Performance and mechanism of zeolite derived from coal gasification coarse slag for adsorbing Ni(II) from wastewater

The heavy metal Ni²⁺ in water, posing a serious threat to humans and other organisms through food accumulation, can be removed using high-performance zeolites. The study successfully prepared a highly efficient Y-zeolite adsorbent from coal gasification coarse slag (CGCS) via alkali melt-seed induced hydrothermal synthesis, with an average pore diameter of 8.3 nm. The comprehensive characterization and adsorption experiments were conducted on the synthesized Y-zeolite to investigate diverse factors' influence on performance. The removal efficiency of Ni²⁺ reached 98.325 % within 20 min and then stabilized at 99.760 % at a dosage of 1 g L⁻¹, pH maintained at 7.0, and an initial concentration of Ni²⁺ at 100 mg L⁻¹. The adsorption process conforms to the Pseudo-second-order kinetic model and Langmuir adsorption isotherm model, with the adsorption capacity of 98.943 mg g⁻¹ and the theoretical maximum adsorption capacity of 515.500 mg g⁻¹. The adsorption mechanism was analyzed by SEM-EDS and FTIR, based on the ion exchange interaction between Ni²⁺ and T-O groups. Furthermore, DFT calculations were employed to prove the most stable site for Ni²⁺ adsorption on Y-zeolite. The successful adsorption of Ni²⁺ on suitable sites located in six-membered rings of SuCage-6mr and Cage-6mr. In conclusion, Y-zeolite showed great potential as an efficient adsorbent for Ni²⁺ removal, promoting the comprehensive utilization of solid waste and creating a mutually beneficial outcome.