Sodium adsorption isotherm and characterization of biochars produced from various agricultural biomass wastes

Agricultural biomass wastes, which may pollute the environment yet are inefficiently managed worldwide, can be recycled into biochar, which is subsequently used to remediate salt-affected environments. This creates value-added or dual benefits of treating the wastes while reclaiming saline water/soil for sustainable development. Nevertheless, a lack of knowledge about the linkage between biochar characteristics and sodium adsorption capacity may restrict the wastes from being recycled. The current study aimed to examine physicochemical, nano/microstructural, and functional-group characteristics of biochar and to assess its sodium isothermal-adsorption properties. Four biochars made from rice husk (RH-BC), corn stalks (CS-BC), longan branch (LA-BC), and coconut coir (CC-BC) were used for an isothermal-adsorption experiment. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Brauner-Emmett-Teller surface area (BET area), pore size distribution, and Fourier Transform Infrared spectroscopy (FTIR) were used to characterize biochars, which were additionally analyzed for 9 parameters. RH-BC had the highest BET area (151 m² g⁻¹) and porosity, whereas LA-BC exhibited the lowest BET area (10.6 m² g⁻¹), and LA-BC was more condensed. Functional groups, necessary for cation adsorption, were found in biochars. The maximum adsorption capacity of RH-BC (33.9 mg g⁻¹), estimated by the Langmuir isotherm model, was the highest while that of CC-BC (15.5 mg g⁻¹) was the lowest. The Dubinin-Radushkevich isotherm model showed that the Na adsorption mechanism was dominantly a physical process. The current study provides a feasible value-added and sustainable strategy of recycling agricultural biomass wastes with dual benefits of waste treatment and salt-affected environment remediation, applicable worldwide.