AGRICULTURAL BY-PRODUCTS AS ADSORBENTS FOR METAL-IONS IN LABORATORY PREPARED SOLUTIONS AND IN MANUFACTURING WASTE-WATER

Byproducts of soybean and cottonseed hulls, rice straw and sugarcane bagasse were evaluated as metal ion adsorbents in aqueous solutions. Adsorption capacities were determined by adsorption isotherms using the Langmuir model. Their adsorption capacities for Zn(II) were: soybean hulls > cottonseed hulls > rice straw > sugarcane bagasse. Capacities varied from 0.52 to 0.06 meq/g dry weight of byproduct, Rice straw and sugarcane bagasse were not evaluated further in this study because of their low adsorptive capacities (less than or equal to 0.12 meq/g). At a subsaturating concentration of metal ion (100 mg/L), soybean and cottonseed hulls adsorbed high levels (95.6-99.7%) of Cr(III), Co(II), Cu(II), Ni(II) or Zn(II). The ability of soybean and cottonseed hulls to sequester metal ions was further evaluated with three different samples of manufacturing wastewater. These wastewaters had environmentally unacceptable concentations of Zn(II), Cu(II) and Ni(II). Soybean and cottonseed hulls adsorbed similar amounts of these metal ions from each wastewater. The percentage of metal ion adsorbed ranged from 53.4 to 99.8% depending on the particular wastewater and metal ion. Although not as effective as a commercial chelating resin in removing metals from wastewaters, soybean and cottonseed hulls could be useful adsorbents in metal removal applications, especially when the low cost and high availability of these materials are considered.