Pulps of 20% solids is prepared from -200 mesh pyrite concentrate (after froth flotation), and is inoculated with 5% (V/V) of adapted bacterial solution. The bioleaching tests is carried out in 250 ml Erlenmayer flasks, each contained about 220 ml pulp. The pulps is aerated with air bubbling at one liter per minute air flow rate, and is continuously agitated with a magnetic stirrer while the temperature was kept at 30 degrees C.
The bioleaching tests should be started at pH 2.0. The pH left to decrease during the tests, but not less than 1. Partial replacement of the leaching solution with water done by decantation at the rate of 25% by volume per day i.e., about 55 ml/flask/day. Distilled water is added to the leaching solution to compensate for the replaced solution and evaporation. Only partial re-inoculation with 1% (V/V) of adapted bacterial solution every third day is needed to compensate for lost bacteria.
Samples are withdrawn from the replacement leach solutions and analyzed to determine the dissolved metals by a Perkin-Elmer computerized atomic absorption spectrophotometer model 3030. At the end of the bioleaching test, the residues are collected, dried and weighed before use in cyanide leaching.….Read more