Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2001-09-28
2003-06-10
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C205S291000, C266S101000, C422S269000, C423S027000
Reexamination Certificate
active
06576041
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to pressure oxidation and pressure leaching of metal-containing minerals materials to facilitate metal recovery, and to other chemical processing operations involving mixing of or contact between multiple components.
BACKGROUND OF THE INVENTION
Many chemical processing operations involve intimate contact of two or more components in a reactor. As one example, pressure oxidation of metal-bearing mineral materials involves contacting a slurry of the mineral material with an oxidant, typically oxygen gas, at elevated temperature and pressure to oxidize one or more of the minerals, thereby freeing metal values of interest for possible recovery in subsequent metal recovery operations. Pressure oxidation has been used to process a variety of sulfide ores, including both base metal and precious metal-containing sulfide ores. Sulfide concentrates prepared from flotation of such ores have also been processed by pressure oxidation, either alone or in a blend with whole ore material. During pressure oxidation one or more sulfide mineral is oxidized, with sulfide sulfur of the sulfide minerals typically being oxidized to a sulfate form. This oxidation results in decomposition of the sulfide minerals and release of the metal values. Pressure oxidation operations are typically conducted in an acidic environment, such as in the presence of a sulfuric acid solution, although some pressure oxidation operations have been conducted in an alkaline environment, such as in the presence of a hydroxide or carbonate solution.
In some pressure oxidation operations, the metal(s) are dissolved during the pressure oxidation operation and in subsequent metal recovery operations the dissolved metals(s) are recovered from solution by a variety of techniques, which may involve, for example, one or more of selective precipitation, solvent extraction ion exchange and electrowinning. This will typically be the case when pressure oxidizing base metal sulfide minerals, such as those containing, for example, nickel, copper, zinc and/or lead. If present, silver is also frequently dissolved during pressure oxidation operations.
Some metals, however, do not typically dissolve during pressure oxidation operations. For example, when processing sulfide gold ores, the gold typically does not dissolve and remains with solid residue from the pressure oxidation operation. The gold may then be recovered, for example, by leaching the solid residue with a leach solution containing a lixiviant for gold, such as a cyanide or thiosulfate lixiviant. In sulfide gold ores, the gold is typically contained in one or more iron-containing sulfide mineral, such as for example, pyrite, marcasite, aresenopyrite or pyrrhotite. Direct leaching of gold from these ores, such as direct cyanide leaching, typically results in only very low gold recovery. For this reason, these sulfide ores are often referred to as refractory sulfide gold ores. Recovery of gold from these refractory sulfide gold ores typically involves pretreatment of gold-bearing sulfide minerals to decompose at least a portion of the sulfide minerals to free the gold, thereby facilitating subsequent recovery of the gold by leaching the gold with a leach solution containing cyanide or some other lixiviant. The pretreatment may be performed, for example, on the whole ore, on a sulfide concentrate resulting from prior flotation operations, or on a blend of whole ore and ore sulfide concentrate. Pressure oxidation is one pretreatment technique in which the gold-bearing ore and/or concentrate, is contacted with oxygen gas in a reactor, called an autoclave, under high pressure to oxidize sulfide sulfur in the sulfide minerals thereby releasing gold for recovery. Typically, the sulfide sulfur is oxidized to a sulfate form in an acid environment.
Pressure oxidation operations frequently involve feeding a slurry of particulate ore and/or concentrate slurried in an aqueous liquid to the first compartment of a multi-stage, or a multi-compartment reactor. Oxygen gas is fed to one or more of the compartments of the multi-compartment reactor to effect the desired oxidation of sulfide sulfur for the purpose of freeing the metals of interest for recovery. As used herein, the terms “multi-stage” and “multi-compartment” are used interchangeably in reference to an autoclave, or other reactor, including one or more internal dividers separating the interior reactor volume into zones that progress in series of the general direction of flow through the reactor, with each such divider acting as at least a partial barrier to flow between adjacent zones. The terms “stage” and “compartment” are used interchangeably herein to refer to such a zone within a multi-stage reactor.
A significant expense associated with pressure oxidation is the cost of providing oxygen gas for use in the reactor. There is often significant inefficiency in the use of oxygen gas and it is, therefore, common practice to feed to the reactor a significant excess of oxygen gas over that stoichiometrically required for sulfide sulfur oxidation, with the excess oxygen gas being essentially wasted. Moreover, the oxygen gas is typically fed to the reactor in a gas stream that is substantially enriched in oxygen compared to air. Providing such a purified stream of oxygen gas typically requires building and operating an oxygen plant to prepare an oxygen-enriched gas stream from air, such as for example by membrane or cryogenic separation techniques, which is expensive.
Another frequent problem with current pressure oxidation operations is thermal inefficiency in the reactor. Oxidation of the sulfide minerals is exothermic, but maintenance of a minimum elevated temperature is required to attain acceptable reaction kinetics. Therefore, in many instances heat, often in the form of steam, is added to the first compartment of a multi-stage reactor to maintain an adequate temperature in the first stage, where the oxidation reaction is initiated. Conversely, in one or more subsequent stage of the reactor, it is often necessary to add water to prevent the occurrence of excessively high temperatures, with the quantity of water required increasing as more steam is added to the first compartment.
The addition of steam in the front-end of the reactor is undesirable because of the cost of generating the steam. Also, as the steam condenses in the reactor it reduces the density of solids in a slurry and, therefore, the quantity of ore that may be processed through the reactor per unit time. The addition of water in the back-end of the reactor is likewise undesirable because the added water also dilutes the slurry and reduces the density of solids in the slurry, thereby further reducing potential ore through-put.
Another example of a chemical processing operation that involves intimate contact between multiple components is pressure leaching. Pressure leaching involves contacting a metal-containing material with a leach solution to dissolve at least a portion of one or more metal of interest. The pressure leaching is conducted in a reactor at elevated temperature and pressure to improve leach kinetics. Although the field of pressure leaching is not confined to mineral processing operations, many metal-bearing ores, and concentrates prepared by flotation of such ores, are processed by pressure leaching to dissolve one or more metals of interest into the leach solution. Mineral materials susceptible to processing by pressure leaching are typically oxide ores, and concentrates prepared from such ores. Unlike pressure oxidation, it is not necessary to oxidize a sulfide mineral to release the metals. Rather, the metals are directly leachable from the mineral material of interest. The leach solution used for pressure leaching may be acidic or alkaline, depending upon the materials involved and the specific circumstances. For example, either alkaline (e.g., ammoniacal) or acidic (e.g., sulfate) leach solutions may be used to pressure leach nickel or cobalt from laterite or saprolite ores. As another e
Andrews Melvyn
Marsh Fischmann & Breyfogle
Newmont USA Limited
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