2.1.2. Metal complexes
Synthetic bioleaching solutions were prepared using analytical-grade reagents; Ni(NO3)2·6H2O and Co(NO3)2·6H2O Sigma–Aldrich metal salts and citric, dl-malic and lactic organic acids (Bonnet, Australia). Metal solutions with concentrations from 15 to 2000 mg/L were prepared using 0.01 and 0.1 M of organic acid solutions. These concentrations are typical of the acids produced by fungi microorganisms [1,18]. Acid concentrations of 0.01 and 0.1 M typically generated solution pH of 2.2 and 1.8 in citric acid, 2.8 and 2.0 in malic and 2.6 and 1.9 in lactic acids.