Study On Preparation Of Nano FeS Loaded On Lignite And Its Treatment Of Acid Chromium Containing Wastewater

Aiming at the high toxicity and difficult treatment of acid chromium containing wastewater,based on the adsorption characteristics of lignite and the reduction ability of nano FeS,the nano FeS loaded on lignite（nFeS-Lignite）was prepared by ultrasonic precipitation method.The static and dynamic experimental methods were used to analyze the rule and effect of nFeS-Lignite on removal of Cr（VI）and total chromium from acid chromium containing wastewater,the remediation mechanism of nFeS-Lignite was preliminarily revealed by instrumental analysis and detection,which provided new ideas for the application of lignite in adsorption materials.The main conclusions are as follows:Under the ultrasonic frequency treatment environment of 40 k Hz,FeSO₄ solution was dropped on the lignite particles adsorbed S^2-at a certain flow rate,so that Fe²⁺and S^2-were crystallized and coprecipitated on the surface of lignite,washed with water and centrifuged to obtain nFeS-Lignite.The effects of lignite size fraction,the concentration of Na₂S and Fe/S molar ratio on the preparation of nFeS-Lignite were evaluated based on single factor and response surface experiments.The results show that when lignite size fraction is 0.18～0.25 mm,the concentration of Na₂S is 0.30 mol·L^-1,and Fe/S molar ratio is 2.5:1,the prepared nFeS-Lignite has the best remediation effect on acid chromium containing wastewater,the removal rates of Cr（VI）and total chromium were 87.5%and 75.6%,respectively.XRD,TEM and SEM analysis show that the rod-shaped nano FeS with average length of 40-80 nm can be successfully loaded on lignite particles by ultrasonic precipitation method.The adsorption properties of nFeS-Lignite for Cr（VI）and total chromium in acid chromium containing wastewater were studied.The results show that the optimal dosage of adsorbent is 5 g·L^-1;when the initial pH of the solution was 3,the removal rates of Cr（VI）and total chromium by nFeS-Lignite were 94.5%and 87.2%,respectively;the adsorption process reaches the adsorption equilibrium after about 150 min;the Langmuir isotherm model can better fit the adsorption process,and the adsorption kinetics follows the lagergren second-order kinetics,indicating that the adsorption reaction is monolayer adsorption,mainly chemical adsorption.Two dynamic column models of nFeS-Lignite（1#）and lignite（2#）were constructed to study the dynamic removal effect of Cr（VI）and total chromium and pH change in acid chromium containing wastewater treated by nFeS-Lignite and lignite.The results showed that the average removal rates of Cr（VI）and total chromium were 71.6%and 53.1%respectively,the pH of effluent decreased from 6.6 to 5.3,the average removal rates of Cr（VI）and total chromium were 54.4%and 28.8%respectively,and the pH of effluent increased from 6.6 to 7.3.XRD,SEM,EDS and FTIR analysis showed that the reducing groups in the structure of nFeS-Lignite,such as-CH₃,-CH₂,C-O and AR-OH,participated in the reaction and were oxidized to C=C,C=O,and new diffraction peaks such as Fe OOH,Cr（OH）₃ and Cr₂S₃ appeared,indicating that after Cr（VI）was reduced to Cr（III）,it would be fixed on the surface of nFeS-Lignite in the form of hydroxide and sulfide.The paper has 32 pictures,28 tables and 110 references.