Understanding the Effect of Attrition Scrubbing on the Efficiency of Gravity Separation of Six Inorganic Contaminants

Abstract

Physical separation methods are normally preferred over chemical methods, but their efficiency often fails to meet the remediation targets for various reasons. Attrition scrubbing could possibly be used to improve their effectiveness. The aim of this study was to demonstrate the usefulness of attrition scrubbing prior to a gravity separation technique and to understand the mode of action involved. Contaminated soil divided into three fractions (0.250–1-, 1–2-, and 2–4-mm) and containing six inorganic contaminants was submitted to attrition scrubbing prior to a gravity separation method (shaking table or jig). The proportions and contaminant contents of attrition sludges and separation products were characterized. A dense media separation was realized to predict the efficiency of gravity separation. The shape of particles and the liberation of contaminants for the 0.250- to 1-mm soil fraction were characterized from image analysis. Attrition significantly improved the gravity separation efficiency for five out of six contaminants. However, attrition moderately impacted the gravity separation efficiency of contaminants for coarser soil fractions. Attrition significantly improved the sphericity of particles from the 0.250- to 1-mm fraction of 3 % and significantly reduced their size. The liberation of contaminants was also increased for Pb and Sn together from 17 % for the same soil fraction. However, despite the attrition scrubbing treatment, differences in the removal efficiencies between the dense media separation and the gravity separation remain important for most of the contaminants. This study suggests that the attrition scrubbing effects and mode of action depend on the size of particles.