Study On Environmental Geochemistry Characteristics And Life Cycle Analysis Of Lithium And Boron In Salt Lake Area Of Taijinar

Qinghai province is rich in salt lake mineral resources.The Taijinar Salt Lake located in the central Qaidam Basin possesses large amount of potassium,lithium,boron,magnesium and other mineral elements to have great economic value.At present,the lithium and boron resources in the Taijinar Salt Lake have been developed on a scale.However,exploitation and utilization of salt-lake mineral resources will inevitably induce the environmental impact.Therefore,it is necessary and urgent to evaluate the possible environmental impact of salt lake industrial process to“build world-class salt lake industrial base and build national clean energy industry highland”.This study investigated the occurrence characteristics of lithium,boron,and trace elements in the sediments of the Taijinar Salt Lake area.The life cycle assessment（LCA）method was used to evaluate the environmental and economic impact of natural concentration process of lithium and boron,actual production process of lithium and boron,new extraction technology of lithium and boron,lithium-boron co-extraction technology to discuss sustainability of lithium and boron production in the salt lake.This study aims at providing theoretical guidance for the environmental protection and sustainable development of the production process of lithium and boron in the salt lake region.The main results of this study included the followings:（1）The contents of lithium and boron in sediment samples of the Taijinar Salt Lake area near the factory were higher while those far away from the industrial area were lower.The contents of other trace elements followed the order of As>Pb>Hg>Zn>Cr>Cd.The chemical speciation of lithium and boron was mainly Fe-Mn oxide and residual.The exchangeable Li-Zn and Cr-As showed a very significant positive correlation while the correlation between Zn-Li and Cr-B was very significant.The results of correlation analysis showed that p H,electricity capacity and cation exchange capacity had significant influence on the content and chemical speciation of lithium and boron.Different chemical speciation of Zn,Cr and Pb had certain influence on the occurrence of lithium and boron.（2）The life cycle analysis on the lithium extraction process in the Taijinar Salt Lake was perfomed to find that the environmental impact of the natural evaporation and concentration of salt lake was mainly manifested in two aspects including global warming and dust emission.The pollutant discharge of calcination method was greater than that of electrodialysis method except NO_X.Calcination stage produced a greater environmental load than electrodialysis.The external cost and the total water consumption of calcination method were much higher than those of electrodialysis method.Therefore,calcination method is not resource-friendly and sustainable from the perspective of life cycle evaluation.（3）The life cycle analysis on the new nanofiltration membrane method was performed to show that the nanofiltration stage induced the largest environmental emission,and followed by the reverse osmosis stage.GWP（global warming potential）was the highest in the whole process of lithium extraction by nanofiltration membrane.The environmental emission and environmental impact index showed a similar trend in each stage:nanofiltration>reverse osmosis>electrodialysis>MVR evaporation>drying.LCC_In（life cycle internal costs）/LCC was 99%while the cost of NO_X,SO₂and PM₁₀ served as the major contributors in LCC_Ex.The LCC_Ex（Life cycle external costs）of lithium extraction by nanofiltration membrane was generally much smaller than that of LCC_In.（4）The environmental effects of boron extraction by acidification crystallization were mainly reflected in three aspects:global warming,acidification and dust emission.The environmental impact assessment results of boron new extraction technology illustrated that the GWP value was the highest.Other indicators followed the order of the GWP（global warming potential）>AP（acidification potential）>NE（eutrophication potential）>POCP（photochemical ozone potential）>SA（dust emission）.The production process of boron in the impact of climate change might be higher than that of the other processes.The use of new chemicals and advanced technology can greatly reduce the LCC_In of boron production.（5）The environmental emission in the process of boron-lithium combined extraction was larger than that in the stages of nanofiltration,evaporation,extraction and back extraction.The environmental impact indicators followed the order of GWP>AP>SA>POCP>NE.The evaporation,nanofiltration,extraction and back extraction stage produced the largest environmental load.LCC_In was significantly higher than LCC_Ex while the consumption of electricity and water accounted for a larger proportion of LCC_In.LCWC_direct（life cycle direct water consumption）was much larger than LCWC_indirect（life cycle indirect water consumption）while the direct water consumption accounted for 97.55%of the total water consumption.The total water consumption in the nanofiltration stage was the largest,which could be explained by that direct water consumption in these two stages was higher and the direct water consumption occupied the dominant position.