A Study On New Pretreatment Methods For Typical Geological Samples And Their Applications In Trace Analysis

Mineral resources are the foundation and guarantee for the development of human society.They are widely used in the fields of electronics,catalysis,energy,materials and agriculture.In particular,the"three rare resources"(rare,sparse and rare earth),as the"bottle-neck"minerals,have attracted great attention.The development of"three rare resources"is inseparable from the accurate analysis of related elements in geological samples.However,the variety of minerals that make up geological samples,and the occurrence states of each element differ significantly,necessitates the development of complementary analytical methods to meet actual requirements.The end products of"three rare resources"are often used as high-end materials in high-tech fields.The special properties of these high-end materials are not only related to the main elements,but also to the trace(impurity)elements.With the development of analytical testing techniques,in most cases,analytical techniques such as ICP-OES and ICP-MS can quantitatively meet the requirements of determination of most trace elements.As a result,the pretreatment of geological samples is a key factor to determine whether the analytical method can be applied to the analysis of samples under test.In this paper,a series of pretreatment methods are systematically studied from the aspects of sample representativeness,sample digestion methods and separation and enrichment measures,and their application in geological sample analysis is explored by combining them with analytical techniques such as ICP-OES and ICP-MS.The main contents are as follows:?In view of the fact that geological samples have large particle size and poor uniformity,which are not suitable for modern detection technology,a laboratory wet ball milling method is established to prepare ultra-fine geological samples.Based on a large number of comparative studies,the preparation conditions of ultrafine samples were optimized:agate ball milling tank,20g sample(200 mesh),water as grinding aid,liquid-solid ratio of 1:1,grinding ball configuration of 8 large,16 medium and 48 small,ball milling time of 30 minutes.For three representative samples(rock,soil and sediment),after ball milling by this method,the particle size of the samples reached1000 mesh.After ball milling of 60 samples of unknown matrix type,the median diameter is less than 5?m and D90 is less than 19?m.The effect of ball milling on the crystalline structure of the sample is not obvious,the number and average particle size of large particles in the sample are significantly reduced,and the distribution tends to be uniform.Forty-six elements in three samples(rock(GBW07104),soil(GBW07426)and sediment(GBW07320)were detected,and even if the sample amount could be reduced to 2 mg(except Mo,Cd,Cr and other elements),satisfactory results could be obtained.?A sample pretreatment method for HF-HNO₃-H₃BO₃ closed pressure digestion was established by combining ultra-fine samples with high temperature and high pressure closed dissolved samples.In the process of sample digestion,boric acid solution is added for redissolution,which can complex excessive HF,effectively store Si in the solution,and prevent the formation of insoluble fluoride.Combined with silicon molybdenum blue spectrophotometry,the accurate determination of Si in geological samples has been realized.The method has low blank,low reagent consumption and high detection efficiency,and can be used for mass sample detection.The sample amount is reduced to 10 mg,and the acid dosage is 0.6 m L(HF 0.5 m L,HNO₃ 0.1 m L)to realize the complete digestion of rock,soil and sediment samples.The dilution ratio of 1:1000 can meet the analysis requirements of ICP-OES and ICP-MS for major and trace elements simultaneously.?A method for digestion of high purity quartzite samples based on NH₄HF₂-HNO₃ was established.The XRD results show that the matrix Si is converted into(NH₄)₃Si F₆NO₃ while high purity quartzite samples are digested with NH₄HF₂ and HNO₃,and TGA results show that(NH₄)₃Si F₆NO₃ is completely decomposed and evaporated at 250?unlike(NH₄)₂Si F₆.Combined with ICP-OES and ICP-MS,40trace elements in high purity quartz sand can be detected,the detection limit of elements is between 0.0005?6.23?g/g;The RSD of all elements was less than 10%for the determination of three national first-class certified reference materials.The method has short digestion time(4 hours),less reagent consumption,and avoids using toxic substance HF;While the matrix element Si is completely removed,trace elements such as rare earth are enriched,the dilution ratio is small(100 times),and the analysis efficiency is greatly improved.?The mixed flux of sodium peroxide and sodium carbonate was used to dissolve the rare earth ore samples of associated barite.The separation was carried out by precipitation,that is,triethanolamine was used to extract the samples,followed by secondary precipitation with ammonia water.The separation efficiency of Si,Al,Fe,Ca,Ba,Sr and other matrix elements in the samples reached more than 91%.The method of ion exchange can separate the rare earth element into light rare earth group and heavy rare earth group.The results show that there is a certain degree of interference in the determination of rare earth elements by ICP-MS.The detection limit of rare earth element method is between 0.003?0.36 ng/m L,and the satisfactory analysis results are obtained in the detection of actual samples,with high accuracy and good precision.