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BACKGROUND Sepiolite is a very important non-metallic mineral, which is widely used in aviation, animal husbandry, the chemical industry, environmental protection and other fields. Sepiolite is in great demand and needs a lot of analysis and testing. However, the existing sepiolite reference materials are inadequate and do not satisfy the needs of sepiolite composition analysis. Furthermore, there are no sepiolite reference materials in China, making it necessary to develop one. OBJECTIVES To prepare a reference material for composition analysis of sepiolite whose certified value components cover as many elements as possible. METHODS Sepiolite samples were collected from Xiangtan, Hunan Province. The samples were subjected to primary crushing, coarse-grain sieving, inactivation, fine grinding and fine grain sieving. After passing the initial inspection, samples were bottled and numbered. Random samples were taken for homogeneity test, stability test. 24 components were selected for homogeneity and stability test. RESULTS The results showed that the RSD of 20 components were less than 3%, and the F value of the variance test was less than the critical value of the list[F0.05(29, 60)=1.65], indicating that the homogeneity of the reference material was good. During the investigation period, the contents of 24 components had no significant change, indicating that the standard material was stable. Nine laboratories cooperated with traditional chemical analysis methods and modern instrumental analysis methods to determine the value. The final values were 63 components, covering major, trace and all rare earth elements. The contents of characteristic components MgO and LOI were 18% and 8.55%, respectively. These two components form a certain ladder with the existing reference materials, which can better satisfy the requirements of sepiolite composition analysis. CONCLUSIONS The developed sepiolite reference material can be used as the quality control standards for geological prospecting, geochemical investigation and testing of geological and mineral products, as well as for other industries to analyze similar materials. Moreover, in the process of developing the reference material, improvements and developments to the new methods will provide technical support for the subsequent development of the sepiolite reference material.

BACKGROUND Sepiolite is a widely used fibrous magnesium-rich silicate clay mineral. Sepiolite is mainly composed of silicon and magnesium, with minor aluminum, potassium, sodium and other impurities. Determination of the major element of sepiolite usually adopts the classical chemical analytical method. After the alkali melting treatment, the sample is determined by volumetric method, photometry and atomic absorption spectrometry, which is inefficient and time-consuming. Moreover, potassium and sodium cannot be simultaneously determined. OBJECTIVES To find an efficient method for the determination of seven major elements in sepiolite. METHODS The samples were digested by hydrofluoric acid, nitric acid, and perchloric acid. Contents of major elements such as Al2O3 were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The dosage of hydrofluoric acid was optimized. The analytical spectral lines were Al 396.153nm, Ti 334.940nm, K 766.490nm, Na 589.592nm, Ca 422.673nm, Mg 285.213nm and Fe 238.204nm, and elements were determined by axial observation. The content of magnesium in sepiolite was high, and there was a certain matrix effect during ICP-OES analysis. A series of high magnesium mixed standard solutions were prepared to match the matrix. RESULTS The linear correlation coefficient of the standard curve of each element was greater than 0.9990, the detection limits of the method were 0.53-3.25μg/g, the relative standard deviations (RSD, n=10) of the measured results were 0.66%-5.65%, and the recoveries of each element were 95.3%-108.5%. CONCLUSIONS Acid dissolution is easy to operate compared with the alkali fusion method. The results are consistent with those obtained by classical chemical analytical methods and thus meet the analytical requirements of sepiolite samples.

BACKGROUND The sampling weight can be as low as milligram level when the contents of rare earth elements in rock and soil samples are determined by inductively coupled plasma-mass spectrometry (ICP-MS). However, the size of 200 mesh samples requires 100mg to ensure representativeness, which makes it difficult for ICP-MS to make full use of its advantages of high sensitivity and small sampling volume. OBJECTIVES To establish the method for the determination of rare earth elements in ultra-fine rock and soil samples by ICP-MS with microwave digestion. METHODS A method was developed for the determination of rare earth elements in ultra-fine rock and soil samples by ICP-MS with microwave digestion. The ultra-fine rock and soil samples were prepared by the planetary superfine pulverizing machine with wet grinding. Some parameters influencing the preparation of ultra-fine rock and soil samples, including grinding method, grinding time and the proportion of grinding balls were optimized. Microwave digestion of ultrafine-grained rock and soil samples in a nitric acid-hydrofluoric acid-hydrogen peroxide solution system, the sampling amount was reduced to 5mg, the total acid amount was reduced to 0.25mL and the digestion time was reduced to 25 minutes. RESULTS The results indicated that the samples were best refined when the wet-milling was adopted with ethanol as a dispersant and the milling time was 10 minutes and 15 minutes for 200 mesh soil and rock samples, respectively. The material ratios were 7g materials, 500 grinding balls, 45mL dispersants for the preparation of ultra-fine soil samples, whereas 5g materials, 500 grinding balls, 45mL dispersants for the preparation of ultra-fine rock samples. The particle size distribution D95 of soil standard substance GBW07404 and GBW07447 can be as low as 7.51μm and 7.05μm, and the D95 of rock standard substance GBW07104 and GBW07121 can be 8.42μm and 8.30μm under the optimized conditions. Microwave digestion of ultrafine-grained rock sample GBW07104 in a nitric acid-hydrofluoric acid-hydrogen peroxide solution system, the sampling amount was reduced to 5mg, the total acid amount was reduced to 0.25mL, the digestion time was reduced to 25 minutes, and the measured value of rare earth elements was consistent with the certified value with the relative standard deviation is between 1.64% and 5.21%. CONCLUSIONS This method was used for the detection of rare earth elements in other ultra-fine standard materials (GBW07404, GBW07447 and GBW07121), which yielded the relative standard deviation of 0.17%-6.60%, meeting the first criterion of Geology and Minerals Laboratory Testing Quality Management Standards.

BACKGROUND Solid sampling technology applied in soil sample measurement has the limitation of sample size, and cannot be applied to the mainstream element analysis instrument. OBJECTIVES To determine the trace elements by smashing soil samples to micron scale by high-speed grinding technology and under the action of a dispersant. METHODS The ultra-fine grinding technology of soil samples was systematically studied. The sample was crushed to micron level in a few minutes in an ethanol medium. The prepared solid suspension was directly measured by ICP-MS, avoiding blockage of pneumatic atomizers. RESULTS The determination of the reference materials shows that the solid suspension still has interference when the particle size is 6.8μm. By adding a small amount of hydrofluoric acid and nitric acid to modify the solid suspension, the solid particle size was reduced and thereby the impact of the sample size was reduced. The 13 trace elements of lithium, beryllium, vanadium, chromium, nickel, copper, zinc, rubidium, strontium, cadmium, cesium, barium and lead were successfully determined by ICP-MS. Accuracy experiment showed that the maximum relative error is 10.5%±3% and most of the elements have a relative error less than 5%. The precision experiment showed that most elements have a relative standard deviation (RSD) of less than 5.4%. CONCLUSIONS The determination results meet the requirements of DZ/G 0130-2006 'Test of Geology and Mineral Resources Quality Management Standards'.

BACKGROUND Sepiolite is a fibrous hydrous magnesium rich silicate clay mineral with the content of rare earth elements between 1×10-7 and 1×10-5. There is no national standard method for the determination of rare earth elements in sepiolite. Determination of rare earth elements in rocks commonly uses ICP-MS. Sample pretreatments generally use closed digestion and alkaline fusion, but these two treatments are time consuming and inefficient. OBJECTIVES To find an efficient dissolution method for the determination of 15 rare earth elements in sepiolite. METHODS By comparing three sample pretreatment methods of nitrate hydrofluoric acid hydrogen peroxide, nitric acid-hydrofluoric acid and nitric-acid hydrogen peroxide, the nitric acid-hydrofluoric acid solution system was selected. Microwave digestion was carried out and the hydrofluoric acid was driven off to avoid the formation of insoluble fluorides from the hydrofluoric acid. The content of 15 rare earth elements was determined by ICP-MS. RESULTS Due to the high content of magnesium in sepiolite, two internal standards of 103Rh and 185Re are selected to compensate for the drift of analytical signals and to correct matrix effects. The recoveries of the method range from 91.2% to 110.9%. The detection limits are 0.002-0.011 μg/L, and the precisions are 0.81%-2.79%. CONCLUSIONS The result of this method is in good agreement with that of the closed acid-digestion ICP-MS method, and with a small amount of acid (7 mL), high digestion efficiency (1 h), and a lower detection limit.

BACKGROUND The reductive environment of uranium is the most important influencing factor of uranium mineralization. The study of various redox markers in interlayer oxidation bands is of great significance for finding interlayer oxidation zone sandstone-type uranium deposits. OBJECTIVES The reduction experiments were carried out on reducing materials commonly found in sandstone-type uranium deposits such as ferrous, sulfide, pyrite, ilmenite, humic acid, biogas, and hydrogen. The reduction capacity of ferrous ion, sulfur ion, pyrite and other reduction factors at room temperature and pressure was studied. METHODS By polarography and spectrophotometry experiments to determine U(Ⅵ) and U(Ⅳ) content respectively. Their reduction capacity was analyzed. RESULTS Iron ion and sulfur ion had strong reducing properties, andhumic acid had certain reducing properties. Such as pyrite, ilmenite experiment in different acidity and sage green sandstone water soaking experiments showed that the soaked solution of gray-green sandstone contained a certain amount of ferrous ions, and there was no sulfur ion. CONCLUSIONS These ferrous ions were the main reason for the strong reducibility of gray-green sandstone. It also indicated that the gray-green sandstone was one of the most important factors in the subsequent mineralization of sandstone type uranium deposit in Ordos area.

The powder pellet compression method for X-ray Fluorescence analysis is an ideal environmentally friendly sample preparation technique with the added advantages of being simple and having high efficiency. However, due to the impact of particle effects and mineral effects, its measurement error is within about 5%, which hinders the application of this technology in the detection of major elements. Powder pellet technology is mainly used in the determination of trace elements as well as the analysis field with less precision. In this study, the stream sediment and soil reference material were crushed to an average particle size about 4-5 μm within a few minutes by ultra-high-speed planetary pressure prototype. The method of ultra-fine pressed powder pellet sample to determine SiO2, Al2O3, Fe2O3, CaO, MgO and other major elements was established by using X-ray Fluorescence Spectrometry. Measurement precision (RSD) of the method for most of the major elements is less than 2%, and detection limits are 0.003%-0.021%, which is an improvement on the melting method detection limit (0.006%-0.081%), especially for small atomic sodium with four times improvement on the detection limit. The development of this ultra-fine powder compression method for stream sediment and soil, minimizes the impact of the particle size effect by crushing the sample into several microns. X-ray Diffraction analysis demonstrates that the mineral composition of river sediments and soil preparation is dominated by quartz. Therefore, the mineral composition is simple with negligible mineral effect. Measured data with added LOI normalized processing shows that normalized measurements for each element is consistent with the standard value. The accuracy of the method is a significant over the conventional pellet sampling method.

The main analysis error of pressed powder pellet of carbonate comes from particle-size effect and mineral effect. So in the article in order to eliminate the particle-size effect, the ultrafine pressed powder pellet sample preparation is used to the determination of multi-elements and carbon-dioxide in carbonate. To prepare the ultrafine powder the FRITSCH planetary Micro Mill machine and tungsten carbide media is utilized. To conquer the conglomeration during the process of grinding, the wet grinding is preferred. The surface morphology of the pellet is more smooth and neat, the Compton scatter effect is reduced with the decrease in particle size. The intensity of the spectral line is varied with the change of the particle size, generally the intensity of the spectral line is increased with the decrease in the particle size. But when the particle size of more than one component of the material is decreased, the intensity of the spectral line may increase for S, Si, Mg, or decrease for Ca, Al, Ti, K, which depend on the respective mass absorption coefficient . The change of the composition of the phase with milling is also researched. The incident depth of respective element is given from theoretical calculation. When the sample is grounded to the particle size of less than the penetration depth of all the analyte, the effect of the particle size on the intensity of the spectral line is much reduced. In the experiment, when grounded the sample to less than 8 μm(d95), the particle-size effect is much eliminated, with the correction method of theoretical α coefficient and the empirical coefficient, 14 major, minor and trace element in the carbonate can be determined accurately. And the precision of the method is much improved with RSD < 2%, except Na2O. Carbon is ultra-light element, the fluorescence yield is low and the interference is serious. With the manual multi-layer crystal PX4, coarse collimator, empirical correction, X-ray spectrometer can be used to determine the carbon dioxide in the carbonate quantitatively. The intensity of the carbon is increase with the times of the measurement and the time delay even the pellet is stored in the dessicator. So employing the latest pressed powder pellet is suggested.