Bacterial Activity at Low Temperature in Cultures Derived from a Low-Grade Copper Sulphide Bioleaching Heap at the Escondida Mine, Chile

Abstract

The majority of mining companies in the north of Chile that use biohydrometallurgical processes to leach low-grade copper sulphide ore are located in the high Andes. This makes the study of the effect of low temperature on bacterial activity important for the design and optimization of the bioleaching process. In this study bacterial activity of iron and sulphur oxidizing microorganisms was analyzed in the laboratory at various temperatures. Flask tests were carried out at a range of temperatures to determine the bacterial activity in pregnant leaching solution (PLS) from a pilot plant at the Escondida Mine. Ratkowsky curves were constructed by monitoring the concentration of ferrous iron and acid production during the tests. Also leaching tests were carried out at ~10 and ~20°C on a 1 m column using a copper ore sample. In an industrial solution in flask tests, iron oxidizing activity was observed until the temperature was reduced to 20°C. In the same culture, after an adaptation process, iron oxidizing activity was observed down to 5°C. In the column tests, 41.2% of copper was recovered after 91 days of leaching at 10 °C and 57.2 % at ~20°C. Predominant 16S rRNA gene sequences were related to Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferriphilum.