Preparation Of Polymeric Ferric Sulfate And Its Performance As Coagulant For Treating Industrial Wastewater

Polymeric ferric sulfate,or PFS, an impoisonous and highly efficient coagulant, is playing a more and more important role in the field of water treatment by right of its good characteristics.There are many mothods of preparing PFS .Generally,it is prepared with ferrous sulfate by using hydrogen peroxide(H2O2) or potassium chlorate as oxidant in lab; while in industry, different preparing mothods can be chosen according to the situations. We prepared liquid PFS by using H2O2 as oxidant and analyzed its main specifications by using mothods standardised by the government.A sort of industrial wastewater containing both Zn²⁺ and Cd²⁺ was treated experimentally by using self-prepared PFS as coagulant; the relationships between several main coagulating conditions (e.g.coagulant dose,coagulating reaction period and pH) and the removal efficiency of Zn²⁺ and Cd²⁺ were discussed. Thus the optimum condition of treating that wastewater was obtained, which was as follows: pH=7.0; coagulating reaction period: 30 min; coagulant dose: determined according to the original level of Zn²⁺ and Cd²⁺ in wastewater. Nevertheless, it is certain that PFS do have a good effect on removing Zn²⁺ and Cd²⁺ from wastewater.Seeing that ferric sulfate, ferrous sulfate and aluminium chloride are still superior in being chosen as coagulant in industry when treating heavy metal wastewater, we treated the same water specimen containing both Zn²⁺ and Cd²⁺ by using individually ferric sulfate, aluminium chloride and PFS. After the optimum conditions of treatment and the results of coagulation were compared among the three coagulants, it came to the conclusion that PFS has the best effect on treating that wastewater.Besides, an experiment of removing fluorine was conducted by using self-prepared PFS to a water specimen in which the concentration of fluorine was 24mg·L^-1, and the relationships between the coagulant dose, the coagulating reaction period and the removal efficiency of fluorine were discussed. The experiment result showed that PFS has a good effect on removing fluorine from that water specimen, and that after having been treated the concentration of fluorine in the water can be reduced to less than 1mg·L^-1, which has fulfilled quality requirement of drinking water standardised by the government.