Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ib metal
Statutory Invention Registration
1999-06-30
2001-11-06
Jordan, Charles T. (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ib metal
Statutory Invention Registration
active
H0002005
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the leaching of low sulphur ores.
BACKGROUND OF THE INVENTION
There are large reserves of so-called secondary ores containing base and precious metals which it would be desirable to recover. Such secondary ores include oxides, sulphates and partially oxidised or weathered sulphides. The ores may be complex containing portions of sulphide, sulphate, oxide and weathered sulphide, any of which may require a different kind of hydrometallurgical treatment to enable the recovery of metals from the particular one. Nevertheless, whatever the geology, the sulphur content of the ore is much less than would be encountered with a massive sulphide orebody. Accordingly, such ores may be described as “low sulphur ores”. Secondary ores of copper including antlerite, brochantite, malachite and other mineral types, typically reflect an association of small amounts of copper sulphide minerals with a large amount of carbonate or oxide minerals. Weathered or partially oxidised sulphides may also be present within the ore. Other base metals exhibit similar oxidised mineralogy, for example lead and zinc.
Generally, such ores may be treated to separate sulphides and the other secondary minerals present. The secondary minerals are not amenable to pyrometallurgical treatment as gangue heating and slag handling requirements are too high. Such costs dictate a hydrometallurgical route to recovery which may involve treatment by a process which involves acid leaching, such being basically the only hydrometallurgical route to recovery. The economics of acid leaching of course will vary with the location of the ore body and proximity to sources of acid producing materials such as sulphide ores, pyrites or sulphur. Nevertheless, in some locations, there will be no source of acid producing material and it may be necessary to plan on the basis that sulphuric or sulphurous acid will require to be imported to the site. The transportation and material costs of pursuing this option may be sufficiently high that the proposed project remains unviable even though on a grade basis the resource would be attractive to develop. The problem may be increased by the acid consuming nature of carbonate minerals that increase acid costs and further impact on economic viability.
Other ores, such as the refractory ores, may include appreciable content of precious metals such as gold and silver. Such ores are also low sulphur ores and as described in U.S. Pat. No. 5,246,486 may have a sulphur content of 0.2 to 0.3%. Thus only a limited extent of bacterial leaching is possible, and such ores need to be subjected to cyanidation or other hydrometallurgical treatment for the liberation of the precious metals.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a hydrometallurgical route to the recovery of metals from low sulphur ores containing them which avoids, to the maximum possible extent, the costly import of leaching acid. The “low sulphide materials” of particular interest contain the oxides, sulphates and weathered sulphides of the base metal family.
With this object in view, the present invention provides a process for leaching low sulphur materials for recovery of metals contained in them comprising leaching a first low sulphur material containing metal values with a leaching agent produced by bacterial oxidation of a second material with sulphur oxidising bacteria thereby liberating metal values from the first material by a substantially indirect bacterial process.
Typical low sulphur materials to be treated by such a process would be the oxide, sulphate and partially oxidised or weathered sulphide ores of base metals such as copper, cobalt, lead, zinc and nickel and mixtures thereof. Such ores may contain an appreciable quantity of carbonate minerals but have a sulphur content lower than would be necessary to achieve an economically appreciable extent of metal leaching by bacterial action in the absence of the second material. Typical sulphur content of the low sulphur content material is between 0 and 10% by weight.
The first material could be the low sulphur ore itself, a mixture of low sulphur materials, perhaps a mixture of different low sulphur ores, or could be a concentrate or residue of another metallurgical process which is low sulphur in content but still containing an appreciable metal content. Slags, concentrates, tailings and other metallurgical materials such as residues from electrolytic zinc plants, may be suitable for treatment by the process of the invention. The material may be primary crushed or subjected to secondary size reduction. Any size reduction should be to a size range that allows effective heap or dump or other leaching especially reactor leaching, for example leaching in stirred tank(s). Aeration costs in the latter case may affect process economy.
The first material may include iron as iron oxides or sulphides, typically in a range of 0% to 40% by weight. Action of the leaching agent or bacteria on the first material may liberate ferric ion which may itself act as a leaching agent.
The second material is selected such that bacterial action on that material produces a leaching agent. Most advantageously, bacterial action on the material by sulphur oxidising bacteria produces sulphuric or sulphurous acid, a conventional leaching agent. Materials that meet this criterion include elemental sulphur, most preferred in the case of the present invention since it will introduce a minimal level of impurities, as well as sulphuric acid by bacterial oxidation, into the leaching process. Milled or unmilled sulphur could be employed. Sulphur particles may be agglomerated using a suitable agglomerating agent, as discussed.
The second material may itself be a mixture of materials. The key constituent of the mixture will be a mineral or material which may be bacterially oxidised to produce the desired acid requirement of the process. Mixtures of sulphides and low sulphur content materials could be used, the rich sulphur materials reducing the necessary sulphur addition to promote indirect bacterial oxidation. Other materials could be used such a pyrite or pyrrhotite though these will introduce iron into the process and this may be undesirable. Nevertheless, a controlled proportion of ferric ion produced by bacterial action could be desirable being an effective leaching agent.
The second material must be employed in such amount, relative to the quantity of the first material, that a sufficient amount of acid will be available to dissolve the required quantity of metals from the first material. Particularly where the first material includes carbonate or other acid consuming minerals or materials, the quantity of second material should include a component, which when converted to acid, is sufficient to at least neutralise the acid consuming minerals or materials. The required quantity, taken into combination with the achieved extraction, will be at least that to make the treatment scheme economically viable.
The second material may be combined, or not, with the first material dependent upon the desired process design. For example, the first material could be slurried and the second material, say sulphur, added in a process suitable to be conducted in one or more continuous stirred tank reactors. Batch reactors could also be used.
The first and second materials could be mixed prior to being formed into a heap or dump for a heap, dump or other percolation leaching process. The first and second materials could be arranged in layers or otherwise in proximity such that bacterial action on the second material produces the leaching agent for the first. Alternatively, the second material could be bacterially treated in a separate stage, the leaching agent generated being transferred to the first material leaching stage. Thus the heap of the first material could be irrigated with an acidic liquor guaranteed by bacterial oxidation of the second material. Of course, the leaching agent could be supplied to a continuous stirred tank reactor system f
Maritz Lenhart G
Miller Paul C
Pinches Anthony
Winby Richard
Baker Aileen J.
Jordan Charles T.
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