Removal Of Inorganic As (Ⅲ) By Titanium Salt Coagulation

In natural waters, the predominant forms of As are inorganic species of arsenateAs(V) and arsenite As(III), with the latter being more soluble, mobile and toxic.Coagulation-precipitation is recognized as one of the best available options to removelarsenic from water because of its low cost and high efficiency. However, coagulationprocess is generally not efficient for As(III) removal due to the uncharged form ofAs(III) at environmentally-relevant pH. Using traditional coagulant to remove As (III)is relatively inefficient, and the process of arsenic removal will produce arsenic-richwaste, increasing the cost of subsequent treatment.In this study，the influence of solution pH, coagulant dosage, initial arseniteconcentration, and the presence of silicate and phosphate on removal of arsenite inwater by coagulation of titanium sulfate were investigated. The size and Zeta potentialof hydrolytic precipitate of titanium sulfate and titanium tetrachloride, and arsenicremoval efficiency of the system were compared. Experimental results show that theisoelectric point (IEP) of titanium sulfate was found to be at pH5; the maximumhydrolytic precipitate size of titanium sulfate occurred at pH=6. In the pH range from5to8, As (III) removal efficiency reached the maximum and was relatively stable; whilethe Zeta potential of the precipitates decreased significantly. This indicates that Zetapotential has only negligible effect on the As(III) removal in the coagulation process.As the coagulant dosage increased from2.5to10mg/L, As (III) removal efficiencyincreased significantly. However, above the coagulant dosage of15mg/L, only a slightincrease in As (III) removal was observed as the coagulant dosage further increased.The presence of silicate and phosphate decreased the As (III) removal efficiency bycoagulation of titanium sulfate. The arsenic removal efficiency by titanium sulfate andtitanium tetrachloride showed the same trend, but the removal efficiency of the titanium sulphate was better than titanium tetrachloride. This study revealed thatTi(SO4)2can be an alternative coagulant for efficient As(III) removal.