Synthesis Of LSX Zeolite From Coal Gangue Of Wuhai And Its Adsorption Performance On Simulated Wastewater Containing Zn²⁺?Ni²⁺

Inner Mongolia is one of the main coal-producing areas in China.A large amount of coal gangue was discharged in the process of coal mining and washing,which not only occupied land resources,but also polluted the environment by heavy metal ions and sulfides released from coal gangue.In this experiment,zeolite of LSX was synthesized from coal gangue in Wuhai area by traditional hydrothermal synthesis method in sodium-potassium system.The effects of pre-activation,proportion of different components,aging and crystallization process on the synthesis of LSX zeolite were investigated,and the optimum conditions for synthesis of LSX zeolite were determined.The synthesized products were characterized by XRD,SEM,TEM,BET,IR and other characterization methods.The synthetic LSX zeolite was used to study the adsorption of simulated wastewater containing Zn²⁺and Ni²⁺.The optimum adsorption conditions were determined and the adsorption process was fitted and analyzed.The specific conclusions are as follows:?1?The coal gangue collected in Wuhai area was crushed,pulverized and screened to obtain the pretreated samples,the samples were roasted and activated,the roasted temperature and time determined the degree of activation.The activated coal gangue was mixed with NaOH,KOH,SiO₂ and H₂O in a certain proportion,different proportions affected the structure and alkalinity of the products,the aging and crystallization time and temperature affected the crystal growth direction and crystallization degree.The results showed that the zeolite of LSX under the conditions of roasted temperature was 700?,roasted time was2 h,n?Si?/n?Al?=1.1,n?Na₂O+K₂O?/n?SiO₂?=3.75,n?Na?/n?NaK?=0.79,n?H₂O?/n?Na₂O+K₂O?=20,aging temperature was 60?,aging time was30 h,crystallization temperature was 100?,crystallization time was 4 h,had high crystallinity and complete morphology.?2?The zoelite of LSX synthesized under the optimum conditions was characterized and analyzed.The results showed that the synthetic zeolite with complete crystal form and well-defined and multi-surface spherical structure was synthesized.The specific surface area was400.978 m²/g,the bore diameter was 3.828 nm and the average partical size between 11 and 12?m.The characteristic peaks of vibration of hydroxyl adsorbed by sieve at 1627.89 cm^-11 in infrared spectrogram,crystal formation can be clearly seen from the TEM pattern,lattice spacing was 0.3639 nm and the molecular formula of the crystal was K₇Na₄₇Al₅₇Si₅₂O₃₅₁51 by energy spectrum analysis.?3?The synthetic LSX zeolite was studied to simulate the adsorption of wastewater containing Zn²⁺,Ni²⁺.The optimal adsorption conditions were as follow:the initial concentration of the solution were200 mg/L and 150 mg/L,the dosage was 2 g/L,adjust the initial pH of the solution to 7,oscillate for 120 minutes at a frequency of 250 r/min in a thermostatic oscillator.Under the optimal adsorption conditions,the removal rate of Zn²⁺and Ni²⁺were 96.36%and 96.83%,the adsorption capacity of Zn²⁺and Ni²⁺were 96.36 mg/g and 72.62 mg/g.?4?The results of adsorption kinetics showed that the time for the adsorption of LSX zeolite to simulate wastewater containing Zn²⁺,Ni²⁺were 90 minutes and 60 minutes,respectively.The saturated adsorbents fitted by the pseudo-second order kinetic equation in the adsorption process were 100.00 mg/g and 75.19 mg/g,they were closed to the experimental result.Therefore,the quasi-secondary kinetics was used to describe the adsorption process,and the chemisorption was present in the adsorption process.The fitting results of the Weber-Morris intraparticle diffusion model showed that adsorption does not only existed intraparticle diffusion,but also influenced by the liquid film diffusion,the whole adsorption process was greatly affected by the boundary effect.?5?The results of isothermal adsorption showed that the correlation coefficient R² of Freundlich isothermal adsorption equation fitting the adsorption process of wastewater containing Zn²⁺,Ni²⁺were 0.9032 and0.8828,respectively,which were higher than the results of Langmuir isotherm adsorption fitting,and could be used to describe the adsorption process better.The results indicated that the adsorption of zeolite to Zn²⁺,Ni²⁺belong to heterogeneous multilayer adsorption and the values of 1/n between 0.1 and 0.5,so the adsorption process was easy to proceed.?5?The saturated zeolite can be recycled four times with 6%NaOH+1%NaCl mixed solution as the reclaiming agent,and the regeneration rate were more than 90%.