PO4(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 PO4(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, PO4(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% PO4(3-) removal while CS-AC removed 70–79% of initial PO4(3-) concentrations. In contrast, silica sand and zeolite removed 21–58% of PO4(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 PO4(3-) and should be considered for use in treatment of agricultural effluent.