Representative samples taken ore screening test, a more accurate particle size can be obtained the mineral composition of rock properties. The ore can be sieved into several fractions, such as +150, -150+65, -65+25, -25+10, -10 mm. Each grade ore is sorted separately. Generally fine-grained grades (eg -10 mm) ore cannot be sorted (except diamond ore). For a mine, if there are too few coarse-grained ore that can be selected, it will lose its meaning when it is picked. As the ray passes through the material, its activity will gradually decrease as the thickness passed increases. When the thickness is constant, the radiation will decrease as the absorption coefficient of the substance increases. Experiments have shown that the weakening of the ray is subject to the exponential function form of equation (8). I=I 0 e -μd (8) Where I 0 - the activity of the original ray; As can be seen from Table 3, as the black, non-ferrous metals and rare minerals useful components atomic number (Z> 25) is larger than the atomic number of the components surrounding rock (Z≈1 ~ 15), which mass absorption coefficient μ m . There are also significant differences. This allows the ore to be separated from the surrounding rock by the gamma absorption method. Ore such as iron , chromium , tin , antimony, lead - zinc can be sorted by this method. [next] Selective gamma irradiation sources and neutron detectors can be used for effective gamma neutron sorting of certain ores.
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(3) Relevance degree of sorting characteristics and useful components of ore Picking is a method of sorting ore and waste rock by using a certain feature of ore, generally not directly sorting according to useful components, so There is a good correlation between the selected sorting features and the useful components. If the color is selected according to the color of the nugget, the color of some nuggets is not strictly proportional to the grade. If the color is selected by the χ-light fluorescence method, the amount of fluorescence emitted by the ore and the ore are limited. The block grade does not necessarily have a strict proportional relationship, so when the sorting feature is selected, the ideal process index is not obtained.
To understand the relevance of the sorting features to the useful components, an optional curve is drawn based on the sorting characteristics. The difference between this curve and FIG. 4 is that, when drawing, the ore is grouped according to the grade of the useful element, but by the sorting feature (such as color depth, fluorescence intensity, etc.) into a useful element grade.
According to the optional curve and formula, the ore degree index M' of the ore can be obtained. If the value is close to the M value, that is, M'/M→1, the selected sorting characteristics are reasonable. When M'/M is less than 0.7~0.8, it means that the sorting feature selection is inappropriate, and it is difficult to perform picking efficiently.
Second, the theoretical basis of various sorting methods
The theoretical basis of the various sorting methods is described separately in the order of the sorting method.
(1) Radioactive sorting method The radioactive sorting method is selected from uranium ( é’ ) ore. The sorting method is a sorting method for separating uranium ore and waste rock according to the natural radioactivity of uranium ore. The γ-rays in the uranium (é’) ore have a strong penetrating ability. When the uranium (é’) ore passes through the scintillation crystal detector, the photomultiplier tube matched with the crystal generates a pulse signal, and the pulse obtained by the photomultiplier circuit The number of the number is proportional to the γ-ray activity in the nugget. According to the activity of the γ-ray per unit weight of the nugget, the uranium (é’) grade of the nugget can be judged, thereby separating the ore from the waste rock. . [next]
Since the γ-rays in the uranium ore are basically all emitted by the radium group elements, the necessary condition for radioactive sorting is that the uranium-radium in the ore is basically in a state of radioactive equilibrium. In the equilibrium of uranium radium, the weight ratio of radium to uranium (Ra/U) is 3.4 × 10 -7 . At this time, the gamma activity is proportional to the uranium content. Therefore, measuring the gamma-ray activity as a sorting feature can measure the uranium content. Due to geochemical reasons, the radioactive balance of some uranium ore is destroyed, may be radium, or may be partial uranium. The gamma-ray activity of the former is relatively increased. When radioactive sorting is carried out, some of the poor ore blocks with low uranium grade will enter the concentrate, which will reduce the uranium grade of the concentrate; the latter will be relatively weakened, resulting in partial uranium. A high grade ore falls into the tailings. Therefore, if the deviation of the radioactivity balance coefficient is greater than 10%, it needs to be corrected. Radioactive sorting cannot be performed in cases where the deviation is severe.
(2) γ absorption method (χ absorption method)
The gamma absorption method (χ absorption method) is a sorting method that separates the gamma-ray (or x-ray) absorption ability by using the nugget and the waste rock.
When γ-rays penetrate a substance, it is absorbed by the effects of photoelectric effect, the Copton-Wu-Tang effect, and the generation of electron pairs, as shown in Fig. 5. The absorption of gamma rays is related to the characteristics of the absorber. Let γ-ray energy be E, the density of matter is Ï, the atomic number is Z, the atomic weight is A, then the absorption coefficient Ï„ of photoelectric effect, the coefficient σ of Copton-Wu Youxun scattering and the absorption coefficient 电å generated by electron pair χ as follows. [next] [next]
I—— the ray activity when passing through an absorber of thickness d;
Μ——the bus absorption coefficient of the absorber to γ-ray, cm -1 ;
d - the thickness of the absorbent body, cm.
The ore blocks contain different chemical elements, and the bus absorption coefficient μ can be obtained by a weighting method by the linear absorption coefficient μ i of each element. In practical applications, the thickness of the absorbent body is always in grams per centimeter. In units of units, the absorption coefficient corresponding to such a thickness unit is called the mass absorption coefficient μ m and its unit is cm 2 /g. The relationship between the mass absorption coefficient and the linear absorption coefficient is μ m = μ / Ï.
It can be seen from equations (4), (5), and (6) that the atomic number has a great influence on the absorption of γ-rays, that is, the ore of different composition of materials has a great difference in the absorption capacity of γ-rays. The data of the measured ray activity before and after the ore absorption also prove this point. Some ore and gangue have significant differences in the total mass absorption coefficient and can be used for gamma absorption picking.
Table 3 gives the total mass absorption coefficients of some chemical elements at the energy of the gamma radiation source of 0.05 and 0.1 MeV. [next]
Although the difference between the effective atomic number of some ore and surrounding rock is not large, if the density differs greatly (such as coal and shale ), it can also be sorted by absorption method.
Factors affecting the separation of the absorption method In addition to the chemical composition of the ore block, the size of the ore also has an effect. Therefore, it is necessary to strictly screen the ore or install a device for detecting the size of the ore block on the sorting machine.
The gamma source of the gamma absorption method is generally used as a radioisotope. Choosing the right source of illumination increases the difference in absorption coefficient. A scintillation detector or a Geiger counter tube is usually used as the gamma ray detector.
The disadvantage of the gamma absorption method is that in the ore that needs to be sorted, the grade of the useful element is high, otherwise it is difficult to distinguish. In the industry, iron ore was successfully sorted by gamma absorption.
(III) γ Scattering Method The γ scattering method is a sorting method that separates ore from waste rock by utilizing the difference between the γ-ray and the scattered ray generated by the action of the nugget.
When the energy of γ-rays is low (such as less than 1 MeV), after it interacts with the substance, it mainly produces photoelectric effect and the effect of Commington-Wu. When the gamma-ray scattered by the Copthorn-Wu Youxun effect is used as a marker for sorting nuggets, it is the γ-scattering method.
It can be seen from equations (4) and (5) that the photoelectric effect is proportional to the atomic number of the elements in the sample from 4.1 to 4.5, that is, the photoelectric effect has a great relationship with the composition of the sample, and the Copton-Wu Youxun scattering The effect is only proportional to the power of the atomic number.
Choosing two gamma sources with different energies, when one source and the nugget act, mainly produces the scattering effect of the Copthorne-Wu-Tong, and the other source mainly produces the photoelectric effect. After measuring the intensity ratio of the two gamma-sources, the intensity ratio can be measured. The effect of the weight of the nugget is removed, and the content of useful elements in the nugget is quantitatively measured.
If the effective atomic number of the useful elements constituting the ore is significantly different from the atomic number of the rock-forming element, the ore can be sorted by the gamma scattering method.
The gamma scattering method can be used for the sorting of heavy metal elements containing a large atomic number, such as chromium, iron, cobalt , nickel , lead, zinc and the like.
(4) γ fluorescence method (χ fluorescence method, ultraviolet fluorescence method)
A method of measuring the fluorescence emitted by the ore after being irradiated by electromagnetic waves to separate the ore from the waste rock is called a fluorescence separation method. The fluorescence that the ore can emit can be visible fluorescence, or it can be neon or infrared. Depending on the type of illuminating electromagnetic wave used, the fluorescence sorting method is correspondingly referred to as gamma fluorimetry, krypton fluorescing, and ultraviolet fluorescemetry. [next]
When a ray (χ-ray, χ-ray, ultraviolet ray, etc.) interacts with a substance, an electron in a certain layer of the atom (k, l, m, n, etc.) is energized, and the atom is in an excited state. When it returns to its normal state, excess energy is released and the resulting emission is fluorescence.
There are many minerals in nature that can fluoresce, and the luminescence properties of minerals are mainly in their crystalline state. The center of the luminescence may be the molecule or ion of the main elemental lattice, or it may be an impurity in the crystal lattice. There are also many minerals in the mineral that cannot emit light. These minerals mainly include minerals with strong electron conductivity.
In addition to the type and wavelength of the source of illumination, the color of the fluorescence is also affected by impurities in the mineral. Minerals of the same name in different mining areas emit different fluorescence if they contain different impurities. For example, fluorite can be green, cyan or purple under ultraviolet light.
X-ray fluorescence separation of diamonds has been widely used in the industry. Fluorescence sorting by γ tin, tungsten, nickel ore, sorting by an ultraviolet fluorescence method and the like are also scheelite promotion process.
(5) γ neutron method The γ absorption method, the γ scattering method, and the γ annihilation method described above are all sorted by the effect of the action of the lower energy gamma ray and the substance.
High-energy γ-rays and substances may produce nuclear reactions. There are many kinds of nuclear reactions. The most common reaction is (γ, n), that is, γ-rays react with substances to emit neutrons. The gamma neutron method is a beneficiation method that separates the ore from the waste rock by utilizing the difference in the neutron intensity of the detected nugget after being irradiated by gamma rays.
Each element has a certain (γ, n) reaction threshold, and the characteristics of some isotopes with low reaction thresholds are listed in Table 4. [next]
From Table 4, the minimum response threshold beryllium, only 1.665 MeV neutrons by γ beryllium ore sorting method obtained good results. The nuclear reaction 9 Be(γ,n) 8 Be is most suitable for the gamma ray source with the isotope 124 Sb because its energy is 1.693 mega-electron volts, which is higher than the reaction threshold of erbium.
(6) Neutron absorption method
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October 29, 2021