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AssigneeOutokumpu Oy
InventorsJussi K. Rastas, Jens R. Nyberg, Kauko J. Karpale, Lars-Goran Bjorkqvist
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A hydrometallurgical process for the treatment of a raw material which contains oxides and ferrites of zinc, copper and cadmium is disclosed, wherein the raw material is neutral leached by means of a sulfuric-acid-bearing solution to leach the oxides without substantial dissolving of the ferrites, a ferrite-bearing residue is separated, and a sulfuric-acid-bearing or ferrisulfate-bearing solution is mixed with the residue in order to leach the ferrite and to precipitate the iron in the form of jarosite in the presence of alkali or ammonium ions under atmospheric conditions at 80.degree.-105.degree. C., and the solid phase is separated from the solution. The sulfuric-acid-bearing or ferrisulfate-bearing solution is added to the ferrite-bearing residue in such an amount that approximately 50-60% of the ferrite dissolves and its iron is precipitated as jarosite, and the slurry of the solid phase is treated at such elevated pressure and temperature that the zinc of the solid phase is converted to zinc sulfate and the iron to hematite in accordance with the following reaction: (5) 3ZnFe.sub.2 O.sub.4(s) +2A[Fe.sub.3 (SO.sub.4).sub.2 (OH).sub.6 ].sub.(s) .fwdarw.3ZnSO.sub.4(aq) +A.sub.2 SO.sub.4(aq) +6Fe.sub.2 O.sub.3(s) +6H.sub.2 O.sub.(aq) (A=K, Na, NH.sbsb.4.sub.)
A hydrometallurgical process for the treatment of a raw material which contains an oxide and a ferrite of at least one element selected from the group comprising zinc, copper and cadmium, comprising:
Dependencies are inferred from the claim text.
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Compounds of zinc: sulfates
Oxides; Hydroxides: ferric oxide [Fe2O3]
With acids or salts thereof: containing sulfur
Treating solutions: by chemical methods
Term ended 29 Sep 2001 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
The present invention relates to a hydrometallurgical process by which the zinc-ferrite-bearing leach residue regularly appearing in connection with an electrolytic zinc process is treated so as to bring its valuable metals zinc, copper, cadmium, lead, silver and gold to a form economical to recover.
The starting material of an electrolytic zinc process is a sulfidic zinc concentrate, from which an oxidic product, zinc calcine, is obtained by roasting. This calcine contains, in addition to the principal constituent, zinc oxide, practically all of the iron of the original concentrate, combined with zinc as zinc ferrite. The iron content in the concentrate usually varies between 5 and 15%, depending on the concentrate. An iron content of about 10% in the concentrate represents a typical value of currently used raw materials. This means that about 10% of the zinc of the concentrate is bound in zinc ferrite, ZnFe.sub.2 O.sub.4, the content of which in this typical case is 21.5% of the total amount of calcine.
In addition to zinc, the zinc concentrate also contains other valuable metals such as Cu, Cd, Pb, Ag and Au, and the recovery of these metals is of considerable significance for the total economy of the zinc process. However, in planning a zinc process or in modifying a process, it is necessary to take into account the behavior of several elements present in the concentrate in the process. Some of these elements (Zn, S, Cu, Cd, Pb, Ag, Au) are of primary importance for the economy of the zinc process, whereas others (Fe, Co, Ni, Ge, Tl, In, Ga, Mg, Mn, Cl, F) have less or no economic importance but have to be taken into account precisely, with regard to the functioning of the process. In addition, there are elements which are significant in terms of environmental protection (S, Hg, Se), the quality of the byproducts (Hg, Se, As, Sb, Sn), or waste formation (Fe, Si, Al, Ca).
The FIGURE illustrates diagrammatically the leach system for zinc calcine in accordance with the invention.
In the process of the FIGURE, the entire calcine feed is directed to a neutral leach stage (NL). The neutral leach can be carried out in one or two stages (Finnish Patent Application Nos. 410/73 and 760486), and the two-stage leach, for its part, either as a countercurrent or a cocurrent leach (Finnish Patent Application No. 410/73). From the separation stage (preferably thickening) connected with the neutral leach, the solution (raw solution) is directed to a semi-conversion stage (1/2.times.CS). To this stage there is a fed a return acid amount (or ferrisulfate amount) which, first, is equivalent with regard to the zinc ferrite fed into the stage in accordance with Reaction (4 or 4a)
(4) 6ZnFe.sub.2 O.sub.4(s) +A.sub.2 SO.sub.4(aq) +6H.sub.2 SO.sub.4(aq) .fwdarw.3ZnSO.sub.4(aq) +3ZnFe.sub.2 O.sub.4(s) +2A[Fe.sub.3 (SO.sub.4).sub.2 (OH).sub.6 ].sub.(s)
(4a) 9ZnFe.sub.2 O.sub.4(s) +2A.sub.2 SO.sub.4(aq) +3Fe.sub.2 (SO.sub.4).sub.3(aq) +12H.sub.2 O.sub.(aq) .fwdarw.3ZnSO.sub.4(aq) +6ZnFe.sub.2 O.sub.4(s) +4A[Fe.sub.3 (SO.sub.4).sub.2 (OH).sub.6 ].sub.(s) A=K, Na, NH.sub.4