Mechanism insight into highly efficient stabilization of Cd contaminated soils by steam flash heating

Abstract

Soil cadmium (Cd) contamination is a world-wide challenge and chemical stabilization is the most used remediation strategy. To solve the disadvantages of high stabilizer dosage and cost, we innovated a cost-efficient steam flash heating (SFH) approach to chemically immobilize Cd in contaminated soils, which introduced high-pressure saturated water vapor into soil microstructure, broke their binding with soil particles and accelerated Cd reactions with stabilizers by ultrafast pressure release. Using calcium dihydrogen phosphate, potassium hydrogen phosphate or calcium carbonate as stabilizer, Cd stabilization efficiency was 10.4%, 13.4% and 17.1% higher by SFH than conventional chemical stabilization, and the lowest Cd content in leachate was 0.61 mg/L. Additionally, SFH approach averagely reduced 50.1 ± 7.29% of stabilizer dosage, 34.1% of cost, and 29.9% of CO2 emission. BCR sequential extraction results suggested that acid extractable Cd was preferentially transformed into residual Cd by SFH. Analysis of X-ray absorption near edge structure (XANES) documented that SFH treatment produced more stable Cd-minerals of Cd3(PO4)2, CaCO3-Cd, and CdCO3. Our findings proved the state-of-the-art SFH approach and uncovered its mechanisms to stabilize Cd in contaminated soils, offering a green and cost-efficient remediation alternative for heavy metal contaminated site management.