Aplicação de bentonitas como potenciais adsorventes no tratamento de rejeitos de mineração: remoção de um reagente coletor

Abstract

The industry-discarded residues on water body without proper treatment before the process of waste release are responsible for large impacts on the environment. The shortage of clean water sources is increasingly evident as a consequence of such activity, so efficient methods focusing on the treatment of industrial effluents need to be developed. Mining represents a sector in industrial activity highly water-dependent, hence is among the major polluters. The aim of this study was to develop an economically viable alternative to the conventional waste treatments of effluents produced especially by mining activity using natural (N1, N3 e N4) and modified bentonite (N3CTAB). The clays were tested according to their potential as adsorbents for the removal of fatty acid-based contaminants. The effect of the variables involved in the removal process such as initial concentration, pH and adsorbent mass was studied through a full factorial design. The adsorption tests caused high removal rates of fatty acids close to 90%. The adsorbents N1 and N4 tested in the assays are natural materials presenting high efficiency (values of about 800 mg g-1) at pH’s close to 8.0 and mass close to 0.4 g. At the N3 material was required treatment for increasing its efficiency like adsorbent. The N3 improvement process (called organophilization) proved to be satisfactory, demonstrating the versatility of bentonites. The materials were undergone to methods of characterization such as zeta potential analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption/desorption and cation exchange capacity (CEC). The analyzes showed the presence of negative charges on the bentonite structures, as well as high surface area and ion exchange capacity, important characteristics for the adsorption process. Theoretical studies carried out using potential maps, interaction energy and atomic charge calculations revealed the possibility of formation of a substrate on the modified N3 material which allowed increasing the interaction between adsorbate and adsorbent. According to the results, bentonites have great potential to be applied as adsorbents for the treatment of mining tailings, especially for removing fatty acid-based collectors, employed in the flotation of phosphate minerals.