Humic acid enhances adsorption effect: Application foundation of high-temperature composting products for remediation of heavy metals pollution

Abstract

High-temperature composting products are rich in humic acid, which contains abundant oxygenated functional groups capable of binding to heavy metals, and thus can be considered for remediation of heavy metals pollution. However, the specific adsorption properties of high-temperature composting humic acid (HHA) remain unclear. In this study, humic acid was extracted from composting products using the acid-base extraction method, and the adsorption effect and mechanism were investigated. The experimental results showed that the maximum adsorption capacity of HHA for Cu(II), Zn(II), and Pb(II) was 69.43 mg/g, 58.55 mg/g, and 65.84 mg/g, respectively, representing an average enhancement of 21.80 % compared to conventional composting humic acid. Spectra analysis revealed that the enhanced adsorption mechanism of HHA was mainly due to a 51.63 % increase in hydroxyl and carboxyl groups, which were bound to heavy metals through chelation reactions. Furthermore, kinetics and thermodynamics studies indicated that the adsorption process was an endothermic reaction and predominantly driven by ion exchange. Additionally, the application of high-temperature composting products is economical and feasible due to their production from cheap organic waste. This study aims to demonstrate the superiority of HHA in the adsorption of heavy metals and enhance the comprehension of the adsorption mechanism, which provides an application foundation of composting products for the remediation of heavy metals pollution.