Synthesis And Adsorption Properties Of Red Mud-coal Gangue Based Magnetic Zeolite

Zeolites are widely used in the treatment of organic matters and heavy metals contaminated wastewater due to their ion exchange and adsorption properties.The improvement of recycling performance of zeolites has become a research hotspot due to its poor recovery efficiency in the practical application process.Based on the chemical composition characteristics of industrial solid waste（red mud and coal gangue）,this thesis innovatively proposed a new method for the preparation of magnetic zeolites with efficient separation and recycling capacity through sodium reduction roasting-hydrothermal reaction.The synthesis conditions,phase transition mechanism and adsorption properties of red mud-coal gangue-based magnetic zeolite were investigated.This study will provide theoretical support for the simultaneous synthesis of magnetic zeolite from red mud and coal gangue.The main results are as follows:（1）The effects of roasting conditions（n（Na:（Al:Si））,temperature and time）and hydrothermal conditions（n（Na:H₂O）,temperature and time）on the synthesis of magnetic zeolite were investigated.The results showed that magnetic zeolite A with complete crystalline structure was successfully synthesized with the roasting conditions of n（Na:（Al:Si））of 3.6:1:1,calcined temperature of 600°C,calcined time of 9h and hydrothermal conditions of n（Na:H₂O）of 2.8,hydrothermal temperature of 90°C,hydrothermal time of 9 h.This means that the magnetic zeolite A with Al:Si molar ratio of 1:1 could be synthesized by adjusting the mass ratio of red mud and coal gangue.（2）The morphology,composition and structure changes of red mud and coal gangue during the sodium reduction roasting-hydrothermal reaction process were investigated.The results showed that magnetic particles were dispersed on the surface of zeolites.The phase transition followed"calcium chalcopyrite,hydrated garnet,kaolinite,quartz→sodium aluminate,calcium aluminate,sodium silicate→zeolite A”and“hematite→magnetite,sodium iron oxide→magnet”.Six-coordinated[Al O₅^-]was transformed to four-coordinated[Al O₃^-]and highly reactive Al-O and Si-O tetrahedral were formed.Zeolite A with double-ring structure and magnetic iron particles was prepared in the hydrothermal process.The Fe₂O₃ in the red mud was reduced to Fe₃O₄,and partially existed as sodium salt(Fe²⁺,Fe³⁺form).（3）The adsorption properties of red mud-coal gangue-based magnetic zeolite for methylene blue（MB）and heavy metal ions(Pb²⁺,Cd²⁺and Cu²⁺)in aqueous solution were investigated.The Langmuir model and the first-order kinetic equation could describe the adsorption of methylene blue.The adsorption rate was controlled by the inter-particle adsorption resistance.The Langmuir model could also reflect the adsorption behavior of heavy metal ions(Pb²⁺,Cd²⁺,Cu²⁺)on magnetic zeolite A.The heavy metal ions adsorption was in accordance with the secondary kinetic equations.The obtained saturation adsorption amounts of red mud-coal gangue-based magnetic zeolite A for methylene blue,heavy metal ions of Pb²⁺,Cd²⁺and Cu²⁺are 125.96,180.22,86.35 and 90.30mg·g^-1,respectively.