Flotation of mixed copper oxide and sulphide minerals with xanthate and hydroxamate collectors
Introduction
Many copper sulphide mines around the world have significant copper oxide ore reserves associated with the larger primary copper sulphide deposit. The traditional techniques for processing oxide ores, either by leaching – SX/EW or flotation have caused many problems for these operations. Leaching – SX/EW requires capital expenditure to construct a dedicated plant to process oxide ore. Until recently, flotation of copper oxides would normally have been conducted in distinct campaigns to produce a copper concentrate which may not be saleable under existing contracts. With the introduction of n-octyl hydroxamate as a complementary collector to traditional sulphide collectors, flotation plants can now process blends of sulphide and oxide minerals to produce saleable concentrates.
Generally copper oxide minerals do not respond well to traditional sulphide copper collectors and require alternative flotation techniques to concentrate the copper oxides. The classical method involves controlled potential sulphidisation (CPS) to sulphidise the surface of the oxide minerals by the addition of a sulphidisation agent, such as sodium hydrogen sulphide (NaHS). When NaHS is used for CPS the pulp redox potential (Eh) is reduced to a target value between −450 and −550 mV (versus a standard hydrogen electrode) (Soto and Laskowski, 1973, Jones and Woodcock, 1978). Other normal sulphidisation reagents used in this process are sodium sulphide (Na2S) and ammonium sulphide ((NH4)2S).
In principle CPS works well in a controlled environment of the laboratory for copper oxide minerals. When practised in a plant operation, CPS can often produce a variable response in oxide copper recovery. The main drawback of CPS is that the optimum dose of the sulphidisation agent is highly dependent on the time of conditioning, procedures of mixing and other variables, leading usually to poor reproducibility in a plant situation (Castro et al., 1974a, Castro et al., 1974b). Insufficient addition of the sulphidisation reagent will cause poor recoveries and an excess will cause the depression of oxide copper minerals (Lee et al., 1998). For mixed oxide and sulphide ores, CPS is unsuitable for simultaneous flotation of copper oxide and sulphide minerals, as the sulphides are usually heavily depressed by the sulphide ions from NaHS additions necessary to sulphidise the oxide copper.
A number of different collectors have been evaluated for oxide copper flotation without sulphidisation. They include organic complexing agents, fatty acids, fatty amines and petroleum sulphonates (Nagaraj, 1987, Deng and Chen, 1991). All of these collectors showed promise in the laboratory tests but they had limited success when applied to a plant situation (Lee et al., 1998). The limitation of some of these collectors is their lack of selectivity over carbonate gangue minerals, such as dolomite and calcite. It has been reported that the gangue minerals even float preferentially over the copper oxides (Deng and Chen, 1991).
The application of alkyl hydroxamate as a metal oxide mineral collector has been studied since the early 1940s. Popperle (1940) first patented the use of hydroxamic acids or their salts as collectors for ore flotation. Much research followed with the development of a number of different hydroxamate collectors. In the former USSR, a hydroxamic acid collector named as NM-50 was used as a collector for wolframite, cassiterite and rare metal ores (Gorlovskii et al., 1969). In the United States flotation of chrysocolla and hematite with n-octyl hydroxamates and some applications in platinum group metal flotation were studied (Peterson et al., 1965, Fuerstenau et al., 1967, Fuerstenau and Peterson, 1969, Nagaraj, 1992). Evrard and De Cuyper (1975) pioneered the use of alkyl hydroxamates for floating copper–cobalt ores in Africa. In the 1970’s, flotation studies in the laboratory and at plant levels were carried out on ores from China with basic hydroxamic acids and other compounds with different non-polar groups, such as naphthenic, oleoyl, tallol, abietic and salicyl hydroxamic acid (Kong et al., 1984).
Since the latest mining boom over the last few years, many copper oxide deposits have become economic to operate and interest has been generated in using alkyl hydroxamates where traditional processing techniques using sulphidisation have failed to produce consistent plant recoveries. Several operations are currently using the alkyl hydroxamates that have been developed by Ausmelt. The Ausmelt alkyl hydroxamate is synthesised and supplied as an alkaline chemical, which differs from other hydroxamate collectors on the market. The stereochemistry of Ausmelt’s alkyl hydroxamates has been studied to show that the hydroxamate exists with the oxygen atoms in a cis- (or Z-) structure relative to the C–N bond.
In the research reported here, the flotation response of the Minto sulphide ore with xanthate collector, the oxide ore with hydroxamate collector and a blend of sulphide and oxide ores using a mixture of xanthate and hydroxamate collectors was determined. The response for the blend was compared with the corresponding performance when only xanthate was used following CPS near the optimum potential.
Section snippets
Samples tested
Three separate composite samples were tested, namely sulphide composite which was composed from Minto’s sulphide ore, oxide composite which was composed from Minto’s oxide ore and the blend composite which was composed by blending the sulphide and oxide ores at a ratio of 70:30, respectively.
Reagents
Reagent grade chemicals were used for all experiments. The frother used was methyl iso butyl carbinol (MIBC) which was provided by Orica Mining Services. The collectors, potassium amyl xanthate (PAX) and
Optical microscopy
Sulphide Composite: The copper was present in the composite as bornite and chalcopyrite containing magnetite inclusions. The mineralisation was hosted by foliated granodiorite or gneiss. Higher-grade mineralisation often occurs in quartzo-feldspathic gneiss, biotite quartz feldspar gneiss and siliceous gneiss which are similar to the foliated granodiorite apart from the added minerals implied in their description and more intense foliation.
Oxide Composite: The copper was present in the
Conclusion
An advantage of treating sulphide/oxide blends is that many operations have commitments to produce a concentrate at a minimum sulphur and copper content, which may not be achieved if the ore types are treated independently. Traditional sulphidisation flotation techniques, which are widely used on copper oxide ore, can not be used in sulphide/oxide blends for simultaneous sulphide and oxide copper flotation as the sulphidising reagent will suppress the flotation of sulphide minerals as shown
Acknowledgement
Thanks are given to the Minto Mine and Mr. Dave Archibald for the samples and for permission to publish this work.
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