Molybdenum Isotope Composition Of Coal In China

Molybdenum(Mo)is a redox sensitive element,and its isotopes are widely used in the evolution of atmospheric oxygen in paleoenvironment,redox conditions of paleo-ocean and source tracer of Mo in metallogenic material.The composition and distribution of Mo isotopes in various reservoirs in nature and the corresponding fractionation mechanism have been basically clarified by the study of Mo isotopes in recent years.However,as an important reservoir of surface environment molybdenum,the study of Mo isotopic composition in coal is still very limited.China holds coal reserves ranking third in the world and coal consumption ranking the first in the world.The study on the composition of Mo isotopes in coal cannot only fill the gap of high precision Mo isotope data in Chinese coal,but also verify the temporal and spatial distribution of Mo isotopic composition in Chinese coal,expanding the trace application of Mo isotopes in the field of environmental geochemistry.The major findings of this thesis are as follows:One is to establish a continuous purification process of anion exchange column,which can effectively separate complex matrix elements and homotopic elements and obtain high purity Mo,and the recovery rate over 85%,suitable for all kinds of low molybdenum content geological or environmental samples.By using 97Mo-100Mo isotope double-spike method,several geological standard samples were analyzed on Nu plasma II type MC-ICP-MS.The results show that the δ98/95Mo values of BHVO-2 and BCR-2 are-0.10±0.04 ‰o(2SD,n=4)and-0.05±0.06 ‰(2SD,n=7)respectively;theδ98/95Mo value of shale SGR-1b is 0.46±0.03 ‰(2SD,n=4);the δ98/95Mo value of IAPSO in the Atlantic Ocean is 2.09 ±0.08 ‰(2SD,n=4),which is in good agreement with previous reports,proving the reliability of the process.Therefore,theδ98/95Mo=1.19±0.03 ‰(2SD,n=3)CLB-1 of USGS coal standard sample is reported for the first time in this thesis.Second,a total of 151 coal samples from 21 provinces and cities in China were measured for Mo isotopes.The variation range of Mo content in Chinese coal is from 0.25 μg/g to 24.6 μg/g,with the average is 2.40 μg/g,lower than the average Mo content in the world coal(5.0 μg/g).The values of δ98/95Mo in coal range from-1.03‰ to 3.00‰,with an average value of 0.26 ± 0.08‰,which is lower than that of coal standard sample CLB-1(1.19 ‰).Mo isotopes in coal in most areas of China are generally enriched in heavy isotopes(δ98/95Mo>0),only for coal in Hebei,its Mo isotopes tend to be lighter.By comparing the δ98/95Mo values of coal in different coal-forming periods,coal-forming environments and different coalification levels,it is preliminarily concluded that seawater intrusion is a major factor for Mo isotopic enrichment in coal.