Study On The Migration And Partition Of Tgermanium During Germanium Extration From Lignite By Dry Distillation

Germanium,a high-value rare metal,is the key basic material for a variety of strategic emerging industries,and it has been collected and stored as a strategic metal in China.Germanium extraction from lignite by dry distillation can produce high-value tar,gas and semi-char while recovering germanium to realize the coordinated utilization of multiresources from lignite-hosted germanium deposit,which is conducive to increasing enterprise benefits and fully meets the requirements of the National Energy Technology Revolution Innovation Action Plan(2016-2030).In this paper,high-Ge lignite(91.3 ppm)from Ximeng area,Inner Mongolia was selected for carbonization test in steel retort,the distribution of dry distillation products under different conditions and the rule on migration and partition of germanium during coal retorting were studied,and the main factors affecting germanium volatilization were determined.In addition,the occurrence forms of germanium in lignite were determined by float-sink test,SEM–EDX and sequential chemical extraction,and the variation of occurrence forms of germanium in semi-char with carbonization temperature was studied.Finally,the formation law of each component of pyrolysis gas was studied with the mothod of TG–MS,and on this basis,the effect mechanism of carbonization temperature on germanium volatilization was tentatively discussed.The main conclusions are as follows:(1)Dry distillation can effectively volatilize germanium from lignite,and the main factor affecting germanium volatilization is pyrolysis temperature.Only part of germanium can be volatilized at 450 ℃,and the volatilization ratio is 21.84 % after holding for 300 min.Most of the germanium can be volatilized at about 550 ℃,and the volatilization rate is faster,the volatilization ratio of germanium increases rapidly from 31.18 % for 30 min to94.86 % for 300 min.The volatilization ratio can reach more than 98 % at medium temperature(650 ℃ and 750 ℃),and the holding time has little effect on the germanium volatilization.At 850 ℃,the volatilization ratio of germanium decreases significantly to87.64 %,and the longer the holding time,the greater the decrease.Most of the volatilized germanium during coal retorting is transferred to the pyrolysis gas,the Ge content in coal tar and pyrolysis water was extremely low,so germanium needs to be further separated from coal gas.From the perspective of maximizing the volatility of germanium and tar yield,lignite carbonization at 650 ℃ for 30 min can obtain the better indexes: germanium volatility is 98.29 % and the tar yield is 5.13 %.(2)Germanium in raw coal is mainly combined with humic matter(93.64 %),the germanium-containing organic matter is decomposed and transformed during dry distillation,and most of it is released in gaseous state.With the rise of dry distillation temperature,most of germanium in the form of organic bound state(especially humus bound state)in semi-char disappears,while the germanium proportion in water-soluble and exchangeable state,carbonate and Fe-Mn oxide bound state and residue state increases,and germanium-containing organic matter and sulfides are converted.(3)With the progress of dry distillation,the reducibility of volatile phase increases.When the pyrolysis temperature is 550 ℃ and holding time is 300 min,the volatilization ratio of germanium increases significantly,Germanium in coal is released mainly in the form of gaseous small molecules(Ge O and Ge S).With the increase of carbonization carbothermal over-reduction occurs at 850 ℃,and some Ge-containing compounds are deeply reduced to germanium metal,which is deposited and attached on the surface of fine particles,resulting in a decrease of the germanium volatilization ratio.In conclusion,this study clarifies the general rules of germanium migration and partition during dry distillation of high-Ge lignite,which can provide scientific guidance for the coordinated development of multi resources from lignite-hosted germanium deposit,and enrich the basic theory of extracting germanium from Lignite by dry distillation to a certain extent.