Study On Influence Factors And Coagulation Mechanism With FSS And PFS

Aluminous coagulants are the most widely applied inorganic salt coagulant in waterworks in our country currently, especially polyaluminium chlorides(PAC). Compared with aluminous coagulants, ferrous coagulants have many advantages, especially the excellent flocculation performance of resulting floc and no concentration of aluminum in drinking water. Ferric subsulfate(FSS) is a kind of ferric coagulants prepared from ferrous sulfate, whose preparation method is more safe and reliable compared with polyferric sulfate(PFS). However, there are few articles about FSS.So in this paper, coagulation efficiency, effect factors of coagulation, and coagulation mechanism of FSS and PFS has been studied contrastively to analyze the possibility with application of FSS. The main content and results were as follows:(1) Kaolin clay suspension was treated by PAC, PFS and FSS. Charge neutralization ability, hydrolysis ability, and sedimentation capacity of flocculation and second flocculation were investigated. By comparing the effect treating Kaolin clay suspension with PAC, PFS and FSS, the coagulation efficiency was studied contrastively. The result indicated that PFS and FSS had a better coagulation efficiency, i.e., they had a better effect to treat Kaolin clay suspension.(2) The factors influencing the coagulation efficiencies were studied by response surface method, and the researching factors were content of Kaolin, content of humic acids, content of calcium hydroxide and dosage of coagulant. The research results were as follows. The order of influence degree of the supernatant turbidity and UV254 treating with PFS were: dosage of coagulant> content of humic acids> content of calcium hydroxide> content of Kaolin. The order of influence degree of the supernatant turbidity and UV254 treating with FSS were: content of humic acids> dosage of coagulant> content of calcium hydroxide> content of Kaolin. FSS was worth applying due to its good effect and cleaner production.(3). The structure of PFS and FSS was characterized with IR, XPS and SEM, and the change of the degree of iron polymerisation of PFS and FSS were analyzed by the ferron-timed spectroscopy method to analyze their coagulation mechanism. The result indicated that there were much change with the degree of iron polymerisation of PFS and FSS after coagulation, which implied that the coagulation mechanism of PFS and FSS included charge neutralization, adsorption bridging and sweep flocculation, and charge neutralization was the main action of PFS, adsorption bridging was the main action of FSS.