Compositions – Absorptive – or bindive – and chemically yieldive
Reexamination Certificate
1999-04-26
2001-03-06
Bos, Steven (Department: 1754)
Compositions
Absorptive, or bindive, and chemically yieldive
Reexamination Certificate
active
06197214
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the recovery of precious metals, such as gold and silver, from aqueous ammoniacal thiosulfate leach solutions by extraction of the precious metal values from the aqueous thiosulfate leach solution with organic amine extractants, such as guanidine compounds or mixtures of a quaternary amine and a phenol.
Conventionally, precious metals have been leached from ore using cyanide containing solutions and the precious metals recovered therefrom. However, other metals present tend to cause problems in the process of recovery of the precious metals. One method proposed for overcoming the problems involved the use of extractant reagents to remove the precious metals from the aqueous cyanide containing solution, either by liquid/liquid extraction or by liquid/solid extraction systems.
More recently a South African patent application, Serial No. 937288 to Newmont Gold Co. (Newmont Mining Corporation) was published relating to a process of recovering precious metals from ores employing a thiosulfate lixiviant as leach solution from which the precious metals are recovered from the lixiviant leach solution by means other than extraction technology, preferably by precipitation and cementation techniques.
No fully satisfactory process has been developed however, for precious metals recovery from ore materials containing other base metals which interfere with or render the process of recovery of the precious metals non-viable from a practical or commercial standpoint.
SUMMARY OF THE INVENTION
It has now been found that by leaching the gold containing ore with an aqueous ammoniacal thiosulfate solution and extracting the metal values therefrom, a viable, practical process is provided, affording a simple means for avoiding the problem arising from the presence of other metals present with the precious metals in the aqueous ammoniacal thiosulfate leach solution provided, but also providing for the recovery of the precious metal, particularly gold, in a purer form than that provided by other techniques.
Briefly, in its broadest scope, one aspect of the present invention is a process for recovering precious metals, particularly gold and silver, from ores containing the precious metals and other base metals, comprising:
(a) providing an aqueous ammoniacal thiosulfate leach solution containing the precious metal values and other base metal values contained in the ore;
(b) contacting the aqueous ammoniacal thiosulfate leach solution from step (a) with a metal value extraction reagent for a time sufficient to extract precious metal values from the aqueous ammoniacal thiosulfate leach solution;
(c) stripping the precious metal values from the extraction reagent; and
(d) recovering the precious metal values from the aqueous stripping solution.
Extraction step (b) is carried out by either a liquid/liquid solvent extraction or by a liquid/solid extraction technique employing an extraction reagent capable of extracting precious metal values from aqueous solutions. In a liquid/liquid solvent extraction system, a water insoluble extraction reagent capable of forming a complex with the metals to be extracted is dissolved in a water-immiscible organic hydrocarbon solvent. In the solid/liquid extraction system, the extractant reagent is one incorporated and/or chemically bonded onto a solid ion exchange resin matrix or carrier or backbone. Both of these extraction systems will be discussed in more detail hereafter.
The extraction reagents for use in the present invention to be described in more detail hereafter are (i) guanidine compounds employed as hydrocarbon solvent solution in the liquid/liquid extraction system or chemically bonded to a resin matrix or backbone to provide an ion exchange resin carrying guanidyl functionality and (ii) a reagent comprising a mixture of a quaternary amine and a weak organic acid, such as a phenol, which reagent may be employed in the same manner as the guanidine reagent, in the liquid/liquid solvent extraction system.
A second aspect of the invention is the provision of precious metal (gold or silver) ammonium thiosulfate complexes of the extractant reagents employed, guanidyl or quaternary amine complexes.
DETAILED DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”.
The aqueous ammoniacal thiosulfate leach solution is provided by contacting a body of particles or particulates of precious metal ore material containing the precious metals with a thiosulfate lixiviant under conditions providing for intimate contact of the two. The body of particles or particulates may comprise a heap of particles and particulates and contacting the heap by passing the thiosulfate solution through the heap by applying it to the heap at a flow rate under conditions which cause the solution to flow through the heap and intimately wet the ore particle. The thiosulfate solution containing precious metal values, such as gold or silver, is recovered at the bottom of the heap. With higher grade ore materials containing greater amounts of precious metals may be processed by forming a slurry of the thiosulfate solution and finely ground ore in a stirred vessel.
The thiosulfate leach solution or lixiviant can derive the necessary thiosulfate ion from a variety of sources of thiosulfate, such as ammonium thiosulfate or alkali metal or alkaline earth metal thiosulfates, such as sodium or potassium, which are preferred, or calcium thiosulfate. The thiosulfate leach system preferably has (a) an ammonium thiosulfate or sodium thiosulfate (or mixture of both) concentration of at least about 0.025M of ammonium thiosulfate corresponding to about 4 grams of ammonium thiosulfate per liter of leach solution preferably from about 0.05M to about 0.2M (corresponding to about 7.5 to about 30 grams of ammonium thiosulfate per liter of leach solution). (b) The aqueous leach solution will preferably have a pH of about 8 to about 10, and more preferably about 9 to about 9.5, and an ammonia concentration in an amount sufficient to stabilize the thiosulfate complex, generally at least about 0.05M preferably at least about 0.1M.
As earlier briefly noted, in a liquid/liquid extraction method, the reagent must be soluble in an organic solvent which is immiscible in relation to the aqueous ammoniacal thiosulfate leach solution. Thus, the guanidine reagent is dissolved in the organic solvent, which is then brought in contact with the aqueous thiosulfate cyanide solution containing the desired metal values. The guanidine reagent extracts the gold and/or silver metals from the thiosulfate leach solution which are now found in the organic phase which is immiscible with the aqueous phase. After separation of the organic phase from the aqueous phase, the organic phase containing the desired metal values is then stripped by contact with an aqueous caustic solution which strips the metal values from the organic phase. It may be desireable to add a small amount of cyanide to the aqueous caustic strip solution to maintain the precious metals in solution, especially silver. The metal values now in a more concentrated aqueous solution are then recovered by conventional methods such as those used in the carbon absorption method through elctro-winning.
In the liquid/solid extraction method, a guanidine reagent is first incorporated into a solid ion exchange carrier. Recovery of the gold from the thiosulfate solution is accomplished by contacting the thiosulfate solution with the ion exchange reagent carrier containing the guanidine functionality, at which point the metals are extracted from the aqueous thiosulfate solution onto the ion exchange carrier containing the guanidine reagent. The metal barren aqueous solution is then separated from the carrier containing the guanidine. The metal values are then stripped from the ion exchange carrier containing the guanidine functionality and recovered in
Sierakoski J. Michael
Virnig Michael J.
Bos Steven
Drach John E.
Henkel Corporation
Span Patrick J.
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