. Such weak base moieties are present in resins which are polymerization products of the condensation reaction of aromatic and/or aliphatic polyamines, formaldehyde or epichlorohydrins and phenol. Such amine groups can be introduced onto the preferred crosslinked styrenic copolymer matrix by chloromethylation of the copolymer ) followed by amination using an appropriate amine.

Methods for preparing such anion exchange resins are described in Ion Exchange, Helfferich, McGraw-Hill,

1962.

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Preferably, the resin contains a sufficient concentration of weak base groups to impart thereto dry weight capacity of 2 to 3 milliequivalents per gram of dry resin. Examples of especially preferred resins

I *” include those sold under the trade names DOWEX* MWA-1 * anion exchange resin and DOWEX 66 anion exchange resin, both sold by The Dow Chemical Company.

The weak base groups on the resin employed herein are converted to the sulfate salt form by treating *Trademark of The Dow Chemical Company

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-4-5said resin with a solution of sulfuric acid prior to use. Typically, the resin is contacted with a dilute solution of sulfuric acid under conditions such that the amine groups are protonated and the sulfate ions become counterions to the protonated amine groups. Generally, such contact may be done at room temperature by contacting said sulfuric acid solution with the resin.

In addition to the weak base groups, the ' resin may contain a minor proportion of strong base groups. The presence of strong base groups reduces the amount of swelling and shrinkage exhibited by the resin during use and regeneration. Accordingly, when such strong base groups are present, a resin having lower tested bulk density may be employed, since there is less tendency for the resin to lose barium sulfate while in use. Thus, when a resin having a low treated bulk density, i.e., 0.33 - 0.36 g/ml, it is generally advantageous to employ a. resin containing strong base groups. However, the strong base groups do not contribute to the operating capacity of the resin, and the presence of strong base groups is generally accompanied by a corresponding decrease of weak base groups. For this reason, it is preferred that no more than 20 mole percent of the strong and weak base groups on the resin are strong base groups. Preferably, from 10-20, more preferably 15-20 mole percent of the strong and weak base groups on the resin are strong base groups.

The resin employed herein comprises a macroporous polymeric matrix having a treated bulk density of 0.33 to 0.41 g/ml. Treated bulk density as used herein, refers to the bulk density of a quantity

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-6Vb of copolymer which has been swelled with a swelling agent and subsequently dried in such a manner as not to cause the collapse of the pores upon drying. Preferably, the copolymer is treated by swelling the resin with toluene in order to open the pores, and then displacing the toluene with an organic diluent such as isoctane which does not swell the copolymer. The diluent is then driven off with vacuum heating so that upon removal of the diluent, the pores of the dried polymer do not collapse. The bulk density of the resin is then measured in the conventional manner.

It has been found that resins prepared from copolymers having too low a bulk density tend to readily lose the barium sulfate precipitate disposed therein upon use of the resin. When the treated bulk density is too high, it is difficult to cause sufficient barium sulfate to precipitate inside the resin. Preferably, the treated bulk density of the resin is at least 0.36 g/ml, unless the resin contains strong base groups in the amounts described hereinbefore.

The ion exchange resin is in the form of a particulate preferably having a volume average particle diameter range from 20 to 2,000 microns, more preferably 700 to 1,400 microns.

The ion exchange resin further has dispersed therein colloidal particles of a barium sulfate precipitate. In general, sufficient barium sulfate precipitate is dispersed in the resin to measurably increase the density thereof. Preferably, sufficient barium sulfate precipitate is dispersed therein to increase the density of said resin by at least 10 percent, more preferably at least 35 percent.

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. Most preferably, the resin containing the precipitate has fluidization properties such that it can be employed in a commercially viable upflow system for metals, and in particular, molybdenum recovery.

For the purposes of this invention, suitability for use in such an upflow system is determined by measuring upflow rates of liquids through a column containing the resin. When a fluidized bed column is operated, the resin particles are borne upward by the liquid being passed therethrough. The fluidization properties of the resin can be measured by the increase in height of the resin bed when an upflow system is in operation.

To be suitable for such metal recovery, the resin advantageously has fluidization properties such that the bed is expanded by 80 to 90 percent of its original height at a flow rate of no less than 5 gallons per minute per square foot (gpm/ft²) (34 x 10“⁴ cubic meter per second per square meter, m³/s/m²) of cross-sectional area of the bed. Preferably, said 80 to 90 percent expansion is seen at no less than 15 gpm/ft²-4 (102 x 10 m³/s/m²), more preferably, at no less than gpm/ft² (136 x 10^-4 m³/s/m²).

The impregnated resin of this invention is advantageously prepared by treating the resin in free base form with an aqueous solution of sulfuric acid.

While concentrated sulfuric acid solution may be employed, typically only dilute acids are used. Sufficient of said acid solution is employed to convert substantially all of said free base groups to the sulfate salt form.

Such contact is advantageously made at room temperature or at slightly elevated temperatures.

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-8Following conversion of the resin to the sulfate salt form, the resin is washed with deionized water to remove excess acid, and then contacted with an aqueous solution of a water-soluble barium compound. Barium nitrate, barium hydroxide and barium chloride are all suitably employed herein, with barium chloride being most preferred. Generally, a saturated solution of the barium compound is employed. If desired, in order to obtain a solution having higher concentration of barium, a hot solution can be employed. The resin in sulfuric acid form is contacted with barium solution under conditions such that the barium solution is imbibed by the resin, wherein the barium reacts with the sulfate ion to form a barium sulfate precipitate.

The resin is simultaneously converted to the form of the anion of the particular barium compound employed.

For example, when the preferred barium chloride solution is employed, the resin is converted to the hydro£ chloride gait form.

The resin is subsequently washed in sulfuric acid to again load the resin with sulfuric acid. Then the resin is washed with deionized water to remove excess acid.

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While the resin of this invention is especially suitable for the removal of molybdate values from aqueous solutions, the resin is also useful for recovering values of other metals, especially transition metals, from aqueous solutions, which metals exist in aqueous solutions as anionic complexes or radicals. Exemplary, such metals include, for example, tungsten, chromium, uranium and the like.

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-8-9In the recovery of said metal values, particularly molybdenum values, from aqueous streams, a bed of the resin is contacted with an aqueous stream containing the metal values by flowing said stream upwardly through a bed of said resin at a rate such that the length of the bed is expanded by about 10 to 150 percent, preferably 50 to 100 percent of its original length.

As discussed hereinbefore, the resin preferably has fluidization properties such that said preferred expansion is seen at flow rates of not less than 5 gpm/ft², (34 x 10 m³/s/m²), preferably not less than gpm/ft² (102 x 10 m³/s/m²), more preferably not less than 20 gpm/ft² (136 x 10^-4 m³/s/m²). In a most preferred embodiment, the system is operated at a flow rate of at least 20 gpm/ft² (136 x 10 ⁴ m³/s/m²) with a bed expansion of 50 to 100 percent.

In order for the resin to recover said metal values from the aqueous stream, the pH of the stream is adjusted to acidic values, preferably in the range of between 1 and 6, more preferably 3.0 to 4.5, most preferably between 3.5 and 4.0. Often said waste stream will have the desired pH but if not it can be adjusted into the desired pH range by addition of acid or base.

The column is operated until the resin is exhausted, i.e. the resin bed can no longer remove the metal values at a commercially available rate. Exhaustion of the resin bed is indicated by the presence of increasing amounts of metal values in the treated stream which have passed through the resin bed. Upon exhaustion of the resin, regeneration is effected by treating said resin with a solution of a base, preferably

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-10an alkali metal hydroxide, more preferably sodium hydroxide, to remove molybdenum values therefrom. Typically, a 2.0 molar aqueous solution of said base is suitable for eluting the metal values from the resin. Following elution of metal from the resin, the resin is washed and contacted with an aqueous sulfuric acid solution in order to convert the resin to the sulfate salt. The resin is then washed with deionized water as described hereinbefore and is ready for reuse.

The molybdenum values removed from the aqueous stream may be further processed to obtain molybdenum metal or useful molybdenum compounds or may be discarded as desired. Similarly, other metal values may be processed or found in conventional manner, or discarded.

The following examples are provided to illustrate the invention. All parts and percentages are by weight unless otherwise indicated.

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Example 1

A 100 ml sample DOWEX*66 anion exchange resin was converted to the sulfate salt form by washing the resin in 400 g of a 0.19 molar aqueous sulfuric acid solution. This resin was prepared from a macroporous styrene divinyl benzene copolymer having a treated bulk density of 0.380. The resin is then washed with 2,000 g deionized water. The washed resin was impregnated with barium by immersion in 125 ml of a 1.2 molar barium chloride solution at 22°C for 60 minutes. The resin was then filter washed to remove free barium sulfate particles and excess barium chloride solution from the resin. The resin was then neutralized with NaOH and washed. The impregnation process was repeated. The * trademark of The Dow Chemical Cornea

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-11resin was then converted to the sulfate salt form by washing the resin in 400 g of 0.19 molar sulfuric acid solution prior to use.

The density of the untreated resin was 1.05 g/ml. Following precipitation of barium sulfate therein, the density was increased to 1.4 g/ml. The water retention capacity of the treated resin was 35.3 percent and the weak base capacity was 1.05 millieguivalents per milliliter of wet weak base resin.

The treated resin was evaluated for utility in molybdenum loading according to the following procedure

Three millileters of the wet resin was decanted to remove excess water. This resin was then immersed in 4-liters of a standard pregnant solution containing 9 ppm molybdenum ion, 1,700 ppm sulfate ion, 3.0 ppm fluoride ion, 40 ppm chloride ion and having a pH of 3.7; and agitated for 24. hours. The resin was then separated from the pregnant solution, and the pregnant solution was analyzed for molybdenum. The capacity of the resin was then determined to be 19.6 mg molybdenum per cubic centimeter of resin.

The fluidization properties of this impregnated resin were evaluated by subjecting a column of the resin to an upflow system. At a flow rate of 20 gpm/ft²-4 (136 x 10 m³/s/m²), the resin bed was expanded by 65 percent.

A sample of commerically available macroporous anion exchange resin prepared from a copolymer having a treated bulk density of 0.33 and a strong base capacity i,

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f+“ of less than 15 percent of the total capacity was treated as described herein to precipitate barium sulfate therein. This resin was then subjected to alternating washings with acid and base. Following 100 cycles of such treatment, this resin lost density due to the leakage of barium sulfate particles from the resin. Similar treatment of a treated resin prepared from a copolymer having a treated bulk density of 0.393 and a strong base capacity of less than 15 percent of the total capacity resulted in no measurable loss of .. density.

A sample of DOWEX* 65 anion exchange resin prepared from a copolymer having a treated bulk density of 0.42 was treated as described hereinbefore. It is found that the density of this resin was not increased by such treatment in an amount sufficient to render it useful for molybdenum recovery.

i ·’ trademark of The Dow Chemical Company

Claims

- 13 1· A weak base macroporous anion exchange resin in the sulfate salt form having colloidally dispersed barium sulfate precipitate therein characterised in that said resin comprises a copolymer matrix which, prior to the attachment of active anion exchange sites thereto, has a treated bulk density of 0,33 to 0,41 g/ml and that a sufficient amount of barium precipitate is used to increase the density of said resin by at least 10 percent,
2, The resin of Claim 1 characterised in that said matrix comprises a crosslinked polymer of styrene,
3» The resin of Claim 2 wherein the matrix is a styrene/divinylbenzene copolymer,
4, The resin of Claim 1, characterised in that when employed in a fluidised bed operation, it exhibits a bed expansion of about
5θ to 100 percent at a flow rate of not less than 15 gpm/ft² (102 x lO’^/s/m²),

The resin of Claim 4 characterised in that when employed in a fluidised bed operation, it exhibits a bed expansion of 50 to 100 percent at a flow rate of not less than 20 gpm/ft² (136 x 10~^m^/s/m²),
6, The resin of Claim 3 wherein the resin has a treated bulk density of at least 0,36 g/ml.

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7· The resin of Claim 3 characterised in that the anion exchange sites comprise strong base and weak base groups and the strong base groups comprise from 10 to 20 mole percent of said weak base and strong base groups.
8. A resin of Claim 1 characterised in that the anion exchange sites comprise a sufficient concentration of weak base groups to impart thereto a dry weight capacity of 2 to 3 milliequivalents per gram of dry resin.
9· A resin of Claim 1 characterised in that said barium sulfate precipitate is dispersed therein in an amount sufficient to increase the density of said resin by at least 35 percent over the density of the said resin without a dispersion of barium sulfate precipitate therein.
10. A process for removing dissolved metal values from an aqueous stream containing said metal values, characterised in thatvsaid aqueous stream is contacted with a bed of a macroporous anion exchange resin in the sulfate salt form, said resin having colloidally dispersed barium sulfate precipitate therein, and said resin comprising a polymeric matrix which, prior to the attachment of active anion exchange sites thereto, has a treated bulk density of 0.33 to 0.41 g/ml, which resin contains an amount of said precipitate sufficient to measurably increase the density thereof, said contact being made under conditions such that the quantity of metal values in said stream is measurably reduced. bad original
11« The process of Claim 1Φ characterised in that said metal values comprise molybdenum values,
12. The process of Claim 11 characterised in that said aqueous stream has a pH of about 1 to 5·
13. The process of Claim 10 characterised in that said resin has fluidisation properties such that when employed in a fluidised bed system said resin bed exhibits an expansion of 50 to 100 percent at a flow 2 —4 3 2 rate of not less thaix 15 gpra/ft (102 x 10 m /s/m ).
14. The process of Claim 10 characterised in that the treated bulk density of the resin is at least Θ.36 g/ml.