Permanganate gel (PG) for groundwater remediation: Compatibility, gelation, and release characteristics

• Chitosan and aluminosilicate gels are not compatible or miscible with MnO4-.
• Colloidal silica and silicate gels are compatible and miscible with MnO4-.
• KMnO4 grains are added to colloidal silica to create permanganate gel (PG) solution.
• PG showed delayed-gelling and sustained MnO4- release characteristics.
• PG can be injected via wells to treat large, dilute, deep DNAPL plume in groundwater.

Permanganate (MnO4-) is a strong oxidant that is widely used for treating chlorinated ethylenes in groundwater. This study aims to develop hyper-saline MnO4- solution (MnO4- gel; PG) that can be injected into aquifers via wells, slowly gelates over time, and slowly release MnO4- to flowing water. In this study, compatibility and miscibility of gels, such as chitosan, aluminosilicate, silicate, and colloidal silica gels, with MnO4- were tested. Of these gels, chitosan was reactive with MnO4-. Aluminosilicates were compatible but not readily miscible with MnO4-. Silicates and colloidal silica were both compatible and miscible with MnO4-, and gelated with addition of KMnO4 granules. Colloidal silica has low initial viscosity (<15 cP), exhibited delayed gelation characteristics with the lag times ranging from 0 to 200 min. Release of MnO4- from the colloidal silica-based PG gel occurred in a delayed fashion, with maximum duration of 24 h. These results suggested that colloidal silica can be used to create PG or delayed-gelling forms containing other oxidants which can be used for groundwater remediation.