Analysis of minerals

ANALYSIS OF MINERALS (EN: mineral analysis; DE: Mineralienanalyse, Analyse der Bodenschatze; FR: analyse des mineraux utiles; ES: analisis de minerales; RU: анализ полезных ископаемых) is the complex of the mineralogical-petrographic, physical-chemical, and technological researches for the purpose of determination of the elemental or substantial composition, and of the beneficiation ability of the mineral raw materials.

The analysis of minerals is performed on the samples, which are collected at the deposit (during the process of exploration or extraction and ore dressing) in such a way, so that they would be representative for the studied property, that is characteristical for the minerals of the given deposit. The elemental composition of the sample is determined by the methods of the chemical (for the major components) and spectral analyses, and by other methods (for the micro-admixtures). For the determination of the types of the chemical compounds, which form the major components, they use the phase analysis of the minerals, which is based on the selective dissolution of the sample within various solvents. They use the thermal analysis for the carbonatic and hydrous minerals. It is the constituent part of the mineralogical analysis, which includes also the determination of minerals under the microscope, sometimes with the additional treatment of their surface. The identification of minerals during the microscopic analysis may be performed on the polished sections with reflected light (polarized in certain cases), sometimes with transient light. The major diagnostic features are colour, brightness (reflectivity of the surface), hue (dispersion), hardness (the level of the relief on the polished section), anisotropy in polarized light, internal reflections (for the transparent and translucent minerals).

The impact of the ultraviolet rays or of the flux of electrons onto the certain minerals causes their specific glow, namely, luminescence. The luminescent analysis, which is based on this phenomenon, permits to determine the varieties of minerals, structural peculiarities, and defects of the crystal lattice. There solve these same issues the X-ray structural analysis and electronography. For the diagnostics of the micro-inclusions of minerals they use the methods of the microphase analysis with microscope, namely, etching, droplet and film reactions with reagents, which are selectively interacting with specific minerals. They record the distribution of minerals within the polished section onto the photo paper, or describe according to the results of the visual observations of the shape of particles, of their mutual association and intergrowth. They also measure then the sizes of the inclusions, determine the quantitative content of the individual minerals. They use for these purposes the automatic and semi-automatic installations (for the counting of the content of minerals within the sample), ocular grids, micrometres, or perform the comparison with the standard sample preparation. There widens the usage of the modern instrumental methods of analysis of minerals. The X-ray radiometric phase analysis, which is based on the diffraction of the rays with specific wave length from the crystal lattice, permits to identify minerals within the small samples (less than 300 milligrams) with the size of the particles less than 0.1 micrometres. At this time, there are determined the mineralogical varieties, which are having the same composition, but different crystal lattice. Electron probe X-ray spectral microanalysis permits to reveal the composition of the sample at the sites with the area of several square micrometres and with the depth of approximately 1 micrometre for all elements from Be to U. The information about the structure of the distribution of elements, their mutual associations, the sizes of the inclusions, and other properties, may be obtained with the help of the electronic probing, while performing at the same time the processing of the materials of the researches with the computer. The obtainment of the data of this type is the subject of the petrographic or structural-textural analysis, which is dealing with the structure of the mineral aggregates, and permits to determine the conditions of the formation of minerals, genetical type of the deposit. For the placer deposits, they perform the mineralogical analysis only of the heavy fraction of minerals (heavy concentrate), which has been washed out from the gangue. The relative assessment of the content of the heavy minerals within the heavy concentrate and original sample is performed during the analysis of the heavy concentrate.

The most important characteristic of the ore, which is arriving for benefication after crushing and grinding, namely, the granulometric composition, is the characteristic of the size of the particles. They use for the material, which is larger than 40-70 micrometres, the sieve analysis, comprising the sieving of the sample through the standard set of the sieves, and determination of the weight yield of the each fraction. The accuracy of the sieve analysis is ensured by the thorough drying of the material, and by the automatic shaking and vibrating of the sieves. Through the sieves with the size of the holes 74 and 44 micrometres, the material is washed with water. The thinner particles are subjected to the sedimentation analysis.

They use for the conduct of the granulometric analysis the automated installations, the operation of which is based on the photometric measurement of the opacity of the suspension, or on the change of the electrical resistance during the passage of the particles between the electrodes. When the necessity is present of the quantitative assessment of the distribution of the free mineral grains and intergrowths according to the fractions of the different density and size, there is performed the fractional analysis. At this time, the gravitational fractional analysis of minerals is performed within the heavy liquids and solutions, the density of which is selected with dependence on the composition of minerals. They separate thin classes (20 micrometres) within the heavy liquid and centrifuge. They analogously conduct the fractional analysis of minerals according to the magnetic susceptibility (see the "Magnetic analysis" article). According to the results of this analysis, they plot the curves of the beneficiation ability in the coordinates of output relative to the density (composition) of the fractions.

For the radioactive ores, the corresponding measurements of the radioactivity of the fractions permit to construct the curves of contrast, which are characterizing the beneficiation ability of the ore by the method of the radiometric separation (see the "Radiometric analysis" article).

During the study of the beneficiation ability, they sometimes determine electrical conductivity, electrical-chemical potential of the particles, bulk mass, and other properties. For the coal and certain other minerals, which are beneficiated by flotation, they measure the specific surface area.