The use of an agricultural waste material from Ziziphus jujuba as a novel adsorbent for humic acid removal from aqueous solutions

Abstract The purpose of our work is the development of a local agricultural waste biomass material, Ziziphus jujuba known as Nebka (NB), into activated carbons to remove humic acid (HA) from aqueous solutions. This was further treated with nitric acid solutions. The surface characteristics of the adsorbent were calculated using the standard Brunauer–Emmet–Teller method (BET). The microstructures of the samples were observed with scanning electron micrographs. Chemical characterization of the samples was carried out by selective titrations and Fourier Transform Infrared Spectroscopy (FT-IR). On the basis of the BET results, we have obtained the best microporous activated carbon oxidized (surface area of 970 m 2 /g, microporous volume of 0.170 cm 3 /g and total pore volume of 0.326 cm 3 /g). Adsorption studies were conducted using a batch process, to study the effects of contact time, pH and temperature. The pH dependent sorption of HA was found maximum at pH range 4–6 for an initial concentration of 50 mg/L. The equilibrium adsorption data was analyzed using Langmuir and Freundlich isotherm models, and the kinetic data was analyzed using pseudo-first order and pseudo-second order kinetic models. The equilibrium data were well fitted to the Freundlich isotherm. The adsorption reached equilibrium after 300 min and the maximum adsorption capacity was about 76.92 mg/g at 20 °C according to the Langmuir model. The adsorption kinetic was found to follow the pseudo-second-order kinetic model. Thermodynamic study showed that the adsorption of HA onto oxidized activated carbons was feasible, spontaneous and endothermic at 20–40 °C.