Abstract:
Formation of hydrous alumina in the reticules of a weak-base anion exchange resin, wherein AlCl 3  has been precipitated as hydrous alumina by reaction with ammonia, is improved by employing a subsequent treatment with HCl or with NH 4  Cl and HCl to convert the exchange resin to the chloride form, thereby increasing the reticular volume of the resin, thus permitting subsequent precipitation of additional hydrous alumina therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a divisional, of application Ser. No. 095,681, filed Nov. 19, 1979 now U.S. Pat. No. 4,381,349. 
    
    
     BACKGROUND OF THE INVENTION 
     We have obtained U.S. Pat. Nos. 4,116,858; 4,116,856; and 4,159,311 which pertain to the formation of hydrous alumina within a particulate anion exchange resin; the hydrous alumina is shown to be reacted with LiCl to form crystalline LiCl.2Al(OH) 3  or reacted with LiOH to form crystalline LiOH.2Al(OH) 3 . The hydrous alumina is shown to be prepared by the ammonia precipitation of AlCl 3  dispersed in the anion exchange resin. 
     SUMMARY OF THE INVENTION 
     Formation of hydrous alumina dispersed within a weak-base anion exchange resin (formed by ammonia precipitation of AlCl 3  in the resin) is improved by treatment of the resin (containing the hydrous alumina) with aqueous HCl or NH 4  Cl and HCL at slightly acid conditions, thereby converting the resin to the Cl -  form, thus permitting the subsequent precipitation of additional hydrous alumina therein. 
     As used herein, the term &#34;weak-base&#34; refers to anion exchange resins wherein salt forms of the functional amine groups are converted to the OH -  form by NH 4  OH. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Our U.S. Pat. Nos. 4,116,858; 4,116,856; and 4,159,311 are incorporated herein by reference. 
     The patents disclose anion exchange resins of the weak-base or strong-base varieties and disclose that the neutral halide salt forms of the strong-base resins may be used as the starting material. During the process of precipitating hydrous alumina in the resin by the ammonia precipitation of AlCl 3 , the halide salt forms of weak-base anion exchange resins are converted to the OH -  form. Anion exchange resins can have functional amine groups which are substantially all of the weak-base variety, some which are substantially all of the strong-base variety, and some which contain both varieties. This disclosure deals with anion exchange resins which contain any groups of the weak-base variety as the term &#34;weak-base&#34; is defined above. 
     We have found that the amount of hydrous alumina which may be incorporated into the resin by the ammonia precipitation of Al halide is limited in any one step by the maximum solubility of Al halide and the free volume in the resin. The ammonia treatment also converts the weak-base resin to the OH -  form, which is approximately only 80% of the volume of the halide form and thus there is less volume available to imbibe more Al halide solution. We have discovered that the resulting OH -  form of the resin, already containing substantially all the hydrous alumina that can be dispersed within the said OH -  form, can be treated with acid halide at a slightly acid pH of not lower than about 5, thereby converting the OH -  form to the halide form of the resin, without solubilizing the Al(OH) 3  in the resin; this permits additional amounts of Al halide to be imbibed and then converted, by ammonia treatment, to additional amounts of Al(OH) 3 . The preferred acid halide is HCl. The preferred Al halide is AlCl 3 . 
     The acid halide treatment of the Al(OH) 3  -containing OH -  resin should be done carefully, taking care that the acid addition is not so rapid that a localized drop in pH to lower than about 5 is reached. Slow addition of acid, with stirring and while monitoring the pH, is recommended. Any convenient method for lowering the pH, by addition of acid halide, may be used so long as the method does not result in solubilizing a substantial amount of the Al(OH) 3  which is already in the resin. Converting the Al(OH) 3  back to Al halide would be counterproductive, considering that the intent is to form Al(OH) 3  in the resin. 
     The acid halide treatment step is beneficially aided and speeded by the addition of ammonium halide, especially NH 4  Cl. The amount of NH 4  Cl added may be over a fairly broad range, with about 5-25% aqueous strength of NH 4  Cl being particularly beneficial. Other amine hydrochlorides may be used, but NH 4  Cl is preferred. The ammonium halide acts as a buffer against localized over-acidification during the acid halide addition, thereby allowing faster addition of the acid halide. The ammonium halide added initially, prior to the acid halide addition, may be mostly removed when the resin is drained before addition of more Al halide. Then when NH 4  OH is added to convert Al halide to Al(OH) 3 , more ammonium halide is formed. 
     HCl is the most appropriate acid to use if one intends to convert the hydrous alumina, Al(OH) 3 , to LiCl.2Al(OH) 3 . However, if one intends to convert to LiX.2Al(OH) 3 , where X is a different halogen than chlorine, then it is recommended that the corresponding acid halide be used and that the corresponding ammonium halide be used, thus avoiding a mixture of halo compounds. 
     The temperature for use with the HCl or the NH 4  Cl/HCl treatment should be in the range of about 20° C. to about 100° C., preferably about 45° C. to about 100° C. If higher temperatures are desired so as to speed the treatment, superatmospheric pressures may be needed to avoid substantial loss of ingredients through vaporization. 
     It appears that the HCl or NH 4  Cl/HCl treatment swells the resin, thereby permitting further sequential treatment steps, thus providing for appreciable increases in the aluminum content of the resin. As much as a three-fold increase or more in the Al content of the resin is readily attained. By this increase in the Al content in the resin (first as hydrous alumina and then as LiX.2Al(OH) 3 ), the composite has greater capacity for recovering Li +  values from brines or other aqueous Li +  solutions and a more efficient Li +  recover process is attained. The higher loading of aluminate in the resin permits greater concentration of LiX in the effluent of the exchange column when recovering Li +  from brines or other aqueous Li +  solutions. 
     We have also found that the formation of crystalline LiX.2Al(OH) 3 , formed by heating LiX (where X is Cl -  or OH - ) within the resin/Al(OH) 3  composite, is enhanced by performing the heating at high pH of, say, about 11 to about 11.5 which is done in a metal (non-glass) container to avoid heating the highly alkaline mixture in glass. Heating of highly alkaline mixtures in glass can result in minute amounts of lithium silicate which can interfere to some extent with the formation of highly crystalline LiX.2Al(OH) 3 . 
    
    
     The following examples are to illustrate certain embodiments, but the invention is not limited to the embodiments shown. 
     For purposes of comparison, the same resin (DOWEX® MWA-1 anion exchange resin) is employed in each of the following examples. The DOWEX® resin (a tradename of The Dow Chemical Company) is a particulate, macroporous anion exchange resin comprising a styrene-divinylbenzene cross-linked polymer having pendant tertiary amine groups. 
     EXAMPLE 1 
     A portion of the resin is flooded with a concentrated aqueous solution of AlCl 3 , dried to free flowing, and then treated with NH 4  OH to cause precipitation of Al(OH) 3  dispersed within the resin. Extraneous NH 4  Cl, NH 4  OH and Al(OH) 3  are washed out, leaving the resin (in OH -  form) containing the Al(OH) 3  dispersed therein. At this point the resin contains about 1.1 millimole per cubic centimeter of Al per cc of dry resin in the base form. 
     The resin preparation in the dried form is screened and 223.58 g of -30 mesh beads are further treated in the following manner: Enough water is added to make a slurry, which is stirred from above with a Waco motor paddle blade stirrer. About 40 g of NH 4  Cl is stirred into the slurry; the temperature is raised to about 80°-95° C. and 750 meq. of HCl is slowly added, during which the pH is not permitted to go lower than pH 5. 
     After all the acid is in, the pH is a stable pH 5.2. Yield is 645 ml of resin. After the product is well washed with water and drained dry to 460.3 g, a saturated solution of AlCl 3  (200 cc) is added to the resin with stirring, then 20 g of AlCl 3  additional is added. After the exotherm begins to subside, the resin is filtered. The filtrate has a specific gravity of 1.28. The product resin is dried in a dry nitrogen stream to a weight of 476.8 g. The dried material is slurried in 380 cc of 30% aqueous NH 3  (exotherms). After stirring for one-half hour the solids are washed well by decanting the Al(OH) 3  which forms outside of the resin. The washed resin is re-slurried in water and heated. Again NH 4  Cl and 720 meq. of HCl are added to again attain slight acidity not lower than pH 5. The washed resin volume is 640 cc. after drying back to 507.3 g; 250 cc of saturated AlCl 3  solution and 83 g of anhydrous AlCl 3  are stirred with the resin, then allowed to stand overnight. 
     The resin is filtered to a weight of 563.3 g and the damp-dry resin slurried in 380 cc of 30% NH 3  aqueous. After washing, the volume of product is now 580 cc. 
     About 500 cc of the resin are then added to excess 35% AlCl 3  solution, slurried, then filtered and dried in a N 2  stream to 446.8 g. The dry resin then is slurried in 300 ml of 30% aqueous NH 3 . After washing thoroughly to remove external Al(OH) 3  the resin volume is 450 ml. Each ml contains about 3.33 millimole of Al. 
     Fifty grams of LiCl and saturated NaCl brine (low Ca and Mg) are added to volume of 750 ml., warmed to 68° C. and pH 7.75 is read. After cooling 20 hours, the slurry is heated to boiling and 250 meq. NaOH added slowly to pH 8.5. The resin/LiX.2Al(OH) 3  composite is filtered and put in a metal beaker at 95° C. in the oven for 24 hours. Then 40 g NH 4  Cl are added and heated with stirring as 722 meq. of HCl are added to give pH 5 at 90° C. Al content is now about 3.1 millimole per cubic centimeter of resin. Yield is 470 cc of resin composite. 
     A 118 cc sample of the resin is tested in a temperature controlled, jacketed column. A lithium-containing brine from Arkansas is passed through at 20 cc per min. and 90° C. until the effluent is the same as the influent with respect to Li + . Water containing 60 ppm Li +  is passed through at 3.08 cc per min. and 90° C. and the effluent collected. The first cut is 50 cc; all others 10 cc. The analysis by flame photometer shows in milligrams of Li +  per liter: 
     
         ______________________________________Cut    4-740  5-5000  6-7650         (taking #5, 6, 7, the average LiCl  7-6800         content is 3.97%, or about 20 times the  8-3266         loading brine)  9-2450______________________________________ 
    
     EXAMPLE 2 
     Substantially in accordance with the method employed in Example 1 above, it is found that multiple precipitations of Al(OH) 3  in the anion exchange resin, prior to reaction with LiCl to form crystalline LiCl.2Al(OH) 3 , is beneficial in giving increased strength of Li +  in the effluent from the Li +  recovery process than is a single precipitation such as is shown by the issued patents identified supra. Data are shown below: 
     
         ______________________________________Precipititions     Al loading in resin                   Conc. Li.sup.+  in Effluentof Al(OH).sub.3     mmole Al/cc resin                   Mg Li.sup.+ /liter (peak)______________________________________single*   ˜1.2    3000multiple  2.0           4000multiple  3.0           5200multiple  4.0           6200______________________________________ *For comparison purposes with prior patents. 
    
     It is within the purview of the present invention that the Li +  -containing solution (from which Li +  values may be recovered) be a natural or synthetic brine or an aqueous solution from an ore-dressing or ore-treatment operation.