Quantitative evaluation of the abrasion rate in attrition washing on lead contaminated soil from shooting ranges

The effects of attrition on sandy and silty Pb-contaminated soil from shooting ranges were quantitatively investigated. The abrasion rate could be quantitatively evaluated using a population balance model from the size distribution of soil particles before and after attrition in an intensive mixer. The maximum abrasion rate was 0.047 μm/s in the first stage of attrition (1min of grinding), and then declined between 2 and 4 min of grinding. The two samples had similar maximum abrasion rates, but the decline in the abrasion rate was larger in the silty soil, which would have a thinner soft layer on the surface of the soil particles, than the sandy soil. The incremental change in the mass fraction of Pb in the <20μm particle size fraction increased proportionally with the abrasion thickness from the surface of the soil particles. Although the Japanese regulatory standard for the Pb concentration in soil (150 mg/kg) was not met for either sample, the Japanese regulatory standard for the concentration of leached Pb (0.01 mg/L) was met for silty soil after attrition. Sequential extraction using Tessier's procedure for the >20 μm size fraction before and after attrition showed the attrition was more effective for the oxides or organic-bound species and carbonate species of Pb chemical forms.