Experimental conditions affecting estimation of natural oxidant demand of soil using permanganate.

摘要

During field applications of in situ chemical oxidation with permanganate, excess oxidant requirements have been observed. This excess oxidant, generally referred to as Natural Oxidant Demand (NOD), is consumed by the organic matter and other naturally occurring oxidizable species present in the aquifer material. Lab-scale experiments are typically used to determine the NOD of the soil (g of KMnO4/kg of dry aquifer solids). Though many researchers have reported NOD values in the literature, few have taken the experimental factors that affect NOD into consideration. There is currently no standard test method for determining the NOD of the soil using lab-scale experiments. This study provides a broader perspective of the issues and concerns related to determining the NOD of soil and evaluates the effect that initial permanganate concentration, soil to water ratio, and mixing have on the rate and extent of NOD. A series of batch experiments were performed using a composite soil sample to study the kinetic effects of each parameter. It was found that in a NOD reaction the fast reactions dominate the overall kinetic expression early on and later the kinetic expression transfers from fast reaction control to slow reaction control. Also, the mixing conditions in the vial determine whether the kinetics is mass transfer controlled or reaction rate controlled. The soil to water ratio ratio does not affect the reaction kinetics as long as the permanganate concentrations in the vials were the same. Finally it was concluded that the NOD value reported in the literature so far does not take all these experimental conditions into consideration and hence cannot be compared and analyzed directly.