Biooxidation Case

OBJETIVE

Establish at a laboratory scale the parameters of the process of Biooxidation of arsenopyrite and pyrite concentrate from the La Demajagua mine and the treatment arsenical residuals, as a way to enhance the extraction of gold and silver with minimum environmental impact.

HYPOTHESIS

Through the process of Biooxidation using the bacteria Acidithiobacillus ferroxidans, the efficiency of extraction of gold and silver from Cuban refractory ores will increase.

SPECIFIC OBJECTIVES

* Determine the effect of solid percentage of the concentrate and the microorganism Acidithiobacillus ferroxidans adaptability in its growth.

* Obtiene an active microorganism culture capable to oxidize arsenopyrite and pyrite.

* Reduce the presence of (iron, sulphur, antimony, arsenic) through Biooxidation of the concentrate to guarantee an efficient cynadation.

* Define the parameters of Biooxidation in the stirred tank.

* Establish the treatment process of arsenical residuals.

* Demostrate the effectiveness of Biooxidation in the enhancement of cynadation.

A detailed research on biomining and the occurrence of refractory ores was carried out. The governmental regulations on emission of poisonous gases and those who can indirect contribute to global warming, has forced a shift from pyrometallugical technology which oxidizes and emit sulphur as sulphur dioxide and volatilize metals like arsenic to the atmosphere, which are responsible for the refracteriedad of these minerals, to more environmental friendlier ones like microbial oxidation. With Mintek being one of the pioneers of the use of microorganism to open the structure of these refractory ores so as to allow the leaching agent to reach the encapsulated gold and silver, a lot of actualized bibliography from Mintek was used and some from Professor Lawrence R.W from the University of British Columbia had a great contribution to the success of the project and others more.

The project was carried out in a period of six months, and the parameters which their effect on Biooxidation were being studied in agitated tanks were: Acidity, presence of iron (II), solid percentage of the concentrate in the culture medium.

Parameters of study were as follows:

Parameter Variable Maximum Minimum Central point

%Solid X1 20 10 15

Acidity X2 2,2 1,8 2,0

Concentration of Fe(II) g/L X3 4 0 2

A factorial experimental design was done 23 and 8 agitated tanks were mounted, with all the possible combinations and 3 others with condition of the central point to determine possible errors and one control without microorganisms. My Y values, which were to be determined after, the experiments were: % Extraction of Sulphur, %Ex.Ars, %Ex.sb, Ex.Fe.

After processing the experimental data in STATGRAPH 5.0, the following results were obtained.