Sorption of chromate and other inorganic anions by organo-zeolite

Abstract

We performed batch sorption experiments that showed a significantly enhanced removal of inorganic oxyanions from aqueous solution by clinoptilolite-dominated zeolite modified by the quaternary amine hexadecyltrimethylammonium (HDTMA). Since HDTMA is too large to enter into the internal portion of the zeolite, sorption of the amine only occurred on the zeolite's external exchange sites. HDTMA was exchanged with extrastructural cations of the zeolite up to the external cation-exchange capacity. The HDTMA-modified surface was stable when exposed to extremes in pH and ionic strength and to organic solvents. While the natural zeolite had no affinity for the oxyanions, the HDTMA-modified zeolite showed significant removal of chromate, selenate, and sulfate from 0.005 M CaCL aqueous solution. Sorption data for each anion were well-described by the Langmuir isotherm equation. We found that anion sorption was highest when the zeolite was modified such that HDTMA satisfied 100% of its external cation-exchange capacity. The mechanism of anion retention appears to be the formation of an HDTMAanion precipitate on the zeolite surface.

Chromium (VI) Adsorption Characteristics of Bentonite Under Different Modification Patterns

“…Many experiments were performed to study the adsorption characteristics of differently modifi ed clays or soils to heavy metal anions. Data from Haggerty and Bowman [10] and Li and Bowman [11,12] indicated that clays such as kaolin and montmorillonite, modifi ed with CTMAB (cetyl trimethyl ammonium bromide), provided suffi cient adsorption capacity to nitrate, arsenate, chromate, and other oxygen-containing acid anions. These modifi ed clays exhibited the best adsorption ability when the modifi cation ratio was set to be 200% CEC (cation exchange capacity) of clay, and the heavy metal anions were mainly adsorbed by electrostatic interactions on modifi ed clays [13].…”

Adsorption of methylene blue and orange II onto unmodified and surfactant-modified zeolite

“…Chen). framework structure bearing AlO 4 and SiO 4 tetrahedra that are linked to each other by sharing all of their oxygens to form interconnected cages and channels containing mobile water molecules and alkalis and/or alkaline earths [11,12]. Zeolite is a good adsorbent for heavy metal ions from wastewater [13][14][15] and for organic dyes [5,[16][17][18].…”

Adsorption of ions onto treated natural zeolite

“…Many authors show the use of modified natural zeolite on environmental applications, mainly anions uptake from effluents by adsorption processes 10,11,20,21 . The present work describes studies of characterization, modification (treatment) and application of a natural zeolite from Chile.…”