To postpone the precipitation of manganese oxides in the degradation of tetrachloroethylene by controlling the permanganate concentration.

Controlled-release permanganate (CRP) is a relatively new technology used to treat contaminated groundwater. This study tested the encapsulation of permanganate using stearic acid to realize controlled-release properties. Batch experiments were conducted to investigate the performance of manganese oxides (MnO2) in the reaction between CRP and the contaminant of interest: tetrachloroethylene (PCE). The results showed that higher ionic strengths (I = 0.1 mol/L) cause earlier precipitation of MnO2 colloids. Using CRP to degrade PCE could decrease the amount of MnO2 colloids produced and postpone precipitation compared to raw potassium permanganate (KMnO4) under high ionic strength conditions by controlling the KMnO4 concentration in the solution. The amount of MnO2 colloids produced and the time of precipitation depended more on the CRP grain size than on the CRP mass ratio. Controlling the KMnO4 concentration used in the reaction could control the formation of MnO2 precipitates in the premise of guarantee the removal rate of PCE.