Influencing factors on sorption of TNT and RDX using rice husk biochar

2,4,6-Trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) are the most commonly used nitro-organic explosives in contemporary military munitions, and readily be introduced into the environment, especially in groundwater supplies. In the present study, rice husk biochar (RHBC) prepared by pyrolysis at 700°C was used for the treatment of TNT and RDX in waste water by batch sorption. The prepared RHBC chemical and physical characteristics were well characterized using analytical spectroscopic techniques. In order to develop the sorption mechanism of TNT and RDX onto RHBC, the factors influencing sorption were studied. The results demonstrated that TNT and RDX sorption depended on the pH value of the aqueous solution, and decreased as pH increased from 2.0 to 6.0 and was attributed with their pKa₁ values along with their physical and chemical characteristics. The batch sorption results revealed that the sorption of the two explosives onto RHBC was rate limiting monolayer chemisorptions on homogeneous surface. These results suggested that the sorption of TNT and RDX occurs through weak electrostatic interactions as well as through charge transfer between -NO₂ and ππ electrons of explosives and RHBC surface functional groups.