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.
Highlights
Fluorine, an element with atomic number 9, has high electronegativity and can readily react with other elements, such as Fe, Al, and Ca
The applicability of chemical washing was evaluated for the treatment of a soil containing high levels of fluorine that originated from mica
Various conditions, similar to those of the general washing method for soil contaminated with heavy metals and the washing method previously applied to soil contaminated with fluorine of an artificial origin [17], were tested; from all methodologies applied, the maximum washing efficiency achieved in our study for natural fluorineenriched soil was 6.2%
Summary
An element with atomic number 9, has high electronegativity and can readily react with other elements, such as Fe, Al, and Ca. Human activities (e.g., fertilizer use, coal use, and aluminum and steel industrial activities) have resulted in the accumulation of fluorine in soil. Coal combustion releases hydrogen fluoride (HF), silicon tetrafluoride (SiF4), and carbon tetrafluoride (CF4), which can be accumulated in the soil environment [3,4]. Fluorine levels in soil can be elevated by fluorine-containing rocks (natural origin) [5,6]. Studies have shown that fluorine-containing mica, fluorite (CaF2), and apatite can contribute to the accumulation of fluorine in soil and groundwater through weathering [5,6,7,8,9,10,11,12]
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