Poly Aluminium Chloride Preparation Conditions Optimization And Application Research

This paper researches the preparation process of PAC.It optimizes the preparation conditions from five aspects of the addition ratio of calcium aluminate powder,hydrochloric acid and water,reaction time,reaction temperature,addition sequence and addition speed,and thus finds the best reaction condition.It researches the removal rates of water indicators,such as turbidity,color,UV₂₅₄,ammonia nitrogen and COD_Mn,when using prepared PAC and normal coagulant respectively.It also researches changes of water indicators over the settling time when adding same amount of prepared PAC and normal coagulant,and the distribution of aluminium form under different pH values.Finally,by using potassium ferrate as pre-oxidation agent and combining with prepared coagulant,it researches the rules that the interaction of addition amount of potassium ferrate and water's pH value influences the removal rates of turbidity and UV₂₅₄,and establishes the quadratic response model to optimize technical parameters.The research results show that the best condition to prepare PAC is to add deionized water first,then add calcium aluminate powder and fully stir and mix,and finally drop hydrochloric acid slowly;the best reaction temperature is 95?;the best reaction time is 2h;the best addition ratio of hydrochloric acid,deionized water and calcium aluminate powder is 1:1:2.5.In prepared PAC,the Al₂O₃ content and basicity are 9.57%and 72.53%respectively.With the same addition amount,when using prepared PAC,the removal rates of turbidity,color,UV₂₅₄ and COD_Mn,are higher than the rates when using normal PAC.The effect on removing ammonia nitrogen by using both coagulants is not good.When the addition amount of prepared PAC is 25mg/L,the removal rates of turbidity,color,UV₂₅₄ and COD_Mn,are 91.18%,78.61%,58.9%and 52.88%respectively.With the same addition amount and within a relatively short time,prepared PAC could achieve stable removal effect earlier than normal PAC.When combining potassium ferrate as pre-oxidation agent and prepared PAC as coagulant,the effect on removal of turbidity and UV₂₅₄ is obviously better than the removal effect when only using PAC,and the combination could enhance the effect on removal of contaminants to some extent.By simulating and verifying the influence of potassium ferrate's addition amount and water's pH value on coagulation effect,it is concluded that their interaction has a greater influence on coagulation effect,of which the removal rate of UV₂₅₄ is influenced more greatly than that of turbidity.By utilizing the response surface model to optimize parameters and conducting experimental verification,it is concluded that the removal rates of turbidity and UV₂₅₄ could reach 92.5%and 63.8%respectively when the addition amount of potassium ferrate is 2.13mg/L and pH value is 6.52.When water is slightly acidic or neutral,combination of PAC and potassium ferrate has better effect on enhancing coagulation.Meanwhile,if there is a certain addition amount of coagulant and potassium ferrate is used for pre-oxidization to enhance coagulation,then the addition amount of potassium ferrate should be controlled within a proper range.