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

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.

The effect of operating parameters of hydrodynamic cavitation – assisted alkaline catalyzed transesterification of sunflower oil with methanol on the degree of triglyceride conversion

The effect of operating parameters such as reaction mixture inlet pressure p 1 (101.3–1013.2 kPa), methanol to oil molar ratio M 1 (3–12), the concentration of catalyst C c (0.0–1.0 wt%), temperature T (25–50 °C) and the number of passes of the reaction mixture through the venturi type hydrodynamic cavitation reactor n (1–12) on alkali-catalyzed transesterification of sunflower oil with methanol assisted by hydrodynamic cavitation (ACTC) on the value of the degree of triglyceride conversion (DTC) was investigated. ACTC was performed by the venturi-type hydrodynamic cavitation reactor (VCR) of our construction. It was found that the values of DTC increase with the increase in p 1, M 1, C c, and n, and decrease with the increase in T. Cavitation yield (CY) values were calculated. The ACTC was proved to be the simplest, fastest, and most highly energy-efficient current technology for the production of biodiesel.

Physical Separation of Contaminated Soil Using a Washing Ejector Based on Hydrodynamic Cavitation

A washing ejector is a pre-treatment technology used to remediate contaminated soil by separating fine particles. The washing ejector developed in this study is a device that utilizes fast liquid jets to disperse soil aggregates by cavitation flow. The cavitation phenomenon is affected by the Bernoulli principle, and the liquid pressure decreases with the increase in kinetic energy. The cavitating flow of the fluid through the Ventrui nozzle can remove surface functional groups and discrete particles. The main methodology involves the removal of small particles bound to coarse particles and the dispersion of soil aggregates. Particle collisions occur on the surface soil, such as the metal phase that is weakly bound to silicate minerals. It was observed that the dispersed soil affected the binding of toxic heavy metals and the mineralogical characteristics of the soil. The quantity of oxides, organic matter, and clay minerals affected the properties of the soil. An almost 40–60% removal efficiency of total metals (As, Zn, and Pb) was obtained from the contaminated soils. After treatment by a washing ejector, the volume of fine particles was reduced by 28–47%. When the contaminants are associated with particulates, separation using a washing ejector can be more effective. Therefore, physical separation improves the removal efficiency of heavy metals from soil aggregates.