HEAVY-METAL SOIL REMEDIATION - THE EFFECTS OF ATTRITION SCRUBBING ON A WET GRAVITY CONCENTRATION PROCESS

The US military has historically conducted activities which have eithe r directly or indirectly contributed to environmental contamination. M etal contaminated soil at military sites has resulted from operations such as weapons production, small arms training activities, metal clea ning, and metal plating activities. Soil washing is an effective appro ach to the treatment of contaminated soils employing both physical ant i chemical separation techniques. Physical separation methods encompas s many different unit operations including screening, grinding, flotat ion, hydroclassification, attrition scrubbing and gravity concentratio n such as tabling and spiraling. The primary focus of this paper will be to address the effects of attrition scrubbing (nn abrasive soil par ticle to soil particle interaction in a high solids environment) on a gravity concentration process. Soil from an Army small arms training r ange with lead contamination in the bulk soil at approximately 40,000 mg/kg, was evaluated using a WEMCO(R) Laboratory Attrition Scrubber in conjunction with a Wilfley(R) Laboratory Wet Shaking Table. Results i ndicate attrition scrubbing enhanced the physical separation process o n the wet shaker table by liberating the Pb contamination from the bul k soil, which resulted in a large volume of clean soil while simultane ously producing a small volume of Pb concentrated soil. Laboratory tes ts indicate over 96% of the contamination could be concentrated on 20% of the original soil mass.