Chemical Reduction of Hexavalent Chromium Present in Contaminated Soil using a Packed‐bed Column Reactor

Soil samples extracted from a contaminated landfill with hexavalent chromium, Cr(VI), were treated in a packed‐bed column reactor applying different reductant solutions under controlled flow conditions. In all cases, the kinetic study concerning removal of Cr(VI) from packed soil revealed the overall process (leaching and redox reaction) is described by pseudo‐first order kinetics. The complexity of the process taking place in non‐isotropic medium (packed soil) was evidenced by dependence of the overall pseudo‐first order kinetic rate constant, k *, on treatment time, volumetric flow rate, and composition and concentration of the reductant solution. A phenomenological equation was proposed in order to represent k * in non‐ideal conditions. The comparative study concerning the use of different reductants revealed application of ferrous sulphate, Fe(II), under flow conditions furnished the best results, since in this case the redox process reached a considerable extent and the reduced chromium, Cr(III), was immobilized in packed soil as an insoluble mixed compound.