Preparation Of Poly-Ti-Fe-Si Water Purifying Agent And Coagulation Test For Simulated Humic Acid Water

In this paper, poly-Ti-Fe-Si(PTFSi) coagulant was prepared by copolymerization using metatitanic acid waste(derived from production process of titanium dioxide) as main material and poly-silicate(PS) as additive, and was characterized by scanning electron microscope(SEM). Jar test was used to study the storage stability and coagulation performance of PTFSi in comparison with those of poly-Ti-Fe(M-PTF) which has been developed successfully in the previous work and poly-Al-Fe(PAF) using simulated humic acid water as the tested water sample. And then the better coagulation conditions of PTFSi were studied and coagulation mechanism was simply analyzed.According to the orthogonal experiment results and analysis, the results showed that the removal rate of turbidity, chroma and COD of PTFSi were all higher when the molar ratio of Ti to Si, the pH of poly silicate and the pH of base polymer was 46, 2 and 0.5 respectively. PTFSi had a larger and complex interspace reticulate structure, so it could better adsorb the water particles, forming larger aggregates, and then improving the water purification effect. The stability of PTFSi was improved compared with that of M-PTF.The removal of turbidity, UV254 and DOC by PTFSi was studied using coagulation tests as changes of dosage, coagulation pH, concentration of humic acid, and concentration of kaolin, respectively. The results showed that the best dosage of PTFSi was 0.5mmol/L. Under this dosage the maximum removal rate of turbidity,UV254 and DOC were 93.8%, 67% and 52.5% respectively. PTFSi had a better water purification effect in both acidic and alkaline conditions, so it had a wide range of pH in application. But the water purification effect was better in pH=7. In addition, the water purification effect of PTFSi increased significantly compared with M-PTF in acid conditions. When the humic acid concentration was 4~10mg/L, the DOC removal rate of PTFSi was higher than M-PTF and PAF. Adding a certain amount of kaolin to the water, the water purification effect of PTFSi, M-PTF and PAF can increase, especially for the removal of turbidity. But when the kaolin concentration was greater than 75 mg/L, the UV254 and DOC removal rate of the three kinds of coagulant had a certain degree of decline.The coagulation process conditions of PTFSi were studied by the orthogonal experiment method. As the orthogonal experiment results showed that PTFSi water purification effect was better when the fast stirring speed was 250 r/min, fast stirring time was 120 s and slow stirring gradient was 60r/min for 3 min, 40 r/min for 9 min, and 20 r/min for 3 min. But as the analysis of the orthogonal experiment results, it could be known that the best water conservancy conditions of PTFSi were the fast stirring speed, the fast stirring time was 250 r/min, 120 s respectively and slowed stirring gradient was 60 r/min for 4 min, 40 r/min for 7 min, and 20 r/min for 2 min.The DOC removal effect of PTFSi was better. It is because that the free inos of titanium, iron and silicate or the hydrolyzed polymer of poly-titanium, poly-ferric and poly-titaniumferric –silicon in PTFSi could performe the function of compression of double electric layer, electrical neutralization, adsorption bridging and sweeping adequately.