Effects of Boric Acid Remediation on the Geotechnical Properties of CuSO₄-Contaminated Sandy Soil

Abstract

 This study investigates the effects of boric acid remediation on the geotechnical and strength properties of sandy soils contaminated with copper sulphate (CuSO₄). Boric acid was selected as the remediation agent due to its low cost, wide availability, and known chemical affinity for immobilizing heavy metal ions through borate complexation; in this context, remediation refers to the in-situ immobilization of copper ions rather than their physical removal. Experimental analyses evaluated specific gravity (Gs), fine content (FC), liquid limit (LL), optimum moisture content (OMC), maximum dry unit weight (MDU), and internal friction angle (ϕ). Increasing boric acid content led to a systematic decrease in Gs and MDU (up to ~6%), attributed to the low density of boric acid and its influence on soil–metal interactions. At a given CuSO₄ concentration, LL and OMC increased with boric acid content, whereas increasing CuSO₄ concentration itself suppressed LL, reflecting opposing effects of contamination and remediation on soil plasticity. FC decreased by up to ~88% with increasing boric acid content, indicating enhanced particle aggregation. Internal friction angle decreased by up to ~42% (from 35.6° to 20.8°) with both increasing heavy metal concentration and boric acid addition, consistent with the SEM and FTIR observations. The findings demonstrate that boric acid immobilizes heavy metal contaminants but simultaneously reduces soil shear strength, revealing an important trade-off between environmental and geotechnical performance that should be considered in practical remediation applications