The biosorption of Cr (III) ions from aqueous solutions by groundnut husk, a low-cost biosorbent was studied on a laboratory scale batch experiments. The effects of pH, contact time, particle size, biosorbent dosage and temperature on the adsorption of Cr (III) ions were investigated. Determination of Chromium ion concentration in solution was done using Atomic Absorption Spectrophotometer (AAS). The results show that the removal mechanism is predominantly by chemisorption and it is dependent on the physical and chemical characteristics of the biosorbent material. From the initial concentration of 0.5 mM, optimum Cr (III) ions removal was obtained at pH of 4, particle size of 0.15 nm, contact time of 180 minutes and biosorbent dosage of 50 mg, with the highest biosorption efficiency of 81.15 %. The biosorption process was best described by the BET adsorption isotherm with R2 value 0.9814 indicating multiplayer adsorption. Analysis of the experimental data revealed that the biosorption of Cr (III) ions from aqueous solution by groundnut husk is a spontaneous process with a ?Go value of -24.38 kJmol-1 at 298 K and follow the pseudo second order kinetics with a rate constant of 0.0151 min-1. The results indicate that groundnut husk can be employed as a low cost alternative to commercial adsorbents in the removal of Cr (III) ions from wastewater.

Introduction: The conversion and utilization of agricultural wastes in environmentally friendly processes have transformed these materials into useful rather than waste materials. Aim: This study investigates the adsorption of indigo blue dye from aqueous solution onto coconut shell, a low cost agricultural waste material in a batch process. Materials and Methods: Pulverized coconut shell was chemically modified and characterized using the Fourier Transform Infra Red spectroscopy and Scanning Electron Microscopy. Adsorption process using the chemically modified coconut shell was studied as a function of pH, initial dye concentration, adsorbent dose, and contact time. The adsorption equilibrium data were analyzed with Langmuir, Freundlich and Temkin isotherm models. Results: The results revealed that percentage of the indigo dye adsorbed from aqueous solution varied linearly with the adsorbent dose, concentration and time with maximum percentage dye adsorption of 88.4% at 70 mg dosage, 95.8% at 0.05 mg/L concentration and 90% at 1 hr contact time but varies non-linearly with pH with maximum percentage dye adsorption of 92.9% attained at pH of 5. The adsorption equilibrium data were analyzed with Langmuir, Freundlich and Temkin isotherm models with the Langmuir isotherm having the best fit to the adsorption process with R2 value of 0.998. The experimental data were best described by the pseudo-second order kinetics model. FTIR analyses reveal that the adsorption process was through a chemical interaction of the dye with some functional groups at the surface of the adsorbent Conclusion: The chemically modified coconut shell is an effective adsorbent for the removal of indigo dye from aqueous solution is by chemisorption process with the adsorbent surface energetically homogeneous (n < 1). Keywords: Adsorption, Indigo blue dye, Coconut Shell, Kinetics, Aqueous solution.