The Study Of Preparing Polyaluminium Chloride (PAC) From Kaolin

As a kind of inorganic polymer coagulant, polyaluminium chloride (PAC) can be widely used in purifying water and Wastewater treatment. There are very rich resources of kaolin in China, but it did not be effectively used. Kaolin is a low-cost raw material of PAC preparation because of the certain contents of aluminum.In this dissertation, the processing of preparing polyaluminium chloride by using kaolin as raw material has been studied. The step of pretreating was added in the traditional processing of preparing PAC from kaolin. The effects of the proportion of pretreated, roasted temperature, roasted time, acid-dissolved time, acid-dissolved proportion and acid-dissolved temperature on the quality of PAC were studied by orthogonal text method. The quality of PAC was investigated by coagulating test, and the best process parameters of producing PAC from kaolin were determined.The process for preparing polyaluminium chloride coagulant which uses kaolin as raw material is as follows: pretreated the kaolin with hydrochloric acid at first, and then roasted it, soaked it in hydrochloric acid, filtrated, concentrated, mixed with water for polymerization and at last adjusted the pH of the reaction fluid. The leaching rate of Al₂O₃ can be improved significantly by pretreatment. The result shows that the leaching rate of Al₂O₃ was increased 16.59% with pretreating when the other conditions were all the same.According to the results of coagulating test, the best process parameters of producing PAC from kaolin were determined as follows: the proportion of pretreated with hydrochloric acid is 2.6 g/ml; roasted at 750℃ for 3.5 hours; then soaked in hydrochloric acid for 3 hours at 85℃;the proportion of acid to kaolin is 4.0 ml/g. Considering the feasibility and the economic efficiency in actual production, the appropriate process parameters of producing PAC from kaolin were finally determined as follows: the proportion of pretreated with hydrochloric acid is 2.6 g/ml; roasted at 700℃ for 1.5 hours; then soaked in hydrochloric acid for 2 hours at 85℃;the proportion of acid to kaolin is 4.0 ml/g.The effects of all the process parameters of producing PAC from kaolin on the quality of PAC were also studied. The order of process parameters affecting the quality of PAC was acid-dissolved proportion> the proportion of pretreated> roasted temperature> acid-dissolved temperature > acid-dissolved time> roasted time.The coagulation efficiency of PAC made from kaolin is better than the commercial PAC's. It can be seen that PAC made from kaolin possesses excellent performance.