Physicochemical Characterization Of Biochar Obtained From Coffee Husk: A Circular Economy Approach

Abstract

This work presents the physical and chemical characterization of biochar obtained from the controlled calcination of coffee husks. Coffee husk, a residue from the pulping process in coffee production, was dried, pulverized, and sieved to obtain a fine powder. Thermal analysis (TGA-DTA-DSC) was performed under nitrogen and air atmospheres to determine the material’s thermal decomposition and calcination temperatures. X-ray fluorescence (XRF) revealed the elemental composition, showing the presence of C, O, K, S, Ca, P, and Si. X-ray diffraction (XRD) analysis demonstrated significant structural changes due to calcination. The untreated coffee husk showed an amorphous structure with peaks corresponding to cellulose and hemicellulose. After calcination at 550°C, these organic phases disappeared, and new crystalline phases, including CaO, SiO₂, graphite, and Fe₂O₃, were identified. The formation of these phases suggests improved structural stability and potential benefits for soil applications. Decomposition stages were observed, with residue percentages of 7.6% in air and 25.8% in nitrogen at 1000°C. Based on these results, calcination at four temperatures (160°C, 330°C, 430°C, and 550°C) was selected, followed by analysis using infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Structural changes, including the disappearance of C=O bands and increased intensity of C-O bonds, indicated the potential to produce biochar at temperatures above 330°C. These findings suggest that coffee husk biochar could improve soil nutrient bioavailability, supporting its use in a circular economy framework.