GB856851A - Process for recovering platinum group metal values from composites containing the same - Google Patents

Abstract

Arsenic - contaminated platinum - containing catalysts, and other composites containing platinum with arsenic contaminants, are treated to remove the arsenic and recover the platinum group metal values, by forming a solution of the composite and distilling the solution in the presence of added hydrochloric acid and a ferrous salt, whereby the arsenic is volatilized. The invention is particularly useful to the recovery of platinum values but is applicable to the recovery of palladium, iridium, rhodium, rhenium and ruthenium. The initial solution is normally formed with aqua regia. Platinum group metal catalysts, normally containing an inorganic oxide carrier such as alumina, silica, zirconia, magnesia, titania, thoria, boria or strontia or mixtures thereof are preferably first freed from substantially all carbonaceous contaminant by oxidation and the carrier material is then dissolved with an inorganic acid, particularly sulphuric acid of 25 to 90% strength. The dissolution of the carrier is facilitated by increased pressures. The platinum- and arsenic-containing insoluble sludge is then dried and if necessary oxidised to remove residual carbon, and then taken up in aqua regia, preferably with a hydrochloric/nitric acid ratio of 3 to 1, at a temperature of 65 to 93 DEG C. and if desired under super-atmospheric pressure. The solution is filtered and distilled at 98 to 178 DEG C. in the presence of hydrochloric acid supplied in a concentration of 20 to 90% and of ferrous salt which may be the chloride, bromide, fluoride or sulphate, added as such or an aqueous solution in an amount equivalent to at least 2 and preferably up to 4 atomic weights of iron per part of arsenic. The hydrogen chloride addition is made at the rate at which the overhead distillate is collected. After arsenic has been removed, excess hydrochloric acid is recovered by evaporation and the resulting arsenic-free solution of, for example, chloroplatinic acid, may be employed to produce new catalysts. Elemental platinum may be recovered from such concentrated chloroplatinic acid by precipitating with hydrazine hydrochloride, hydroquinone, formaldehyde, catechol or an aminophenol. The chloroplatinic acid may also be purified by precipitating the platinum and redissolving in aqua regia or by subjection to ion exchange.