Application of termite nests for adsorption/desorption of cr(vi)

摘要

This work proposes the use of tree termite nest as an adsorbent for the reduction/removal of Cr(VI) present in aqueous solution. In laboratory experiments, adsorption of Cr(VI) was sensitive to pH in the range investigated (2- 5), with maximum adsorption capacity achieved at pH 2 (3.70 ± 0.04 mg g~(-1) , 93.2% removal of Cr). The EPR g- factor for the termite nest samples varied between 2.0037 and 2.0038, indicating the presence of organic free radicals .A second line with g-factor values of 1.9790, only observed for the samples after contact with Cr(VI) solutions at different pH values, was assigned to Cr(III)-Cr(III) exchange coupled pairs, which explained the capacity of the adsorbent to retain a large portion of the Cr(III) ions produced after reduction of Cr(VI) to Cr(III). Fixed-bed column experiments showed that the termite nest had a maximum adsorption capacity of 18.60 mg Cr g~(-1) , an adsorption efficiency varying between 60.8 and 97.4%, and a desorption efficiency varying between 54.5 and 91.4%, for three successive cycles.