Occurrence Of Lithium In High-alumina-coal Fly Ash And Its Leaching Behaviors During Pre-desilication

High-alumina coal(HAC)has been found in the northern part of Shanxi Province and in the middle-western part of Inner Mongolia,China.High-alumina-coal fly ash(HAFA)is the by-product during the conversion from HAC into electricity.Currently,the huge amount of unutilized HAFA is treated by stockpiling,which causes serious eco-environmental concerns.HAFA with a high Li content is regarded as a potential resource for Li production.However,the mode of occurrence of Li in HAFA and its migration during leaching process are still not clear,which limit the development of the recovery of Li from HAFA.In this project,the distribution of Li in phases of HAFA were determined based on mineral separations,and chemical imaging of Li in HAFA were studied using time-of-flight secondary ion mass spectrometry(TOF-SIMS).Mode of occurrence of Li in the glass phase of HAFA was analyzed using "Si solid-state-magic angle-spinning nuclear magnetic resonance(MAS NMR)and molecular simulation.Based on the mode of occurrence of Li in HAFA,the leaching behaviors of Li during pre-desilication were studied.The main conclusions were presented below.(1)The magnetic particles,glass phase and mullite-corundum-quartz(MCQ)of HAFA were separated based on the magnetic separation and acid-alkali combination method,and the raw HAFA samples and the separated phases were analyzed.The results showed that the lithium contents in HAFA were 260-420 ?g/g.Magnetic particles,glass phase and mullite-corundum-quartz(MCQ)were effectively separated by the separation methods.Based on the quantification and chemical composition of mineral phases in HAFA,79-94%of the Li was found in glass,with the remaining 5-16%and<5%of Li in MCQ and magnetic particles,respectively.(2)Mode of occurrence of Li in HAFA is hard to be analyzed for its low content and light atom.Chemical state imaging of Li in HAFA and its phases was obtained using TOF-SIMS.Lithium was found relatively uniformly distributed in the HAFA particles and strongly correlated with A1 and Si.Lithium was barely detected in MCQ by TOF-SIMS.It was deduced that Li occurred in glass phase of HAFA with high content.The 29Si MAS NMR analysis and molecular simulation results showed that the coordinate structures of Si in glass phase of HAFA were Q4(3A1),Q4(2A1),Q4(1A1),and Q4(0A1).Lithium occurred in Q3(0A1)and Q3(1A1)structures by reacting with Q4(0A1)and Q4(lAl).(3)Leaching behaviors of Li during pre-desilication were studied.According to the condition optimization,it was found that the leaching efficiency of Li during pre-desilication reached>80%under the optimal conditions.After the studies of leachingkinetics of Li during pre-desilication,it were found that the leaching of Li was greatly affected by the reaction temperature and NaOH concentration,and was controlled by the solid product layer.The activation energy and reaction order were determined to be 103.31 kJ/mol and 1.55,respectively.The concentration of Li in desilication solution reached approximately 240 mg/L after being recycled for 5 times.