Optimization of preparation technology for modified coal fly ash and its adsorption properties for Cd²

This work focused on preparation a novel adsorbent from coal fly ash (CFA) and solid alkali (NaOH) by low temperature roasting method. The modification parameters (mass ratio, calcination time and temperature) were specifically studied and optimized. The adsorption experiment results indicated that, the adsorption amounts of Cd²⁺ were enhanced with the decreasing mass ratio of CFA and NaOH, and the adsorption amounts of Cd²⁺ were 32.44, 31.66, 38.5 and 79.85 mg/g at the mass ratio (CFA/NaOH) of 5:5, 5:6, 5:7 and 5:8, respectively. The higher modification temperature was not conducive to the removal of Cd²⁺, as the adsorption capacities of Cd²⁺ calculated were 62.42, 69.53 and 41.73 mg/g at the reaction temperature of 250, 300 and 400 ℃. Interestingly, the modification time slightly effects on the adsorption ability of materials. According to the results, the optimum modification condition for preparing adsorbents were CFA/NaOH mass ratio of 5:8 and calcined at 300 ℃ for 3 h. Moreover, the influence of pH, ionic strength and Glycine concentration on Cd²⁺ uptake were also investigated. The kinetic, adsorption isotherm and thermodynamics models were applied to investigate the adsorption mechanism, which indicated that the adsorption process was better fitted by Langmuir and pseudo-second-order models.