Green Remediation for Lead-Contaminated Soil Using Carbon Dioxide Injection

Numerous studies have been conducted to remove lead (Pb) from the soil. This study proposed a novel approach that used carbon dioxide (CO₂) as a cleaning reagent for the remediation and immobilization of Pb contamination in sandy soil. First, contaminated soil with 5,000 ppm lead nitrate (Pb(NO₃)₂) was prepared in a setup box. Then, sodium hydroxide solution (NaOH) (2 M) was injected into the soil to react and create sodium tetrahydroxyplumbate (II) [Na₂[Pb(OH)₄]]. The CO₂ gas was then introduced into the contaminated soil to react, which resulted in the formation of lead carbonate (PbCO₃) minerals. The soil samples were collected from across the setup box at different distances and depths from the injection tube after various times. PbCO₃ crystals were identified as cerussite by scanning electron microscope (SEM) and X-ray diffraction (XRD) investigations. Cerussite had poorer solubility under acidic conditions (e.g., 0.5% at pH 7 and 6.25% at pH 5), according to the results of mineral durability. PbCO₃ precipitated more near the injection tube during mineral sequestration and CO₂ carbonation. The highest precipitation was 0.12% with an inlet CO₂ rate of 0.7 L/min. In conclusion, Pb was removed from the soil at a rate of 99%. The permeability of the contaminated soil was reduced (from 4.6 × 10⁻³ to 3.7 × 10⁻⁴ cm/s) as PbCO₃ deposition increased between soil particles, although this did not affect the soil hydraulic conductivity. The results demonstrated the efficacy of CO₂ use as a unique technique to remove Pb from the soil.