A Study On Synthesis And Modification Of Polyaluminium Silicate Sulfate Flocculants

A series of polyaluminum silicate sulfates(PASS) with different conditions by the reactions of alum sulfate with sodium silicate and sodium aluminate were prepared and modified by polydimethyldiallyl ammonium chloride(PDMDAAC) as well as polyacrylamide(PAM). Their structural characteristics , aluminum species, stability of hydrolysis and coagulation performance were studied. Their applications as coagulants in wastewater treatment were investigated.The stability of PASS were investigated by gelation time and the change of transparence. It showed that the PASS with the Al/Si molar ratio of 20 and synthesized at 60℃can preserve as long as 6 months.The structural characteristics of PASS were analyzed by means of infrared and X-ray diffraction spectra. It was found that the PASS had similar structures with polyaluminum sulfate(PAS), the Si in PASS complexed with the polyhydroxy aluminum at same behavior with aluminum.The aluminum species in PASS aqueous solutions were identified with Al-Ferron complex timed colorimetric method. As expected that the content of Ala decreased, but the content of Alc increased with the Al/Si molar ratio increasing. It shows that the degree of polymerization of PASS increased with the increased Al/Si molar ratios. Alb had a stable content about one third in PASS.The coagulation–flocculation of PASS was investigated with kaolin suspension. The results showed that the most effective PASS for removal of turbidity had the Al/Si molar ratio of 15 as well as at the pH of 6~8 when the dosage of PASS used was 40mg/L The high efficiency of removal of turbidity can reach to 97%.When treated the crude wastewater of low turbidity at low temperature with coagulation method, PASS was more effective than PAS both in removing turbidity and chromaticity.When PASS was modified by PDMDAAC, it can form a homogeneous and steady solution. It can decrease the dose of PASS distinctly when using PDMDAAC as a modifying agent. However, when PAM was used as a modifying agent, it will be hard to succeed.