Influence of solution pH and ionic strength on chromate uptake by surfactant-modified zeolite

In this study, the influence of solution pH and ionic strength on sorption of chromate by surfactant-modified zeolite was tested. The sorption of chromate followed a Langmuir isotherm under different pH and ionic strength conditions. However, as the solution pH and ionic strength increased, the Langmuir sorption coefficient of chromate decreased systematically, reflecting an increased competition of background electrolyte anions against chromate for sorption sites. The chromate sorption maximum also decreased slightly as the solution pH and ionic strength increased. The stoichiometric relationship between chromate sorption and counterion desorption further indicated that chromate sorption on surfactant-modified zeolite surfaces was mainly due to surface anion exchange. In addition, increases in background electrolyte reduced counterion desorption and resulted in a better surfactant bilayer formation.