GB2156328A

GB2156328A - Recovery of metals

Info

Publication number: GB2156328A
Application number: GB08507350A
Authority: GB
Inventors: Brian Jeffreys; Dr David Caldwell Goodall; Dr John Bernard Gill
Original assignee: IMP SMELTING PROCESSES
Current assignee: IMP SMELTING PROCESSES
Priority date: 1984-03-24
Filing date: 1985-03-21
Publication date: 1985-10-09
Also published as: GB8407692D0; GB2156328B; GB8507350D0

Abstract

A process for the recovery of metallic powder, e.g. copper, from oxidic feeds involves leaching the feed with an SO2/aprotic polar solvent combination to form a metal sulphur oxyanion salt, and then decomposing this salt to yield a metallic product. Other oxides may be eliminated or re-cycled to the leaching stage.

Description

SPECIFICATION Recovery of metal values from oxidic materials This invention relates to the recovery of metallic values from oxidic materials and more especially a process for the recovery of metal values by a dissolution/decomposition process based on metal oxides.

There are many processes in which oxidic metal compounds are dissolved e.g. in acids and then recovered from solution. However such processes normally depend upon the use of electrical energy or chemical reductants (e.g. hydrogen) for the recovery of metal ions from solution as elemental metal.

We have now devised a process in which oxidic metal compounds are dissolved in a specific range of solvents and the metal may be recovered, in metallic form, by a decomposition process.

This invention consists in a process for the recovery of metal values from oxidic metal compounds, wherein the oxidic metal compound is dissolved in a combination of sulphur dioxide and another polar aprotic solvent to form a sulphur oxyanion compound of the metal.

The latter compound may then be decomposed to form a metallic product.

Preferably the metal is one chosen from Groups I, II, III, V, VII or VIII of the Periodic Table. More preferably the metal is chosen from Groups I or II of the Table. Most preferably the metal is copper.

By "oxidic metal compound" we mean one in which the metal is chemically combined with oxygen, with or without other elements being present in the compound.

Preferably the polar aprotic solvent is dimethylformamide althought other solvents such as dimethyl sulphoxide or acetonitrile may also be used in combination with sulphur dioxide.

The solvent system should be substantially non-aqueous and non-proton-donating.

The decomposing stage may be promoted e.g. by heat or by agitation.

The decomposition is believed to be due to a disproportionation mechanism and should preferably be carried out in a non-oxidising (neutral or reducing) atmosphere.

The oxides of copper(l) and copper(ll) undergo a remarkable reduction at room temperature with the mixed system dimethyl formamide (dmf)-sulphur dioxide, yielding very pure copper metal. Both oxides dissolve to give an orange-coloured solution, but copper precipitates when the solution has stood for three days. This is the first reported reduction of oxides of copper to metal using SO2, and is of enormous significance in that it is a low temperature process.The orange intermediate is probably a sulphur oxyanion compound of copper (I) and the reaction may involve the direct conversion of oxide to sulphite, followed by solvation by sulphur dioxide and disproportionation of copper (I) to copper (0) and copper (II), the latter being further convertible to copper(l) sulphite:

The orange intermediate is readily oxidised, giving a green solution, but this process can be reversed if air is then excluded, as a result of reduction by the SO2. Unlike dmso-SO2, dmf-SO2 cannot oxidise sulphur (IV) to sulphur (VI), and thus the orange intermediate is likely to contain an anion of sulphur (IV), possibly disulphite. Similar orange solutions have been seen when copper (I) disulphite dissolves in nonaqueous media.The reaction proceeds with any concentration of SO2, but is most rapid at high SO2 concentration.

Dmf-SO2 also reacts with the oxides mgO, V2Os, CrO3, MnO2, CoO, ZnO, SnO2, PbO3, Lea203, and Ag2O.

The products, however, could not be purified, but they do contain sulphur (lV); sulphite was detected amongst the reaction products. The oxides generally dissolve neither in dmf nor in SO2 alone; the mixed solvent is necessary for dissolution. Reactivity may again relate to the presence of adducts between dmf SO2, and to the nature of the subsequent sulphur oxyanions which form. CrO3 is the only oxide soluble in dmf alone. No evidence exists for intermediate involvement of SO2 radical ion, in contast with the reaction between metals and dmf-S02.

The mixed system acetonitrile-sulphur dioxide is highly selective for copper, as it only reacts with the oxides of copper, and not with any of the oxides which have been treated with dmf-SO2 or dmso-SO2.

Various modifications are possible within the scope of the invention. For example the polar aprotic solvent may be varied and other oxidic compounds e.g. carbonates or silicates may be used as starting materials.

The invention provides a versatile low temperature process for the recovery of metallic copper from oxidic compounds e.g. oxidic concentrates or residues from industrial processes.

The invention will be further described by reference to the accompanying schematic flow-sheet drawing which illustrates the production of metallic copper from a mixed oxide feed (e.g. a roasted or calcined feed) containing a mixture of metal oxides including CuO, NiO, and PbO.

In this flow-sheet, the mixed oxide feed is treated with SO21dmf leach solution and passed to a thickener and a filter where residual solids are filtered out. The Cu-bearing solution is passed on to a digester where with the aid of heat and/or agitation the Cu/sulphur oxyanion complex is slowly decomposed to yield metallic copper powder. The precipitated solids are filtered and dried, with SO2/dmf driven off from the solids being recycled to the dissolution stage. The mother liquor from this filtration stage is passed to a crystalliser where CuSO3 is precipitated and then filtered off.The solid is calcined to CuO,and SO2 is recycled to the leach stage or neutralised with CaO. CuO may be recovered as product or sent back to the digester for further copper recovery.

In this way a mixed oxide feed is converted to Cu and CuO product with recycle of most of the reactants used.

Claims

1. A process for the recovery of metal values from oxidic metal compounds, wherein the oxidic metal compound is dissolved in a combination of sulphur dioxide and another polar aprotic solvent to form a sulphur oxyanion compound of the metal.

2. A process as claimed in claim 1 in which the oxidic metal compound is a copper oxide and the sulphur oxyanion compound is decomposed to yield metallic copper as a product of the process.

3. A process as claimed in claims 1 or 2 in which the polar aprotic solvent is dimethyl formamide.

4. A process for the recovery of metallic copper from a mixed metal oxide material substantially as hereinbefore described with reference to the accompanying flow-sheet.