International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Acid mine drainage waters polluted by iron, several non-ferrous metals (mainly copper, zinc and cobalt) and sulphates as the main pollutants were efficiently treated by a lab-scale passive system consisting of an alkaline limestone drain and a permeable reactive multibarrier connected in a series. The multibarrier was filled by a mixture of solid biodegradable organic substrates (mainly of plant biomass) and was inhabited by different metabolically connected anaerobic microorganisms (mainly different heterotrophs including some iron-reducing and sulphate-reducing bacteria). The effluents from this system were rich in soluble organic compounds and were treated in a microbial fuel cell in which consortium of electrochemically active microorganisms used these compounds as donors of electrons for electricity generation.

A sulphide flotation concentrate containing 15.2 g/t gold and 893 g/t silver finely disseminated in pyrite (4.1 % sulphidic sulphur in the concentrate) was treated by a two-stage process to recover these precious metals. Initially the concentrate was subjected to microbial oxidation by means of different acidophilic chemolithotrophic microorganisms (bacteria at 37 ^oC and archaea at 59 and 86 ^oC) to expose the precious metals encapsulated in the pyrite. The precious metals liberated in this way were then subjected to leaching by means of solutions containing different reagents (protein hydrolysate, thiosulphate, cyanide and some chemical oxidizers). The leaching was carried out in agitated reactors and up to 93.6 % of the gold and 80.8 % of the silver were solubilised in this way for 48 hours from a pulp density of 20 % at 57 ^oC.

Copper final slags containing 0.62% Cu, 1.07% Zn, 0.08% Co and 32.5% Fe as the most essential components were subjected to chemical (by means of sulphuric acid and ferric ions) and biological leaching by means of chemolithotrophic microorganisms of three different types: mesophilic and moderate thermophilic bacteria and extreme thermophilic archaea, with temperature optimum at 37, 55 and 75 degrees Celsius, respectively. The leaching was carried out by the shake-flask technique and in agitated bioreactors. The highest rates of extraction of the non-ferrous metals and iron were achieved by means of some archaea but at relatively low pulp densities (5 – 10%). The moderate thermophilic bacteria were the most efficient for the leaching at a higher pulp density (within 15 – 20%).