Characteristics of poly-silicate aluminum sulfate prepared by sol method and its application in Congo red dye wastewater treatment

A novel method for synthesizing poly-silicate aluminum sulfate coagulant (PSAS) using a silica-alumina sol was reported. Herein, two modalities (nSiO(2)/nNa(2)O: 1.11 and 3.27) of self-made water glasses were used as the silica source for synthesizing the sol precursor. Then, the PSAS(1.11) and PSAS(3.27) with different basicity were obtained by controlling the Al molar ratio of precursor to aluminum sulfate. The results showed that the PSAS(1.11) coagulant prepared with low modulus water glass (LMWS, 1.11) has low turbidity and good stability. Using low modulus water glass, the effect of the Al molar ratio of precursor to aluminum sulfate on the basicity and stability of PSAS(1.11) with Al/Si of 20 and the effect of the molar ratio of aluminum to silicon on the basicity and stability of PSAS(1.11) were studied, respectively. Based on XRD and Fourier infrared (FTIR) characterization of the sol precursor and PSAS(1.11), the synthesis mechanism of PSAS by the silica-alumina sol method was discussed. Al species distribution of PSAS(1.11) was determined using the Al-Ferron timed spectrophotometric method. Moreover, the performance of PSAS(1.11) coagulant was examined, regarding its efficiency towards color removal of Congo red. The results showed that PSAS(1.11) coagulant with Al/Si of 20 and Al molar ratio of 1/12 exhibits excellent performance, and the color removal rate reached 98.6% at an initial pH of 11 and coagulant dosage of 40 mg L-1 (Al mg L-1). Finally, the PSAS coagulant mechanism was discussed in detail through infrared characterization, Al-27 NMR, Raman, morphology and mapping of the flocs.