Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-03-22
2002-03-12
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S639000, C210S651000, C423S029000, C075S744000
Reexamination Certificate
active
06355175
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the processing of metal-contaminated, precious metals-containing solutions, and more particularly to a method in which gold ore that also contains copper and other contaminant metals is treated to effectively separate gold from the copper and other contaminant metals.
BACKGROUND
To recover elemental gold (Au) from gold-containing ore, the ore is typically contacted with one or more aqueous cyanide-containing leach solutions (or lixiviant). The gold and other metals are dissolved in the solution, forming various metal cyanide complexes such as Au(CN)
2
−1
and Cu(CN)
3
−2
.
A variety of different physical methods may be employed to contact the ore with the cyanide-containing leach solution. Two common methods are heap leaching and vat leaching. In heap leaching, coarsely comminuted ore is placed in a pile which is positioned on an impervious liner. The cyanide-containing leach solution is applied to the top of the ore pile and allowed to travel (e.g. percolate) through the heap. A pregnant leach solution containing one or more monovalent gold-cyanide complexes and other dissolved metal cyanide complexes collects on the liner at the bottom of the pile. In vat leaching, finely comminuted ore is placed in a large container or “vat” along with the cyanide leach solution to form a slurry. The solution extracts gold and other metals from the ore forming the pregnant leach solution.
A number of different procedures may be employed to recover the dissolved gold from the cyanide solution. Two common gold recovery methods are the Merrill-Crowe process and the activated carbon process.
In the Merrill-Crowe Process, the pregnant leach solution undergoes zinc cementation/precipitation reaction. Specifically, the pregnant leach solution containing the gold-cyanide complex is combined with elemental zinc (Zn) to generate solid elemental gold (Au) which resides within a gold-zinc solid sludge reaction product. The product is removed by filtration from the residual liquid fraction (which consists primarily of free cyanide ions [(CN)
−
] and a dissolved Zn(CN)
4
−2
(aq)
complex). The product is processed to isolate and recover the elemental gold by combining the product, after water washing, with sulfuric acid (H
2
SO
4
) in the presence of air to dissolve excess (unreacted) elemental zinc and other metals including copper and cadmium. The remaining solid material is smelted in the presence of a flux to produce a highly pure gold dore.
In the activated carbon process, the pregnant leach solution is placed in contact with activated carbon and the dissolved gold-cyanide complexes in solution are adsorbed onto the surface of the activated carbon. After adsorption, the gold-containing carbon product is filtered to remove residual “barren” liquid, followed by “desorption” or removal of the gold-cyanide complex from the “loaded” activated carbon (e.g. the gold-containing carbon product) by passing an eluant solution through the carbon. It is theorized that cyanide ions [(CN)
−
] in the eluant solution effectively replace/exchange the adsorbed aurocyanide ions (gold-cyanide complex) which are released into the eluant solution. The resulting gold-containing eluant product (which contains the desired gold species [aurocyanide ions/gold cyanide-complex]) is then processed by any suitable technique to recover elemental gold.
Regardless of which methods are ultimately used to obtain elemental gold from gold-cyanide complexes, numerous technical and economic problems can occur when gold ore is processed which contains substantial amounts of elemental copper and other contaminant metals. Such metals can have a stronger affinity for cyanide ions than gold and form metal cyanide complexes. For example, the copper-cyanide complex (Cu(CN)
3
−2
) which is generated as a result of this reaction is incapable of extracting gold from gold ore to yield the desired gold-cyanide complex and consumes three moles of (CN)
−
. As more copper leaches into the recirculating leaching solution (which occurs during reuse of this material and repeated passage thereof through incoming quantities of gold ore), increasingly large amounts of cyanide are lost to this complex. Such contaminant metals can therefore cause excessive cyanide consumption, thereby increasing process operating and capital expenses and substantial reductions in the operating efficiency of the entire gold production facility.
In addition to excessive cyanide consumption, copper and other metals within the gold ore can also result in an increasingly impure elemental gold product. Additional and more costly refining procedures must therefore be employed to solve this problem. By way of example, if the Merrill-Crowe process is used, extraneous copper materials in the solution can dramatically reduce the precipitation efficiency of the system by causing zinc passivation, with the term “passivation” involving a process in which the zinc is rendered non-reactive to the gold-cyanide complex which prevents the gold precipitation process from taking place. Additional zinc is often required which again increases overall production costs. Excessive contaminant metal contamination of the leaching solution can also reduce the operating efficiency of the smelting process associated with this embodiment by causing prolonged smelting times. For example in systems which employ the activated carbon process, copper materials (e.g. copper-cyanide complexes) will substantially inhibit the functional capabilities of the activated carbon, thereby “fouling” this material and causing increased carbon consumption. Power consumption is likewise increased in subsequent electrowinning stages if many contaminant metals are not removed from the system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for separating gold and/or silver from copper and other contaminant metals in a gold and/or silver processing system which enables the removal of copper and/or other contaminant metals from the system.
It is another object of the invention to provide a method for separating gold and/or silver from copper and other contaminant metals in a gold and/or silver processing system which enables the purity levels of elemental gold and/or silver to be relatively high.
It is a further object of the invention to provide a method for separating gold and/or silver from copper and other contaminant metals in a gold and/or silver processing system in which the removal of copper and other contaminant metals is accomplished with relatively low consumption of cyanide and other reagents so that the overall efficiency of the system is improved.
The claimed process overcomes the problems outlined above in a very effective manner which will become readily apparent from the detailed information presented below. While specific processing systems and gold and/or silver recovery technologies will be discussed in connection with the claimed procedure, the present invention shall not be limited to any particular cyanide-based gold and/or silver extraction method or to leaching solutions generally. Instead, the invention is prospectively applicable to any production system which places gold- and/or silver-containing materials in physical contact with solutions containing free cyanide ions [(CN)
−
] so that a gold- and/or silver cyanide complex as defined above is generated as well as any other application in which gold- and/or silver-containing solutions contaminated by other metals are treated to recover the gold- and/or silver. For example, the processes of the present invention are applicable to electroplating solutions.
In one embodiment of the present invention, a process for recovering a dissolved monovalent precious metal cyanide complex (e.g.,Au(CN)
2
−1
) from a cyanide solution containing the dissolved monovalent precious metal cyanide complex and one or more dissolved multivalent metal cyanide complexes (e.g., Cu(CN)
3
Green Dennis H.
Lombardi John A.
Mueller Jeff
Fortuna Ana
HW Process Technologies, Inc.
Ross P.C. Sheridan
Ward Richard W.
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