Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2000-09-29
2002-05-28
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C266S101000, C422S269000, C423S027000
Reexamination Certificate
active
06395063
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of mineral processing for the recovery of gold from gold-bearing sulfide minerals and, more particularly, to mineral processing operations involving pressure oxidation of gold-bearing sulfide minerals to free gold to facilitate gold recovery.
BACKGROUND OF THE INVENTION
Sulfide gold ores include gold contained in one or more sulfide minerals, such as for example pyrite, marcasite, arsenopyrite 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 ore and/or concentrate, is contacted with oxygen gas in 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. A typical pressure oxidation operation involves feeding particulate ore and/or concentrate slurried in water to the first compartment of a multi-stage, or multi-compartment, autoclave. Oxygen gas is fed to one or more of the compartments of the multi-compartment autoclave to effect the desired oxidation of sulfide sulfur for the purpose of freeing the gold for recovery. The gold remains in solid residue discharged from the autoclave following pressure oxidation, and the gold is recoverable from the residue by any suitable gold recovery technique, such as lixiviation of the gold with a cyanide, thiosulfate or other lixiviant for gold. As used herein, the terms “multi-stage” and “multi-compartment” are used interchangeably in reference to an autoclave including one or more internal dividers separating the interior reactor volume within the autoclave into zones that progress in series in the general direction of flow through the autoclave, 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 autoclave.
A significant expense associated with pressure oxidation is the cost of providing oxygen gas for use in the autoclave. There is often significant inefficiency in the use of oxygen gas and it is, therefore, common practice to feed to the autoclave 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 autoclave 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 autoclave. Oxidation of the sulfide mineral is exothermal, but maintenance of a minimum elevated temperature is required for adequate reaction kinetics. Therefore, in many instances heat, often in the form of steam, is added to the first compartment of a multi-stage autoclave to maintain an adequate temperature in the first stage, where the oxidation reaction is initiated. Conversely, in one or more subsequent stage of the autoclave, 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 autoclave is undesirable because of the cost of generating the steam. Also, as the steam condenses in the autoclave it reduces the density of solids in the slurry and, therefore, the quantity of ore that may be processed through the autoclave per unit time. The addition of water in the back-end of the autoclave is likewise undesirable because the added water also tends to reduce the density of solids in the slurry, thereby further reducing potential ore throughout.
There is a need for pressure oxidation processes that more efficiently utilize oxygen gas fed to the autoclave and/or operate in a more thermally efficient manner.
SUMMARY OF THE INVENTION
The present invention generally relates to gold recovery operations and, more particularly, to a method and system for pressure oxidizing a gold-bearing mineral material feed to free gold from association with at least one sulfide mineral with which gold is associated.
Mineral material feed to the autoclave may be any gold-bearing material containing gold in association with at least one sulfide mineral, for which it is desirable to decompose at least a portion of the sulfide mineral to facilitate gold recovery. These mineral materials may be referred to as refractory sulfide materials, because at least a significant portion of the gold cannot generally be recovered by direct leaching of the mineral material with a lixiviant for gold, such as a cyanide or thiosulfate lixivant. The mineral material feed may include a whole ore, a sulfide concentrate prepared from prior flotation operations, or a blend of the two. Also, the mineral material feed may be or include tailings or other solid residue from prior mineral processing operations. With the present invention it has been found that autoclave performance, and especially oxygen gas utilization efficiency, is often significantly improved with the present invention.
A first aspect of the present invention generally relates to agitation of a mineral material slurry in an autoclave in which a pressure oxidation operation is being effected for gold recovery purposes. The Mineral material feed is introduced into the autoclave in a manner so that, in the autoclave, the mineral material is in a slurry, typically with water. Oxygen gas, typically under high pressure, is also introduced into the autoclave for use as an oxidant to oxidize at least a portion of the sulfide sulfur in the mineral material, thereby freeing at least a portion of the gold for possible subsequent gold recovery operations.
According to the first aspect of the invention, slurry present in the autoclave is agitated during pressure oxidation by at least one agitator disposed in the autoclave and operated to provide a pumping action in which portions of the slurry are continually drawn into and expelled from a cavity in the agitator. This pumping action is typically effected through rotation of at least a portion of the agitator in a manner to expel the slurry from the cavity in a generally radially outward direction, thereby creating a fluid suction within the cavity to draw additional slurry into the cavity for continuous cycling of slurry through the agitator while the rotation is continued.
Various refinements exist for features noted in relation to this first aspect of the present invention, and additional features may also be incorporated as well. These refinements and additional features may be incorporated individually or in any combination. In one refinement, the agitator has a fluid intake that is preferably axially aligned with a center of the noted cavity, and the agitator further has an axis of rotation that is aligned with the center of the cavity. Additional refinements involve directing a flow of the oxygen gas and/or the mineral material feed toward a fluid intake of the agitator through which slurry is directed to the cavity. In a prefe
Andrews Melvyn
Marsh & Fischmann & Breyfogle LLP
Newmont Mining Corporation
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