Effects of Ca~(2+) and Mg~(2+) on Defluoridation in the Electrocoagulation Process

摘要

Because aqueous ions can influence the defluoridation of the electrocoagulation (EC) process, the effects of Ca~(2+) and Mg~(2+) were investigated. The behaviors and mechanisms of EC defluoridation in Ca~(2+)-comaining systems were different from those in Mg~(2+)-containing systems. An increase in Ca~(2+) concentration improved the defluoridation efficiency (εF). but it could not change the optimal molar ratio of OH~- and F~- to A/~(3+) (r_(OH)+F). The highest εF can usually be obtained at (r_(OH)+F) = 3 for defluoridation. Only a small portion of Ca~(2+) entered into the flocs, and Ca~(2+) could not influence the mechanism of EC defluoridation. For the Mg~(2+)-containing system, the optimal (r_(OH)+F) increased with increasing Mg~(2+) concentration. The optimal r_(oh+f) was maintained at 3 after the Mg~(2+) concentration was corrected using the obtained correction coefficient of 03435. About 50% to 70% of the total Mg~(2+) entered into the flocs. From the XRD analysis, it was found that some Mg-AI-F layered double hydroxides (LDHs) were formed by Mg~(2+), F~-, and Al~(3+) during electrolysis. It is proposed for the first time that the formation of Mg-AI-F LDH is one of the mechanisms for EC defluoridation in systems containing both F~- and Mg~(2+).