Adsorption of Cr(VI) onto cetylpyridinium bromide modified zeolites: Effect of surfactant loading, solution pH, ionic strength and coexisting anions

Surfactant-modified zeolites (SMZ) with different coverage types were prepared by loading the cetylpyridinium bromide (CPB) onto the surface of the natural zeolite collected from Jinyun County, Zhejiang Province, China. The adsorption behavior of Cr(VI) on SMZ was investigated. Natural zeolite and SMZ with CPB monolayer coverage were inefficient for the removal of Cr(VI) from aqueous solution. However, SMZ with CPB patchy bilayer or bilayer coverage was efficient in the removal of Cr(VI) and the Cr(VI) adsorption capacity of SMZ increased with its CPB loading. The Cr(VI) adsorption capacity of SMZ showed a maximum at pH 3-6 and decreased with increasing pH from 6 to 11. The presence of competing anions such as chloride, sulfate and bicarbonate ions reduced the Cr(VI) adsorption capacity of SMZ. The adsorption process was strongly dependent on ionic strength, indicating that anionic exchange and electrostatic interaction were the main mechanisms that govern the adsorption of Cr(VI) on SMZ.