Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy...
Reexamination Certificate
2001-11-09
2004-02-24
Bos, Steven (Department: 1754)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
C423SDIG001, C435S252100
Reexamination Certificate
active
06696283
ABSTRACT:
THE INVENTION
This invention relates to recovery of precious metals, e.g. gold and silver, from ores having a sulfidic sulfur and/or elemental sulfur content, such as sulfide-containing leachable ores of the pyritic, arsenopyritic, or arsenian pyrite type, refractory carbonaceous sulfide ores which have been pretreated, ores which are being post-treated, tailings, previously considered waste grade ores (which still have sufficiently high gold and silver content) and overburden ores having fairly low gold content and which may be considered waste ores.
This invention also relates to the recovery of non-precious metal values from ores having a sulfidic and/or elemental sulfur content whether as an incident to the recovery of precious metals or as a recovery of the nonprecious metals.
More particularly this invention relates to a specific treatment of particularly prepared ores of vast quantities and typically leached in heaps, dumps, tailing dumps, or waste dumps and the like. Still more particularly this invention relates to an ore treatment which starts with a preparation of particulates of specific design characteristics making the recovery of precious metals in low amounts and/or the recovery of nonprecious metals especially attractive and suitable for a heap or dump leaching, a construction of these specifically inoculated particulates and a heap or dump constructed from the specifically inoculated particulates suitable to an outstanding degree for biooxidation reactions with either single, mixed, layered, or staged biooxidant bacteria cultures.
Further, this invention relates to especially suitable form of a biooxidized and treated ore used in subsequent down-stream precious metal extractions such as by thiourea, or, after heap reconstruction, by thiosulfate or cyanide extraction of the precious metal values in the ore heap or in subsequent downstream nonprecious metal extractions, such as by suitable lixiviants, of the desired metal value(s) in the ore heap. Foremost amongst the ores being treated for precious metal recovery are gold ores. Foremost amongst the ores being treated for nonprecious metal recovery are copper, zinc, nickel, molybdenum, cobalt and uranium ores.
BACKGROUND FOR THE INVENTION
Typically precious metal containing ores are leached with cyanide as the most efficient leachant or lixiviant for the recovery of precious metal values from the ore. It would also be highly desirable to recover nonprecious metal values by heap leaching or lixiviation.
However, because of the mineralogy of various ores, access to the precious and/or nonprecious metal in the ore by cyanide or other lixiviant is low for an economical extraction of the precious metal and/or nonprecious metal values in an ore. If the cyanide extraction produces small or negligible amounts of gold, an ore is said to be refractory or highly refractory. Various methods have been employed to increase the extractability of the precious and/or nonprecious metals. A good summary article describing the prior problems is that authored by Kantopoulos et al.,
Process Options for Refractory Sulfide Gold Ores: Technical, Environmental, and Economic Aspects
, Proceedings EPO '90 Congress, D. R. Gaskell, Editor, The Minerals, Metals & Materials Society, 1990.
A typical component which causes the refractoriness of the ore is predominantly a carbonaceous type component either inorganic or organic. The organic carbonaceous materials are also classified as acid insoluble carbonaceous materials. Gold found in ores dispersed within or occluded in a sulfide matrix may be considered refractory because of inaccessibility of such gold by cyanide leaching. Similarly, nonprecious metal values found in ores either dispersed within or occluded in a sulfide matrix or present as metal sulfides are also not readily recoverable by heap leaching or lixiviation.
When treating such ores, the economic considerations dictate the selection of the process or the pretreatment of the ore to render it amenable first and foremost to cyanide extraction even though other gold lixiviants may be used. Similarly, it is highly desirable with nonprecious metal values in sulfidic ores to render them recoverable by heap leaching or lixiviation.
As one of the desired treatment steps prior to cyanidation or comparable lixiviation, roasting of ores in presence of air is typical. Lately oxygen or oxygen and air roasting, at low temperatures, have showed considerable promise. Other commercial ore treatment methods prior to cyanidation are high pressure oxygen and/or oxygen-ozone pretreatment, chlorine pretreatments, hypochlorite pretreatments and the like.
To improve cyanidation of ores, during such cyanidation ozone, or ozone and oxygen, or oxygen, or a surfactant, or combinations of these are also employed. In the instance of gold recovery, methods such as “carbon-in-pulp” (or “CIP”) and “carbon-in-leach” (or “CIL”) are used to improve cyanidation reactions and gold recovery.
However, cyanidation has certain shortcomings, primarily an ore material must be neutralized after an acid generating treatment as cyanidation must be carried out on the alkaline side of the pH scale; likewise high cyanide consumption renders a process less attractive. When using thiourea, neutralization of the ore is not as demanding and does not affect thiourea extraction of gold, but the extraction economies are impaired by the higher cost of thiourea and the reduced efficiency when compared with cyanide.
Other compounds which have been used and offer promise because of reagent costs are compounds such as thiosulfates of which ammonium thiosulfate is one of the desirable candidates. Although still other materials are used for gold recovery, these are not yet of industrial significance.
When ammonium thiosulfate and the like are used, neutralization of ore is required as appropriate pH ranges are neutral to alkaline, e.g. to about pH 7 to 10 and preferrably to at least about 9. As pyritic sulfidic ores and many other ores need to be neutralized because of the acidity of these ores when subjected to oxygenation or biooxidation and like treatments, separate process steps are required.
Inasmuch as gold is occluded in the sulfide matrix of the ore, the accessibility by cyanide has sought to be improved for these ores; the same is also true when considering an appropriate sulfide, e.g., pyrite for oxidation or biooxidation. Although various oxidation or biooxidation reactions have been tried such as vat, autoclave, slurry or liquid solution oxidations, these reactions are not practical when using large ore bodies having low gold content. As one of the approaches to oxidation of low content metal sulfide ores, biooxidation has come into prominence and much effort has been expended in research. Biooxidation was first applied to copper. Biooxidation of copper ore has been a well tried method although it is considered fairly slow.
When biooxidation is coupled with oxidative bioleaching, i.e. when direct, indirect and even galvanic leaching reactions are involved, some of the disadvantages of the slow biooxidation reactions are mitigated. Biooxidation reactions typically involve arsenopyritic and pyritic iron sulfide-containing ores including those that have some refractory carbon components present. Biooxidation, however, can suffer from inhibitory concentrations of some metals present in the ore. Biocidically active metals are such as arsenic, antimony, cadmium, lead, mercury, molybdenum. Ions such as chlorine, bromine and the like affect the biooxidation processes. Because of slow growth rates for some bacteria as well as temperature variations in a typical ore dump undergoing sulfide oxidation, considerable efforts have been expended to improve the rate constraints which have limited or held back the potentially very useful application of biooxidation.
Hence, considerable investigation has been made of the various limiting conditions concerning commercial biooxidation including such factors as ores in heaps or in slurry form, the use of surfactants, the use of potentiators or bi
Brierley James A.
Hill David L.
Bos Steven
Marsh & Fischmann & Breyfogle LLP
Newmont USA Limited
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