Estudo comparativo do uso das argilas bentonita chocolate e verde na adsorção de metais pesados - níquel e cobre

Abstract

The deposition of contaminated industrial effluents by heavy metal in surface waters and soils, shows like one of the biggest problems found today, once that these metallic compounds are resistant to decomposition e accumulates itself in food chains, keeping its toxic characteristics. Between the methods used to treat waters contaminated by metals, the adsorption stands out, showing that is important to search for alternatives adsorbents like the bentonite. The objective of this research was to evaluate the actuation of two types of bentonite, the chocolate and the green one, as adsorbent of metallic ions of Copper (II) and Nickel (II) in aqueous solution. The clays were washed, dried, manually ground, part of them were calcinated in 500ºC, the natural and calcinated ones were ran through a 100 Mesh sieve. With the intention of optimizing the adsorption process, an experimental factorial planning of type 23 was carried out, having as independent variables the Concentration, Adsorbent mass, and Contact time. The experiment results performed with Bentonite, calcinated and in natura showed high metal removal values, in a short period of time, however, with the calcination, the clays lost some capacity of metal removal (reaching values above 97,79% in natura and maximum of 92,50%, calcinated). Based on the best conditions obtained from the experimental planning, we performed Kinect tests, adjusting the experimental data to the empirical models of pseudo-first and pseudo-second orders. The data were well adjusted for both models, however, the kinetic model of pseudosecond order obtained higher values of correlation coefficient (R²) and Test F, indicating that the adsorption of the metal by the clays occurred by chemisorpton. In the adsorption balance study, it was also used the best condition of experimental planning, and the experimental data were adjusted to the Langmuir Freundlich and Redlich-Peterson models. The model of isotherm balance that showed the best fit was the Redlich-Peterson model, with β tending to zero, indicating that, in higher concentrations, this isotherm assumes the form of Freundlich, corroborating what we saw in the Kinetic study. The removal results obtained for Bentonite in natura and calcinated was satisfactory, due to the high power of removal of metallic ions in a short period of time, indicating that the Bentonite clay has a high potential of application, due its low acquisition cost and good performance in Copper (II) and Nickel (II) removal in aqueous solutions. Comparing the results of each clay, in natura and calcinated, in the absorption of each metal, it was measured that the natural Bentonitas showed the best results in Copper (II) adsorption, being that, in the considered conditions to the copper ion adsorption, the chocolate natural Bentonita obtained the greatest results of removal, when compared to green natural Bentonita.