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The biosorption potential of three different agro-industrial waste materials of lignocellulosic origin, i. e., coir pith (CP), sawdust (SD) and sugarcane fiber (SF), is investigated in the case of basic dyes, i. e., crystal violet (CV) and rhodamine B (RB). The uptake of dyes from aqueous solutions is found to be rapid when using these candidate biosorbents. The application of various kinetic models reveals good correlation of a pseudo-second order kinetics model with the experimental data. Equilibrium adsorption data have been analyzed using nonlinearized forms of the Langmuir, Freundlich and Redlich-Peterson isotherms, to determine the best fit equation for the adsorption process. Experimental results show that all of the adsorbents are effective for the removal of dyes from aqueous solutions and their adsorption capacities are comparable with other reported adsorbents. Since the agricultural solid waste materials used in the present investigation are freely and abundantly available, the adsorption process is expected to be economically viable for wastewater treatment.

The applicability of low-cost lignocellulosic biosorbent-coir pith, for removal of cobalt (II) from aqueous solutions using batch adsorption studies has been explored herein. Adsorption characteristics of coir pith were investigated systematically by varying the experimental parameters such as, solution pH, initial metal ion concentration, contact time, adsorbent dose and temperature. The studies revealed that optimum adsorption of cobalt onto coir pith occurred in the pH range of 4.0 - 7.0. Sorption kinetics of cobalt was found to be quite rapid under ambient conditions and the process followed second-order kinetics. The experimental data have been analyzed using non-linearized forms of Langmuir, Freundlich and Redlich-Peterson adsorption isotherms for mathematical description of the process. Desorption studies showed that the quantitative recovery of Co (II) from the spent coir pith was achieved by using 0.5 N HCl. The suitability of this adsorbent for real situation has been observed, when complete removal of cobalt from nuclear power plant coolant water was obtained. The present studies successfully demonstrated the use of coir pith as an efficient adsorbent material for removal of cobalt from aqueous solutions.