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Preparation Of Coal-Based Kaolinite Magnetic Composites And Adsorption On Pb(Ⅱ) & Cr(Ⅵ)

Posted on:2023-02-14Degree:MasterType:Thesis
Country:ChinaCandidate:M XueFull Text:PDF
GTID:2531306821994409Subject:Mining engineering
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China is the world’s largest producer and consumer of coal,and a large amount of solid waste coal gangue is produced during coal mining and washing.Coal gangue with high kaolinite content can also be called coal-based kaolinite.It has a large specific surface area and cation exchange capacity,and abundant active hydroxyl groups on the surface.It can be used as the adsorption framework of suspended solids,oil organic matter and heavy metal ions in water,and plays an important role in the adsorption,migration and degradation of pollutants.At the same time,coal mining and electroplating industries produced wastewater containing heavy metal ions,these wastewater seriously threatened the safety of the people.Therefore,in this paper,the idea of waste to waste is proposed to modify coal-based kaolinite and prepare a variety of composite materials as heavy metal ion adsorbents to achieve recycling of resources.On the basis of rational utilization of coal-based kaolinite resources,the healthy development of water resources in China can be realized.In this paper,two adsorbents,magnetic coal-based kaolinite and chitosan coated magnetic coal-based kaolinite,were successfully prepared from tashan coal-based kaolinite in Datong,Shanxi Province by means of superfine crushing and coating.The adsorption effect of Pb(Ⅱ)and Cr(Ⅵ)on simulated wastewater was investigated.The main research contents and achievements of this paper are as follows:(1)C-F-1,a magnetically recoverable adsorption material,was prepared by co-precipitation method with coal-based kaolinite and ferric salt as raw materials.C-F-1 was characterized by XRD,SEM,BET,XPS and so on.The optimum conditions for the adsorption of Pb(Ⅱ)by C-F-1 are determined as follows:the maximum adsorption capacity is 201.69 mg/g when the adsorption dose is 3g/L,the temperature is 25℃,the initial concentration of Pb(Ⅱ)is 700 mg/L,the initial p H is 6,and the adsorption time is 90 min,which is better than that reported in most literatures.The results of adsorption thermodynamics and kinetics show that the adsorption of Pb(Ⅱ)by C-F-1 conforms to the quasi-second-order kinetic model,and chemical adsorption is the main method.The adsorption isotherm conforms to Langmuir model and is monolayer adsorption.The adsorption of Pb(Ⅱ)by C-F-1 is endothermic and spontaneous.1 mol/L EDTA has a good analytical effect on C-F-1,and the adsorption rate is still close to 90%after 4 cycles.The adsorption mechanism mainly includes the removal of Pb(Ⅱ)by electrostatic attraction of negatively charged C-F-1,ion exchange between active hydroxyl group on C-F-1 surface and Pb(Ⅱ),and formation of Pb(OH)2(CO32 precipitation induced by C-F-1 surface.(2)Using C-F-1 and chitosan as raw materials,the C-F-1 was coated with chitosan by reverse suspension crosslinking method to prepare the C-MK magnetic coal-based kaolinite composite microspheres.The optimum conditions for Cr(Ⅵ)adsorption by C-MK were determined as follows:the adsorption time was 150 min,the adsorption dose was 2 g/L,the initial p H value was 6,and the adsorption temperature was 25℃.The maximum adsorption was 87.53 mg/g.The results of adsorption thermodynamics and kinetics show that the adsorption of Cr(Ⅵ)by C-MK conforms to the quasi-second-order kinetic model,and the adsorption is dominated by chemical adsorption.The adsorption isotherm conforms to Langmuir model and is monolayer adsorption.The adsorption of Cr(Ⅵ)by C-MK is a spontaneous endothermic process.2 mol/L Na OH has a good analytical effect on C-MK,and the adsorption rate is still above 90%after being recycled for three times in Cr(Ⅵ)solution with an initial concentration of 50mg/L.The adsorption mechanism is mainly that the positively charged C-MK attracts HCr O4-,Cr2O27-,and the surface of C-MK contains a large number of active hydroxyl groups and produces ion exchange with Cr(Ⅵ),and the outer nuclear vacant orbit of Cr(Ⅵ)can accept the lone pair electrons on the amino group on the surface of C-MK to form coordination bonds and remove them through chelation.C-F-1 and C-MK prepared from coal-based kaolinite are cheap and easy to obtain.They have good adsorption properties and can be easily separated and recycled,so as to transform waste into treasure and treat waste with waste.It provides a theoretical basis for the development of high-value utilization technology of coal gangue and has a good prospect of industrial application.
Keywords/Search Tags:coal preparation soild waste, coal-based kaolinite, Fe3O4, chitosan, adsorption, Pb(Ⅱ), Cr(Ⅵ)
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