New Process and New Technology of Iron Ore Electrification--Electrical Properties of Minerals

The so-called mineral electrical properties refer to the electrical resistance, dielectric constant, specific conductivity and rectification of minerals. These are the basis for judging whether or not electrification can be used for sorting. Due to the different composition of various minerals, the electrical properties exhibited are also distinct. Even if they belong to the same mineral, their electrical properties are different due to different impurities. However, there is always a certain range of variation. for our reference.
(1) Resistance
Resistance refers to the ohmic value measured when the particle size of the mineral is d = 1 mm. According to the measured resistance values ​​of various minerals, the minerals are often classified into the following three types, namely:
--- conductor resistance of less than ¹⁰⁶ ohms who show this type conductive mineral is preferably, selected in the conventional electric, make it separated from the conductor portion.
Non-conductor—The resistance of the mineral is greater than 10 ⁷ ohms. The conductivity of such minerals is very poor. In the normal electrical selection, it can only be separated as a non-conductor.
Medium --- i.e. the conductivity of the conductor is interposed between the conductor and the non-conductive, ohmic resistance of greater than ¹⁰⁶ but less than ¹⁰⁷ ohms who often selected mineral ore such as electrically separated.
The concept of conductors and non-conductors in electrical selection is quite different from conductors, semiconductors and insulators in physics. The conductor mineral referred to in this article refers to the electron energy that can move freely on the ore after adsorption of electrons in the electric field, or can be positively and negatively charged after being induced by the electrode in a high-voltage electrostatic field. This positive and negative charge can also be free. mobile. The opposite of the non-conductor, after it adsorbs the charge in the corona field, the charge cannot move or conduct freely on its surface. It can only be polarized in the high-voltage electrostatic field, and the center of the positive and negative charges only deviates, and the positive and negative charges are bound. The charge cannot be removed, and once it is separated from the electric field, it returns to its original state without exhibiting positive and negative electrical properties. Minerals with medium conductivity (or semiconductor) are such minerals between conductors and non-conductors. Except for some of these minerals, in the practice of electro-option, they are usually mostly connected.
(2) Dielectric constant
The dielectric constant refers to the ratio of a capacitor with a dielectric to a capacitor without a dielectric (referred to as vacuum or air). At the same voltage, if a dielectric is placed between the two plates of the capacitor, the capacitance of the capacitor will inevitably increase. The dielectric constant ε can be expressed by the following formula:

Where C _m ———the capacitance of the mineral or material, F;
C _o ———The capacitance of the air, F.
The value of the dielectric constant value is an important criterion for measuring and determining whether minerals can be separated by electro-election. The larger the dielectric constant, the better the conductivity, and vice versa. In general, the dielectric constant ε>12, belonging to the conductor, is separated by conventional electric selection as the conductor; if less than 12, if the dielectric constant of the two minerals still has a large difference, the frictional electrification can be used. Separate them.
According to the results of the study, the magnitude of the dielectric constant is not determined by the strength of the electric field, but depends on the frequency of the AC power source used for the measurement, and is related to the temperature. The RM Fouss study concluded that the dielectric at low frequencies The constant is large, and the dielectric constant is small at high frequencies. The mineral constants listed in the current publications are all measured under alternating current conditions of 50 or 60 Hz. In the MKS system, the vacuum dielectric constant ε ₀ = 8.85 × 10 ^-12 (pul) / m or coulomb ² cattle / • m ² .
The dielectric constant is measured by a plate capacitance method and a dielectric liquid method, the former being a dry method and the latter being a wet method. [next]
A plate capacitance method
Between two parallel metal plates placed in the test of pure mineral sheet, this sheet was determined by the size of the mineral slice, polished and size as the metal plate. It can be used to measure the capacitance of the instrument, or to use the difference frequency capacitance meter. The form and measurement method are shown in Figure 1. The size of the two metal plates is completely equal, and the area A is much larger than the distance d between the plates. If the mineral is not placed, the capacitance of the two plates is C _{0 .}

    Under the same conditions, after the mineral to be tested is placed, its capacitance must be many times larger than the capacitance of the air, that is, C _m >C ₀ , the dielectric constant of the mineral is:

The units of C _m , C ₀ and ε _m are the same as before, but the unit of capacitance is too large, so the micro method (μμf) is adopted, 1μμf=10 ^-12 F. This method is only suitable for large crystal pure mineral or gangue. Mine, not suitable for granular minerals. [next]
B Wet Method for Measuring Dielectric Constant In reality, most of the minerals are granular, and the fine particles are particularly large. The flat method is not applicable at all. The principle of this method is to determine the dielectric constant of the mineral by using the attraction or repulsion of the ore to be measured in the dielectric liquid. The simple structure is shown in Fig. 2. That is, in a container, two very thin steel needles are placed from the upper bakelite cover, about 1 mm apart, a certain amount of dielectric liquid is added to the container, and then a single phase is passed to the two needles. (50 or .60 Hz) AC. The ore particles to be tested are placed in the liquid in the container, and the ore particles having a higher dielectric constant than the dielectric liquid are attracted to the needle pole, and those lower than the liquid are repelled from the electrode.

According to the need, the dielectric constant of the dielectric liquid is prepared in advance and then continuously adjusted. For example, when measuring the dielectric constant of quartz , 5 ml of carbon tetrachloride and 0.5 ml of methanol are added to the vessel, and after mixing, the dielectric constant ε _h = 5.1. Several quartzs are added, and after electrification, the quartz particles are sucked. To the electrode, it is proved that the dielectric constant of the liquid is still small, and then 0.1 ml of methanol is added. At this time, the dielectric constant ε of the dielectric liquid has been increased to 5.63. If the quartz particles are just repelled, the dielectric constant of the quartz is Between the two, so εQ = (5.1 + 5.63) / 2 = 5.36. This method is quite troublesome, but more accurate, suitable for granular minerals.
(3) Specific conductivity The specific conductivity refers to the ratio of the ease with which electrons flow into or out. This difficulty level is related to the contact interface resistance between the ore particles and the electrode, and the interface resistance is related to the potential difference of the contact surface or point of the ore particles and the electrode, that is, the voltage. If the voltage is too low, electrons cannot flow into or out of those less fertile mineral particles. When the voltage is increased, the electrons can flow or flow well. At this time, the conductor ore particles exhibit the nature of the conductor. Non-conductors exhibit different behaviors and motion trajectories in an electric field. Figure 3 shows the minimum voltage required to determine various minerals. The measured mineral is given to the drum if the voltage reaches

When a certain value is reached, the ore particles are attracted by the electrode 3, and the trajectory of the drop is deviated, and the voltage at this time is the lowest voltage. Conversely, if the voltage is low, the ore particles do not exhibit the deviation of the conductor, but fall along the normal trajectory. Different voltages can be used for this purpose, and different polarities (positive or negative) can be used to determine the minimum voltage required for each mineral. Graphite is a good conductor and requires the lowest voltage of only 2800 volts. It is customary internationally to use it as a standard to compare the minimum voltage required for various minerals with it. This ratio is defined as the specific conductivity. For example, the minimum required voltage of 7800 volts titanium iron ore, the total (i.e., the ratio of 7800 to 2800) than the conductive 2.51 degrees, it is on.
It must be stated that these measured and calibrated voltages are the lowest voltage, not the optimal sorting voltage, and the actual sorting voltage is often much higher than those listed in the table.
(4) Rectification Due to the different electrical properties of various minerals and the polarity of the charged electrodes (positive or negative), they exhibit different behaviors in the electric field. For example, calcite only has negative voltage when the electrode is negative, and the voltage is 10,920 volts. It appears as a conductor, and vice versa. When sorting quartz, only when the polarity of the electrode is positive, the voltage is 8892 to 14820 volts, it is a conductor, and when the electrode is negative, it is a non-conductor. When sorting magnetite and ilmenite, the opposite of the above two cases, regardless of whether the polarity of the electrode is positive or negative, as long as the voltage reaches a certain value, it shows a conductor, which is exhibited by various minerals. The electrical property is called rectification. For this purpose, it is stipulated that only positively-reported minerals are called positive-rectifying minerals, such as the calcite described above, in which case the electrodes are negatively charged; quartz is only negatively charged, so the minerals are called negative-rectifying minerals, and the electrodes are positively charged; Iron ore, whether it is positive or negative with electrodes, is a conductor, it is called full rectification.
The minerals we want to sort are conductors or non-conductors, and we can find out their specific conductivity, determine the lowest sorting voltage, and determine whether to use positive or negative electricity according to its rectification. In most cases, the electrodes are negatively charged without Use positive electricity.

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