Resíduos orgânicos naturais e biochars: produção de material com elevada capacidade adsortiva por metais potencialmente tóxicos

Abstract

Waste management and the development of environmentally efficient alternatives are among the most discussed issues today. For a better understanding of the potential of different natural organic residues that do not always have a specific application, this work addresses three main objectives: to carry out a systematic review of the literature to evaluate the distribution of research carried out with a focus on the relationships between the conversion of natural organic residues in biochars and their interaction in the adsorption of potentially toxic metals (PTM); characterize and evaluate the adsorption capacity of Cd2+ and Pb2+ ions by different natural organic residues in natura and biochars; use an espresso coffee machine to extract humic substances (HS). The review carried out covered the period from 2002 to 2022 in the Scopus and Google Scholar databases, followed by simulations in VOSviewer. The natural organic residues and biochars were characterized in terms of organic matter, total metals and structurally by spectroscopic techniques in the infrared region by Fourier transform, nuclear magnetic resonance and diffusion ordinate, thermogravimetric analysis, spectrophotometry in the visible ultraviolet region, spectrometry fluorescence, pH, pHzpc, stereomicroscopy and scanning electron microscopy with energy dispersion X-ray spectroscopy analysis, which were submitted to adsorption tests. The HS extraction using an espresso machine was compared with the fractions obtained by the standard methodology described by the International Society of Humic Substances (IHSS). The results of the review showed that there was a deepening in the studies focused on the properties of biochars from different natural residues, with 35 residues being selected from which the experimental conditions favored the adsorption processes by PTM were verified. The characterization of in natura residues and their biochars made it possible to observe their heterogeneity and structural alterations after pyrolysis, allowing an increase in porosity and surface area that possibly favored the adsorption tests. For Cd2+ and Pb2+ ions, adsorption capacities of 3.8 mg g-1 and 4.5 mg g-1 were achieved in filter cake and eucalyptus sawdust biochars, respectively. The extraction of HS using the coffee machine allowed yields of up to 8.22% for the soluble fractions of HS and 90.90% for the poorly soluble fraction, and 15.57% for the soluble fractions of HS and 59, 01% for the poorly soluble fraction of HS, using the methodology proposed by the IHSS. The results obtained made it possible to highlight the growing progress of research aimed at mitigating the impacts caused by the inadequate disposal of natural organic waste, highlighting the possibilities of each natural organic waste and its biochars in the retention of PTM. Finally, the extractions carried out using an espresso coffee machine proved to be a viable alternative for the fractionation of HS, being able to contribute to its microscale extraction with applicability in studies on a laboratory scale and in didactic applications for teaching the properties of HS.