Formation and stability of Pb-, Zn- & Cu-PO4 phases at low temperatures: Implications for heavy metal fixation in polar environments

Low temperatures and frequent soil freeze–thaw in polar environments present challenges for the immobilisation of metals. To address these challenges we investigated the chemical forms of Pb, Zn and Cu in an Antarctic landfill, examined in vitro reaction kinetics of these metals and orthophosphate at 2 and 22 °C for up to 185 days, and subjected the products to freeze–thaw. Reaction products at both temperatures were similar, but the rate of production varied, with Cu-PO4 phases forming faster, and the Zn- and Pb-PO4 phases slower at 2 °C. All metal-orthophosphate phases produced were stable during a 2.5 h freeze–thaw cycle to −30 °C. Metal immobilisation using orthophosphate can be successful in polar regions, but treatments will need to consider differing mineral stabilities and reaction rates at low temperatures.

► We identify Cu, Pb and Zn species in an Antarctic Landfill.
► We identify the products and rates of reactions between metals and PO43− at 2 and 22 °C.
► We test the stability of metal-orthophosphate species during freeze–thaw.
► We conclude that orthophosphate may immobilize metals in freezing ground.