Biosorption of copper from aqueous solutions by plant root tissues

Root tissues of two common weeds, Amaranthus spinosus and Solanum nigrum, were found to adsorb dissolved Cu²⁺ in aqueous solutions. The adsorption can be represented by Langmuir and Freundlich isotherms. The equilibrium adsorption level was determined to be a function of initial solution pH and temperature. The adsorption capacity decreased with decreasing pH and increasing temperature. Alkaline pretreatment of the root tissue doubled the adsorption capacity. Ground powders of the root tissues were immobilized within alginate gel beads (3 mm diameter) for use in a packed-bed column. The mass transfer coefficient was calculated using the rate of metal ion adsorption to the gel beads. Surface film mass transfer resistance was important. Continuous adsorption/desorption cycles for removing and concentrating Cu²⁺ in solution were performed using the packed-bed column, which would be useful for treating wastewater containing trace amounts of copper ions.