Design of a washing ejector and column flotation based on the microbubble for heavy metal contaminants removal from contaminated soils: A pilot and laboratory-scale studies

Abstract

This study mainly examines the effects of combined washing ejector and column flotation process by remediation equipment for heavy metal remediation at a contaminated site. A washing ejector system is a sustainable technology that considers the concept of hydrodynamic cavitation. Soil aggregates strongly binding to poorly crystalline minerals and Fe oxide bonding with the soil create challenges for their elimination from soils contaminated with complex contaminants. The effects of the operating conditions of the cavitation flow on increasing the separation of fine particles were evaluated by determining the mass balance during the washing system process on a pilot scale. Cavitation flow in the washing ejector system can increase the dispersion of soil aggregates owing to the generation of hydroxyl radicals (•OH) and the increase in mixing intensity. Cavitation flow during the process can increased the dispersion of soil aggregates owing to the release of Fe oxides into the soil. The coarse and fine particles were readily separated from the bulk soil, and the fine particle distribution per mass increased after washing. The levels of Fe in the coarse fraction soil met the KS requirements after separation, whereas the Fe levels in the fine fraction soil were above than the KS limits. To reduce waste volume, column flotation was used to selectively separate Fe oxides from contaminated soil. Microbubbles in column flotation have the important function of facilitating the collision and attachment between air bubbles and Fe oxides and subsequently recovering the Fe oxides. When AF65 as a frother and oleic acid as an anionic collector were used in the column flotation, the concentration of Fe oxides increased from 9.67 % to 13.76 %, a recovery of approximately 10 % from the fine soil. According to the mass balance of the study area, after treatment using the washing ejector system, coarse (60 %) and fine (40 %) soils in the total soil were separated. Column flotation can be applied to fine soil to achieve a volume reduction of approximately 30 % of the total soil volume. The results of this study illustrate the feasibility of the proposed remediation process to reduce waste volume and improve sustainability while meeting Korean standards for heavy metal pollution in soil, thereby minimizing environmental risk.