Abstract: Arsenic, in the form of As.sub.2 O.sub.3, is recovered from arsenical ores or concentrates by leaching with a hot acidic ferric salt solution to extract arsenic, followed by cooling the pregnant leach solution to crystallize As.sub.2 O.sub.3. Leaching of some ores or concentrates is facilitated by addition of silver sulfate or mercuric sulfate to catalyze the leaching reaction.

Abstract: A method for the separation of bismuth from a complex chloride solution obtained by leaching with chloride reagents ores containing bismuth and high concentrations of other metals comprising adding to said complex chloride solution at least a stoichiometric amount of a precipitating agent selected from the group consisting of hexamminecobalt (III) salts and hexamminechromium (III) salts soluble in said solution to precipitate said bismuth as a hexamminecobalt (III) bismuth salt or a hexamminechromium (III) bismuth salt and separating said precipitate from said solution.

Abstract: A rapid, energy efficient, low cost, nonhazardous method for the selective removal of mercury from mercury-containing metal cyanide solutions, particularly the cyanide solutions resulting from the cyanidation of gold ore and the like, wherein a reactive sulfide is admixed with the solution for a time sufficient to form an insoluble mercuric sulfide precipitate. The mercuric sulfide precipitate is then separated from the metal cyanide solution by filtration or other conventional means.

Abstract: A low cost, effective method for removing heavy metal ions from aqueous solution which utilizes a porous, high surface-to-weight ratio siliceous adsorbent comprises the steps of activating the siliceous adsorbent, which is preferably a kaolin clay leach residue, with a basic salt of an alkali metal to incorporate alkali ions into the siliceous adsorbent and contacting the heavy metal ion-containing solution with the activated adsorbent whereby the heavy metal ions exchange with the alkali ions to remove the heavy metal ions from solution. The heavy metal ion loaded adsorbent may be stripped for subsequent reuse or, alternatively, utilized for flux in base metal smelting and the like.