Biochar as a sustainable alternative for the use of residues from the processing of açaí and the removal of glyphosate

In this study, adsorbents produced from residues from the processing of açaí from the Amazon were acquired and impregnated or not with FeCl2 and FeCl3 to remove glyphosate present in the aqueous matrices. The effects of pH, adsorbent mass, glyphosate concentration, contact time and temperature on the adsorption capacity, kinetics, isothermal and thermodynamic parameters were studied via batch adsorption tests. The removal of glyphosate in the açaí seed biochar with Fe was higher than that in the açaí seed biochar, reaching a removal efficiency of 87.9% when using 20 mg L−1 glyphosate and 10 g L−1 adsorbent. The pH study demonstrated greater adsorption capacities at pH 4.0 (18.6 mg g−1). The pseudo-first-order model was the most appropriate to describe the adsorption kinetics. The Weber-Morris model showed that the adsorption occurred by film and intra-particle diffusion. Adsorption equilibrium isotherms were better fitted to the Langmuir model (qm= 351.4 mg g−1). Thermodynamic data demonstrated that the process was spontaneous and favorable and that the adsorption was exothermic in nature. Because they have magnetic characteristics, açaí seed biochar with Fe can be easily separated and reused. Therefore, depending on the adsorption capacity of the adsorbent with iron and the adsorption efficiencies demonstrated in this study, it is concluded that the adsorbent can be used as an intermediate in the processes of removing glyphosate present in aqueous matrices.