The Removal Mechanism Of Cr(?) By Brown Coal And Corresponding Kerogen And The Pyrolysis Property Study Of Absorbent Solid Waste

Adsorption is a common method to remove Cr???in solution,and the choice of adsorbent will directly decide the removal efficiency of Cr???and further treatment of Cr-loaded adsorbent.Due to the characteristics of abundant pore structures and high oxygenic functional groups,brown coal with lower coal rank has the function of adsorption,complexation and ion exchange,and hence it is an alternative adsorbent.For now,it has been proved that brown coal shows excellent removal efficiency toward Cr???.However,most of reports focus on studying the optimal adsorption conditions and exploring the maximum uptake amount,the reports where the Cr???removal mechanism by brown coal is studied in system and depth is rare,meanwhile,this has also received less attention and solution for how to deal with the Cr-loaded coal-based adsorbents wastes.Therefore,in this study,we will systematically study the removal mechanism of Cr???by brown coal and corresponding kerogen,and further explore the best solution for dealing with Cr-loaded brown coal wastes.In this study,the batch technique was used to study the optimal adsorption conditions of Cr???removal;the X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared spectroscopy?FTIR?and solid state NMR?SS-NMR?were adopted to analysis the change of Cr???valence state during Cr???removal,the structural variations of brown coal and kerogen before and after Cr???removal,and the binding mode of reduced Cr???with oxygenic functional groups in brown coal;finally,the approach of pyrolysis was employed for the treatment of Cr-loaded solid waste.The main conclusions were listed as follows:1.Brown coal and corresponding kerogen showed excellent removal efficiency toward Cr???,and the maximum adsorption capacity of Cr???can be achieved 3.38 and 4.38 mmol/g,respectively?pH=1,96 h,25 °C?.Cr???removal process by brown coal as well as kerogen was a low speed reaction that was highly related to the pH value of solution and can be accelerated by raising the temperature.2.Cr???removal mechanism by brown coal and kerogen was mainly redox,most of adsorbed Cr???from solution were reduced to Cr???,and reducing groups in brown coal and kerogen including –CH₃,–CH₂,C-O and Ar-OH participated in the redox process and reduce the Cr???to Cr???,consequently they were oxidized to C=O and O-C=O groups.3.The mechanism of reduced Cr???immobilization was mainly that the content of C=O and O-C=O groups were abundant in the brown coal after Cr???adsorption,that the reduce Cr???were bonded to above oxygenic functional group,and electrons were delocalized over –O-Cr-O-domain.In these groups containing oxygen,the O atoms of C=O and C-O groups were bonded to Cr???along with the decrease of electron density,while the O atoms of O-C=O group are along with the increase of electron density,and finally they formed the stable structure.4.In the Ar and CO₂ atmosphere,chromium showed the catalytic effect during pyrolysis of brown coal.Especially in CO₂,chromium catalyzed the reaction between CO₂ and carbon to form CO;and the adsorbed chromium in demineralization sample can realize a complete recovery through the control of reactive time and temperature.When the recovery experiment of chromium was carried out at 850 °C for 150 min in CO₂,the maximum mass fraction of Cr₂O₃ climbed to 94.8 %,which means that almost all of the organic part in XK-Cr has decomposed and the chromium is recovered in the form of Cr₂O₃.