Preparation Of Lignite Humic Acid Nanomaterials And Study On Cr(Ⅵ) Ions Adsorption Performance

As a mineral coal with a low degree of coalification,lignite was mainly used for burning to generate electricity,which will not only cause serious pollution to the environment,but also waste of resources.In order to enhance the comprehensive utilization of lignite,this paper extracted humic acid which was the main active substance from Xinjiang lignite,and modified by sulfonation in order to obtain humic acid nanomaterials with high added value,economic and environmental protection.Then compared and analyzed the effects of humic acid before and after sulfonation on the adsorption performance of Cr(VI)ions in aqueous solution,and discussed the adsorption mechanism,which provided a new idea for exploring green and efficient adsorbent materials with low costs.The optimum experimental conditions for the extraction of humic acid were obtained by designing single-factor and orthogonal experiments using base-dissolving acidification method from lignite,the extraction rate of lignite humic acid was 76.94% under the conditions of lignite mass to mixed lye volume ratio of 1:30 g/m L,Na OH concentration of0.1 mol/L,reaction temperature of 70 ℃,reaction time of 2 h,and centrifugal speed of 6000 r/min.In order to enhance the dispersion properties of humic acid and thus obtain humic acid nanomaterials,this thesis utilized paraformaldehyde and anhydrous sodium sulfite to modify humic acid by sulfonation,while the effects of different factors on the sulfonation degree and particle size of humic acid were investigated.Under the optimal process conditions,the obtained humic acid sulfonation degree was 16.75%,the average particle size was 151.8 nm,which had good dispersion in aqueous solution.The industrial composition of lignite humic acid and the changes of H/C and O/C before and after the reaction were analyzed by industrial analysis and elemental content testing.The structure and morphology of humic acids before and after modification were characterized by FT-IR,UV-Vis,X-ray energy spectrometry,scanning electron microscopy and specific surface area analyzer.In comparison,it was found that the modified humic acid showed reduced aromatization,decreased average particle size,increased specific surface area,and showed needle-like morphology.In conclusion,the introduction of sulfonic acid groups not only increased the dispersion performance of humic acid in aqueous solution,but also improved its anti-temperature performance.The effects of different factors on the adsorption performance of Cr(Ⅵ)ions in aqueous solution were investigated by using humic acid and modified humic acid as adsorbents,and the kinetic and isothermal adsorption studies were performed.Under the optimal adsorption conditions,both conformed to the fitted secondary kinetic equation and Langmuir isothermal model,the fitted maximum equilibrium adsorption capacity of humic acid for Cr(Ⅵ)was 5.74 mg/g,and the maximum equilibrium adsorption capacity of modified humic acid for Cr(Ⅵ)was 14.72 mg/g,which was about 2.56 times higher than that of humic acid.The characterization analysis revealed that the adsorption mechanism mainly contains three parts: redox,complexation and electrostatic adsorption.