PO^sub 4^^sup 3-^ Removal by and Permeability of Industrial Byproducts and Minerals: Granulated Blast Furnace Slag, Cement Kiln Dust, Coconut Shell Activated Carbon, Silica Sand, and Zeolite

Excess PO^sub 4^^sup 3-^ from agricultural subsurface drainage and runoff degrades the overall water quality of the receiving surface waters in a cumulatively damaging process known as eutrophication. In the past 25 years, PO^sub 4^^sup 3-^ removal by industrial byproducts and minerals has received considerable attention because these materials are both abundant and inexpensive. In this study, the saturated falling-head hydraulic conductivity and phosphate removal capability of granulated blast furnace slag (GBFS), cement kiln dust (CKD), zeolite, silica sand, and coconut shell activated carbon (CS-AC) were assessed. GBFS, zeolite, silica sand, CS-AC, and 5:95% and 10:90% CKD/sand blends all exhibited hydraulic conductivities ≥0.001 cm/s. GBFS and the CKD/sand blends exhibited >98% PO^sub 4^^sup 3-^ removal while CS-AC removed 70-79% of initial PO^sub 4^^sup 3-^ concentrations. In contrast, silica sand and zeolite removed 21-58% of PO^sub 4^^sup 3-^. The phosphate removal data for each material was modeled against the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Frumkin sorption isotherms to yield insight into possible removal mechanisms. Overall, GBFS, CKD, zeolite, silica sand, and CS-AC were sufficiently permeable and removed significant amounts of PO^sub 4^^sup 3-^ and should be considered for use in treatment of agricultural effluent.[PUBLICATION ABSTRACT]