The Study Of Preparing Polyaluminium Chloride (PAC) From Fly Ash

Polyaluminium chloride(PAC),as a kind of inorganic polymer coagulant,can be widely used in purifying water and wastewater treatment.There are very rich resources of fly ash in China,but it don't be effectively used.Fly ash is a low-cost raw material of PAC preparation because of the certain contents of aluminum.Through analyzed the fly ash specimen of Lanzhou Second Thermal Power Plant, it showed that the quartz,the mullite,the hematite characteristic peak were appeared in this fly ash,and it reflected Al₂O₃,SiO₂ and Fe₂O₃ contents were higher,and this fly ash included 58.64%SiO₂,21.32%Al₂O₃ and 7.20%Fe₂O₃ by the multi-elements chemic analysis determines.This resulit is consistence with the former.With the roasted at 800℃and for 90min,SEM pictures analysis showed:Without activated fly ash particle surface was smooth and had dense structure;Roasting directly activated fly ash vitreous surface became relatively rough,and the surface appeared flocculation,but the structure of fly ash maintained complete;Joined activator HCl and NaCl to roast activation respectiveiy,fly ash vitreous surface became rough and loose, and there were many honeycomb particles.XRD analysis showed:in the original fly ash the main characteristic peaks were quartz and mullite;if roasted directly activation or added NaCl activated activator,the mullite characteristic peak became stronger in fly ash,but mullite characteristic peak had a little change.After added HCl activator,the mullite characteristic peaks changed a lot,and numerous new mullite characteristic peaks appeared.In this paper,the processing of preparing PAC by using fly ash as raw material had been studied.The traditional processing was improved,and the step of activition pretreatment was increased.The effects of the proportion of pretreated,roasted temperature,acid-dissolved time,acid-dissolved proportion and acid-dissolved temperature on the quality of PAC were studied by the orthogonal text method.As the quality of PAC was investigated with the leaching rate of Al₂O₃ to determine the best procession parameters of producing PAC from fly ash.The process for preparing PAC with useing fly ash as raw material was:pretreated the fly ash with HCl first,and then roasted,soaked it in hydrochloric acid,filtrated, concentrated,and at last dried.The leaching rate of Al₂O₃ can be improved significantly by pretreatment.According to the results of test,the best process parameters of producing PAC from fly ash were determined as follows:the proportion of pretreated with HCl is 0.20ml/g(v/m);roasted at 800℃;then soaked in HCl for 3 hours at 90℃;the proportion of acid to fly ash is 4.5ml/g(v/m).The effects of all the process parameters of producing PAC from fly ash on the quality of PAC were also studied.The order of process parameters affecting the quality of PAC was acid-dissolved temperature＞roasted temperature＞the proportion of pretreated＞acid-dissolved proportion＞acid-dissolved time.Through contrasting the sewage treatment effect with PAC made from fly ash by this way and the commercial PAC,it was indicated that,the effect of PAC made from fly ash treated sewage was better than the market PAC in pH value,the turbidity and COD_Crremoval rates.It can be seen that PAC made from fly ash by this way have excellent performance.