Green Remediation for Lead-Contaminated Soil Using Carbon Dioxide Injection

Abstract

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.