Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2000-09-18
2002-08-06
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C205S370000, C205S594000, C205S591000, C423S027000, C423S028000, C423S150100
Reexamination Certificate
active
06428604
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydrometallurgical process for the separation, extraction and recovery of nickel and cobalt values from a sulfidic flotation concentrate. More specifically, the process involves an atmospheric pressure chlorine leach conducted under acidic conditions, followed by an oxidative acid pressure leach, and recovery of nickel by an electrowinning step.
BACKGROUND OF THE INVENTION
Metallurgists have long sought to develop economically viable hydrometallurgical processes for the recovery of base metals from sulfidic flotation concentrates, as an alternative to the conventional smelting and refining processes. Smelters have become increasingly costly to build and to operate as a result of more stringent environmental emission controls. Many of the processes studied over the past fifty years have utilized the leaching of an aqueous slurry of the sulfidic flotation concentrate in an air or oxygen atmosphere in a pressure autoclave, to achieve the primary separation of the metal values from the iron, sulfur and gangue components of the concentrate. Few of these processes have achieved commercial success.
A hydrometallurgical process based on the pressure leaching of nickel-copper sulfide flotation concentrates in ammoniacal ammonium sulfate solution in an atmosphere of air at 95 C., was commercialized by Sherritt Gordon Mines Limited in Canada in the early 1950s. (J. R. Boldt, Jr. and P. E. Queneau,
The Winning of Nickel
, Longmans Canada Limited, Toronto, 1967, pp 299-314), and was operated successfully for forty years. Due to its relatively high energy consumption, and the necessity for providing a market for the ammonium sulfate fertilizer by-product, this process has not been widely adopted by other nickel producers because it was particularly adapted to the general location and available feedstocks of the Sherritt Gordon plant.
A sulfuric acid based pressure leaching process for the treatment of zinc sulfide flotation concentrates has also been in successful commercial operation since 1981 and has subsequently been adopted by several zinc producers to replace the conventional roasting technology. In this process, the zinc sulfide flotation concentrate is oxidatively pressure leached in a sulfuric acid solution at 150° C., to produce a solution of zinc sulfate, and a residue consisting of elemental sulfur and iron oxide. The zinc sulfate solution is purified to remove trace impurity metals, and zinc metal is recovered from the purified leach solution by the long-established electrowinning process. Typically less than 10% of the sulfide in the concentrate is oxidized to sulfate in the pressure leach, with the balance being recovered as elemental sulfur in solid form, for sale or storage. The deportment of the sulfur in this process gives it a major advantage over the older roasting process, in which the sulfur is all converted to sulfuric acid, which must frequently be marketed at a loss, or converted to a solid waste such as gypsum for landfill disposal.
There have been numerous attempts to extend this oxidative acid pressure leaching technology to the direct treatment of copper and nickel-copper sulfide flotation concentrates, but no such process has as yet been successfully commercialized. A major obstacle to the application of oxidative pressure leaching at temperatures above the melting point of sulfur, to the treatment of chalcopyrite-containing flotation concentrates, has been the tendency of molten sulfur to coat the surface of the metal sulfide particles. This inhibits and prevents the reaction of the metal sulfide with the acid solution. Consequently, the oxidative pressure leaching of copper concentrates in sulfuric acid at temperatures above 120° C. typically results in slow reaction rates and low metal extractions. Zinc and nickel sulfide particles have a weaker affinity for molten sulfur than do copper sulfides, and the successful zinc oxidative pressure leach process described above utilizes organic additives, such as lignosulfonate salts or quebracho, to prevent the coating of the sulfide particles during the leaching process. These additives are ineffective for copper sulfide concentrates, but recently, (see U.S. Pat. No. 5,730,776 to Collins et al.), the addition of low grade coals has been found to prevent the coating of both zinc and copper sulfides in oxidative pressure leaching in sulfuric acid solution at 150° C.
A different approach to overcoming the problem of the occlusion of the sulfide particle surfaces by molten sulfur is described in U.S. Pat. No. 4,039,406 to Stanley et al. This patent discloses the addition of low concentrations of chloride ion to the leach solution in the oxidative pressure leaching of a chalcopyrite concentrate in sulfuric acid solution at temperatures above 120° C. The benefits of the chloride addition were shown to be greatly increased rates of leaching of chalcopyrite and a major reduction in the amount of sulfide oxidized to sulfate, and as a result, the recovery of virtually all the iron content of the concentrate as hematite in the solid residue. In the absence of the chloride ion addition, oxidative pressure leaching of chalcopyrite in sulfuric acid at 150° C. typically produces a leach solution containing high levels of acid and dissolved iron. With the chloride addition, the leach solution typically has a pH value of 2.5 to 3, and the iron concentration is less than 1 g/L. A further consequence of the low degree of sulfur oxidation, and the resulting low level of acidity in the chloride containing leach solution, is that a large portion of the leached copper can be reprecipitated as basic copper sulfate. The extent of this effect can be varied by adjusting the amount of acid added to the leach. This ability to control the deportment of the copper between solution and leach residue provides considerable flexibility in the design of the copper recovery process.
The applicability of oxidative pressure leaching with a chloride ion addition to a sulfate solution in the pressure leaching of nickel-containing sulfide flotation concentrates was subsequently described in a paper entitled “Oxygen Pressure Leaching of Fe—Ni—Cu Sulfide Concentrates at 110° C.—Effect of Low Chloride Addition” Subramanian et al. (
Hydrometallurgy
2, (1976), pp. 117-125).
More recently, D. L. Jones in U.S. Pat. Nos. 5,431,788; 5,645,708; 5,650,057; 5,855,858; 5,874,055; and 5,902,474 discloses the combination of the chloride-assisted sulfuric acid oxidative pressure leaching of copper sulfide concentrates with the recovery of copper by a variety of process flowsheets based on conventional solvent extraction and electrowinning.
U.S. Pat. No. 5,650,057 issued to Jones, describes a hydrometallurgical process for the extraction of copper from an ore or concentrate. The process broadly comprises subjecting the ore or concentrate to an oxidative pressure leach in an acidic solution containing halogen ions and a source of bisulfate or sulfate ions. The process extends to the extraction of non-cuprous metals such as zinc, nickel and cobalt. Significantly, during the oxidative pressure leach the metal may be precipitated as an insoluble basic salt, such as basic copper sulfate, or substantially completely solubilized and precipitated later as the basic copper salt. The specific application of this process to nickel-cobalt containing sulfide concentrates is described in greater detail in U.S. Pat. No. 5,855,858, also issued to Jones.
Of interest to the present invention is the process illustrated in FIG. 1 of U.S. Pat. No. 5,855,858. The process involves subjecting a copper-nickel flotation concentrate to an oxidative pressure leach. Following separation of the leach solution and leach residue, the leach solution is passed to a copper solvent extraction circuit. The raffinate from the copper extraction step is then passed to a conventional nickel hydroxide precipitation step using lime. Following liquid/solid separation, the residue containing substantially the total nickel and cobalt values is subjected to a
Kerfoot Derek George Eagland
Krause Eberhard
Love Bruce John
Singhal Avinash
Inco Limited
King Roy
McGuthry-Banks Tima
Steen Edward A.
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