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Pore Water Chemistry of Phosphogypsum-Treated Soil

Dep. of Soil Science, Univ. of Alberta, Edmonton, AB. T6G 2E3, Canada.

^* Corresponding author.

ABSTRACT

Phosphogypsum (PG) is a gypsum-based by-product of phosphate fertilizer production and is commonly stored at plant sites. As stockpiles of the material accumulate worldwide, elemental leaching from repositories is of potential environmental concern. In this study, samples of glacial till, PG, and mixtures of the two were incubated with deionized water. Solution extracts were analyzed for chemical constituents. Speciated activities of Al, Cr, and Cu, obtained using GEOCHEM, were related to theoretical levels estimated from solubility constants of potential solubility-controlling solids. Maximum pore water levels of As, B, Ca, Fe, K, Mn, Na, NH⁺₄-N, NO^–₃-N, Ni, P, Se, Si, Sr, V, and Zn were less when PG was mixed with soil and allowed to equilibrate. However, only the concentrations of Cd, Fe, Ni, P, Sr, V, and Zn were less by close to an order of magnitude or more. The increase in pH with soil addition influenced these substantial changes in elemental concentrations. The activities of Cr and Cu species decreased with soil addition, but the suspensions were considerably undersaturated relative to potential solubility-controlling solids. GEOCHEM indicated Al activities were in equilibrium with alunite, basaluminite, gibbsite, and jurbanite. As PG was neutralized through the addition of calcareous glacial till, solution levels of Al, Cd, Cr, Cu, Fe, Ni, P, Sr, V, and Zn all decreased substantially.