Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 21, 2006
Publication Date: June 9, 2006
Citation: Marshall, W.E., Wartelle, L.H. 2006. Chromate and copper adsorption by dual-functional ion exchange resins made from agricultural by-products. Water Research. 40:2541-2548. Interpretive Summary: The production of ion exchange resins is a technology that relies on the chemical interaction between reactive entities to form stable covalent bonds between a synthetic water insoluble support and a water-soluble functional group possessing a positive or negative charge. In recent years, attention has focused on the application of plant material as the water insoluble support. While various protocols are in place of impart anion or cation exchange properties on plant by-products and cellulosic fibers, there remains a need to create dual-functional ion exchange material from agricultural by-products that are cost effective and simultaneously efficacious toward both anions and cations of environmental concern. Scientists at the Southern Regional Research Center, New Orleans, LA have developed dual-functional ion exchange resins from soybean hulls, corn stover and sugarcane bagasse, effective with both cations and anions, that adsorbed as much as or more of the marker ions, copper and chromium, compared to commercial cation or anion exchange resins used for comparison. None of the commercial resins exhibited dual-functional properties to the same extent as the by-product-based resins. These dual-functional resins may be used in place of mixed bed resins, which combine the same ion exchange properties on two different resins rather than a single resin.
Technical Abstract: Ion exchange resins commonly have a single functionality for either cations or anions. Resins that have a dual functionality for both cations and anions are uncommon. The objective of this study was to create dual-functional ion exchange resins derived from soybean hulls, sugarcane bagasse and corn stover. Dual-functional resins were prepared by two separate two-step processes. In the first two-step process, by-products were reacted with a solution of citric acid in order to impart additional negative charge, and then reacted with the cross-linking reagent dimethyloldihydroxyethylene urea (DMDHEU) and a quaternary amine (choline chloride) to add positive charge to the lignocellulosic material. In the second two-step process, the order of reaction was reversed, with positive charge added first, followed by the addition of negative charge. These combined reactions added both cationic and anionic character to the by-products as evidenced by the increased removal from solution of copper (Cu2+) cation and the chromate (CrO4 2-) anion compared to unmodified by-products. The order of reaction appeared to slightly favor the functionality that was added last. That is, if negative charge was added last, the resulting resin sequestered more copper ion than a comparable resin where the negative charge was added first and vice-versa. Cu2+ and CrO4 2- were used as marker ions in a solution that contained both competing cations and anions. The dual-functional resins adsorbed as much as or more of the marker ions compared to commercial cation or anion exchange resins used for comparison. None of the commercial resins exhibited dual-functional properties to the same extent as the by-product-based resins.