| In order to study the leaching characteristics of rare earth elements(REEs)in fly ash under low temperature and atmospheric pressure conditions,improve the REEs leaching efficiency and clarify the mechanism of REEs leaching,the basic properties of fly ash in a power plant from Guizhou was studied in this paper.The analysis of REEs characteristics and the kinetic analysis under acid leaching conditions were performed.Comprehensive comparison of various enhanced leaching methods were made and the test results were optimized.The leaching efficiency of REEs was enhanced by physical activation and chemical activation.The enhanced leaching mechanism was studied by means of SEM,XPS.The analysis of the basic characteristics of fly ash shows that the tiny overall particle size of fly ash from Guizhou Power Plant,the less ignition loss,indicating that the fly ash is fully burned,which is beneficial to the leaching of REEs in ash.From the view of the occurrence characteristics and distribution pattern of REEs,REEs are proportional to Al and Si,and REEs are encapsulated in the glass phase.From the analysis of the foreground coefficient of REEs in fly ash,the fly ash has high development potential.The results of the acid leaching experiments showed that the leaching effect of hydrochloric acid was better than sulfuric acid and nitric acid.Except for the small influence of stirring speed,the temperature,acid concentration,liquid-solid ratio,and reaction time all have a great influence on the leaching efficiency of REEs.Leaching efficiency of 71.9%,66.0%,and 61.9% for La,Ce,and Nd,respectively,was obtained under the conditions of a stirring speed of 200 rpm,temperature of 60°C,HCl concentration of 3 mol/L,liquid-solid ratio of 10(v/m),and leaching time of 120 min.The leaching mechanism of REEs from fly ash tends to be more controlled by chemical reactions.In addition,La is more easily leached from fly ash than Ce and Nd.The physical activation leaching experiments shows that mechanical grinding can effectively improve the leaching efficiency of REEs in fly ash.Under the optimal conditions of the concentration of a hydrochloric acid of 3mol/L,acid leaching temperature of 90°C,grinding time of 10 min,and acid leaching time of 90 min.The leaching efficiency reached to 79.19%.The optimization experiments improves the REEs leaching efficiency by increasing the acid leaching temperature,shortening the acid leaching time and the grinding time.However,when the particles reached the minimum size(-5?m)after grinding,the grinding time has little influence on REEs leaching efficiency.For physical reinforcement of REEs leaching efficiency.Chemically enhanced leaching methods indicated that basic structure of the glass is not dissociated under direct acid leaching environment which lead to the REEs can not be effectively released.The leaching efficiency of REEs in fly ash is greatly improved by alkali activation at low temperature(<100°C)and acid solution leaching.The specific conditions as follows:the fly ash was pretreated by 3 mol/L sodium hydroxide solution at 95°C for 3 h,and the solid after hot alkali treated is further leached by 2 mol/L hydrochloric acid at 60°C for 2 h.After the ICP-MS test,the REEs leaching efficiency beyond 95%.After orthogonal test,the concentration of hydrochloric acid and the activation temperature of alkali were the main influencing factors of REEs leaching.The comparison among the original fly ash,the solid after alkali leaching and the residue after alkali activation-acid leaching indicated that the leaching efficiency of REEs is closely related to the structure and react activity of fly ash;The higher react activity of the fly ash,the better the leaching efficiency of REEs,the alkali treatment decreased the binding energy of Al,Si in the fly ash,and increased the fly ash react activity.Reasonable interpretation of the intrinsic mechanism about enhanced leaching behavior was performed,which has a important significance for further research on the extraction of REEs in fly ash. |
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