Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1991-10-04
1993-06-01
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
B01G 500
Patent
active
052155757
DESCRIPTION:
BRIEF SUMMARY
This invention relates to improvements in recovery of noble metals from ores and tailings. Throughout this specification noble metals are intended to include gold, silver and the platinum group.
This invention is partly predicated on the discovery that noble metals in extremely fine form are often present in higher concentrations than is revealed by normal assay techniques in common use.
For example, platinum or gold ores can contain more metal than that recovered in conventional wet chemical or fire-assay methods. It is thought that where there are metal absorbing materials such as clay, carbon, or sulfides in the ore or other metals being analysed, some of the metal taken into solution becomes adsorbed onto these materials and is not detected. In the case of gold leached into solution by aqua regia in wet assays or by cyanide in the cyanide extraction process, the gold complex becomes absorbed by clay, carbon, sulfides, or other material and is thus undetected by solution assay. In the fire assay technique, because clays convert to a boron silicate glass under fire assay conditions, gold is also lost to detection in that technique. Conventionally, gold leached by the cyanide process, usually at pulp densities of 35 to 50% may be recovered from the leach solution in a subsequent stage by contacting the solution or pulp with activated carbon, usually in a concentration range of 10 to 20 grams of carbon per liter of solution (carbon in pulp (CIP) process), but on occasions up to 40 grams per liter have been used. In some instances the carbon has been added to the leaching circuit as well (CIL process), in the same concentration ranges in order to improve gold leach rates so that the gold recorded equated with the assayed grade of the ore.
Particular treatments for clay or sulfide ores have been proposed. Australian Patent 569175 treats sulfide ores in a pressure oxidation step prior to cyanide leaching. After leaching, the pulp is diluted by washing to improve the flocculation in the subsequent thickening stage, following which the liquor is separated from the pulp. Gold is then extracted from solution and the concentrated pulp is then subjected to a carbon in leach circuit at 35 to 40% solids to extract further gold.
The conventional assay technique for gold is either by the wet method, which is leaching with aqua regia followed by measurement of the dissolved gold by atomic absorption spectroscopy or similar techniques, or by fire assay. In some instances when the recovery of gold by the CIP process was not up to the assayed grade, adoption of the CIL process, with addition of carbon to the leach circuit resulted in increased recovery. The amount of carbon was increased, in some cases to 40 grams per liter, until the head grade recovery was achieved. In other instances, the Carbon in leach (CIL) process was adopted to improve gold leach rates and gold recovery rates and thereby decrease the required number of carbon contacting tanks, thus decreasing the capital cost of construction of the gold recovery plant. In some circumstances, however, increasing the carbon loading to the leach vessel, or the subsequent contacting stages, was found to be undesirable because of the formation of fine carbon particles caused by attrition during pulp agitation. The consequent loss of carbon with its attached gold reduced the effectiveness of the process. However prior to this invention it was not suspected that there were also undetected values of metal in some ore samples. These comments also apply to ore concentrate and tailings.
It is an object of this invention to improve recovery rates of noble metals including gold or other valuable metals from ores particularly clay containing ores.
In another aspect of the invention, there is provided a method of recovering metal values by the leaching method in which the pulp density of the slurry is adjusted to below 15% either, prior to, during, or at the end of the leaching stage and subsequent to the leaching step localized zones of high pulp density are avoided.
Pulp is def
REFERENCES:
patent: 4654078 (1987-03-01), Perez
patent: 4971625 (1990-11-01), Bahr
patent: 4980134 (1990-12-01), Butler
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