Cleaning Treatment Of Tannery Waste Sludge

Huge amount of sludge was produced from tannery waste water treatment,which was considered hazardous solid waste due to the existence of chromium.With the improvement of environment protection requirement incineration used for tannery sludge treatment has attacted much attention.Because it has several advantages such as significantly reduce the volume of sludge,completely estimate the pathogens and reduce the toxicity of chromium containing salts.However the incineration may lead to chromium chemical valence transformation,which from low-toxic chromium to carcinogenic hexavalent chromium.Therefore,it is significant to explore the change of chromium existed in ash.This paper summarized the previous research methods and results and used the sulfuric acid extraction to treat tannery sludge incineration ash.The aim was to reduce the environment risk of tannery sludge,while improve the feasibility of chromium recycling in future.Tannery sludge sample of this study was collected from a tannery industry in Jinhai Tianjin.Ash samples were produced by incineration in the muffle furnace.Element analysis showed that calcium and chromium were two main elements in the ash,the concentration reached 393 mg/g and 122 mg/g respectively.The sulfuric acid extraction condition was optimized including concentration of sulfuric acid,temperature,time,ash concentration of solution,calcium content of the ash,which all had a effluence on the chromium extraction.Afterwards,sulfuric acid concentration,temperature,time and ash concentration of the solution were further optimized.The result showed that the sequence of these four factors was sulfuric acid concentration>temperature>ash concentration of the extraction solution>time.The optimal combination was 5mol/L of sulfuric acid concentration,80 ?of temperature,135 g/L of ash concentration of the extraction solution and 70 min of time.Extraction ratio R(CE/CCr×100%)reached 75.8%under the optimal condition.At last,verification test was conducted under the optimal condition.According to National Standards requirements the results showed that chromium concentration in the leachate was lower than 0.5 ?g/g and the leaching level of all metals could meet the requirement of the state standard.This study proved that the stabilization of ash substantially had been raised by sulfuric acid extraction treatment,and the environment risk was reduced significantly.It provided a new method for tannery sludge treatment and the chromium was recycled and reused hopefully.