Removal characteristics of metal ions using degreased coffee beans: Adsorption equilibrium of cadmium(II)

The feasibility of using coffee beans after being dripped and degreased (DCB) as an adsorbent for base metals such as copper(II), zinc(II), lead(II), iron(III) and cadmium(H) were examined. The compositions of the I)CB were characterized by Fourier transform infrared spectroscopy, scanning electronic micrograph and fluorescent X-ray. It was found that DCB contain sulfur and calcium from the analysis using fluorescent X-ray. The plant cell wall in DCB has the porous structure from the scanning electron microscopy (SEM) analysis, and the specific surface area was determined to be 1.2 m(2)/g using the specific surface area analyzer. Batch adsorption experiments on DCB were carried out at various pHs in order to elucidate the selectivity of metal ions. All metals were adsorbed at low pH region (3.0-5.0). Of particular interest was the adsorption characteristics of cadmium(II) on DCB. The adsorption isotherm for cadmium(II) at pH 8 fitted with a Langmuir equation to yield an adsorption equilibrium constant of 55.2 mmol dm(-3) and an adsorption capacity of 5.98 x 10(-2) mmol g(-1), The desorption of cadmium(II) was easily achieved over 90% by a single batchwise treatment with an aqueous solution of hydrochloric acid or nitric acid at more than 0.01 mol dm(-3). These results suggested that I)CB behaves as a cation exchanger. (C) 2006 Elsevier Ltd. All rights reserved.