Research On Harmless Treatment With Acid Leaching And Resource Utilization Of Electroplating Sludge

Electroplating industry is an important basic industrial sector,the ultimate pollutant after heavy metal wastewater treatment in this industry is electroplating sludge.Electroplating sludge is classified as hazardous waste because of its high content of heavy metals.Harmless treatment of electroplating sludge is the basis and prerequisite for resource utilization.Acid leaching is an effective pre-treatment measure for resource utilization,but its harmless treatment effect and method need to be studied.Aiming at harmless treatment by acid leaching,this research selected three typical electroplating sludge samples,examined the amount of sulfuric acid added,temperature and liquid-solid ratio on the leach rate,residue mass and residual metal content of every sample among leaching process in detail,finally obtained the best leaching conditions for the harmless leaching: at normal temperature,liquid-solid ratio was 10,amount of sulfuric acid added were 0.5,0.75,0.4 mL/g for copper containing,chromium and nickel containing sludge respectively.Under the optimal leaching conditions,except the nickel in nickel-containing sludge residue,the metal content of the leaching residue is lower than the limit of the corresponding project of the lowest standard in the Environmental Quality Standard for Soils.After first sulfuric acid leaching,the nickel-containing sludge can achieve the harmless leaching standard after the leaching by 0.25 mL/g mixed acid of sulfuric acid and nitric acid with volume ratio of 1:2 assisted by 0.25 mL/g hydrogen peroxide.To get clean leaching residue,the residue after leaching needs to be cleaned by water.In this research,the optimal dilution factor was calculated as 2.7.Differ from the characteristics of the sludges,the cleaning stage can be determined according to concentration of the leaching solution.The last stage clean water can be recycled to the leaching process totally,which avoid the discharge of sewage.The optimum amount of sludge required for neutralize excess acid in three leachates were 20,40,50 g/L respectively,thus the excess acid in the leachate was fully utilized,which facilitated subsequent recycling.This research confirmed that the high concentration nickel-containing leaching solution could remove impurities by heating and adding calcium sulfate crystal seeds,and then recovered nickel sulfate with purity of 94% by concentrated crystallization.The iron in leachate can be removed by the yellow sodium iron sputum method and hydrolysis precipitation method.Then the copper in leachate could be recovered by electrodeposition,the chromium and nickel were recovered step by step through adjust pH of the leaching solution to 5.8 and 8.1 respectively,and zinc was recovered as an impurity in the nickel precipitation.The residual liquid can be recycled or discharged after being treated by the conventional method.In summary,this research achieved the aim of harmless leaching of electroplating sludge by means of sulfuric acid leaching and multi-stage countercurrent cleaning.The metals in the leachate can be chemically recovered after neutralized by sludge.