Obtenção de extrato da casca do cajueiro e sua aplicação para remoção de espécies metálicas em matriz aquosa

Abstract

The removal of metallic pollutants from water or effluents requires the application of specific methods and processes, such as chemical precipitation, ion exchange, adsorption, membrane filtration, electrochemical treatment technologies, among others. Natural coagulants are an alternative to chemical precipitants in the treatment of water and effluents. Given the importance of environmental preservation and the need to develop clean technologies and environmentally friendly products, this study aims to obtain and characterize the powder from the cashew bark tree Anacardium occidentale L. and the aqueous extract obtained from the cashew bark, in addition to studying the use of this extract to remove metals in acidic solutions. For this, the raw material, which is the shell of the cashew tree stem, was prepared through the physical processes of drying, grinding and sieving. The material obtained was characterized using scanning electron microscopy; determination of hemicellulose, cellulose and lignin content; thermogravimetric analysis; differential scanning calorimetry; Fourier transform infrared spectroscopy; optical emission spectrometry with inductively coupled argon plasma. The powder obtained after preparing the raw material was subjected to hot extraction with ultrapure water and the extract obtained was characterized through its density, Fourier transform infrared spectroscopy, zeta potential analysis and optical emission spectrometry with inductively coupled argon plasma. Experiments were carried out on a laboratory scale using contaminated water with a concentration of 4,0 mol/L of the metals Ba, Cd, Cr, Cu, Mn, Pb, Sn, Zn in the same solution and different volumes of the extract obtained from the cashew tree bark. After 1 hour of shaking, the system was left to rest for 24 hours. The supernatant was collected and the concentration of metallic species was determined using inductively coupled plasma atomic emission spectroscopy. The coagulation process between the extract and metallic species promoted removal of up to 25% simultaneously for all metals analyzed. Using the principles of green chemistry, the process was evaluated with a very good green approach.