Extraction of chromium from tannery sewage sludge

The leather industry produces a large amount of tannery sewage sludge every year, which is a dangerous solid waste, but also a secondary resource. In the present research, the extraction of chromium from the tannery sewage sludge was investigated through the process of blank roasting-sodium carbonate roasting-water leaching and the process of sulfuric acid curing-water leaching, respectively. The process of sulfuric acid curing-water leaching was characterised by high extraction of chromium, a simple process as well as low cost of mineral decomposition, which made it the better option. For the process of sulfuric acid curing-water leaching, the leaching of chromium reached up to 99.5% under the optimum conditions of sulfuric acid curing (raw tannery sewage sludge cured at room temperature for 5 min with 42 wt% sulfuric acid addition), followed by water leached at 100°C for 30 min with a liquid/solid ratio of 2 mL/g