The Recycling And Using Of Chromium From Polymetallic Electroplating Sludge

In order to recycle valuable metallic chromium from electroplating sludge, in this research the sludge come from one of the Electroplating industry in Guiyang and Sampling, Drying, roasting, leaching and separation methods was used during the process of recycle the chromium. The optimum leaching condition, separation and recycling method was determined, and then obtained chromium product inspection.The physicochemical properties of electroplating sludge samples were studied. Sludge-like natural moisture content of air-dried to 83% and pH 11.8 was obtained. Based on the amount of solid waste determination and ICP-MS methods, the Heavy Metal Fe, Cr and Zn contents were: 3.18%, 5.39%, 3.55%, respectively, were measured in electroplating sludge. Also obtained the rate of loss on ignition within sludge samples was 17.94%, after firing the rate of three heavy metals Fe, Cr, Zn in electroplating sludge contents were: 3.92%, 6.64%, and 4.37%, which laid the foundation for the determination of electroplating sludge recycling process.Wet electroplating sludge recycling heavy metals, is an important step in the leaching of heavy metals in the sludge, the first step is to determine the optimum leaching process and a method for the separation and purification of leachate. Selection HCl and NaOH as the leaching agent, by using single factor and orthogonal experiment and finally determined NaOH as the leaching agent, by using NaOH as the single factor and orthogonal experiments optimum leaching conditions: the amount of NaOH was 2.2ml,stirring time was 70 min,leaching temperature was 30 ?, liquid-solid ratio was 10: 1. In those optimum conditions to do the expand experiments to obtained the leaching rate of Cr, Zn were 95.10%, 93.23% respectively. Choose precipitation metholds to separation Zn from NaOH leaching solution. Choose the methold of adjusting the pH of a solution to precipitate zinc, before adjusting the pH precipitate the zinc needs to oxide from Cr??? to Cr???, then adjust the pH and the zinc to be removed by using a single factor?30% H₂O2, oxidation time and oxidation temperature? experiments to determine 30% H₂O2 dosage 10 m L, oxidation time is 2h and the oxidation temperature is 50 ? to the best oxidation efficiency 99.8%. Then adjust the pH of solution precipitate zinc by using single factor?p H, mixing time, temperature? experimentally determined in pH is 9, stirring time 10 min, temperature 35 ? the precipitation rate of Zinc up to 99.6%.In order to achieve recovery of chromium electroplating sludge, add the production of precipitated barium chromate, barium salt and the chrome recovery in the separation and purification of the chromium-containing cleaning fluid. The optimum conditions for the recycle of chromium obtained: When take filtrate solution of Zinc under the conditions that leaching 10 m L, add BaCl₂.2H₂ O solution 10 mL 0.25mol/L, the pH of solution is 9, stirring 10 min and temperature of 35? the recycle rate of chromium about 99.6%. By measuring the index of barium chromate content in the product, the results reach the quality standards of barium chromate.