Orthophosphate â�£xation of metal contaminated soils in environments that undergo freezeethaw cycles is understudied. Freezeethaw cycling potentially inâ�£uences the reaction rate, mineral chemical stability and physical breakdown of particles during â�£xation. This study determines what products form when phosphate (triple superphosphate [Ca(H2PO4)2] or sodium phosphate [Na3PO4]) reacts with lead (PbSO4 or PbCl2) in simple chemical systems in vitro, and assesses potential changes in formation during freezee thaw cycles. Systems were subjected to multiple freezeethaw cycles from â�£10 C to â�£20 C and then analysed by X-ray diffractometry. Pyromorphite formed in all systems and was stable over multiple freezeethaw cycles. Low temperature lead orthophosphate reaction efâ�£ciency varied according to both phosphate and lead source; the most time-efâ�£cient pyromorphite formation was observed when PbSO4 and Na3PO4 were present together. These â�£ndings have implications for the manner in which metal contaminated materials in freezing ground can be treated with phosphate.
Hafsteinsdóttir, E., White, D., Gore, D., & Stark, S. (2011). Products and stability of phosphate reactions with lead under freeze-thaw cycling in simple systems. Environmental Pollution, 159(2), 3496-3503. https://doi.org/10.1016/j.envpol.2011.08.026