Bioleaching of gold and copper from waste mobile phone PCBs by using a cyanogenic bacterium

Chromobacterium violaceum (C. violaceum), a cyanide generating bacterium has been used to leach out gold and copper from the waste mobile phone printed circuit boards (PCBs) containing ∼34.5% Cu and 0.025% Au in YP (yeast extract and polypeptone with glycine) medium. The bioleaching was carried out in an incubator shaker (150 rpm) at 30 °C and 15 g/L pulp density in the pH range 8-11. Dissolution of gold and copper increased from 7.78% (0.225 ppm) to 10.8% (0.46 ppm) and 4.9% (419 ppm) to 11.4% (879 ppm) in 8 days with increase in pH from 8 to 11 and 8 to 10 respectively. Supplementing oxygen with 0.004% (v/v) H₂O₂ increased the copper leaching to 24.6% (1743 ppm) at pH 10 in 8 days whereas improvement in gold leaching was insignificant with the recovery of 11.31% Au at pH 11.0. The waste PCBs can thus be recycled in environmental friendly manner.     

Evaluation of equilibrium, kinetic and thermodynamic parameters for biosorption of nickel(II) ions onto bacteria strain, Rhodococcus opacus

The present study explores the ability of Rhodococcus opacus bacteria strain for the removal of nickel(II) under different experimental conditions. The effects of relevant parameters such as solution pH, biomass loading, ionic strength, and temperature on nickel(II) biosorption capacity were evaluated. Although the tests were carried out using synthetic solutions, the results are representative of typical waste effluents from chemical, dyestuffs, battery manufacture, porcelain enameling, metallurgical industries and electroplating circuits. The sorption data followed the Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, and Sips isotherms. The maximum sorption capacity was found to be 7.63 mg g⁻¹ at pH 5. Thermodynamic parameters have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The dynamics of the sorption process were studied and the values of rate constants for different kinetic models were calculated. The activation energy of biosorption (E_a) was determined as 12.56 kJ mol⁻¹ using the Arrhenius equation.