Electrochemical reclamation of silver from silver-plating wastewater using static cylinder electrodes and a pulsed electric field
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Silver was reclaimed from silver-plating wastewater by using a pulsed electric field (PEF) combined with static cylinder electrodes (SCE). The conditions that produced the maximal silver recovery rate (RRAg) (99%) were as follows: average retention time of 10 min. interelectrode gap of 50 mm, solution pH of 9.0, temperature of 45 degrees C, initial Ag(I) concentration of 1000 mg L-1, PEF pulse frequency of 1200 Hz, current density of 5.0 A m(-2) and a pulse duty cycle of 60%. Compared with the conventional direct current (DC) technology, the PEF process exhibited improvements in the silver recovery rate (RRAg), total energy consumption (TEC) and physical properties of the silver deposits, especially for low Ag(I) concentrations, for example, from 500 to 1000 mg L-1. For an initial Ag(I) concentration of 500 mg L-1. the PEF process produced an RRAg of up to 99%. and the TEC was 4.56 kWh (kg Ag)(-1). In comparison, the RRAg and TEC were 90% and 5.66 kWh (kg Ag)(-1), respectively, in the DC process. The results of SEM observation and XRD analysis indicated that the silver deposits formed by the PEF process were smaller, denser, and of a higher purity than those produced by the DC process. Therefore, the presented method was effective for reclaiming silver from silver-plating wastewater. (C) 2009 Elsevier B.V. All rights reserved.