Study On The Synthesis Of CAN-Type Zeolite From Coal Gasification Coarse Slag In Solid-Phase And Structure Fixation Of Cr⁶⁺ In Water

Coal is the most widely distributed energy in the world.From the perspective of energy types,coal,natural gas and oil are the main energy consumption components in the world,accounting for 84.3%of the total energy consumption,of which coal accounts for 27.3%,making coal energy occupy an important position in China’s energy.Coal gasification technology is widely promoted and used because of its high efficiency and energy saving.However,the rapid development of Coal gasification has also brought problems.The massive production and discharge of coal gasification slag has posed a huge threat to the ecological environment.At present,the treatment method of Coal gasification slag is all landfill,without resource utilization,which occupies a lot of land resources,and has become one of the main problems restricting the sustainable development of Coal gasification industry.Among them,Coal gasification coarse slag is the molten ash that turns into liquid slag when raw coal ash powder is gasified in the gasifier during Coal gasification.Due to the effect of gravity and airflow,liquid slag flows out from the slag outlet and forms Coal gasification coarse slag with larger particle size after cooling.Therefore,it is urgent for us to carry out research on the resource utilization and high value utilization of Coal gasification slag.The coarse slag of Coal gasification contains rich silicon and aluminum sources,as well as alkaline metal oxides such as calcium,sodium,iron and magnesium.Based on its rich silicon aluminum source,it can be prepared into zeolite,and due to its low silicon aluminum ratio,it is suitable for preparing CAN type zeolite.At present,most industrial methods for preparing zeolite are hydrothermal methods.The preparation process requires acid and alkali leaching,which consumes a large amount of water resources.The generated acid and alkali waste liquid requires human and material resources for reprocessing,which consumes human and material resources.For solid-phase synthesis of zeolite,there is no need for acid leaching or alkali leaching.The steps are simple,the reaction efficiency is high,the reaction pressure is low,and expensive templates are not needed.However,currently,research on solid-phase synthesis of zeolite from solid waste is not mature,and the mechanism of solid-phase preparation of zeolite is not perfect.Based on this situation,this paper takes Coal gasification coarse slag as the main research object,and carries out research on high value transformation of solid wastes and ecological application,which is of great significance for ensuring the national advantages of coal chemical industry and high-quality sustainable development of characteristic Coal gasification industry.In this paper,Coal gasification coarse slag is used as raw material,and the main research contents are as follows:(1)This paper studies the synthesis of CAN zeolite from Coal gasification coarse slag in Na2CrO4·4H2O system and Na2SO4·9H2O system by solid phase synthesis method.This method does not require water participation,template,simple operation,low cost,and environmental friendly in the synthesis process.Compared with traditional hydrothermal synthesis,it is more conducive to industrial production.(2)In this paper,the process of directional synthesis of single phase CAN zeolite by solid phase synthesis of Coal gasification coarse slag under the action of structure oriented agent was studied,and the influence of different types of ions on the synthesis of CAN zeolite was explored,and its products were characterized specifically.The process was carefully analyzed.The main research contents and conclusions are as follows:(Ⅰ)In the process of activating Coal gasification coarse slag,calcium,iron,magnesium and other alkali metal oxides in Coal gasification coarse slag act as flux,which can not only make Coal gasification coarse slag live at a lower temperature,but also accelerate the recombination of silicon and aluminum sources in Coal gasification coarse slag.In the crystallization process,the alkaline metal in the Coal gasification slag can act as a flux to reduce the reaction temperature,so that some structural guidance agents with lower melting temperature,such as sodium nitrate can become molten at the reaction temperature of 120℃,increase the contact area with reactants,and then react,which is conducive to the synthesis of CAN zeolite,but the melting effect of this flux is limited for sodium carbonate,sodium sulfate,For structural directing agents with high melting temperatures such as sodium chromate,they cannot reach the melting state,so their corresponding hydrates need to be used instead.(Ⅱ)In the research of solid phase synthesis of CAN zeolite guided by different anion structures,the type of anions involved,the raw materials used,the silicon aluminum ratio and alkalinity are very important,and the formation of CAN zeolite depends on them to a large extent.In the study of using different types of anionic structures to guide the synthesis of CAN type zeolite,we draw the following conclusions:monoatomic anionic chloride ions can induce the synthesis of sodalite,low symmetric anions such as nitrite ions can not induce the synthesis of zeolite,and carbonate,nitrate,sulfate and chromate anions with three rotating axes can directionally induce the synthesis of single phase CAN type zeolite.Therefore,we believe that the process of inducing the synthesis of CAN type zeolite by anions with three rotational axes depends on the structural symmetry of each anion in the reaction,rather than the elemental types of anions in the reaction.(Ⅲ)The synthesis of CAN zeolite from Coal gasification slag can be divided into four stages:nucleation induction period.Under the combined activation of physical activation,thermal activation,chemical activation,etc.,Coal gasification coarse slag forms nucleation precursor(primary structural unit),namely silicon aluminum tetrahedron,which exists in an amorphous state.During the initial nucleation period,under the action of basic oxide in the Coal gasification coarse slag as the flux,when the silicon aluminum tetrahedron reaches the minimum eutectic temperature under the structure directing agent,the liquid phase begins to appear in the reaction system,which changes from solid solid reaction to solid liquid reaction.Because the contact between the liquids is more complete,the melting reaction of silicon aluminum tetrahedron is accelerated.In the synthesis system,anions with triple rotation axes play a structural guiding role,usually located in the pores or cages of zeolite.Through hydrogen bonds,ion bonds,or van der Waals forces,they guide the surrounding nucleation precursors(silicon aluminum tetrahedra)to aggregate around them to form a skeleton,obtaining ordered particles,namely microcrystalline nuclei.During the crystal growth period,driven by thermodynamics,these nuclei grow into long-range ordered crystals to reduce the Gibbs free energy of the system.The effect of sodium ion and other ions in Coal gasification coarse slag promotes the growth of nuclei.As the crystallization time prolongs,a large amount of amorphous silicon aluminum tetrahedra gradually decomposes and is replaced by crystals.(3)Cr6+is harmful to human health and the natural environment.Its complex molecular structure makes it difficult to treat or extract Cr6+in the effluent discharged into the natural environment.In this paper,the fixation of Cr6+ produced in glass industry,dyes,leather and ceramics in industrial production has been studied as follows:First,Coal gasification coarse slag has always been considered as a feasible method to adsorb Cr6+from water.However,as an adsorbent,Coal gasification coarse residue has its disadvantages,because its number of adsorption sites is limited,resulting in insufficient extraction efficiency.In this paper,the structure of Cr6+in simulated wastewater was fixed by Coal gasification coarse slag,and then the CAN zeolite was derived.Compared with the simple adsorption of Coal gasification coarse slag,the adsorption capacity is larger,the adsorption rate is higher,and it is more difficult to leach.Using this method can achieve waste treatment and achieve green chemical industry.