Efficient removal of Mn²⁺ ions from aqueous solutions using apple pomace biochar

The increasing contamination of water resources is a severe environmental problem. Manganese is highly soluble in water, has adverse effects on the environment and human health during excessive exposure, and is difficult to remove. Biosorbents have been suggested to remove metals from aqueous solutions, therefore, apple pomace was utilized to prepare activated biochar (activated charcoal from apple pomace, ACAP). The biochar sample was characterized by X-ray fluorescence spectrometry, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller analysis. The aim of this study was to use ACAP as an adsorbent to remove Mn2+ ions from aqueous solutions. Adsorption experiments were performed in the pH range 3.2-6.5, with various masses of ACAP biochar and Mn2+ ion concentrations. The results were evaluated using the pseudo-first order, pseudo-second order, general order, Elovich, and Webber and Morris kinetics models. All the models fitted the experimental results, the equilibrium time was 15 min, and the pseudo-second order model presented the highest constant (k2), indicating that chemosorption is an important mechanism in adsorption. The adsorption isotherm results were adjusted using different models, wherein the Langmuir and Temkin models exhibited the best fit to the experimental results. Adsorption experiments yielded a 97.5% removal rate of Mn2+ ions at pH 6.5 and <5% at pH 3.2, and the desorption of manganese in nitric acid (0.1 M) was 97.5%. Overall, apple pomace biochar is an efficient adsorbent for removing Mn2+ ions in aqueous media, and is applicable for treating water for human consumption.