Recovery of NH ₄ ⁺ by corn cob produced biochars and its potential application as soil conditioner

NH ₄ ⁺ ion, a main pollutant in aquatic systems, not only causes eutrophication in rivers and lakes but also contributes to fish toxicity. In this study, an eco-friendly biosorbent was prepared from the pyrolysis of corn cob, a low-cost agricultural residue. The biochars produced by pyrolysis of corn cob at 400°C and 600°C were characterized and investigated as adsorbents for NH ₄ ⁺ -N from an aqueous solution. The biochars were characterized through elemental analysis, Brunauer-Emmett-Teller-N₂ surface area analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Batch experiments were conducted to investigate the NH ₄ ⁺ adsorption process of the corn cob biochars. The Freundlich isotherm model fitted the adsorption process better than the Langmuir and Dubinin-Radushkevich isotherm models. Moreover, the adsorption process was well described by a pseudo-second-order kinetic model. Results of thermodynamic analysis suggested that adsorption was a nonspontaneous exothermic process. Biochars produced at 400°C had higher adsorption capacity than those produced at 600°C because of the presence of polar functional groups with higher acidity. The exhausted biochar can be potentially used as soil conditioner, which can provide 6.37 kg NH ₄ ⁺ -N·t ⁻¹ (N fertilizer per ton of biochar).