A contrast of lead immobilization via bioapatite under elevated CO 2 between acidic and alkaline soils

The feasibility of Pb immobilization via bioapatite ( BA p) and CO 2 in the acidic red soil ( RS ) and saline‐alkaline soil ( SS ) was compared in this study. The elevated CO 2 (10% in air) significantly promoted the dissolution of BA p 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 BA p addition and CO 2 elevation. In RS , the addition of BA p (even without CO 2 ) could significantly increase water‐soluble P. Moreover, some Pb cations were adsorbed onto iron (hydr)oxides within RS . In contrast, CO 2 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 BA p is feasible for acid soil.