Artificial humic acid synthesized from food wastes: An efficient and recyclable adsorbent of Pb (II) and Cd (II) from aqueous solution

Developing green, sustainable, and low-cost adsorbents for removing heavy metals from wastewater while recycling food wastes can avoid secondary environmental damage. In this work, artificial humic acid (A-HA) was prepared through biological fermentation using food wastes as raw materials with the goal to remove Pb (II) and Cd (II) from aqueous solution. The results showed that Pb (II) adsorption by A-HA was superior to that of Cd (II). Electrostatic interaction, surface complexation, ion exchange, and pi-pi interaction played key roles in the adsorption and desorption of A-HA for Pb (II) and Cd (II). The Langmuir isothermal adsorption model was more suitable for the adsorption of Pb (II) and Cd (II) by A-HA, and at 45 degrees C, maximum adsorption capacities were 37.6 mg/g and 3.33 mg/g, respectively. The adsorption kinetics of Pb (II) and Cd (II) by A-HA showed good fit with the pseudo-first-order kinetic model. The adsorption capacities of A-HA for Pb (II) and Cd (II) first increased gradually and finally stabilized with increasing initial concentration of adsorbate. In the pH range of 1-7, the adsorption capacities of A-HA for Pb (II) and Cd (II) first increased and remained stable. However, the adsorption capacities were inhibited by increasing ionic strength. Under optimal adsorption conditions, very little Pb (II) and Cd (II) were desorbed. In summary, A-HA might be a promising and effective adsorbent for metal removal because of its environmental friendliness, low cost, and its origin from food wastes as raw materials.(c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).