University of Mining and Geology “St. Ivan Rilski”
Doi
Abstract
Laden leach solution, generated from bioleaching of pyrometallurgical copper slags with a mixed culture of moderately thermophilic bacteria in a bioreactor, contains several base metals (Cu, Co, Zn) and a very high concentration of iron (33,9 g/ L). Further processing of cobalt and zinc to the respective final products requires preparatory iron removal from the laden leach solution. The direct iron removal from that solution as goethite was unacceptable because of the significant co-precipitation of copper and cobalt from the solution. The main aim of this paper is to study magnetite (Fe3O4) synthesis as an approach for iron removal to a value-added product as a step of the processing of a laden solution generated due to the bioleaching of non-ferrous metals in a bioreactor. Ferrous iron oxidation to ferric state was efficient when the addition of H2O2 (30 %) was combined with maintaining the pH 3,1-3,3 with NaOH and air purging. Solvent extraction with 25 % D2EHPA and 7,5 % TBP dissolved in kerosene efficiently separated the dissolved iron and the base metals from the processed solution. However, in the presence of H2, the iron was stripped from the organic solvent with low acid consumption. The applied precise control of the chemical precipitation and oxidation processes at 50 degrees Celsius allowed the iron content (11,7 g/ L) in the stripping solution to be removed efficiently as magnetite (Fe3O4). Based on the chemical content of iron, copper and sulphur, the synthesised nanoparticles of magnetite could be applicable in many sectors (steel, chemical, and electronics)
