Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing single metal
Patent
1998-01-06
1999-11-30
Valentine, Donald R.
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing single metal
205580, 205581, 205584, 205607, C25C 120
Patent
active
059936355
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of enabling a sulphide mineral composition to be leached at atmospheric pressure instead of above atmospheric pressure which has been hitherto required in order to achieve acceptable rates of leaching.
BACKGROUND ART
Sulphide minerals such as copper, nickel, zinc, gold and the like are recovered from their ores by a number of well known processes. One such process uses the relative solubility of the mineral in solution to allow the mineral to be leached from the ore. Conventional leaching processes require expensive equipment and a high level of technical expertise to maintain and use the equipment. Thus, it is not uncommon for an oxidative hydrometallurgy leaching plant to be located some distance away from the ore body and even in another country. This in turn significantly increases transportation costs, and it should be realised that transportation of ore or only partially enriched ore containing perhaps only a few percent of the desired mineral is extremely wasteful and undesirable, but in the absence of being able to recover the metal of value from the minerals on-site, there is little real alternative.
The processing methods of oxidative hydrometallurgy are commonly used in many different applications. Due to the refractory nature of many of the mineral species treated in such processes, these applications generally require leaching conditions of high temperature and pressure and require substantial supplies of oxygen. For example, base metals such as copper, nickel and zinc can be recovered by hydrometallurgical processes which usually embody pretreatment, oxidative pressure leaching, solid/liquid separation, solution purification, metal precipitation or solvent extraction and electrowinning.
According to conventional technology, oxidative leaching processes usually require very aggressive conditions in order to achieve acceptable rates of oxidation and/or final recoveries of metal. Under these conditions, which often mean temperatures in excess of 150.degree. C. or alternatively temperatures in the range 150-200.degree. C. and total pressures in excess of 1500 kPa, the chemical reactions which occur use large quantities of oxygen, both on stoichiometric considerations and in practice where amounts in excess of stoichiometric requirements are used due to process inefficiencies.
An example of oxidative hydrometallurgy is the treatment of refractory gold ores or concentrates. Refractory gold ores are those gold ores from which the gold cannot readily be leached by conventional cyanidation practice. The refractory nature of these gold ores is essentially due to very fine (sub microscopic) gold encapsulated within the sulphide minerals. This gold can often only be liberated by chemical destruction (usually oxidation) of the sulphide structure, prior to recovery of the gold, which is usually done by dissolution in cyanide solution. Of course, other lixiviates such as thiourea and halogen compounds and the like may also be used.
A number of processing options are available for treating refractory gold ores which contain sulphide minerals like pyrite, arsenopyrite and others. Pressure oxidation, typified by the so-called Sherritt process, is one such process which typically consists of the steps of feed preparation, pressure oxidation, solid/liquid separation, liquid neutralisation and gold recovery from oxidised solids usually by cyanidation.
A cryogenic oxygen plant is usually required to supply the substantial levels of oxygen demand during the pressure oxidation step, which is the heart of the Sherritt process. Typically, the conditions for the pressure oxidation step require temperatures in the region of 150.degree. C. to 210.degree. C., a total pressure of 2100 kPa, a pulp density equivalent to 20% to 30% solids by mass, and a retention time of two hours to three hours.
The typical oxidative hydrometallurgical processing methods referred to above generally have oxidation reactions that are carried out in multicompartment autoclaves fitted
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Holzberger Ian Raymond
Hourn Michael Matthew
Turner Duncan William
Highlands Frieda Pty. Limited
M.I.M. Holdings Limited
Smith-Hicks Erica
Valentine Donald R.
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