Purification of chromium(VI) finishing wastewaters using calcined and uncalcined Mg-Al-CO3-hydrotalcite

The applicability of calcined and uncalcined hydrotalcite for the purification of industrial effluents has been studied using chromium finishing wastewaters. Using a batch method, the influence of the initial concentration of chromium (10-450 mg/l), hydrotalcite (HT) dose (0.5-5 g/l) and time (0.5-72 h) has been evaluated. The process could be described by the Langmuir model and gave a maximum removal of chromium of 16.3 mg Cr(VI)/g on uncalcined HT and 128 mg Cr(VI)/g on calcined hydrotalcite (C-HT). Removal using the calcined product provided an effective system to treat chromium finishing wastewaters with the most stringent discharge limit for such industrial streams being achieved with between two and four consecutive removal cycles on C-HT at a dose of 2 g/l.