Selective recovery of Cr and Cu in leachate from chromated copper arsenate treated wood using chelating and acidic ion exchange resins

Abstract

The purpose of this study was to selectively remove chromium and copper from CCA-treated wood acid leachates (initial concentrations of 447–651 mg As l −1, 374–453 mg Cu l −1 and 335–622 mg Cr l −1) using ion exchange resins and precipitation techniques. Batch experiments revealed that the chelating resin Dowex M4195 had a high copper selectivity in the presence of chromium while the Amberlite IR120 resin had a high chromium sorption capacity. Combining M4195 and IR120 resins in four successive columns, made with Plexiglas tube, led to 96% copper extraction and 68% chromium extraction. NH 4OH (4 M) efficiently eluted copper from the chelating resin while H 2SO 4 (10% v/v) was used for IR120 resin elution. Copper and chromium recovery by elution reached 94% and 81%, respectively. Successive sorption and elution steps using M4195 and IR120 ion exchange resins presented similar metal removal capacities over the five cycles. No resin deterioration was observed but the results suggested arsenic bulk diffusion into the M4195 resin. Successive treatments of CCA-treated wood leachate with M4195 and IR120 allowed for copper and chromium removal while arsenic could be extracted by coagulation treatment with ferric chloride and precipitation with Ca(OH) 2 at pH 5.7. This final process led to 99.9% arsenic removal. The final effluent contained less than 1 mg l −1 of arsenic, chromium and copper.