A process for the separation of lead and zinc in roasted compound ores

摘要

Roasted lead-zinc ores are leached with a concentrated solution of an alkaline earth (including magnesium) chloride preferably containing over 200 grams of chlorine per litre without the addition of acid. This dissolves the lead but very little of the zinc. When magnesium chloride is employed it is preferable to use a solution containing more than 280 grams of chlorine per litre, as then most of the magnesium sulphate formed remains with the residue. The residue may be freed from chlorine by treatment with water and lime and then washing, and forms a good metallurgical zinc product. The silver may be dissolved with the lead by adding an oxidizing agent such as bromine, bleaching-powder, peroxides, and persalts such as persulphates and permanganates. The silver may be precipitated with zinc dust or iron powder. The lead chloride may be recovered by cooling the solution, or the lead may be obtained in the metallic state by electrolysis or by cementation. When too much zinc accumulates in the solution it is precipitated by means of lime.