Simultaneous deep purification of fluoride and trivalent arsenic by a bimetallic composite xerogel coagulant

Abstract

Arsenic-fluoride (As-F) co-existence pollution seriously threatened the drinking water safety of residents using groundwater as water sources. At present, coagulation technology was widely used in the removal of arsenic and fluoride due to its economic efficiency and simple operation. While traditional aluminum (Al) and iron (Fe) coagulants could not remove fluoride and As(III) simultaneously, and high metal residues would bring additional risks. Based on the hydrolysis properties and pollution removal performance of zirconium (Zr) and titanium (Ti) salts, here we developed a new bimetallic composite xerogel coagulant (ZTXC) for simultaneous deep purification of fluoride and As(III). The characterization of physicochemical properties showed that ZTXC was a high-polymerization amorphous hydroxide similar to titanium xerogel coagulant (TXC) and zirconium xerogel coagulant (ZXC). ZTXC with a Zr/Ti molar ratio of 4:1 could effectively purify fluoride and As(III) at the same time, reducing fluoride and As(III) to 0.45 mg/L and 9.07 μg/L at pH 5.0 with dosage of 0.4 mM, respectively. Combining the advantages of Zr and Ti salts, ZTXC showed better coagulation performance and lower metal residues than PAC and PFS. Through the analysis of hydrolysis precipitation species and charge differences, fluoride removal mainly relied on the electrostatic attraction by positively charged hydrolysates, while neutral As(III) was mainly removed through hydroxyl coordination. This study could provide reference and theoretical guidance for the development and application of materials and technologies for As-F co-contaminated drinking water treatment.