Removal of cyanide by anodic oxidation for wastewater treatment

The aim of this work was to investigate the feasibility of using a bipolar trickle tower electrochemical reactor consisting of graphite Raschig rings as the electrodes to remove cyanide from a cyanide containing effluent. Dir ect and indirect methods were both found to be efficient for removing the c yanide in either continuous or recirculating batch modes. The cyanide conce ntration in the solution was reduced from 1500 to less than 60 mg l(-1) and from 1000 to less than 30 mg l(-1) with an energy consumption in the order of 18.4-26.8 kW h per kg cyanide removed during continuous operation. In t he case of a cyanide concentration of 300 mg l(-1), full removal of cyanide was achieved with an energy consumption of 78.5 kW h kg(-1). However, less than 30 mg l(-1) could be achieved with an energy consumption of 8.75 kW h kg(-1) for this initial concentration. During treatment the rate of remova l decreased as the concentration decreased with time. More energy was used to reduce the cyanide content from 30 mg l(-1) to zero (70 kW h kg(-1)) tha n to reduce the cyanide concentration from 300 to 30 mg l(-1) (8.75 kW h kg (-1)). Moreover, the cyanide content could be reduced from 1500 to less tha n 300 mg l(-1) with quite a low energy consumption (3 kW h per kg of CN rem oved, i.e. 3.6 kW h per cubic metre of effluent treated). Full removal of c yanide has also been achieved for all initial cyanide concentrations during the recirculating batch operation. The energy consumptions for these exper iments were 5.15 for 300 mg l(-1), 5.14 for 1000 mg l(-1) and 6.3 for 1500 mg l(-1) in kW h per kg cyanide removed. The mass transfer coefficient for this reactor was also determined with an average value of 4.35 x 10(-4) ms( -1) being obtained. This is a typical value for such a cell. (C) 1999 Elsev ier Science Ltd. All rights reserved.