Simultaneous reduction and coagulation removal of perrhenate with titanium (III) trichloride: Performance and mechanism

Abstract 99Tc is a common radioactive element in nuclear waste. Due to its long half-life and high mobility, it easily leads to environmental pollution. This study firstly reported the use of titanium trichloride (TiCl3) as reductant and coagulant to remove perrhenate (ReO4−), which is a non-radioactive chemical substitute for 99TcO4−. The results showed that ReO4− could be completely removed (removal efficiency of Re reach 99.6%) under the optimal coagulation conditions and achieved rapid separation of pollutants from water. When competing ions (such as ClO4−) coexist at a concentration of 1850 times, the removal efficiency of Re can still reach 93.9%. The standing experiment of flocs in aerobic condition exhibited the existence of high affinity between flocs and Re oxides, guaranteeing the fixation of Re. Based on the experimental results and various characterizations of the flocs, it is proposed that the mechanism is the reduction-electrostatic interaction-coagulation process. Firstly, the added Ti(III) hydrolyzed to generate the Ti(III) hydrates and reacted with ReO4−. And then, the titanium hydrates and ReO2 aggregated with each other through electrostatic interaction to form flocs, which settled down quickly to achieve the removal of Re. The results indicated TiCl3 may be used as a candidate reagent to eliminate 99Tc pollution in water efficiently.