Caracterização e capacidade sortiva de elementos potencialmente tóxicos de um subproduto da indústria cerâmica

Abstract

Elements potentially toxic to plants, animals and humans are found naturally in nature. However, some anthropogenic activities concentrate these elements in the air, soil, and water, endangering the lives of plants, animals, and humans. Additionally, there exist those anthropogenic activities that can also generate materials with the potential to be reused, and thus avoid environmental damage, which may result when disposing of such elements in the natural environment. Some of these materials may present the potential for reuse as adsorbents of toxic elements and enable the decontamination of effluents. Ceramic industry by-product (SIC) formed by the fragments/shards of tiles and bricks could, in this sense, be an interesting alternative for reducing zinc, copper, cadmium, and lead concentrations in aqueous solutions. This by-product is found in large amounts in the tile and brick ceramic industry and has the added benefit of low cost. In this context, the present study aimed to characterize the SIC and evaluate its zinc, copper, cadmium and lead adsorption and desorption capacity compared to its raw material (MP) used during the tile and brick manufacturing process, and a Typic Dystrustox sample (LV). Fragments/shards of tiles and bricks (SIC), as well as their PM, based on a mixture of clays used in their manufacturing, were collected from a ceramic industry for characterization and adsorption and desorption assays. An LV sample was also collected for comparison. The samples were processed, and chemical and physical analyses were performed for characterization, as follows: particle size (pipette method), chemical attributes (available concentrations of plant nutrients), trace element concentrations (microwave oven acid digestion) and point of zero salt effect (potentiometric titration curves). Adsorption and desorption assays were carried out at pH 5.75(±0.12), using 10 mmol L-1 Ca(NO3)2 as the background solution. The adsorbent: solution ratio was of 1:100, with addition of 0.3 g of adsorbent and 30 mL of solution containing zinc, copper, cadmium, and lead concentrations varied from 0 to 0.75 mmol L-1 added as nitrate salts. SIC presented the highest percentage of coarser particles (0.053 - 2.0 mm), higher pH value, phosphorus and potassium available, remaining phosphorus and point of zero salt effect compared to MP and LV. Zinc, copper, cadmium, and lead sorption were described through the Langmuir and Freundlich models, except for cadmium with respect to Langmuir model. In general, sorption parameters indicated lower adsorption capacity for SIC compared to MP and LV, with lead being the most adsorbed and least desorbed element, followed by copper, zinc, and cadmium. In general, lower adsorbed amounts and desorbed percentages were observed for the SIC, when compared to MP and LV.