Coal Gasification Fine Slag as a Low-Cost Adsorbent for Adsorption and Desorption of Humic Acid

Coal gasification fine slag (CGFS) is a kind of amorphous silica-alumina solid waste with large surface area and broad pore-size distribution which has the potential to store and release humic acid (HA). In this study, the adsorption capacity of HA onto CGFS tuned by contact time, HA initial concentration, temperature, pH and CGFS dosage was investigated. Experimental results showed that the adsorption kinetics was well described by the pseudo-second-order model and Weber's intraparticle diffusion model. The adsorption isotherm followed Langmuir monolayer absorption isotherm model with an adsorption capacity (q(max)) of 60.67 mg/g (293 K, pH = 7). The thermodynamic parameters indicated that the adsorption was exothermic reaction. In addition, enhanced HA adsorption performance was found at low pH, indicating that electrostatic interaction played an important role between HA and CGFS. Furthermore, desorption and resorption experiment results demonstrated that CGFS had favorable properties for HA-releasing and resorption. The characterization results of CGFS and HA-adsorbed CGFS revealed that hydrogen bonding was one of the adsorption mechanisms. The exploration in our work demonstrated evidently that CGFS is a promising candidate as a suitable medium to store and release HA for soil. Mechanisms of adsorption and desorption of humic acid by coal gasification fine slag.