Biosorption of chromium, copper, and nickel from aqueous solution by Tamarindus indica fruit nut testa (TFNT) in its pristine and acid-treated forms was studied under equilibrium and column-flow conditions. TFNT, a tannin-containing material, was characterized by energy dispersion x-ray fluorescence (EDXRF) and Fourier transform infrared (FTIR) spectral techniques and surface analysis. The effect of experimental variable parameters such as pH, concentration of metal ions, amount of adsorbent, and contact time on adsorption was investigated. Batch isothermal equilibrium data were analyzed on the basis of Langmuir and Freundlich adsorption isotherms. The kinetics of the adsorption process were studied in terms of Lagergren first-order kinetic model. The monolayer adsorption capacities of pristine and acid-treated forms of tamarind seed coat were found to be 44.8 and 77.5 mg/g for Cr(VI), 55.8 and 99.0 mg/g for Ni(II), and 84.7 and 85.4 mg/g for Cu(II) ions, respectively. The column-flow adsorption data were used to obtain breakthrough curves. The biosorbent loaded with the metal ions was regenerated using 1.0 M HCl and the regenerated bed was used for subsequent adsorption-desorption cycle.
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