RU2424860C1 - Method of separating diamond-containing materials - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed method may be used in dressing dry diamond-containing materials, for example, primary preparation concentrates. Separated material is conveyed subjected to tribo charging by friction and electromagnetic radiation flow with wavelength sufficient for initiation of photo effect in useful component. Electric charges of minerals are measured by contactless method. Measured values are compared with preset separation threshold. Detected grain of useful component is deflected into concentrate receiver by means of actuator.

EFFECT: higher separation stability and yield of diamonds.

3 cl, 3 dwg, 2 tbl

Description

The invention relates to the field of mineral processing, and in particular to methods for the separation of dry diamond-containing materials, for example primary concentrates.

There is a known method of triboelectric separation (Handbook of ore dressing. Basic processes. / Ed. By Bogdanov, 2nd ed., Revised and additional M., Nedra, 1983, p. 209), which is used to separate minerals having close conductivity values .

According to this method, the separated particles acquire an electric charge by triboelectrification by friction against a metal or dielectric surface, for example, when a vibrating transport mechanism moves along a vibrating surface. When a triboelectrified material is fed into a region of a strong electric field, it separates due to various deflection of particles under the influence of an external electric field.

This method is not applicable for the separation of material larger than 2 mm due to the fact that with an increase in the size of the separated particles, the magnitude of electric forces becomes less than gravity.

Closest to the proposed method is a method for the separation of diamond-containing materials, including moving the sorted material into the measurement zone, non-contact measurement of electrophysical properties, comparing the measured value with the separation threshold, further moving the material to the actuator action area and rejecting the detected grain of the useful component to the concentrate receiver using the actuator (Russian patent No. 2353439, IPC B07C 5/344, publ. Bull. No. 12, 04/27/2009). As a physical characteristic by which diamonds are separated from a mixture of minerals, an electric charge is used, which is created simultaneously with the movement of the separated material due to friction on the surface of the conveying device - a grounded metal vibrating tray (tribo-charge). The material, size and vibration mode of the tray are selected so as to ensure the maximum value of the tribo-charge imparted to the diamond, with a minimum value of the tribo-charge of associated minerals. Non-contact measurement of the sign and magnitude of the induced electric charge is carried out with a free fall of a charged separated material using a high-speed electrometric amplifier, and the separation threshold is selected based on previously estimated values for natural diamonds of a given size class. The specified method allows you to detect and extract diamonds, for example, from the products of the primary enrichment of enrichment plants and has advantages compared to other methods for the extraction of diamonds, for example, with methods of X-ray fluorescence separation, since it allows you to additionally remove non-luminescent diamonds from the tailings of X-ray fluorescence separation.

The disadvantage of this method is the instability of its work and not sufficiently complete extraction of diamonds. The instability of this method is associated with the dependence of the tribological charge accumulated by diamond on temperature, humidity of the ambient air, the state of the surface of the diamond and vibratory tray, etc. When these factors affect the process of tribo-charging, the tribo-charge accumulated on the diamond may be insignificant and not exceeding the threshold value; such diamonds will not be extracted.

The technical result of the invention is to increase the stability of the separation process by increasing the differences in the magnitude of the charge on the diamond and the separated minerals, which allows to increase the extraction of diamonds.

The technical result is achieved by the fact that when implementing the method of separation of diamond-containing materials, including transporting the separated material with its simultaneous tribo-charge, subsequent non-contact measurement of the electric charges of minerals, comparing the measured values of the charge with a predetermined separation threshold and deviating the useful component to the concentrate receiver using an actuator , during transportation with simultaneous tribo-charging, the material is additionally irradiated ayut electromagnetic radiation of a wavelength sufficient to stimulate a useful component of the photoelectric effect, for example X-ray, or ultraviolet radiation range of the optical spectrum.

From the course of physics it is known that during friction, substances are charged and acquire some electrical potential. The magnitude and sign of this potential are determined from the relation: Ue = E, where U is the potential (B), e is the electron charge, E (eV) is the energy that the electron needs to overcome some potential barrier and leave the material (electron affinity )

Most substances have a positive electron affinity. This means that the potential barrier E is a positive quantity. During friction against a metal, such substances are negatively charged; a certain excess of electrons remains in the material, since the presence of a positive potential barrier prevents them from leaving the substance.

One of the properties of diamond is its negative electron affinity. The essence of this phenomenon is that for diamond the potential barrier (work function) for electrons is a negative quantity, and electrons easily leave the surface of the diamond. This leads to the fact that upon contact with a grounded conductor (metal), part of the electrons from the surface layer passes into the metal, as a result of which the diamond acquires a positive charge. It is on this property of diamond that the triboelectric separation method is based. However, the charge is usually small. This is because when leaving the electrons, the substance acquires a positive potential U, preventing other electrons from leaving the sample further. Obviously, the equilibrium state will be established under the condition Ue = A (A is the electron affinity energy or the work function of the electrons from the substance. It follows that the more energy the electrons have in the substance, the more charge the substance will acquire upon tribo-charging.

Tests of separator models operating on the basis of charge accumulation by the material during its movement along the grounded tray showed that in some experiments the extraction of the useful component was 97-98%, but repeated experiments under similar conditions sometimes show a drop in extraction to 70-80%. A probable reason for the instability of the work is a small value of the tribo-charge and small differences in the value of the charge on diamonds and related minerals. In addition, the separation process in this way is very sensitive to external destabilizing factors. Such factors may be the condition of the contacting surfaces, air humidity, humidity of the separated material, ambient temperature, light exposure, the influence of electromagnetic fields and several others. All these factors either create an additional potential barrier for the exit of electrons from the crystal, or contribute to the absorption of the accumulated charge, as a result of which the magnitude of the charge on the crystal, therefore, the probability of its extraction, decreases.

From the course of physics, the phenomenon of the photoelectric effect is known - the stimulation of the emission (emission) of electrons by external radiation. When a quantum with an energy E _{k is} absorbed, an electron with an energy E _f (photoelectron) is emitted from the substance, its energy is determined as

E _f = E _to -A,

Where

A is the work of the electron exit from the substance during the photoelectric effect, in physical meaning it is close to the electron affinity for the triboelectric effect.

Obviously, for E _k <A, photoelectrons do not exist, since in this case they must have an energy of less than zero. This is known as the long-wavelength border of the photoelectric effect.

If in a sample with negative electron affinity during its tribo-charging, the photoelectric effect is stimulated, then

Ue = (U _t + U _f ) e,

those. the sample potential will change in proportion to the energy of the quantum of radiation stimulating the photoelectric effect. In this case, for substances with a positive electron affinity (A positive), the potential of the material will decrease, and for substances with a negative electron affinity (A negative) will increase. It is well known that the photoelectric effect can be stimulated by x-ray, ultraviolet, and optical radiation in many substances, including in diamond.

Thus, the stimulation of the emission of photoelectrons from the diamond surface under the influence of external electromagnetic radiation, for example, the ultraviolet range (wavelength of at least 435 nm), during its tribo-charging during movement along the tray leads to an increase in its charge. In addition to ultraviolet, X-ray radiation (wavelength of at least 10 nm) and radiation of the visible spectrum with a wavelength exceeding the red border of the photoelectric effect in diamond (400-900 nm depending on the impurity composition) are suitable for stimulating the photoelectric effect. An increase in the charge of the useful component due to the photoelectric effect will make it possible to further extract diamonds with a weakly manifested triboeffect, or to reduce the sensitivity of the separator, thereby increasing its resistance to the influence of destabilizing factors, which will also increase diamond recovery due to its more stable operation. In addition, the radiation causes a slight increase and, after warming up, constant support of the air temperature in the volume between the emitter and the tray, drying of the tray after passing wet samples of the separated material through it, which also helps to increase the stability of the apparatus as a whole.

The essence of the proposed method is illustrated by drawings, where Fig. 1 shows a diagram of a laboratory bench for studying the effect of ultraviolet radiation on the amount of tribological charge accumulated by minerals; on figa - signals from diamonds after they move along the tray without and when exposed to UV radiation, 2b - signals from minerals after they move on the tray without and when exposed to UV radiation; figure 3 shows a diagram of the layout of a triboelectric separator with a source of additional radiation.

The study of the influence of ultraviolet radiation on the value of the accumulated tribo-charge was carried out on a laboratory bench (figure 1). An internal part of a fluorescent lamp of the DRL type with a power of 125 W with a reflector was used as a radiation source. The inner part of the DRL-type lamp is a quartz flask in which the glow of mercury vapor in the UV spectrum is excited by an electric discharge. Lamp 1 was placed at a distance of about 5 cm from the vibrator 2 so that its axis coincided with its axis. After charging on the vibratory tray 2, the crystals fell into the measuring cell 3. The signal value was recorded by an oscilloscope (not shown).

The measurements were made as follows. With the lamp turned off, diamond crystals were passed by the piece by the piece, the signals from each of them were measured, then, without changing the experimental conditions, the lamp was turned on and measurements were repeated. The results of measurements of signals from diamonds (Fig. 2a) show that an increase in the accumulated charge under the influence of UV radiation is detected for almost all diamonds, but to a different extent. For some of them, the increase is several percent, for some of them the signal increases by 3-4 V, which corresponds to the quantum energy of the used radiation (3-4 eV). Since the magnitude of the photoemissive current substantially depends on the state and purity of the crystal surface, which varies from crystal to crystal, the observed scatter with increasing signal is natural.

Similar measurements carried out with zircon (Fig.2b) did not significantly affect the magnitude of the signals. The signal from the minerals remained approximately the same, within the limits of the measurement error. This is also easily explained, since the radiation used did not have enough energy to overcome the long-wavelength boundary of the photoelectric effect in these minerals.

The proposed separation method was tested in one of the enrichment plants. A triboelectric separator used for processing dry diamond-containing material of particle size class -5 + 2 mm and -2 + 1 mm, extracted from the tailings of the separation radar by the adhesive (grease) method, was used. The separator is additionally equipped with a source of UV radiation: - lamp type DRL 125 with a reflector (figure 3).

The separator consists of a radiation source 1, a hopper 4, a feeding tray 5, a tray 2, on which the material is tribo-charged, a measuring cell 3, an actuator 6, a tail 7 and a concentrate 8 compartments.

The method is as follows. Separated material was fed from hopper 4 to feed tray 5 to tray 2, where it was tribo-charged. Simultaneously with tribo-charging, the material was irradiated with a flux of electromagnetic radiation from source 1 with a wavelength sufficient to stimulate the photoelectric effect in a useful diamond — radiation from a DRL lamp. The value of the charge was determined by a non-contact method in free fall by measuring cell 3. Studies previously conducted in accordance with the above method in laboratory conditions made it possible to determine that when crystal-based material was fed to the tray, the signals from the separated minerals rarely exceeded 0.6 V (Fig. 2). This served as the basis for choosing precisely such a threshold for separation. If the measured signal (charge on the crystal) did not exceed 0.6 V, then the sample fell into the tail product receiver 7, if the signal value exceeded the set separation threshold of 0.6 V, the sample was considered a diamond, actuator 6 was triggered, which deflected the sample to the concentrate receiver 8.

A sample was taken from the separated material and divided into two parts. The first part of the sample was used as an experimental one, the second part of the same sample was used as a control. When processing experimental samples, the material was charged with the radiation source 1 turned on, while processing control samples, the irradiator was turned off without changing other experimental conditions. After processing the sample, the concentrate and separation tails were disassembled manually, the selected diamonds were weighed, and extraction was calculated.

The results of experimental separation at a separation threshold of 0.6 V are shown in Table 1. With index (e), the results of the experiment, with index (k), the results of processing control samples. As follows from table 1, when processing the sample under conditions of irradiation with ultraviolet radiation, higher and more stable indicators for the extraction of diamonds are obtained in comparison with the processing of control samples under the same conditions.

In order to increase the separation selectivity, a separation threshold of 1 V was set. The test results are shown in Table 2.

At a separation threshold of 1 V, diamond recovery decreased both during experimental and control processing of samples, which should be observed in such experiments. However, diamond recovery was higher for the experimental test. The spread of extraction by size classes was less for the experimental sample.

Thus, tests in an industrial environment confirm the efficiency of the method and its advantages compared to the prototype. These advantages (increased diamond recovery and increased stability of the separator) are achieved by additional exposure to the separated material of electromagnetic radiation, which stimulates the photoelectric effect in the diamond. As a result of the combined action of tribo and photo effects, the diamond charge increases, in addition, the creation and maintenance of a stable temperature separation mode also helps to increase the stability of the apparatus as a whole.

Claims (3)

1. The method of separation of diamond-containing materials, including transporting the separated material with its simultaneous tribo-charging by friction, subsequent non-contact measurement of the electric charges of minerals, comparing the measured values with a predetermined separation threshold and deviating the detected grain of the useful component to the concentrate receiver using an actuator, characterized in that during transportation with simultaneous tribo-charging, the material is additionally irradiated with a flow of electromagnetic of radiation with a wavelength sufficient to stimulate the photoelectric effect in the useful component. 2. The method according to claim 1, characterized in that the material is irradiated with a stream of ultraviolet radiation. 3. The method according to claim 1, characterized in that the material is irradiated with a radiation flux of a mercury lamp.

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