Adsorção e dessorção de arsênio(V) pelo compósito magnético hidrotalcita-ferro e seu emprego na remoção deste elemento de águas da região do Quadrilátero Ferrífero, Minas Gerais

• Autor(a) principal: Toledo, Thiago Vinícius
• Data de Publicação: 2010
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2131
• topic: Adsorção; Hidrotalcita-ferro; Arsênio; Adsorption; Hydrotalcite-iron; Arsenic; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA

In the present study, adsorption and ion exchange properties of hydrotalcite were combined with the magnetic properties of iron oxide to produce a magnetic adsorbent (HT-Fe). Its adsorbent potential was evaluated for removal of As(V) species from aquatic solutions. Optimal adsorption conditions were determined and the arsenic concentrations, in all cases, were obtained by hydride generation - atomic absorption spectrometry (HG-AAS). Later, the HT-Fe magnetic compound was submitted to calcinations with the objective of intensifying its adsorption and anionic exchange properties by mean of increasing the surface areas, porosity and also the memory effect . This calcined adsorbent at 500 °C (HT-Fe 500) also had its potential evaluated for removal of As(V) species from water. For both the HT-Fe and HT-Fe 500, the kinetic model which best explained the adsorption removal process, with R2 > 0.961 for HT-Fe and R2 > 0.981 for HT-Fe 500, was of pseudo second order suggesting that chemisorption is the determining stage in the adsorption mechanism. The constant related to adsorption velocity of pseudo second order showed to be dependent on the initial concentration of the adsorbate and of proportionally inverse behavior, reaching, in the case of HT-Fe, a value of 0.441 g mg-1 h-1 for 1.0 mg L-1 of As(V) and 3.09 x 10-3 g mg-1 h-1 when the initial concentration of As(V) was 160.0 mg L-1; however for HT-Fe 500 the obtained value was 2.173 g mg-1 h-1 for 1.0 mg L-1 of As(V) and 0.0114 g mg-1 h-1 for an initial As(V) concentration equal to 160.0 mg L-1. At equilibrium the isotherm model that best explained the adsorption process, for both adsorbents, was that proposed by Langmuir, indicating the adsorbent possessed a defined number of identified active sites where each retains only one adsorbate molecule; also, the adsorption energy is not dependent on the quantity of material adsorbed and the adsorbed species do not react with the medium or among themselves, being that adsorption is restricted to a monolayer. It was observed that the maximum As(V) adsorption capacity estimated in this model for HT-Fe 500 is 31.81 mg g-1. This capacity is 3.12 times greater than that presented by HT-Fe (10.19 mg g-1) for the same pH (7.0) and with a solution 2.5 times more concentrated than that used for HT-Fe 500. At pH values of 4.0 and 9.0, the HTFe presented maximal adsorption capacities of 24.09 and 10.19 mg g-1, respectively. The HT-Fe adsorbent is easily recovered by desorption where the best result was obtained when using a desorbing solution containing NaOH 20% w/v, which desorbed 81.7% of the adsorbate mass impregnated in 100.0 mg of the HT-Fe composite. Yet for the NaOH 3% (w/v) + NaCl 5% (w/v) there was no alteration in the original structure of adsorbent and 53.8% of the adsorbate mass impregnated in 100.0 mg of the same composite was desorbed. For the HT-Fe 500 the best obtained desorption results were also for the NaOH 20% (w/v) and for the solutions resulting from NaOH and NaCl combination, where it was again found that the desorbed mass increased significantly from the first to second desorption cycle. The actuation potential of both adsorbents, calcined and non-calcined, was also tested using natural water samples contaminated with arsenic collected in the Iron Quadrangle region, MG. Results of the analyses in water showed total As concentrations varying between 2.82 and 195.9 μg L-1, demonstrating that in some samples this quantity is greater than the maximum limited recommended by Brazilian administration for monitoring of water destined for human consumption, which is 10.0 μg L-1. The As removal rate was 92.75% with the HT-Fe composite and 95.33% with HT-Fe 500 for the concentration real sample.