Regeneration of surfactant-modified zeolite after saturation with chromateand perchloroethylene

Surfactant-modified zeolites (SMZ) have drawn recent attention as sorbents due to their removal of multiple types of contaminants and low material cos t. Hoc-ever, like most sorbents, SMZ has a finite sorption capacity for dif ferent contaminants. The potential applications, economics, and efficiency of SR IZ as a sorbent are related to the ability to regenerate the material , This paper reports several methods to regenerate chromate- and perchloroe thylene-saturated SMZ. Regeneration of chromate-saturated SMZ was achieved by Bushing with a sodium carbonate:sodium hydroxide solution. However, this high-pH solution increased the counterion competition for chromate sorptio n sites and decreased the chromate sorption capacity of the regenerated SMZ , As an alternative regeneration method, chromate sorbed to SMZ was reduced to Cr[II] in situ using sodium dithionite solution. Although reduction wit h dithionite restored the chromate sorption maximum, the chromate sorption intensity was lowered, possibly due to the competition by sulfate (generate d from oxidation of dithionite) for chromate sorption sites. Carbonate-rege nerated SMZ showed no loss of sorption affinity for perchloroethylene (PCE) compared to virgin SMZ. Air sparging of PCE-saturated SMZ fully regenerate d the SMZ. The results show that it is possible to regenerate and re-use SM Z following saturation with anionic or nonpolar organic contaminants. (C) 2 000 Elsevier Science Ltd. All rights reserved.