Section Nineteen
RESIN TECHNOLOGY
80    CHARACTERIZATION, DEVELOPMENT AND USE OF NEW
BREED ON ANION-EXCHANGE RESINS FOR
SELECTIVE REMOVAL OF Cr(VI) AND
OTHER TOXIC ANIONS
Arup K. Sengupta, Assistant Professor
Tushar Roy, Graduate Student
Civil Engineering Department
Lehigh University
Bethlehem, PA 18015
Dennis Clifford, Associate Professor
Suresh Subramonian, Research Associate
Civil Engineering Department
University of Houston
Houston, TX 77004
INTRODUCTION
Chromate, arsenite and arsenate, nitrate, selenite and selenate, uranyl complexes, organo-arsenic
compounds are examples of some toxic anions present in wastewaters from different types of chemical, agro-chemical and utility industries. ••2'3 Many groundwater sources around the nation have also
been contaminated by most of these anions. Anion-exchange processes using synthetic, organic-base
anion-exchange resins are gradually being found viable for selective removal of these toxic anions
primarily due to synthetic resins with: 1) high exchange capacity compared to hydrous oxides and
other naturally occurring substances with ion exchanging ability; 2) excellent kinetic properties compared to other adsorbents like activated carbon; 3) very good stability under harsh operating conditions, namely, very low and high pH, up to 40°C temperature, mechanical attrition and mild oxidizing
environment; 4) ability to be regenerated and reused over hundreds of cycles. Stringent regulations in
regard to both industrial effluent and drinking water standards and also, an enhanced appreciation of
the importance of recovering toxic substances have played a major role in improving the economic
viability of the ion-exchange processes.
During the last five years, we have been studying the various features of chromate ion-exchange
processes and our findings about the governing chromate ion-exchange mechanism and the effects of
other important process variables have been reported elsewhere45'6 and are not being included here.
The performance of the chromate ion-exchange process, according to our recent studies, is greatly
influenced by the properties of the anion-exchange resins. In particular, the following composition
variables of anion-exchange resins were found to have significant effects on chromate selectivity in
the presence of other competing anions: 1) Polymer matrix; 2) Functionality; 3) Crosslinking; 4)
Charge density and porosity. To start with, we used different types of commercially available
anion-exchange resins for studying the effects of resin properties on chromate selectivity. Based on
the observations and analysis of such results we have synthesized a group of anion-exchange resins
which may significantly improve the performance of the chromate ion-exchange processes.
These new ion-exchange resins needed only a minor modification of the presently available commercial resins and are unlikely to cost significantly higher than their commercial counterparts. Secondly, the outcome of this study on chromate ion exchange may act as a nucleus in characterizing and
selecting proper types of anion-exchange resins for selective removal of other toxic anions, namely,
As(V), U(VI), Se(IV), Se(VI), (CH3)2As02, NO5. In this paper, such parallel analogies will be provided
along with our observations on chromate ion exchange.
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