Application of termite nest for adsorption of Cr(VI).

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), representing 93.2% removal of Cr). The termite nest was characterized by off-line pyrolysis GC/MS (py-GC/MS), infrared spectroscopy (FTIR), and electron paramagnetic resonance spectroscopy (EPR). Pyrolysis of the adsorbent produced a complex mixture of aromatic compounds, including the guaiacyl and syringilic derivatives that are characteristic of lignocellulosic materials. Infrared spectroscopy revealed deprotonation of the carboxylic acid group of the biomass with increasing pH, which was associated with a decrease in the capacity for adsorption of Cr(VI). The EPR g-factor for the termite nest samples varied between 2.0037 and 2.0038, indicating the presence of organic free radicals that were responsible for the redox reaction. 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. The adsorbent presented excellent performance in the removal of chromium under acidic conditions, with the advantage that it could be regenerated and reused.

ICP-AES determination of small amounts of zinc in copper-base alloys after separation by adsorption of the zinc-TAN complex on Sep Pak C18 cartridges.

The use of ICP/AES for the determination of zinc, in low concentration levels, in matrices containing high levels of copper is difficult because copper interferes in the zinc main emission wavelength (213.856 nm). In the present work, a separation of zinc from copper matrices was possible, using the reaction of zinc(II) cation with 1-(2-tiazolylazo)-2-naphthol (TAN), in the pH range of 6.5-8.0, resulting in a stable red complex. Copper also reacts with TAN but its interference was avoided by the addition of ascorbic acid and thiosulphate in the reaction medium. In this way, the aqueous solution was passed through a SEP PAK C18 cartridge, in which the zinc(II)-TAN complex was quantitatively retained, but it did not occur with copper which passes through the cartridge, as [Cu(2)(S(2)O(3))(2)](2-), with the aqueous solution. The cartridge was washed with water and the complex eluted with ethanol. Then, the alcohol was evaporated and the complex decomposed by nitric acid. It results in both zinc pre-concentration and separation from copper. The zinc quantification was carried out by ICP/AES at 213.856 nm. The relative standard deviations, for ten different aliquots, were 5.7% and the average recovery found for zinc was 96%, even when the concentration ratio Cu/Zn was up to 500/1 (mg l(-1):mg l(-1)). Other metals, like nickel, for example, can react with TAN in the same way as zinc but they do not interfere in the emission wavelength 213.856 nm.