Remediation of Toxic Heavy Metal Contaminated Soil by Combining a Washing Ejector Based on Hydrodynamic Cavitation and Soil Washing Process

Abstract

Based on the features of hydrodynamic cavitation, in this study, we developed a washing ejector that utilizes a high-pressure water jet. The cavitating flow was utilized to remove fine particles from contaminated soil. The volume of the contaminants and total metal concentration could be correlated to the fine-particle distribution in the contaminated soil. These particles can combine with a variety of pollutants. In this study, physical separation and soil washing as a two-step soil remediation strategy were performed to remediate contaminated soils from the smelter. A washing ejector was employed for physical separation, whereas phosphoric acid was used as the washing agent. The particles containing toxic heavy metals were composed of metal phase encapsulated in phyllosilicates, and metal phase weakly bound to phyllosilicate surfaces. The washing ejector involves the removal of fine particles bound to coarse particles and the dispersion of soil aggregates. From these results we determined that physical separation using a washing ejector was effective for the treatment of contaminated soil. Phosphoric acid (H3PO4) was effective in extracting arsenic from contaminated soil in which arsenic was associated with amorphous iron oxides. Thus, the obtained results can provide useful information and technical support for field soil washing for the remediation of soil contaminated by toxic heavy metals through emissions from the mining and ore processing industries.

Assessment of the Stabilization of Cu-, Pb-, and Zn-Contaminated Fine Soil Using Cockle Shells, Scallop Shells, and Starfish

“…This is because each heavy metal is extracted at different pH levels. For example, a previous study [38] performed extraction from the heavy metal-contaminated soil stabilized with cement at various pH levels (4)(5)(6)(7)(8)(9)(10)(11)(12) and reported that copper, lead, and zinc were extracted at pH 5 (Pb), 6 (Cu), and 7 (Zn) or less, respectively, and that Zn exhibited the largest elution followed by Cu and Pb at pH 4. In the present study, when heavy metals were stabilized with CKS, SLS, and ASF and then extracted using 0.1 N HCl, the extraction pH varied between 1.3 and 12.3, and Zn also exhibited the largest elution, followed by Cu and Pb, which is consistent with the previous studies (Figures [3][4][5][6][7][8][9][10][11].…”

“…For example, a previous study [38] performed extraction from the heavy metal-contaminated soil stabilized with cement at various pH levels (4)(5)(6)(7)(8)(9)(10)(11)(12) and reported that copper, lead, and zinc were extracted at pH 5 (Pb), 6 (Cu), and 7 (Zn) or less, respectively, and that Zn exhibited the largest elution followed by Cu and Pb at pH 4. In the present study, when heavy metals were stabilized with CKS, SLS, and ASF and then extracted using 0.1 N HCl, the extraction pH varied between 1.3 and 12.3, and Zn also exhibited the largest elution, followed by Cu and Pb, which is consistent with the previous studies (Figures [3][4][5][6][7][8][9][10][11]. After stabilizing the heavy metals with CKS, SLS, and ASF, the leaching concentration of each heavy metal was compared; it was found that the elution of heavy metals increased as the extraction pH decreased, while Zn always showed the largest elution followed by Cu and Pb.…”

“…Recent studies to tackle the shortcomings of conventional acid washing have investigated high-pressure soil washing, which prevents soil acidification and maximizes the physical washing effect by solely using high-pressure water [9,10]. High-pressure soil washing involves the restoration of heavy metal-contaminated soil by dispersing soil aggregates to reduce large particles into small particles through high-pressure water injection and separating only the fine soil contaminated with elevated levels of heavy metals [11].…”

Removal of Inorganic Salts in Municipal Solid Waste Incineration Fly Ash Using a Washing Ejector and Its Application for CO2 Capture

“…In our previous work, a washing ejector technology was used in fine particles enriched in contaminated soil with smelting-related contaminants, and it achieved remarkable results [ 28 , 29 ]. It is well known that the accumulation of metals is significantly affected by the contents of organic matter, clay minerals, and Fe oxides in contaminated soil.…”

Advances in bioremediation techniques for the degradation of hydrocarbons in soils

“…As soil washing is quick and efficient, it is frequently used to remediate severely contaminated soils (Kim et al, 2022). By doing this, the amount of contaminated soil decreases and also the concentration of contaminants.…”