The Study For Separation Of Clay In Carbonate Rocks And The Application Of Rare Erath Elements

Rare earth elements?REEs?of authigenic sedimentary carbonate rocks in carbonatite are the important parameters to trace the sedimentary environment.For example,the REE of sedimentary carbonate that formed under the effect of corals,hydrothermal fluid and cold spring are often used to trace the redox condition of sedimentary envirment.There is not only carbonate rocks in carbonatite but also mixed with non-carbonate minerals,such as clay minerals.The REE contents of terrigenous clays are much higher than that of authigenic carbonate minerals.So even with a small amount of clay minerals mixed,it will also affect the REE concent of authigenic sedimentary carbonate.Then will influence the tracer information of sedimentary environment.To determine the rare earth elements in the authigenic carbonate minerals accurately,it is very necessary to separate the terrigenous clays from carbonate rocks.In this article,we use the ultrasonic assisted elutriation-sedimentation to remove most of the clay in multiple samples first.And optimized the elutriation condition,including the sample size and sedimentation time.Then achieve the best separation efficiency of the method.By analyzing the determination of Al element content in the samples before and after elutriation,to distinguish the clay removal effect.The result found that the sample size in 106-125?m and sedimentation time for 60 min arethe best condition to removal clay.The clay removal rate of sparite samples are over 70%,limestone and marlstone's clay removal rate is between 30%and 55%,dolomite samples'clay removal rate is about 34%.Here we use CH₃COOH to dissolve powder samples in different conditions and separate them with two methods,including centrifuge and elution.It can further improve the removal rate of clay.Then optimized the acid concentration and dissolution time.The characteristic element Al?Ti of clays,were determined by ICP-OES.The results show,after use the acid dissolution-centrifuge samples,the content of Al₂O₃ in limestone and marlstone is below 0.02%,the content of Al₂O₃ in dolomite is below 0.05%;When use the acid leaching samples,the content of Al₂O₃ in limestone and marlstone is below 0.015%,the content of Al₂O₃ in dolomite is below 0.03%.So leaching acid solubie is better than acid dissolution-centrifugation method.The results of ICP-MS analysis of acid leaching dissolve solution show,for limestone and marlstone,when the content of Al₂O₃ is below 0.01%,the PAAS-normalized patterns of REEs and Ce anomaly in the authigenic sedimentary carbonate rocks will not be affected,so can assume no clay mineral dissolution.And can be used to trace sedimentary environment.For dolomite,when the content of Al₂O₃ is below 0.01%,the PAAS-normalized patterns of REEs and Ce anomaly in the authigenic sedimentary carbonate rocks will not be affected,the consequence can be used to trace sedimentary environment.The dissolution of minute quantity clay minerals will not affect the Eu anomaly.