High-efficient removal of arsenite by coagulation with titanium xerogel coagulant

Abstract

Coagulation with inorganic titanium (Ti) salts is a low-cost and high-efficiency technology for arsenic removal. However, the drastic decline of solution pH, which is caused by coagulation process, usually greatly reduces the removal efficiency of arsenite (As(III)). In this study, titanium xerogel coagulant (TXC) was employed for enhanced As(III) removal, and two common Ti-based coagulants, titanium sulfate (TS) and titanium tetrachloride (TC), were used as references. TXC outperformed TS and TC over the initial pH range of 5.0–10.0, especially under acidic condition, which was attributable to the moderate pH decline during TXC coagulation. TXC with dose of 10 mg Ti/L could eliminate above 90% of As(III) at pH 7.0 and 8.0. The maximum coagulation efficiency of the three Ti salts (10 mg Ti/L) at pH 8.0 followed an order of 625 mg/g Ti (TXC) > 588 mg/g Ti (TS) > 526 mg/g Ti (TC). The enhanced mechanisms involved in TXC coagulation were the strong adsorption ability of the in-situ formed flocs and binding affinity between As(III) and hydrolysates. TXC coagulation dominated by the unique network-like hydrolysates would generate in-situ flocs with more binding sites, and thus improved coagulation efficiency. Except for phosphate and silicate ions, the common water matrices did not greatly inhibit As(III) removal efficiency. In addition, TXC performed the highest As(III) removal efficiency in actual arsenic-containing wastewater. This study provided a high-efficient coagulant for As(III) pollution control, and shed light on the application potential of TXC in removing metalloid pollutants.