GB687523A - Improvements relating to the concentration of non-ferrous metals as sulfides from anore concentrate containing non-ferrous metal values - Google Patents

Abstract

Non-ferrous metal sulphide concentrates containing acid-insoluble gangue and usually iron are leached, the pH of the solution is adjusted if necessary, whereby all the metal values are present as salts in acid solution, and the clarified solution is treated for the recovery of non-ferrous metal sulphides by the action under acid conditions and in the presence of a reducing agent, of a metal sulphide whose solubility at the treatment acidity is greater than the sulphide of any metal to be recovered; a temperature of 275 DEG -750 DEG F is suitable for the latter operation. Acid or ammoniacal leaching solutions may be used, a solution of sulphuric acid, or sulphuric acid and ferric sulphate, used in the presence of air or oxygen, and preferably at elevated temperature, e.g. 275 DEG -750 DEG F, and increased pressure, being particularly suitable. The replacing sulphide is normally iron sulphide, and may be an iron sulphide ore, including the ore used in the process. The ore treated may contain the sulphides of iron, copper, nickel, cobalt, zinc, lead, cadmium and molybdenum. The reducing agent may be carbon monoxide, hydrogen, sulphur dioxide, methane, ethane, methyl or ethyl alcohol, oxalic acid, formaldehyde. Precipitation may be effected using a deficiency of iron sulphide, and the mother liquor then treated with an excess of the latter. The sulphide precipitate from the second stage is then returned to the leaching operation, or to the first stage replacement step. The mixed sulphide precipitate is next treated to isolate the individual metals by dissolving it, as in the case of the original ore concentrate, in say aqueous sulphuric acid under oxidizing conditions. The filtrate is treated, e.g. at 250-450 DEG F, say with iron sulphide at differing pH values to precipitate the different metals. Thus, copper sulphide is precipitated at pH up to 3, cobalt at pH 3-5, nickel at pH 5-6.2 and zinc at pH 6.2 to neutrality. The pH values are adjusted by the addition of ammonia, lime &c. Each separate precipitation step may be carried out in two stages using a slight excess of precipitant in the second stage, the precipitant from this stage being returned to the first stage. Instead of using iron sulphide, there may be used another sulphide more soluble than the sulphide to be precipitated; thus, nickel sulphide may be used to precipitate copper sulphide, and zinc sulphide to precipitate cadmium sulphide. Similarly, part of the sulphide mixture may be employed to treat the remainder dissolved in acid, using a two-stage precipitation process as above, whereby to obtain copper sulphide. The filtrate is divided in two, one portion is treated with iron sulphide to precipitate the sulphides of all metals present, and the precipitate is used to treat the other portion, after reduction of its pH, to precipitate the next most insoluble sulphide. The same general procedure is continued to precipitate the other metal sulphides. Replacement may be carried out in basic solution, particularly if gold sulphide is to be recovered, sodium and potassium sulphides then being suitable precipitants.