Interest in the redistribution of As-bearing species during long-term storage of hydrometallurgical tailings is motivated partly by the need to prevent As from being released into the environment. The speciation of As in mine wastes from the Tuva Cobalt Plant (Khovu-Aksy mine site, Tuva Republic, Russia) has been studied using mineralogical techniques, and chemical analyses of solids (tailings, soils, vegetation) and solutions (recovered pore waters, leach solutions). Ore at the plant was processed by hot autoclave leaching with an ammoniacal carbonate solution followed by treatment with CO2(gas) and caustic magnesite, MgO. Pronounced differences in element concentrations were measured in the five separate tailings ponds and one trench that were filled sequentially during operation of the plant. The concentration of each element was relatively uniform within each pond but the correlations among solid-phase Co, Ni, Zn and Cu gradually decrease from the most recent to oldest ponds as does the correlation between solid-phase As, Ag, Cd and Pb. In the oldest ponds, significant correlations are present between solid-phase Fe-As, Fe-Sb and Fe-Zn
