Preparation And Adsorption Properties Of Hierarchical Material From Coal Gangue

As a mixture rich in carbon,silicon and aluminium,coal gangue can be used to prepare multi-component hierarchical materials.Not only does it avoid the problems of complicated component separation process and low product purity,but also the multi-stage pore material produced has multi-functional characteristics.In this paper,two composite materials（activated carbon-mesoporous silica and activated carbon-zeolite）were prepared by alkali fusion-acid leaching and alkali fusion-hydrothermal methods,respectively,using coal gangue as the main raw material.The phase transformation and the development of pore structure in the preparation of hierarchical materials from coal gangue were investigated.The adsorption properties of the produced materials were also investigated for organic matter and heavy metal ions respectively.The main results are as follows:（1）Coal gangue in the alkali fusion process,the aromatic ring mesh structure of carbon contained in the gradual formation of fragmented carbon microcrystalline structure.At the same time,structurally stable aluminosilicates such as kaolinite and quartz in the gangue are transformed into acid-soluble potassium aluminosilicates such as potassium chalcocite and potassium silicate.For aluminosilicates,the silicon component is transformed from a Q3（1Al）lamellar structure to a Q4（4Al）shelf structure.Its aluminium component is transformed from a six-coordinated[Al O₆]octahedral structure to a four-coordinated[Al O₄]tetrahedral structure.（2）Phase transformation of roasted samples during acid leaching.The acidic groups were further increased by the fragmented carbon microcrystalline structure contained in the roasted samples during the acid leaching process.At the same time,the elements such as potassium and aluminium in the roasted sample leach out and silicon is enriched in the slag in an amorphous form.The silicon fraction of the roasted sample changes from a Q4（4Al）shelf structure to a Q4（0Al）and Q3（0Al）amorphous structure.The composite made from the alkali fusion-acid leaching of coal gangue is mainly composed of Si and C elements.The surface of its particles is distributed with micropores and mesopores formed by the accumulation of lamellar structures（the micropores and mesopores account for 1/2,specific surface area is about 835.1 m²/g,average pore diameter is about 2.97 nm and total pore volume is about 0.62 cm³/g）（3）Phase transformation of a roasted sample during hydrothermal process.The roasted samples show a shift from a regular graphitic carbon structure to a defective carbon structure during the hydrothermal process.The aluminium-silica component is transformed from potassium chabazite to a K-chabazite zeolite phase structure.During this process,the silicon structure of the composite is a reconfigured Q4（4Al）shelf structure and the aluminium structure is a reconfigured tetra-coordinated[Al O₄]tetrahedral structure.The composite material produced by alkali fusion of coal gangue-hydrothermal is mainly composed of Si,Al and C elements.The microscopic morphology is"pill-like",with microporous and mesoporous（the specific surface area is about 158.4 m²/g,average pore size is about 3.36nm,total pore volume is about 0.13 cm³/g,micropores and mesopores of 0.07 and 0.06cm³/g respectively）.（4）Adsorption performance of activated carbon-mesoporous silica and activated carbon-zeolite graded pore materials.Activated carbon-mesoporous silica materials can be used for the removal of organic pollutants in water,with maximum adsorption capacities of148.94 mg/g for MB,122.45 mg/g for MO and 156.66 mg/g for Rh B.Activated carbon-zeolite materials can be used for the removal of heavy metal ions in water,with maximum adsorption capacities of 128.1 mg/L for Cu²⁺,220.2 mg/L for Cd²⁺and 437.3 mg/L for Pb²⁺.The adsorption process of both composite graded pore materials was based on single molecular layer chemisorption.