Eliminating the stabilizer antagonistic effects for efficiently stabilizing Pb and As co-contaminated soil by innovative stepwise steam flash heating

Chemical stabilization is frequently used to stabilize lead (Pb) or arsenate (As), but faces challenges in Pb-As co-contaminated soils because of the antagonistic reactions between chemical stabilizers and contaminants. In this work, we innovated an effective and cost-efficient stepwise steam flash heating (SSFH) strategy to simultaneously immobilize Pb and As, and unraveled the underlying mechanisms. The combination of 1.5   % Ca(H 2 PO 4 ) 2   and 2   % Fe 2 (SO 4 ) 3 only decreased 1.99   % Pb by toxicity characteristic leaching procedure (TCLP-Pb) but increased 17.8   % of TCLP-As due to the antagonistic effects. SSFH with Ca(H 2 PO 4 ) 2 in the first step and Fe 2 (SO 4 ) 3 in the second step achieved the minimal TCLP-Pb and TCLP-As of 0.778 and 0.327 mg/L, respectively. It also reduced 69.8   % of leachable As in 100-year acid rain simulation, indicating a favorable long-term stabilization performance. Additionally, SSFH approach reduced 43.2   % stabilizer dosage and 14.9   % cost. X-ray absorption near edge structure (XANES) documented that the stepwise SFH promoted the transformation of Pb(NO 3 ) 2 and NaAsO 2 /NaAsO 3 /As 2 O 3 /As 2 O 5 into stable Pb 3 (PO 4 ) 2 and FeAsO 4 , preventing the formation of AsO 4 3- and FePO 4 . Our findings proved the state-of-the-art SSFH approach and unraveled its mechanisms to stabilize Pb and As co-contamination in soils, offering a green and sustainable remediation alternative for the management of heavy metal contaminated sites. Environmental implication A novel stepwise SFH approach can be applied to overcome the stabilizer antagonist effects by separately immobilizing Pb and As in two sequential steps. It also decreased 43.2   % of stabilizer dosage and 14.9   % of cost comparing to conventional chemical stabilization. This approach can be used for other metal co-contaminated soils facing similar antagonistic challenges, and our work raises a state-of-the-art solution for cost-effective, green and sustainable remediation practices.