PNNL

Abstract

A composite sorbent (GAC-QPVP) was prepared by coating poly(4-vinylpyridine) onto a commercial activated carbon (F400, Calgon), followed by cross-linking and quaternization processes. The sorbent was characterized by scanning electron microscopy, point of zero charge measurement, and BET analysis. Batch experiments with variable pH, ionic strength, and concentrations of Cr(VI), sorbent, and competing anions were conducted to evaluate the selective sorption of Cr(VI) from aqueous solutions. The equilibrium uptake of Cr(VI) increased with decreasing pH, decreasing ionic strength, and increasing sorbent concentration. The estimated maximum equilibrium uptake of chromium was 53.7 mg/g at pH = 2.25, 30.7 mg/g at pH = 3.65, and 18.9 mg/g at pH = 6.03, which were much higher than the maximum capacity of 3.5 mg/g for the PVP-coated silica gel at pH = 5.0 (optimum pH for Cr(VI) sorption) reported in the literature [13]. The effect of phosphate, sulfate, and nitrate was minor on the selective sorption of Cr(VI) and only when above a specific molar ratio. An ion exchange model that was linked with aqueous speciation chemistry reasonably well describe Cr(VI) sorption as a function of pH, ionic strength, and Cr(VI) concentration. Model simulations suggested that sorbed Cr(VI) was partially reduced to Cr(III) on the sorbent when pH