Sorption of Chromate and Arsenate by Surfactant Modified Erionite (E-SMZ)

Abstract

In recent years, growth of various industry has led to the introduction of pollutants in nature, especially heavy metal ions such as Cr(III) and As(V), which are usually present in wastewater. Heavy metals containing waste are generated from metallurgical, mining, chemical, leather, distilleries, sugar, battery, electroplating, and pigment industries, to name a few. Chromium is found in natural water in oxidation states, Cr(III) and Cr(VI). The former is an essential element for mammals whereas the latter is reported to be toxic. Similarly, arsenic is an ubiquitous contaminant that can be found in high concentrations in natural waters and wastewaters. Arsenic containing waste streams are generated mainly by the microelectronic industry and by pesticide and pharmaceutical facilities. It occurs in two oxidation states that form oxyanions, arsenate As(V), and arsenite As(III); arsenite is more mobile and toxic than . As arsenic is a major hazardous contaminant for human health, its removal is an issue of increasing concern. Zeolites are crystalline, hydrated aluminosilicates containing exchangeable alkaline and alkaline earth cations in their structural frameworks. Since zeolites have a permanent negative charge on their surfaces, they have no affinity for anions. However, recent studies have shown that modification of zeolite with certain surfactants or metal cations yield sorbents with a strong affinity for many anions. Zeolite has high internal and external surface areas and high internal and external cation exchange capacities suitable for the surface modification by cationic surfactant (HDTMA). When the initial surfactant concentration is less than the critical micellar concentration (CMC), the sorted surfactant molecules primarily form a monolayer; limited chromate and arsenate sorption indicates that the patchy bilayer may also be formed. When the surfactant concentration is greater than the CMC and enough surfactant exists in the system, the sorbed surfactant molecules form a bilayer, producing maximum chromate and arsenate sorption. Quantitative sorption of chromate and arsenate and desorption of bromide ions indicate that the sorption of oxoanions is primarily due to surface anion exchange.