Multi-parameter optimization of Mn(II) adsorption onto KOH-activated Pinus roxburghii biochar using Box-Behnken methodology

Abstract

Manganese contamination in drinking water poses a significant environmental and public health concern, particularly in regions impacted by industrial discharges and geogenic leaching. This study investigates the potential of activated biochar derived from Pinus roxburghii pinecones (PCB), an abundant forestry residue, as a sustainable and cost-effective adsorbent for the removal of Mn(II) from aqueous systems. The biochar was chemically activated using potassium hydroxide to enhance its adsorption properties. Comprehensive characterization using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed the development of a highly porous structure and the presence of oxygen-containing functional groups responsible for metal binding. To optimize the adsorption process, Response Surface Methodology (RSM) based on a Box–Behnken Design (BBD) was employed, considering key operational parameters such as pH, adsorbent dosage, stirring speed, and contact time. The optimal conditions were determined to be pH 8.0, adsorbent dosage of 5 g/L, stirring speed of 230 rpm, and contact time of 45.6 min. Under these conditions, a maximum Mn(II) removal efficiency of 83.59% was achieved. The developed quadratic regression model demonstrated strong predictive capability, with a coefficient of determination (R²) of 0.9614. The findings highlight the effectiveness of pinecone-derived activated biochar as a low-cost and environmentally sustainable adsorbent for manganese removal. This approach not only supports efficient water remediation but also aligns with circular economy principles through the valorization of forestry waste.