Appraisal of the Laboratory-Scale Tests for Bioleaching of Low-Grade Heavy Metal-(oid) s Resources

Today, various methods such as bioleaching are increasingly used to remove toxic and reuse useful metals from low-grade ores and tailings. Bioleaching is an ecologically based technique carried by iron or sulfur-oxidizing bacteria, which convert insoluble metal sulfide to soluble metal sulfate. The purpose of this study was to test and compare two different methods, including Flask and Column experiments, to remove Zinc, Copper, Arsenic, and Iron. The materials were the same in both tests; inoculum came from the tailings of Neves-Corvo Mine, and the mineral sample was collected from Panasqueira Wolfram-Tin mine. Firstly, the cultures were tested for metal resistance and adapted by 3-day transference, adding sodium thiosulfate as an energy source supplement. Secondly, bioleaching tests were conducted in Flasks and Columns in 35 and 30 days, respectively. Finally, samples were taken to evaluate particle size, chemical compositions, bacterial growth, pH, oxidation–reduction potential (ORP), sulfate concentration, and metal content in the leachate. Besides, the Scanning Electron Microscope (SEM) pictures proved the existence of bacterial cells during the bioleaching tests. The results indicated that the Flask tests were superior to Column experiments in removing Zinc, Arsenic, and Copper from the mineral ore samples. However, Column experiments showed better results in the recovery of Iron in comparison with Flask tests.