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THE USE OF NOVEL BIO OXYDATION TECHNIQUES IN THE HYDROMETALLURGICAL TREATMENT OF MIXED SULPHIDE ORES.

Objective

THE APPLICATION OF THE NOVEL BIO-OXIDATION TECHNIQUES IS AN INNOVATIVE APPROACH TO THE SOLUTION OF THE COMPLEX PROBLEMS POSED IN THE TREATMENT OF THE OLYMPIAS PYRITE DEPOSITS. SIGNIFICANT COMMERCIAL ADVANTAGES MAY BE OFFERED BY THE USE OF THE BIO-OXIDATION TECHNOLOGY AS THE CAPITAL AND OPERATING COSTS OF A PLANT OF THIS TYPE MAY BE LOWER THAN THOSE USING CONVENTIONAL TREATMENT.
Optical observations of polished sections before and after bacterial oxidation indicate the preferential attack of boulangerite and arsenopyrite compared to pyrite. The variation in gold and silver recovery under differing oxidation conditions indicates that the gold and silver values are segregated into different mineral phases.
The preferential attack of boulangerite and arsenopyrite may be attributable to ferric iron attack, while pyrite oxidation is also associated with direct bacterial contact onto the mineral surface. Preferential arsenopyrite dissolution becomes more evident at higher pulpdensities. It has been shown that an optimum pH range around 1.2 may exist for the biooxidation system utilised. The testwork has indicated that a residence time distribution of between 5 and 8 days is required, for the system examined, to achieve the desired degree of sulphur oxidation and hence gold recovery. However, due to the preferential oxidation of arsenopyrite and the differing conditions required for selective arsenopyrite and pyrite oxidation, the actual residence time employed for any given system will be a function of the pyrite, arsenopyrite ratio and gold distribution between these two mineral phases.

Due to the highly refractory nature of Olympias pyrite concentrates, an oxidative pretreatment step is required to render gold amenable to the subsequent cyanide leaching. To exploit this resource research has been carried out into the potential use of the bacterial oxidation process either as an alternative or in conjunction with the commercially used aqueous pressure oxidation process.
State of the art analytical techniques were used to identify the mode of gold occurrence within the concentrate and several parameters critical to the operation of biooxidation processes were evaluated.

Results indicate that biooxidation techniques may be applied to many pyritic ores and concentrates since the mechanisms of bacterial attack on arsenopyritic and pyritic materials have been clearly identified.
With this information it is possible to design a biooxidation system to meet the requirements of a particular feed material. However, testing of a proposed feed material will be required to comfirm the design parameters.
THE RESEARCH AND DEVELOPMENT WORK WILL PROVIDE AN INDICATION OF THE TECHNICAL VIABILITY OF BIO OXIDATION AS AN ALTERNATIVE METHOD FOR THE PRE-TREATMENT OF THE GOLD BEARING REFRACTORY OLYMPIAS PYRITIC DEPOSITS.

THE RESEARCH IS DIVIDED INTO FOUR STEPS:
- STUDY OF THE MINERALOGICAL CHARACTERISTICS OF THE OLYMPIAS PYRITE ORES;
- BIO OXIDATION TESTS USING AIR STIRRED PACHUCHAS AND MIXED BACTERIAL CULTURES;
- IN PARALLEL: CYANIDATION TESTS AND STUDIES ON THE NATURALLY OCCURING BACTERIA;
- OPTIMIZATION OF THE BIO-OXIDATION REACTOR;
- EVALUATION OF THE RESULTS;

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Davy McKee Ltd
Address
Ashmore House
TS18 3RE Stockton On Tees
United Kingdom

Participants (1)

Aegean Metallurgical Industries SA
Greece
Address
1,Eratoshenous Street
11635 Athens