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BY 0.K.5I.E. ATTORNEYS 3,671,187 United States Patent Office Patented June 20, 1972

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BY 0.K.5I.E. ATTORNEYS 3,671,187 United States Patent Office Patented June 20, 1972 June 20, 1972 E. A. CUEVAS 3,671,187 REMOVAL OF DISSOLVED LEAD FROM ALKALI METAL CHLORIDE CONTAINING SOLUTIONS Filed July 13, 1970 INVENTOR PARA/M. A. Cue VAS BY 0.k.5i.e. ATTORNEYS 3,671,187 United States Patent Office Patented June 20, 1972 1. 2 be prepared only by virtually removing the lead ions from 3,671,187 solution before crystallizing the lithium chloride. REMOVAL OF DISSOLVED LEAD FROM ALKALI METAL CHLORIDE CONTAININGSOLUTIONS THE PRESENT INVENTION Ephraim A. Cuevas, Corpus Christi,Tex., assignor to In accordance with the present invention a method of PPG Industries, Inc., Pittsburgh, Pa. 5 precipitating lead, dissolved inorganic lead in particular, Filed July 13, 1970, Ser. No. 54,406 from aqueous solutions is provided. The invention in nt. C. C01d3/04, 11/02 volves contacting alkali metal chloride solutions contain U.S. C. 23-89 6 Claims ing contaminating quantities of dissolved lead compounds O with alkali metal sulfide to thereby convert the lead com ABSTRACT OF THE DISCLOSURE pounds contained in the solution to lead sulfide. In par A process is described for the removal of lead from ticular the invention provides an extremely efficient alkali metal chloride containing solutions by precipi method of removing dissolved lead from lithium chloride tation of the lead ions as a lead sulfide. The method in containing solutions having dissolved lead therein by the volves utilizing an alkali metal sulfide as the precipitat 5 addition thereto of lithium sulfide. The quantity of al ing agent in lieu of hydrogen sulfide. The use of alkali kali metal sulfide utilized is usually slightly in excess of metal sulfide as the precipitating agent precipitates the that stoichiometric quantity necessary to precipitate all lead in large particle sizes rendering filtration easy. The lead present in the solution usually above about 8 per quantity of sulfide ions in the solutions necessary to ac cent excess and in general 1 to 15 percent excess. complish precipitation of dissolved lead is also minimized. 20 In utilizing the instant invention, precipitation of lead Treatments of solutions by the proposed scheme show sulfide from solution is accomplished preferably by uti reductions of the lead content of solutions treated from lizing the sulfide of the same alkali metal which is the quantities of 0.6 percent by weight to 18 parts per mil primary constituent of the solution and thus the desired metal itself is not lost. lion or less lead. The process is described in particular In precipitating lead sulfide from aqueous alkali metal in connection with the treatment of lithium chloride-lith 25 chloride solutions containing contaminating quantities of ium hydroxide solutions containing contaminating lead lead compounds utilizing hydrogen sulfide as the precip ions and utilizing lithium sulfide as the precipitating agent. itating agent, the results leave much to be desired. It has been found when utilizing hydrogen sulfide for this pur 30 pose that the lead sulfide particles formed are extremely BACKGROUND OF THE ENVENTION small and settle only with difficulty in the solutions In Canadian Pat. 813,925 a process is described for the treated. This slow settling of small particles of sulfide re manufacture of alkyl lead compounds utilizing lithium quires considerable effort on the part of the processor metal as an essential ingredient in the reaction system to remove the fine precipitated sulfides. In addition it is employed. In the process described in the aforementioned 35 found that substantial saturation of the solution with sul Canadian patent, lithium metal, lead metal and alkyl ha fide ions is necessary to insure the maximum amount of lide are reacted in an autoclave to provide tetraalkyllead alkali metal sulfide formation. Despite the supersatura compounds, typically tetraethyllead and tetramethylead. tion of these solutions with sulfide ions using hydrogen Also produced during this reaction is lithium chloride sulfide as a precipitating agent, inadequate removal of which is formed by the reaction of the halide of the al 40 lead from these solutions has been experienced. kyl halide with the lithium metal present. Utilizing the alkali metal sulfide additions of the in After completion of the reaction, the reactor charge or stant invention rather than gaseous hydrogen sulfide to mass is typically dropped into a dissolver or flash tank precipitate contaminating quantities of lead occurring in where it is contacted with water to dissolve the alkali alkali metal chloride solutions, large particles of lead sul metal halide, phase separated, and the water phase passed 45 fide are formed. Essentially complete reaction of the lead to storage. This water phase contains lithium chloride contained in the solution is obtained. This is especially and lithium hydroxide as well as substantial quantities so where agitation is also provided during the mixing of dissolved lead. In the flow sheet shown in the afore of the alkali metal sulfide with the solution containing mentioned Canadian patent, water from the solid lead the contaminating quantities of dissolved lead. By pro washing operation is also fed to the storage area that is 50 viding fast settling, large sulfide particles, and essentially used for storing lithium chloride-lithium hydroxide so complete reaction in the solutions treated, it is now pos lutions thus contributing further quantities of dissolved sible utilizing the instant invention to carefully control lead. The lithium chloride-lithium hydroxide solutions so the lead content of alkali metal chloride solutions so that formed are subsequently processed to crystallize lithium only minute quantities of lead are found therein after chloride therefrom. These lithium chloride crystals are 55 treatment. electrolyzed to recover metallic lithium so that this valu The utilization of the instant process still contemplates able metal can be used again in the initial reaction charge. the use of hydrogen sulfide as the primary source of sul These lithium chloride solutions from which lithium fide ions. Thus, in preparing alkali metal sulfides for use chloride crystals are recovered for ultimate recovery of in accordance with the instant invention, hydrogen sul the lithium metal by electrolysis contain, in addition to 60 fide is typically employed as the sulfide ion supply. In ad lithium hydroxide, considerable quantities of dissolved dition, hydrogen sulfide utilized in the formation of lead. Lead contamination in lithium chloride presents a alkali metal sulfides for use in the instant invention may particularly bothersome problem during the electrolysis be reused in the process by treating the process streams of lithium chloride in that quite frequently short circuit after alkali metal sulfide treatment to recover the hydro ing of the electrodes takes place due to the presence of 65 gen sulfide contained therein. These and other advantages contaminating quantities of lead at the bottom of the of the instant invention will become apparent in the ensu cell. For this reason it is extremely important that the ing description. lead in these lithium chloride solutions be removed prior As set forth above, the invention is applicable to the to subjecting them to crystallization procedures for the removal of lead compounds from any alkali metal chlo recovery of lithium chloride. High purity lithium chlo 70 ride solution utilizing alkali metal sulfides as the pre ride crystals substantially free of lead contamination can cipitating agent. In particular the invention has been found 3,671,187 3 4. extremely useful in removing dissolved lead compounds to a tank 12 where it was adjusted to a pH of 7.8 with from solutions of lithium chloride containing lithium hy an inorganic mineral acid, e.g., HC1. During this adjust droxide. Such aqueous solutions of lithium chloride are ment hydrogen sulfide was evolved from the pH treat produced in the process described in Canadian Pat. ment tank 12 and is passed via line 19 to tank 4. The 813,925. Lithium chloride-lithium hydroxide solutions 5 material in tank 12 was then removed via line 17 and containing at least 0.10 percent lead therein can be re filtered. About 0.5 percent solid material (basis total duced in lead content to at least 5 parts per million. solution) was removed in this filtering step. The filter For a more complete understanding of the application cake had the following composition: less than 10 percent of this invention, reference is made to the accompanying lithium; 1 to 10 percent aluminum; 0.1 to 1 percent sili drawing which diagrammatically illustrates the instant in 10 con and sodium; 0.01 to 0.1 percent magnesium and iron; vention applied to a lithium chloride-lithium hydroxide 0.001 to 0.01 percent manganese, molybdenum, chromi solution. um, lead, copper titanium and cadmium; less than 0.001 As shown in the drawing, an aqueous solution of percent vanadium and silver. The filtrate contained 35.4 lithium chloride containing lithium hydroxide and dis percent lithium chloride, 0.02 percent lithium hydroxide, solved inorganic lead compounds is passed through line 1 0.15 percent sodium chloride, 10 parts per million lead into an agitated vessel 6. A small bleed stream 2 is re and 53 parts per million sulfur. moved from the stream in conduit 1 and is passed to a From the foregoing, it will be readily appreciated that reaction vessel 4 which has bubbled through it via line 3 the process of the instant invention lends itself readily to hydrogen sulfide gas. The hydrogen sulfide gas and the the removal of large quantities of lead to very low levels small stream introduced into the reaction vessel 4 are 20 in alkali chloride metal solutions. intimately contacted in this vessel 4 to provide for reac While the invention has been described with Specific tion of the hydrogen sulfide gas with some of the dis reference to lithium chloride solutions, obviously the in solved lead present and with the lithium hydroxide pres vention has efficacy also with other alkali metal chloride ent.
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