Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
1999-04-28
2001-11-13
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C423S022000, C423S027000
Reexamination Certificate
active
06315812
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for the recovery of precious metals from host materials, using pressure oxidation.
2. Description of the Related Art
Traditionally, gold is not included in the group of meals known as the platinum group metals which include platinum and palladium, rhodium, ruthenium, osmium and iridium. For the sake of brevity, the term ‘precious metals’ as used herein will refer to both gold and the platinum group metals. Typically, these precious metals are present in host materials along with other metals such as the base metals copper and nickel, in varying concentrations. These host materials are normally treated by grinding and flotation to produce a concentrate, which is then smelted. The constituent precious and base metals typically report to a matte phase during smelting. The matte phase is then processed by a variety of well established techniques to separate and recover the individual constituents in substantially pure form.
The matte typically undergoes oxidative pressure leaching at temperatures of 130 to 150 degrees Celsius which leaches the base metal component of the matte leaving the platinum group metals in the residue. After separating the solution from the residue, the residue is then typically leached, in atmospheric conditions, with concentrated hydrochloric acid and chlorine gas as the oxidant to dissolve the platinum group metals.
In certain cases, when the concentrations of valuable base metals (such as copper and nickel for example) are low, or when the concentrations of metals that are deleterious to smelting (such as arsenic or bismuth) are high, it is not economical to process the concentrates by smelting. In these instances, it can be advantageous to process the concentrate directly by a pressure leach process to leach the base metals.
Typically, the solid phase leaving the pressure leach step retains the precious metals while the copper and nickel transfer to the leach solution, for further processing by various hydrometallurgical procedures well known to the art. In this case, the precious metal constituent is recovered from the solid phase by relatively complex and expensive procedures, including leaching by chlorination or pressure cyanidation, followed by precious metal recovery by precipitation, solvent extractions and ion exchange techniques well known to the art. Though these processing routes may prove satisfactory in some cases, there are many host materials in which either the leach efficiency or the concentration of precious metals is insufficient for this relatively complex metallurgical flowsheet to be economically viable.
It is an object of the present invention to provide an improved technique for the recovery of precious metals.
SUMMARY OF THE INVENTION
Briefly stated, the invention provides a method for recovering a precious metal from a host material, comprising the steps of:
subjecting the host material to an oxidative pressure leach process, in the presence of a leach solution bearing a halide ion constituent which is reactive with the precious metal, and at a temperature sufficient to cause at least a portion of the precious metal to be extracted by said leach solution; and
recovering the precious metal from the leach solution.
Preferably, the halide ion is selected from the group chloride, iodide or bromide. In this case, fluoride is not included because it is not sufficiently reactive with (or does not effectively complex with) gold and other precious metals.
Preferably, the halide ion originates from a halide salt which is added to the leach solution. Still more preferably, the halide ion is a chloride ion provided to the leach solution by a chloride salt. In this case, the chloride salt may include sodium chloride, calcium chloride or potassium chloride, as well as ferrous or ferric chloride, hydrochloric acid, cupric or cuprous chloride, lithium chloride, magnesium chloride and ammonium chloride, among still others.
Preferably, sufficient chloride salt constituent is present in solution to provide a chloride ion concentration ranging from about 0.5 g/L to about 100 g/L, more preferably from 1 to 20 g/L, still more preferably from 1.5 to 10 g/L. Still more preferably, the chloride ion constituent is present at a concentration ranging from about 3 to about 6 g/L. In one embodiment, the chloride salt is sodium chloride which itself is provided at a concentration of about 10 g/L.
In another aspect of the present invention, there is provided a method for recovering a precious metal from a host material, comprising the steps of:
placing the host material in a pressure leaching vessel;
subjecting the host material to an oxidative pressure leach process, in the presence of a halide ion constituent which is reactive with the precious metal, and at a temperature sufficient to cause at least a portion of the precious metal to be extracted by a leach solution; and
recovering the precious metal from the leach solution.
Preferably, before recovering the precious metal from the leach solution, barren solid is separated from the leach solution, although it may be desirable in some cases to recover the precious metal from the leach solution before separating the barren solid, for example to minimize the loss of precious metals contained in the residual leach solution which can be lost with the separated barren solids.
In one embodiment, the oxidative pressure leach process takes place in the presence of a gaseous oxidant. Preferably, the gaseous oxidant is oxygen gas. The oxygen gas is preferably injected into the vessel at an oxygen partial pressure of between 1 and 500 psig, still more preferably between 10 and 200 psig and still more preferably between 50 and 100 psig. Other oxidants may also be effective including chlorine, the ferric ion, hydrogen peroxide and Caro's acid though these may not in some cases be as economical as oxygen gas.
Preferably, the temperature ranges from about 170 degrees Celsius to about 300 degrees Celsius, more preferably from about 195 degrees Celsius to about 275 degrees Celsius, more preferably from 200 degrees Celsius to 250 degrees Celsius, still more preferably from 210 degrees Celsius to about 230 degrees Celsius.
Preferably, the leach solution is acidic. Still more preferably, the acid constituent is sulphuric acid at a concentration ranging from 1 to 500 g/L. More preferably, the sulphuric acid is at a concentration ranging from about 5 to about 250 g/L, more preferably at a concentration ranging from about 10 to about 100 g/L.
It is important to maintain an elevated oxidation potential in solution during the leach (for example at levels greater than 500 mV versus Ag/AgCl) for maintaining precious metal leaching efficiencies in the process. This can be done by oxidizing, as completely as possible, any reduced species such as sulphide ions or sulphur in the feed to the process, for example. It may also be done by converting most of the ferrous ion in solution to ferric ion. In addition, a tramp ion constituent, which is added as a consequence of grinding or re-grinding the feed to the process, may also contribute to a reduction in the precious metal recovery. This is especially true in the case of gold.
The host material may be in any one of a number of forms, including a primary sulphide or oxide ore body which has been processed by grinding and the like, an ore concentrate, or a secondary material containing precious metals, such as for example a spent oxidation catalyst. The host may also be a matte material from a smelting operation which, in contrast to the ore concentrates, can have precious metal concentrations of up to 10 percent, with the balance being base metals and sulphide. In this case, it may be desirable either to recover the precious metals and base metals together into the leach solution or, alternatively, use a multiple step process to recover the base metals first and then the precious metals second. For example, in a first step, the base metals can be recovered to a first leach solution as in th
Dreisinger David
Fleming Christopher A.
O'Kane P. Terry
International PGM Technologies Ltd
King Roy
McGurthy-Banks Tima
O Rourke Thomas A.
Wyatt Gerbert & O Rourke
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