Feasibility of a Chemical Washing Method for Treating Soil Enriched with Fluorine Derived from Mica

Abstract

High levels of fluorine in soil may pose health risks and require remediation. In this study, the feasibility of using a practical chemical washing method for the removal of fluorine from an enriched soil was evaluated. The chemical washing procedures were optimized through experimental analyses of various washing solutions and washing conditions (i.e., washing solution concentration, solid–liquid ratio, agitation speed, and reaction time). Additionally, the effects of techniques for improving the washing efficiency, such as ultrasonic washing, aeration, and multi-stage washing, were evaluated. Herein, among all applied methodologies, the maximum washing efficiency achieved for the total fluorine present in soil was only 6.2%, which indicated that chemical washing was inefficient in remediating this particular soil. Further sequential extraction analysis showed that the fluorine in this soil was present in a chemically stable form (residual fraction), possibly because of the presence of mica minerals. It was demonstrated that chemical washing may not be effective for remediating soils containing such chemically stable forms of fluorine. In these cases, other physical-based remediation technologies or risk management approaches may be more suitable.

Froth-Flotation Separation as an Alternative for the Treatment of Soil Enriched with Fluorine Derived from Mica

“…The target site of this study has been reported to exceed the Korean worrisome level of soil contamination (level 2 area: 400 mg/kg), owing to the accumulation of F in the soil through the weathering of mica, such as biotite, lepidolite, muscovite, and phlogopite [19]. The F-enriched soil of this site had a residual fraction of more than 99% [19].…”

“…Since it is a site where underground development is planned in the future, it is necessary to confirm the contamination characteristics and remediation efficiency of the soil in a relatively deep depth. The study site soil contains accumulated F derived from mica minerals [19]. After releasing the particles that had aggregated through wet disintegration, the gravel was separated using a 2-mm sieve (10 mesh).…”

“…The target site of this study has been reported to exceed the Korean worrisome level of soil contamination (level 2 area: 400 mg/kg), owing to the accumulation of F in the soil through the weathering of mica, such as biotite, lepidolite, muscovite, and phlogopite [19]. The F-enriched soil of this site had a residual fraction of more than 99% [19]. The basic principle of both the soil washing and the electrokinetic methods is the removal of F by detaching them from soil particles using a suitable washing solution and anolyte.…”

“…Typical methods for treating F-contaminated soil (i.e., removing F from soil) include soil washing and electrokinetic remediation [18][19][20][21][22][23][24]. Soil washing removes F by leaching it entrapped in, and/or adsorbed on, the soil particles using an acidic or basic washing solution.…”

“…Therefore, it is difficult to use these methods to remove the F in soil derived from F-containing minerals because of its strong resistance to extracts. In fact, the applicability of chemical washing methods was evaluated under various washing conditions for the soils collected from the target site, and it was found that chemical washing was not feasible, as the maximum removal efficiency was only 6.2% [19]. Therefore, to remediate F-enriched soils of natural origin (i.e., soils enriched with F from mica weathering) to acceptable levels, the F-enriched mineral particles must be physically separated out.…”