Experimental Design and Process Optimization for Uranium Polluted Soils Decontamination by Acid Washing

摘要

Uranium soil depollution is of great concern as, like any other radionuclide, it may accumulate in time and generate a negative impact on human health. There are several decontamination technologies, among these the acid washing still in use for its simplicity and low cost. Though a classical method, it still can be improved by using the best operating conditions to increase the decontamination degree. The present study aims to propose an optimization approach based on experimental design. The investigation takes into account the main operating parameters (duration, temperature, and pH) and the soil characteristics (texture and organic matter content). This work presents an "ex situ" uranium-contaminated soil treatment using a 0.1 M H2SO4 solution with pulp density of 0.5. The experiments followed a 23 factorial design for the evaluation of factors and interaction effects. The factors' influence differed from one type of soil to another. The 23 experiment was augmented using a non-central composite design that allowed the formulation of a second degree model for the response surface. The best values for the operating parameters were identified using optimization procedures. Statistical modelling and optimization were performed in Matlab (R) v7.7. The results obtained proved that the soil type is very important for selecting better operating conditions. These improvements determined an increased decontamination degree of up to 10-13% compared with standard operating conditions that were considered as central point in the experimental plan.