Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2001-07-27
2004-06-08
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C075S744000
Reexamination Certificate
active
06746512
ABSTRACT:
The present invention relates to hydrometallurgical extraction of copper and other valuable metals from sulphide ores and concentrates.
The present invention relates particularly, although by no means exclusively, to hydrometallurgical extraction of copper and one or more than one of the metals zinc, gold and silver from sulphide ores and concentrates.
There are limited known hydrometallurgical options for treating copper sulphide ores and concentrates to extract copper.
The bulk of copper produced hydrometallurgically on a commercial basis is from solvent extraction and electrowinning plants based on acid heap leaching of ore or from bacterially assisted dump leaching of low grade sulphuric wastes.
However, heap leaching is not a commercial option for a number of ores, particularly those containing refractory sulphide minerals such as chalcopyrite. Heap leaching of chalcopyrite (CuFeS
2
) ores results in poor recoveries and low extraction rates which in turn lead to the need for large leach areas and low copper content in the pregnant liquor for the solvent extraction and electrowinning steps. The non-recovery of gold is also a deterrent in cases where there is the option to produce a concentrate. Residual copper largely prevents further processing to recover gold in the heap.
Heap leaching is also not practised for zinc recovery from sulphide ores because of the difficulty in obtaining a liquor suitable for subsequent economic recovery of the zinc.
The three hydrometallurgical processes with most potential for chalcopyrite-rich sulphides are currently the Intec process, the BHAS process, and the related Cominco (CESL) process. Successful laboratory and/or pilot testing of these three processes has been reported. The processes all rely on the presence of chloride to improve the leaching efficiency for chalcopyrite without excessive attack on pyrite and oxidation of sulphur to sulphate. The BnAS/Cominco processes use conventional solvent extraction/electrowinning technology to recover copper, whereas the Intec process uses a particular novel chloride electrowinning step which produces copper powder. The BRAS process has been operated successfully on a chalcocite (Cu
2
S) like feed for more than ten years. However, the Intec, BRAS, and Cominco processes have not been operated commercially for chalcopyrite ores or concentrates.
There has also been considerable development of processes based on using high pressure and temperature (>200C) oxidative acid sulphate leaching of copper concentrates. These have not been commercially successful presumably because of the high costs associated with the conversion of the sulphur present to sulphate and the difficulties with economic recovery of gold and silver present from the residue using conventional cyanide based technology.
There is also active development of sulphate-based solvent extraction/electrowinning processes based on ferric sulphate leaching, low temperature oxidative pressure leaching, and bio-leaching. These processes are largely targeting the more readily leached sulphide minerals, such as chalcocite, rather than the more difficult to leach ores, such as chalcopyrite. There are no known commercial copper operations using any of these technologies.
An object of the present invention is to provide an alternative process for economic treatment of copper containing sulphide ores and/or concentrates which also contain associated valuable metals such as zinc, gold or silver.
According to the present invention there is provided a hydrometallurgical process for extracting copper and any one or more than one of zinc, silver and gold from a sulphide ore or concentrate which includes a range of mineral species that contain copper and one or more than one of zinc, silver and gold, which process includes two or more than two leach steps using leach liquors of different composition, each leach step selectively leaching one or more than one metal from the minerals, separating a solid residue and an exit leach liquor after each leach step, leaching the solid residue produced in each leach step in a successive leach step, and recovering metal from the exit leach liquor produced in each leach step.
It is preferred that the process of the present invention includes 2 or more of the leach steps summarised below which are tailored to selectively attack minerals so that each metal is recovered through a leach step (or steps) that is suitable to the minerals and the leach steps are complementary in terms of allowing materials transfer between them without one step being detrimental to and seriously interfering with the next step. The leach steps are set out below in order of increasing aggressiveness.
1. A ferric sulphate leach step to extract copper from chalcocite (Cu
2
S) in the sulphide ore or concentrate. This leach enables use of simple atmospheric reactors, gives good copper extraction, and allows regeneration of the leachate using bacteria or pressure oxidation of the liquor. This leach step will also dissolve part of any zinc that is present and some of the slightly more refractory copper minerals but is not ideally suited to high zinc feed. This leach does not dissolve gold or silver which remain in the residue.
2. A pressure oxidation leach in acid sulphate media with oxygen injection to extract zinc from sphalerite (ZnS). In the sulphide ore or concentrate as a first leach step or a leach step on the solids product of the ferric sulphate leach step. This leach step was originally developed by Sherritt-Gordon. This leach can also potentially dissolve copper from primary sulphides but is not very efficient for more refractory minerals such as chalcopyrite. Copper which leaches may be removed from the liquor with solvent extraction or alternatively may be precipitated into the residue by maintaining a moderately high pH (around 4) and then re-leached using one or other of the alternative leach steps. This leach does not dissolve silver or gold.
3. A mixed chloride-sulphate leach to extract copper from copper rich concentrates containing valuable levels of refractory sulphide minerals such as chalcopyrite in the sulphide ore or concentrate as a first leach step or as a leach step on the solids product of the ferric sulphate or the pressure oxidation leach steps and not amenable to leaching in sulphate-only systems. This leach step will dissolve virtually all copper sulphide minerals and zinc from sphalerite. Silver and gold remain in the residue.
4. A halex leach as described in the Intec process to extract copper, silver and gold from solids products materials. This leach step is described as part of the Intec process where it is used to leach chalcopyrite and produce copper powder through a chloride electrowinning step. This leach will dissolve all zinc and copper minerals as well as the silver and gold.
5. An oxidative acid sulphate high pressure, high temperature leach carried out at over 200C such that much of the sulphur present is converted to sulphate and copper and zinc present are leached into the liquor. This leach step has been described in numerous publications such as those, of Dreisinger, or as part of a Sherritt-Cominco process. Although this leach is more aggressive to the sulphur and copper than even the halex leach it does not dissolve the gold or silver. In the invention proposed it is potentially used as an alternative to leach step
3
in special circumstances where there is a wish to deliberately convert significant amounts of the sulphur to sulphate.
The capability of the more aggressive leach steps summarised in items
3
,
4
and
5
above to dissolve more of the valuable metals does not of itself mean that it is preferable to use them as a substitute for the multi-staged approach of the present invention. These more aggressive leach steps have penalties associated with the complexity of the leach and the cost of subsequent metal recovery. Leach steps
3
and
4
both include chlorides which prevent simple direct electrowinning of zinc and requires use of solvent extraction which is not to date very efficient
Andrews Melvyn
Technological Resources Pty. Ltd.
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