Preparation Of Composite Ceramsite Adsorbent By Modification Of Coal Measures Kaolinite And Its Adsorption Property For Cr(?)in Wastewater

In recent years,with the development of industry,the problem of excessive levels of heavy metal ions in the environment has become more and more prominent.Coal measures kaolinite,also known as kaolinite coal gangue,is an associated mineral in coal measures strata.As one of the main solid wastes,its'resource utilization and high value-added utilization have attracted more and more attention.How to achieve"disposal of waste by waste",and then make clear hill and river coming again,which has become a topic of concern for many researchers.In this paper,we started from the study of how to get metakaolin from Coal measures kaolinite,subdivided and optimized the system of calcination temperature,and then introduced slaked lime as the activator to metakaolin.By comparing the effect of removing heavy metal ion in wastewater of the raw Coal measures kaolinite,metakaolin and modified kaolin,we explored the optimal modification conditions of coal measures kaolinite,further adjusted the formula,added carbon powder as the pore-forming agent of metakaolin-based ceramsite to optimize the pore structure of the ceramsite,and finally mixed with the appropriate amount of calcination kaolin as a skeleton.A kind of ceramsites which could be used as light aggregate with good adsorption effect and high strength were prepared through the experiment,at the end we solved the problem that powdered kaolin was difficult to recycle after adsorption to heavy metal,and broadened the application route for solid waste coal measures kaolinite.The whole research showed:?1?The coal measures kaolinite could be evolved into metakaolin with high specific surface after calcined at 800°C in a box furnace.The results of XRD and SEM analysis showed that the kaolin at this time was in an amorphous state,and its'internal ordered structure was destroyed,the pores were greatly increased.The calcination system of coal measures kaolinite could be further refined:increased to 800°C for 3 h,kept 800°C for 3 h,and decreased to300°C for 4 h.After the state the adsorption effect on Cr???of kaolin was the best.?2?In the adsorption performance of metakaolin on Cr???,the adsorption performance was better when the pH value was less than 6.The introduction of Ni?II?into the system to form a competitive state was not conducive to the adsorption of Cr???.The addition of NaCl solution into the system could promote the adsorption of Cr???.?3?The composite adsorbent formed by the calcination of kaolin and slaked lime according to the mass ratio of 2.5:1 had the best adsorption performance on Cr???.The results of Zeta Potential and IR analysis showed that the slaked lime made the surface electrical properties of the kaolin turning from negative to positive,promoted the combination with the chromate.Meanwhile,The addition of calcium-containing compound as a calcium source to kaolin increased the molar ratio of calcium to silicon in the system.Under the conditions of calcium-calcifying and calcining,the group characteristics inside the kaolin were changed,and a new characteristic peak representing the stretching vibration of Si-O-Si or O-Si-O was generated.The characteristic reaction further inspired the silica-alumina activity inside the kaolin.?4?The best formula of ceramsite could be made by 74 wt%coal measures kaolinite composite adsorbent,11 wt%carbon powder,15 wt%calcinate kaolin.At 40°C,the solution pH was 4,the initial concentration was180 mg/L,the dosage was 16 g/L,the adsorption time was 240 min,in this way the adsorption amount on Cr???with the kaolin-bearing ceramsite adsorbent was up to 7.58 mg/g.?5?The adsorption of Cr???by ceramsite adsorbent was an endothermic reaction,which could be carried out spontaneously.The adsorption process could be matched well by the quasi-secondary kinetic model and the Freundlich isotherm model.The fitting results showed that the adsorption process was easy to occur,mainly controlled by the chemical adsorption mechanism,and the temperature rise could promote the reaction.?6?NaOH had the best desorption effect on ceramsite.The reason was that there was competition between OH^-and Cr²O7^2-among the adsorption process,and the alkaline environment provided by OH^-inhibited the adsorption performance of ceramsite.These adsorbed ceramsites were desorbed with 0.1mol/L NaOH solution for 1 h under normal temperature conditions,after 7adsorption-desorption cycles,the adsorption performance of ceramsites on Cr???remained above 95%,while the mass loss of ceramsite was less than 3%.Through desorption,on the one hand,the recycling of ceramsite was realized,on the other hand,the heavy metal Cr???could be enriched and recovered to solved the problem of difficult to use it efficiently.