SORPTION OF ROXARSONE FROM WATER ONTO TYPICAL NATURAL CLAY MINERALS

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid) has been widely used as a feed additive to control coccidial intestinal parasites and to enhance feed efficiency in poultry industry. Nearly all the roxarsone is excreted unchanged and part of that enters animal wastewater and surface water through washing and runoff, posing potential risk to aquatic environment. Suspended particulate matter with a huge specific surface area and a large number of active groups may combine roxarsone onto its surface and determine the fate of roxarsone in aquatic environment. Clays are important components of suspended particulate matter and exhibit good sorption properties for various kinds of pollutants in aquatic environment. In this work, the sorption of roxarsone to three typical natural clay minerals, i.e., kaolinite, illite and montmorillonite, was investigated. The results indicated that 1) Roxarsone can be spontaneously sorbed on natural clay minerals and more easily sorbed at higher temperatures. 2) Ferric ion with a concentration of 0-5 mM significantly promoted roxarsone sorption by forming bridging complexation, while divalent calcium ion and divalent magnesium ions exhibit an inhibitory effect on roxarsone sorption. 3) pH has obvious effect on the sorption and the maximum sorption occurs at pH about 9.0, 5.0 and 5.0 for kaolinite, illite and montmorillonite, respectively.