BIOLOGICAL TREATMENT OF GOLD ORE CYANIDATION WASTE-WATER IN FIXED-BEDREACTORS

The treatment of a cyanidation effluent containing thiocyanate, free c yanide, and complexed cyanide was continuously performed for a period of 6 months. Activated carbon, pozzolana, and a mixture of pumice ston e and zeolite were tested as supports in fixed bed reactors. Activated carbon adsorbed the different forms of cyanide. In contrast, the othe r supports did not remove any pollutants from the effluent during an a dsorption experiment. All supports successfully allowed fixation of ba cteria. More than 90% of the thiocyanate was biologically decomposed i nto NH4+, CO2 and SO42-, even when increasing the feed flow-rate and t he pollutant concentrations. Free and complexed cyanides were eliminat ed, probably through a combination of precipitation and biological deg radation. The oxidation of ammonium into nitrate was only performed by the activated carbon-containing column and with the more diluted feed ing. The nitrification process was inhibited in all reactors when the cyanide concentrations and feed flow-rates were increased. (C) 1997 El sevier Science Ltd.