Patent GB-800868-A (GB)
Title: Improvements in or relating to method of preparation of metal salts
IPC: C22B3/32
Filed: 1955-08-22
Abstract: A normally corrosion-resistant metal or alloy is converted into compounds of the metal or the constituent metals by reaction with an aqueous solution comprising at least 0.5 per cent by weight of sulphuric, hydrochloric, hydrofluoric, nitric, phosphoric, formic or acetic acid (see Group IV (b)) by adding sulphur dioxide (as gas or a solution) to the mixture.  By "normally corrosion-resistant" is meant metals and alloys which when contacted with a particular acid are not readily and continuously corroded.  Metals above hydrogen in the electropositive series (e.g. nickel and chromium) are stated to form the salt corresponding to the acid whereas others (e.g. copper or mercury) form the sulphide, thus enabling separation to be effected with some alloys or mixtures of metals; in the absence of the latter metals, sulphur is precipitated.  Temperatures from 80 DEG  C. up to the boiling-point are preferred, but sub- or super-atmospheric pressures are not advantageous.  The metal should be comminuted. The acid preferably has a concentration of 5 to 10 per cent by weight and with sulphuric acid a concentration of 50 to 60 per cent is a reasonable maximum.  A gas may be introduced to agitate the mixture: preferably air is employed but should not be used in sufficient quantity to oxidize, e.g. copper sulphide to copper sulphate.  Metals and alloys, specified are nickel, cobalt, aluminium, copper, zinc, cadmium, chromium, lead, antimony, tin, iron, tungsten and molybdenum; brass, bronze, "Monel" (Registered Trade Mark) and Crome, metals, copper/cobalt and cobalt/arsenic alloysl and copper/mercury amalgams.  The metals gold, platinum and rhodium are mentioned as being within the scope of the invention but the application to lead with sulphuric acid is excluded from the scope of the invention.  The Specification refers to the following reactions:-(a) with sulphuric acid, Monel metal (forming nickel sulphate and copper sulphide) or a physical mixture of nickel and copper, cobalt, a cobalt-copper alloy, brass, Cromel metal, an alloy of copper, lead, tin, zinc, silver and iron (lead, tin, zinc and iron form sulphates), antimony (forming antimony sulphide) and a copper/zinc mixture; (b) with nitric acid; Monel metal, cadmium, brass, antimony, and a copper/zinc mixture; (c) with phosphoric acid; chromium, Monel metal, brass, tungsten, and a mixture of copper and zinc; (d) with hydrochloric acid; Monel metal, nickel, copper, a mixture of copper and antimony, a mixture of copper and nickel; (e) with hydrofluoric acid; cobalt scrap, Monel metal, brass and a mixture of zinc and copper.ALSO:A corrosion-resistant metal or alloy is converted into compounds of the metal or the constituent metals by reaction with an aqueous solution comprising at least 0.5 per cent by weight of formic, acetic, sulphuric, hydrochloric hydrofluoric, nitric or phosphoric acid (see Group III) by adding sulphur dioxide (as gas or a solution) to the mixture.  By "normally corrosion-resistant" is meant metals and alloys which when contacted with a particular acid are not readily and continuously corroded.  Temperatures from 80 DEG  C. up to the boiling point are preferred, but sub- or super-atmospheric pressures are not advantageous.  The metal should be comminuted.  The acid preferably has a concentration of 5 to 10 per cent by weight.  A gas may be introduced to agitate the mixture; preferably air is employed but should not be used in sufficient quantity to oxidize, e.g. copper sulphide to copper sulphate.  Metals and alloys specified are nickel, cobalt, aluminium, copper, zinc, cadmium, chromium, lead, antimony, tin iron and molybdenum; brass, bronze, Monel (Registered Trade Mark) and Cromel metals, copper/cobalt and cobalt/arsenic alloys, and copper/mercury amalgams.  The metals gold, platinum and rhodium are mentioned as lying within the scope of the invention.  The Specification refers to the following reactions: (a) with acetic acid, Monel metal, zinc, iron, molybdenum and a mixture of nickel and copper; and (b) with formic acid, Monel metal, nickel and a mixture of nickel and copper. Metals above hydrogen in the electropositive series (e.g. nickel and chromium) are stated to form the salt corresponding to the acid, whereas others (e.g. copper and mercury) form the sulphide, thus enabling separation to be effected with some alloys or mixtures of metals; in the absence of the latter metals, sulphur is precipitated.