Harmless treatment experiment and dynamic analysis of chromium eletroplating sludge

We studied the leaching rate of chromium from sludge of electroplating wastewater in a surface treatment industrial park through leaching and recycling heavy metals to achieve the harmless and recycling purpose.The sludge was dried,grinded and leached in sulfuric acid solution with different concentrations,and the leaching time and temperature and stirring speed were under strict control.Suction filtration was applied to separate the lixivium from residue after leaching.Orthogonal experiment demonstrates that the order of factors that impact the chromium leaching effect is sulfuric acid concentration stirring speed leaching timesolid-to-liquid ratio.The results of single factor experiment show that the highest leaching rate of chromium is achieved when leaching temperature is 25℃,solid-to-liquid ratio is 1∶15,leaching time is 20min,stirring speed is 800r/min and volume fraction of sulfuric acid is 30%.Finally,sodium jarosite was applied to remove iron;sodium pyrosulfite was applied to reduce chromium VI and sodium hydroxide was applied to precipitate such heavy metal as chromium and nickel step by step,whereas zinc stayed in the solution.The study of leaching kinetics of chromium leaching from electroplating sludge reveals that the reaction order of sulfuric acid as a leaching agent is 1 and its reaction speed constant is k=0.053 2e-4.52/RT.