Removal of Sulfate Ions From Brine Using Amorphous Polymeric Zirconium Oxide Formed Within a Macroporous Polymer Matrix

Various alkali metal halide aqueous solutions or alkaline earth metal halide aqueous solutions, e.g., NaCl brine or MgCl.sub.2 brine, contain sulfate, borate, bicarbonate, or dihydrophosphate values or ions which are considered detrimental if the aqueous solution is intended for use in certain applications, such as in electrolytic processes. There are commercial incentives to substantially removing the sulfate ions.

It is known that hydrous zirconium oxide and other zirconium compounds, such as zirconium phosphates, are useful as inorganic ion exchangers.

An amorphous polymeric zirconium hydrous oxide is formed within the resin phase of beads of a macroporous cation exchange resin of the sulfonic acid type, thereby forming novel ion exchange composite structures which are useful in removing, e.g., sulfate, borate, bicarbonate, or dihydrophosphate ions from alkali metal halide brines.

It is known that zirconium hydroxide is prepared by alkali precipitation of an aqueous solution of a zirconyl salt. For the present invention it is preferred that the alkali be ammonia since it is more easily washed out than the alkali metal hydroxides or alkaline earth metal hydroxides. Precipitation at cold (ambient) temperature gives a gelatinous product which is substantially Zr(OH).sub.4 containing about 26.5% water or more. A partially dehydrated zirconyl hydroxide, ZrO(OH).sub.2, results from drying it at elevated temperature (e.g., 100.degree. C.), or from hot-precipitation (e.g., 85.degree. C.) followed by hot drying.

Thus, in the present invention the expression "hydrous zirconium oxide" has within the purview of its meaning any of the various amorphous hydrated forms of zirconium oxide which are substantially or largely insoluble in plain water.

The macroporous cation exchange resin is one which contains sulfonic acid (SO.sub.3.sup.-) functional group. Such resins are available commercially, such as sulfonated polymers of styrene crosslinked with divinylbenzene. For instance a macroporous cation exchange resin with SO.sub.3.sup.- Na.sup.+ or SO.sub.3.sup.- H.sup.+ groups affixed to a styrene-divinyl-benzene resin structure is sold by The Dow Chemical Company under the tradename DOWEX MSC-1-Na.sup.+ and DOWEX MSC-1-H.sup.+. It is within the purview of the present invention to use any macroporous cation exchange resin containing sulfonic acid functional groups, so long as the resin is substantially inert or non-reactive, when used in the present invention, except for the reactivity of the sulfonic acid functionality groups.

In general, the polymeric zirconium hydrous oxide is formed within the resin beads by thoroughly wetting the resin with an aqueous solution of a soluble zirconyl compound, such as ZrOCl.sub.2.8H.sub.2 O. Excessive zirconyl solution should be drained off and the resin thoroughly washed with water to substantially remove the zirconyl compound from the void spaces (pores) of the resin, leaving only that which is taken up into the resin phase, then is optionally dried, such as by air-drying. The dried resin, containing the zirconyl compound is neutralized, preferably by use of NH.sub.4 OH, thereby forming polymeric ZrO(OH).sub.2. Excess NH.sub.4 OH and NH.sub.4 Cl (which forms) is washed out, such as by repeated contact with NaCl brine. The composite is acidified, such as with HCl.

In the general process outlined above, the beginning zirconyl or zirconium compound may be ZrOCl.sub.2.xH.sub.2 O or the like, such as Zr(NO.sub.3).sub.4.5H.sub.2 O, ZrOBr.sub.2.xH.sub.2 O, ZrOI.sub.2.8H.sub.2 O, or Zr(SO.sub.4).sub.2.4H.sub.2 O, or any such zirconium compound which will precipitate to form ZrO(OH).sub.2 when contacted with a base, especially NH.sub.4 OH. The so-formed ZrO(OH).sub.2, also called "zirconium hydrous oxide", is an amorphous, polymeric structure. Following the above alkalizing step, the acid used for lowering the pH is preferably HCl, but may also be HBr, HI, NHO.sub.3, and the like.

The present invention relies, in part, on the step of substantially washing the zirconyl compound, such as ZrOCl.sub.2, from the void spaces (pores) of the resin, leaving only the zirconyl compound within the resin phase. Adequate washing with water is determined by analyzing the wash water to determine that substantially no further ZrO.sup.++ or Cl.sup.- (or other salt ions) is being removed. The washing is done with salt-free water so as not to remove the zirconyl compound from the resin phase.

In one representative embodiment there is used a macroporous crosslinked styrene-divinylbenzene copolymer which has been sulfonated to about one --SO.sub.3.sup.- H.sup.+ group per benzene ring. The beads have about 30-40% porosity and a surface area of about 40-50 M.sup.2 /gm. The preferred product contains one Zr atom for each two --SO.sub.3 H groups, having been formed by exchanging all of the H.sup.+ ions in the resin for ZrO.sup.++ ions from excess ZrOCl.sub.2 solution. At this intermediate stage the product is specifically a styrene-divinylbenzene polymer network with affixed --(SO.sub.3.sup.-).sub.2 --ZrO.sup.++ ionic groups. The close proximity of the ZrO.sup.++ ions and the R--SO.sub.3.sup.- ions is maintained during the reaction with

and with NaCl and HCl to the final product

This close proximity enhances removal of Na.sub.2 SO.sub.4 by water, after the Cl.sup.- has been exchanged to SO.sub.4.sup.=.

The range of ratios of Zr/S of .about.0.4 to .about.0.6 is an operable range; preferably, though, the ratio is around or about 0.5.

When using a crosslinked copolymer of styrene-divinylbenzene as the sulfonated polymer for use as a cation exchange resin, it is preferred that the divinylbenzene content of the copolymer be in the range of about 6-20%, preferably around or about 10%.

As stated above, once the resin has been acidized, the composite is ready to take on SO.sub.4.sup.= values from brine. This is done, for example, by placing the composite in a vessel, preferably a column, and passing sulfate-containing brine through the composite until the composite is substantially "loaded" with SO.sub.4.sup.= values and is ready for another water-washing.

It is within the purview of this invention that the alkali metal salt brine may be a natural brine, such as seawater or mineral brine, a LiCl brine, a KCl brine, or an alkali metal salt brine which comes from an ore dressing, ore leaching, mineral dressing, and the like. The alkali metal brine may contain only a small amount, say, less than about 1% of hardness values; preferably the hardness values are less than about 0.1%. The present novel composite exhibits a high affinity for, and a strong preference for, SO.sub.4.sup.=, BO.sub.2.sup.-, HCO.sub.3.sup.-, and H.sub.2 PO.sub.4.sup.- ions.

In contacting the influent brine with the exchange resin composite in accordance with the present invention, it is preferred to operate at about 40.degree. C. to about 60.degree. C. using a brine pH between about 1-2, using a contact flow rate of about 0.05 to about 0.1 bed volumes per minute (BVPM), and using a counterflow water-wash to regenerate the resin once it is loaded with the sulfate or borate or other ions being removed from the brine. At a pH below about 1 and using a concentrated metal chloride brine, some solubility of ZrOCl.sub.2 is likely to be encountered, especially at high temperature. By operating at a pH above about 1.5 (but still at an acid pH) higher temperature of up to 100.degree. C., or even close to boiling point of the brine, are permissible; at 40.degree. C.-60.degree. C., flow rates greater than 0.1 BVPM may cause leakage and an early breakthrough of the sulfate, borate, or other ions sought to be removed from the brine. At pH of 2 and temperature of 100.degree. C., efficient operation may be obtained at 0.2 BVPM.

As stated above, counterflow of the water-wash to regenerate the resin composite is preferred, but co-flow is operable, though at lower efficiency.

The following example is intended to illustrate the present invention, but the invention is not limited to the particular example shown.

About 150 ml of DOWEX MSC-1 in H.sup.+ form, having a mesh size of about 20-50 (U.S. standard sieve size) was washed with water and loaded into a glass column. A 15% ZrOCl.sub.2 aqueous solution was flowed down through the resin until the effluent gravity reached 1.10 gms/cc. Then about 25 ml of 32% ZrOCl.sub.2 aqueous solution was fed in, followed by 1 liter of water. Rinse water was flowed until neither ZrO.sup.++ or Cl.sup.- could be detected in the effluent. This thorough washing removed excess ZrOCl.sub.2 from the voids (pores) of the resin, but did not remove the ionically held groups from the SO.sub.3.sup.- groups in the resin phase.

The resin was removed from the column and treated with excess NH.sub.4 OH (about 25 ml of 30% NH.sub.3). The resin was washed free of excess NH.sub.4 OH and NH.sub.4 Cl (which forms), immersed in 26% NaCl, and titrated with 1 N HCl to 1.5 pH (requiring 87 meq. HCl). The settled volume of the final resin was 144 ml.

116 ml of the resin was loaded into a temperature controlled jacketed glass column and contacted with 1.5 pH 26% NaCl (containing 2000 mg/l SO.sub.4.sup.=) upflow at 10 ml/min and 65.degree. C. No SO.sub.4.sup.= was detectable in the effluent until 850 ml when a breakthrough of 100 ppm SO.sub.4.sup.= was observed. A total 26% NaCl flow of 1000 ml was achieved with a composite analysis of 173 mg/L SO.sub.4.sup.=.

The SO.sub.4.sup.= was eluted downflow with deionized water at 3.2 ml/min. at 65.degree. C. The effluent was collected in cuts and analyzed for SO.sub.4.sup.= content, with the following results:

After this downflow water regeneration, 26% NaCl upflow at 10 ml/min. and 65.degree. C. was resumed. No SO.sub.4.sup.= was detected in the effluent until 500 ml had been purified, at which time about 100 ppm of SO.sub.4.sup.= broke through. The composite analysis of the first 500 ml of 26% NaCl was 76.8 mg/l SO.sub.4.sup.=.