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HIGH TEMPERATURE BIOLEACHING OF COMPLEX MINERAL SULPHIDES

Objective

The overall objective is to obtain rapid and efficient extraction of copper and zinc, lead and possibly precious metals, through biohydrometallurgical processing of complex mineral sulphide from Spain and Portugal by using thermophilic bacteria.
Research has been carried out in order to obtain rapid and efficient extraction of copper, zinc, lead and possibly precious metals in some cases, through biohydrometallurgical processing of complex mineral sulphides from Spain and Portugal using thermophilic bacteria.

The RTM concentrate contains major chalcopyrite, sphalerite and pyrite with lesser amounts of other sulphides, sulphosalts and quartz. The growth of Sulfolobus strain BC at up to 47.5 g copper/l has been achieved and a leach rate of 69 mg copper/(l h{-1}) has been achieved using a 5% w/v copper concentrate in the presence of 28 g copper/l. Some success with preparing pure cultures from the high temperature Iceland culture (HTIC) and the N(mixed) culture has also been achieved.

Chronoamperometric and chronocoulometric experiments have been carried out to investigate the changes in current and charge under constant potential. Passivation of chalcopyrite but not of pyrite is observed.

Shake flask tests using RTM concentrate in the presence of potential catalytic ions have shown that the presence of bismuth ions can increase the total extraction of copper and zinc by adapted Sulfolobus BC although the lag phase of the cycle is extended.
The attachment of Sulfolobus to ore particles is rapid occurring within about 30 min of contact. Semicontinuous bioleaching has been used to study the bioleaching of RTM concentrate and Copper extractions of about 50% have been achieved.

A literature survey has been carried out on the influence of solids concentration on the effectiveness of bioleaching and a model leaching plant has been designed. The need for high power input to maintain oxygen transfer for processing at high solids concentration has also been highlighted. Finally pulsed field gel electrophoresis has been used to carry out genetic investigations of Sulfolobus strains.
Specific tasks are to:
obtain, characterize and provide suitable mineral samples for the project requirements;
isolate, examine and exploit new or better strains of suitable thermophilic leaching bacteria and provide cultures to the other partners;
study electrochemical aspects of the bioleaching of complex sulphide in order to improve the leaching kinetics;
evaluate leaching kinetics and quantify and overcome potentially inhibiting process factors (eg shear stress and metal inhibition);
and genetic studies and molecular characterization of leaching bacteria.

The project is based on 5 work packages: minerals, bacteria, electrochemical, kinetics, and genetics.

In the minerals stage, the type of material (eg ore and concentrate) and the amount will be identified through:
sampling and ore selection (complex or noncomplex sulphide);
blending and preparation of samples;
chemical analysis and size distribution;
mineralogical studies;
an intensive programme of laboratory scale flotation test work and determination of best conditions to achieve different concentrates (bulk and selective);
chemical and mineralogical studies and size distribution in each concentrate;
and metallurgical balance.

In the bacteria stage, methodology and work divide into 4 areas:
provision of cultures to other laboratories;
new strain isolation and first stage screening;
second stage screening of selected strains;
and screening for selected strain improvement.

The electrochemistry stage involves:
more fundamental nature of the electrochemical changes in the mixed sulphide with special reference to the effects of ferrous and ferric iron;
and examination and quantification of the possible beneficial effect on mineral dissolution of ions such as silver, mercury, cobalt and bismuth.

The kinetics stage looks at physiology and inhibition factors. The identification and quantification of the effects of potentially inhibiting factors such as shear, pH and other stress factors and the evaluation of leaching kinetics will be carried out. This will involve:
shear stress studies;
mineral attrition studies;
continuous bioleaching;
clean technology
evaluation of the molecular and kinetic microbial characteristics of relevance to bioleaching;
characterization of stress state by the influence of pH, temperature and solid concentration;
and study of highly charged continuous or semicontinuous reactors.

The genetics stage will involve:
growth of bacterial cultures;
plasmid preparation and analysis;
structural studies of interesting plasmids;
chromosomal deoxyribonucleic acid(DNA) preparation and genome structural characterization;
and studies on the microorganisms genomic organisation and isolation of genomic sequences involved in bioleaching related processes.

Coordinator

Warren Spring Laboratory
Address
Gunnelswood Road
SG1 2BX Stevenage
United Kingdom

Participants (4)

NATIONAL LABORATORY FOR ENGINEERING AND INDUSTRIAL TECHNOLOGY
Portugal
Address
Estrada Do Paco Do Lumiar 22
1649-038 Lisboa
Río Tinto Minera SA
Spain
Address
Minas De Río Tinto
21071 Huelva
Universidad Complutense de Madrid
Spain
Address
Pabellón De Gobierno
28040 Madrid
Universidad de Sevilla
Spain
Address

41012 Sevilla