Chromium(vi) Removal by Modified Pvp- Coated Silica Gel

This research involved the synthesizing of a reactive polymer, long alkyl quaternized poly(4-vinylpyridine) (PVP), and coating it on the surface of silica gel to produce a granular sorbent to remove Cr(VI) from water. Batch experiments were conducted to determine the kinetics, sorption isotherm, pH effects, and influence of other anions on the chromium adsorption onto the coated silica gel. The research demonstrated that the synthesized PVP-coated silica gel (referred to as coated gel) could successfully remove chromium(VI) from solution. The adsorption of Cr(VI) by the coated gel was strongly influenced by the pH. The maximum sorption occurred at about pH 4.5-5.5 under the test conditions. The removal efficiency was 100% when the initial Cr(VI) concentration was 2.5 mg/L with 2.5 g/L of coated gel at pH 5.0. The concentrations of Cr(VI) had a pronounced effect on the rate of sorption. Compared to ion exchange, the sorption kinetics of Cr(VI) were fast (about 5h). The equilibrium sorption data fitted the Langmuir isotherm model. Chromium adsorbed on the coated gel was easily recovered under certain conditions. 1.0 INTRODUCTION Chromium compounds are widely used by modern industries, resulting in large quantities of this element being discharged into the environment. Some of the main uses for chromium compounds are as follows: (1) plastic coating of surfaces for water and oil resistance, (2) electroplating of metal for corrosion resistance, (3) leather tanning and finishing, and (4) in pigments and for wood preservative. Until a few years ago, it also was the favored corrosion control agent in cooling towers whose water blowdown (waste) was dumped into rivers, pits, lakes, and oceans (Norvelle, 1992). In addition, during the 1950's, chromates were used as a highway de-icing agent in the United States. Chromium occurs in wastewaters resulting from these operations in both trivalent [Cr(III)] and hevalent [Cr(VI)] forms. The hexavalent form is more hazardous to animals than the trivalent form. A wide range of technologies is available for the removal of hexavalent chromium from waste-waters, some of which are well-established methods that have been in practice for decades such as These processes simply remove chromium from wastewaters by reduction (Shen and Wang, 1995), coagulation, and filtration. Although these technologies are quite satisfactory in terms of purging chromium and other heavy metals from water, they produce solid residues (sludge) containing toxic compounds whose final disposal is generally by landfilling with related high costs and still a possibility of groundwater …