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A contrast of lead immobilization via bioapatite under elevated CO2 between acidic and alkaline soils

The feasibility of Pb immobilization via bioapatite (BAp) and CO2 in the acidic red soil (RS) and saline‐alkaline soil (SS) was compared in this study. The elevated CO2 (10% in air) significantly promoted the dissolution of BAp in water, that is, the concentrations of released P were enhanced from 2 to 20 ppm as pH decreased from 6.9 to 5.6. Then, it was shown that 30–40% TCLP leached Pb was removed from RS and SS, with the combination of BAp addition and CO2 elevation. In RS, the addition of BAp (even without CO2) could significantly increase water‐soluble P. Moreover, some Pb cations were adsorbed onto iron (hydr)oxides within RS. In contrast, CO2 elevation is essential for enhancing P release in SS as it dramatically increased the dissolution of phosphates. The released P then reacted with Pb cations to form insoluble pyromorphite. Therefore, this combination is effective for Pb immobilization in saline‐alkaline soil whereas adding solely BAp is feasible for acid soil.