Basic Research On Regulatory Preparation Of Silicon-Based Materials By Amorphous Silicon Resources In Coal-Based Solid Waste

The annual discharge of coal-based solid waste exceeds 1 billion tons,whose comprehensive utilization rate is low,thus causing serious environmental pollution due to its massive storage.Typical coal-based solid wastes,such as high-alumina fly ash and coal gasification slag,are rich in aluminum and silicon resources.It is a strategic demand for comprehensive utilization of coal-based solid wastes to develop an economical and feasible cascade utilization technology for aluminum and silicon resources.The key link is to dissolve and remove amorphous silica and aluminosilicate by alkali leaching method and realize effective separation of various resources in coal-based solid wastes.In this paper,aiming at the high-value utilization of low-modulus and high-modulus silicon-containing lye,a by-product of desilication of high-alumina fly ash and coal gasification slag,two technical routes of synthesizing calcium silicate ads orbent and whisker insulation material with low-modulus silicon-containing lye and synthesizing hierarchical ZSM-5 zeolite with high-modulus silicon-containing lye were put forward.The occurrence state of siliceous resources in silicon-containing lye was systematically investigated,and the effects of different moduli and alkali concentrations on the structure of calcium silicate and zeolite were studied.The effect of impurities in silicon-containing lye on the morphology and phase of silicon-based materials was clarified,and the application structure of the above materials was further studied,which can provide technical support for the high-value utilization of associated amorphous silicon resources in coal-based solid waste.The main research contents and conclusions are as follows:（1）The synthesis research of porous calcium silicate hydrate（C-S-H）was developed in the low-modulus silicon-containing lye by mild causticization method.The physical and chemical properties of low modulus silicon-containing lye were systematically analyzed.The effects of caustic calcium source,caustic time,caustic temperature,and Ca/Si molar ratio on the conversion rate of Si components,the chemical composition and structural properties of C-S-H were investigated.The relationship between the migration and transformation of different caustic factors and valuable components and impurity components was clarified,and the transformation mechanis m of C-S-H silicate chain structure was revealed.The optimized C-S-H caustic conditions are as follows:caustic calcium source of Ca O,caustic time of 3 h,caustic temperature o f80℃,and Ca/Si molar ratio of 1.25:1,under which the silicon conversion rate can reach97.64%.The increase of caustic time,caustic temperature,and Ca/Si molar ratio will lead to the decrease of polymerization degree of C-S-H silicate chain structure.The Na component mainly exists in the form of Si-O-Na structure,and the Al component mainl y exists in the form of replacing the Si atom in the bridge Si-O tetrahedron.（2）Based on the microstructure characteristics of porous C-S-H adsorption materials prepared in the silicon-containing lye by mild-causticization method at the optimal conditions,the adsorption isotherm and adsorption kinetics were investigated for the adsorption of Cu²⁺in the heavy metal wastewater and phosphorus-containing wastewater by C-S-H.The application feasibility and the superiority were evaluated for the adsorption and purification wastewater by C-S-H.The adsorption and purificatio n mechanism of two kinds of wastewater by C-S-H were revealed.The adsorption process of C-S-H on two kinds of wastewater is in accordance with pseudo-second order dynamics and langmuir monolayer adsorption,which is controlled by the chemical reaction process.The removal efficiency of C-S-H for Cu²⁺and phosphate ions was99.75%and 95.55%,respectively.The removal mechanism of C-S-H on heavy metal Cu²⁺ions is the formation of metal hydroxide precipitation and surface adsorption,while its removal mechanism of phosphate ions is the formation of calcium phosphate salt and surface chemisorption by ions exchange.（3）The one-step hydrothermal synthesis of flake tobermorite whisker insulation material from low-modulus silicon-containing lye was studied.The effects o f hydrothermal calcium source,hydrothermal temperature,hydrothermal time,and aluminum content on the synthesis of tobermorite were investigated.The optimized hydrothermal conditions are as follows:hydrothermal calcium source of Ca O,hydrothermal temperature of 210℃,hydrothermal time of 3 h,Ca/Si molar ratio of0.83:1,and the silicon conversion rate can reach 94.65%.The aluminum component is easy to enter the crystal lattice structure during the synthesis of tobermorite,mainl y replacing the silicon atom sites of Q² and Q³ SiO₄ tetrahedra in the silicate chain,thus improving the regularity and polymerization degree of the chain structure.The crystallization reaction between low calcium components and low polymerization degree of silicate will make the crystal grow in axial direction to form plate strip and fibrous whisker structure.The high calcium components easily lead to surplus in silicate chai n structure of Ca²⁺ions transferred to the calcium oxide main layer,which will cause the shortening and disorder of the silicate chain structure,thus making the crystal growth priority along the radial direction to form lower crystallinity gel morphology structure.The addition of sheet tobermorite material can reduce the thermal conductivity o f gypsum board from 0.936 W·m^-1·K^-1 to 0.472 W·m^-1·K^-1.（4）The regulatory preparation of hierarchical ZSM-5 zeolite from high-modulus silicon-containing lye was proposed.The occurrence form of silicon in high-modulus silicon-containing lye was studied.The effects of five factors on the synthesis of hierarchical ZSM-5 zeolite were investigated,including the type of template agent,crystallization time,crystallization temperature,SiO₂/Al₂O₃ molar ratio,and CTAB/SiO₂molar ratio.The crystallization mechanism of hierarchical ZSM-5 zeolite was revealed.The optimized crystallization conditions are as follows:crystallization temperature of170℃,crystallization time of 12 h,SiO₂/Al₂O₃ molar ratio of 200,and CTAB/SiO₂molar ratio of 0.09,under which the specific surface area and pore volume of hierarchical ZSM-5 zeolite are 851.20 m²·g^-1 and 0.816 cm³·g^-1,respectively.The induction mechanism of the meso-pore of hierarchical ZSM-5 zeolite is that CTAB dissolves in solution and generates massive CTA⁺cations,and CTA⁺cations migrate to the surface of hierarchical ZSM-5 zeolite to form hydrophobic surface,thus forming the"petal-like"cluster structure in the process of zeolite crystallization grow th.The adsorption capacity of hierarchical ZSM-5 zeolite toward the typical volatile organic pollutants P-xylene and toluene is 447.70 mg/g and 484.73 mg/g,respectively.The high SiO₂/Al₂O₃ ratio and low polarity structure can reduce the demand for cationic charge compensation outside the skeleton,which is easy to adsorb organic molecules with low polarity.