Adsorção de metribuzin em hidrochar ativado de casca de arroz: estudo experimental e modelagem fenomenológica

Abstract

Water pollution caused by pesticides represents a growing environmental concern, mainly due to the high mobility and persistence of these compounds in aquatic environments. In this context, herbicide metribuzin stands out for its high contamination potential and the need for efficient and sustainable removal technologies. This study aimed to synthesize and characterize a hydrochar produced from rice husk, both with and without chemical activation, and apply it as an adsorbent for the removal of metribuzin from aqueous solutions, evaluating the process through phenomenological modeling. The biomass was converted via hydrothermal carbonization (180 °C, 6 h), resulting in a non-activated material (HTCSA) and a chemically activated material using 5 mol/L HCl, referred to as HTCCA. Batch kinetic and equilibrium experiments were performed, with quantification by UV-Vis spectrophotometry (289 nm) and model fitting using MATLAB. HTCCA exhibited superior performance, reaching adsorption capacities close to 45 mg/g and fitting well to the Langmuir model (qmax = 44.04 mg/g; R² = 0.9795; RMSE = 1.9592 mg/g; NRMSE = 4.714%; RSS = 34.55 (mg/g)²; AIC = 16.11; BIC = 16.50), whereas the BET (qBET = 7,18 mg/g; R2 = -0,4033; RMSE = 16,2186 mg/g; NRMSE = 57,004%; RSS = 2367,38 (mg/g)²; AIC = 56,151; BIC = 56,743) model showed physically inconsistent, confirming monolayer adsorption behavior. In the kinetic evaluation, the film-diffusion model (MFD) described only the initial stage of the process (Kfeff= 0.0022 L/g·min; R² = 0.8786; RMSE = 3.1651 mg/g; NRMSE = 10.21%; AIC = 27.35), while the intraparticle diffusion model (IPD) provided a better fit (R² = 0.9658; RMSE = 1.68 mg/g; NRMSE = 5.35%; RSS = 31.17 (mg/g)²; AIC = 15.46), with an effective diffusivity of 1.03 × 10⁻¹¹ m²/in, indicating that internal diffusion is the predominant mass-transfer mechanism. Therefore, the results demonstrate the high potential of HTCCA as a sustainable, low-cost, and high-performance adsorbent, reinforcing the feasibility of utilizing agro-industrial residues to produce efficient materials for treating wastewater contaminated by herbicides.