A novel titanium sulfate modified poly-magnesium-silicate coagulant with improved pH range for dye removal

Coagulation with inorganic Mg-based coagulants is an efficient technology for dyes removal. However, the promising poly-magnesium-silicate (PMS) coagulant with better aggregation abilities can only be used in a very limited pH range. In this study, poly-magnesium-titanium-silicate (PMTS) was prepared by using titanium sulfate modified PMS. For the treatment of Congo red dye wastewater, PMTS(S), PMTS(Cl) and PMTS(N) synthesized under different acid media (H₂SO₄, HCl and HNO₃) were used. PMTSs had the highest coagulation efficiency at Ti/Mg molar ratio of 0.75 and B value of 1.5. PMTSs outperformed PMS in the initial pH range of 5.50-9.00, with a dye removal efficiency of over 90% at 17.1 mg/L. Under optimal conditions, PMTS(S) had higher coagulation efficiency than that of PMTS(Cl) and PMTS(N), and the settling rate of the four Mg-based coagulants followed an order of PMTS(S) > PMS > PMTS(Cl) > PMTS(N). The coagulation mechanisms of PMTSs on Congo red dye were elucidated by further analysis of coagulation precipitates using UV, FT-IR, SEM and EDS. These results showed that the basis mechanism for floc formation was charge neutralization, while the key to floc formation was chemical combination. Based on the SEM and FTIR results, PMTSs could be found to have special shapes and chain structures, such as Si-O-Ti, Si-O-Mg, Ti-O-Ti, Mg-OH and Ti-OH. Combined with the results of zeta potential, the dominant mechanisms of PMTSs were more likely to be adsorption-interparticle bridging and net-sweeping. In a word, this study provided a highly efficient coagulant with a wide range of applicable pH for the control of dye contamination, and shed light on the potential application of PMTS in the removal of dye pollutants.