Removal and recovery of metal-cyanides from industrial effluents

摘要

Biosorption of metal-cyanide complexes viz. tetracyanocuprate(II) {(Cu(CN)_4)_~(-2)} (TCC) and tetracyanonickelate(II) {(Ni(CN)_4)~9-2}} (TCN) from solutions was studied using different fungal biosorbents. Optimum sorption of TCC and TCN by the biosorbents tested occurred at pH 4.0. Among the cultures used, Cladosporium cladosporioides showed maximum loading capacity (40 #mu#mol/g and 34 #mu#mol/g for TCC and TCN, respectively) which was higher than activated charcoal. Further studies on C. cladosporioides showed that rate of uptake of TCC and TCN was maximum in the first 15 mm (>50 percent), though equilibration of the system was achieved in 30 min. Uptake of both the metal-cyanide complexes was found to increase linearly as a function of initial metal-cyanide concentration up to 1.75 mM. The data could be fitted to Langmuir and Freundlich models for adsorption processes. Adsorbed TCC and TCN could be desorbed using 1 M NaOH with more than 95 percent efficiency. Concentrations achieved in the eluant were 38 (TCC) and 32 (TCN) fold of the original, respectively. The traces of metal-cyanide complexes remaining in solution after biosorption were completely biodegraded by a bacterial consortium in 5-6 h. The treated solution fully conformed to the disposal standards prescribed by statutory agencies.