(II) Determination of physical properties of heavy liquids and resuspensions In the case of heavy medium dressing , in order to obtain a satisfactory separation effect, it is required to adjust and control the following physical properties of the selected medium: (1) specific gravity and stability; (2) viscosity . (2) The float type hydrometer and the specific gravity balance float type hydrometer can be divided into two types according to the principle: fixed weight and constant volume. Figure 1 is a schematic view of a float type specific gravity measuring device for continuous test or industrial production. When using the vacuum capillary viscometer to determine the rheological properties of the suspension, the flow through the capillary is measured under different vacuum degrees, and the Q=f(p) map is drawn accordingly to find the intercept of the straight line on the abscissa. Pc, then calculate the ultimate shear stress and plastic viscosity according to the following two formulas. 2 Inner drum viscometer The inner cylinder is rotated by a certain rotating torque by means of a heavy object, and the corresponding relationship between the shear stress and the flow velocity gradient is found by measuring the rotational speed of the inner cylinder under different rotational moments. Nantong Gympro Sports Co.,Ltd , https://www.masportsgympro.com
1. Determination of specific gravity of the medium The method for determining the specific gravity of heavy liquid and heavy suspension in the ore dressing process generally has the following four types: (1) pycnometer method; (2) float method; (3) differential pressure method; (4) radioactive isotope law.
(1) Pycnometer method The essence of the pycnometer method is to measure the weight of a certain volume of medium. The pycnometer used for the heavy liquid is the same as the pycnometer used to measure the specific gravity of the solid powder, and the suspension requires a larger container. Set the empty bottle weight G 1 , the total weight of the bottle and water after filling the water is G 2 , and when the total weight of the bottle and the heavy liquid to be tested is G 3 when the heavy medium to be tested is filled, the specific gravity of the heavy medium to be tested is Δ:
G 3 - G 1
△ = ————·△ W
G 2 - G 1
In the formula, Δ W is the specific gravity (relative density) of water. The density of water at different temperatures can be referred to the relevant data. When the requirement is not high, ΔW=1 can be uniformly taken.
A schematic diagram of an industrial specific gravity measuring device made according to the principle of a pycnometer is shown in FIG. 
Figure 1 Schematic diagram of heavy medium specific gravity measuring device
A- pycnometer type; b-float type, c-pressure differential type; d-radiometer type;
AT—working medium (heavy liquid or resuspension);
D—detector; DL—compressed air; K—compensator; str—ray source [next]
At present, the liquid hydrometer which is commercially available is mainly fixed weight type, that is, the weight of the hydrometer is constant. The volume of the hydrometer is different in the liquid according to the specific gravity of the liquid to be measured, so it can be based on the volume and specific gravity of the sinking part. The weight is calculated from the specific gravity of the liquid, and the value of the specific gravity of the liquid measured directly corresponding to the different sinking depths on the commercially available hydrometer, so that it can be directly read when used, which is very convenient. However, the liquid hydrometer currently supplied by the market is mainly used for measuring the specific gravity of liquids such as milk, organic liquids and inorganic acids, and the specific gravity range is generally not more than 2. Therefore, in the analysis of ore specific gravity components and heavy medium ore dressing tests, it is often necessary to make self-made Hydrometer.
The self-made specific gravity timing can be designed according to the principle of specific gravity or the principle of constant volume. It can also be used to inject a variety of small ampoules or ordinary short glass tubes into different weights of lead sand and then seal them to make a set of floats with different specific gravity for use as a hydrometer. The actual specific gravity of each float can be pre-calibrated by the method of measuring the specific gravity of the ore block.
The liquid specific gravity balance is a special balance formulated according to the principle of constant volume hydrometer. Its structure is shown in the figure below. In the measurement, the balance arm is first mounted on the bracket, the weight F and the counterweight E are hung on the hook A, and the screw B is adjusted so that the arm is in equilibrium (ie, the tip C of the arm is aligned with the tip D on the bracket), and will be The weighting liquid is poured into the measuring cylinder, and then the weight F is immersed in the heavy liquid. At this time, the weight is lifted by the buoyancy of the liquid; the balance is unbalanced, and the weight can be added to the beam to restore the balance. The weight is placed on hook A or placed on a different cut in the beam. The arm at the incision has a shorter arm and the proportion represented by it is also smaller. The weights represented by the different weights at different positions are pre-calibrated, so that the value of the specific gravity of the measured liquid can be directly read. It should be noted that the weight is softly connected with the weight. When the specific gravity of the liquid is greater than the specific gravity of the weight, the weight will float to the liquid level. At this time, only the hammer with a larger specific gravity can be used for the measurement, but the new hammer should be made. The volume is the same as the old hammer, otherwise all weights must be recalibrated.
Figure 2 Liquid specific gravity balance
(3) Differential pressure method The specific gravity of the medium is determined by measuring the pressure difference at different depths below the liquid surface. As shown in Fig. 1c, two tubes are inserted at different depths below the liquid surface, the lower opening is open, and compressed air (or nitrogen) is introduced into the two tubes at a constant flow rate through the regulating valve and the flow meter, so that the nozzle maintains a small amount of bubbles. The liquid level is escaped, and a differential pressure meter is connected to the two tubes to measure the pressure difference ΔP of the two tubes. The density Ï of the medium can be directly calculated according to the relationship of ΔP=ÏgΔH. [next]
(4) Radiometer method The measurement principle is shown in Figure 1d. The advantage of this method is that it can measure the density of liquids as well as the density of gases and solids; because it is non-contact measurement, it can be used under high temperature, high pressure, high viscosity and corrosive conditions. The diameter of the container of the liquid to be measured can be as large as several meters, and the wall can be as thick as several tens of millimeters. This method is mainly used to determine the density of the slurry in the pipeline. A disadvantage of such densitometers is the complexity of the equipment and the need to pay attention to the protection of the radiation.
2. Determination of viscosity of heavy liquid and suspension The heavy liquid is a homogeneous liquid. The rheology of most homogeneous liquids obeys Newton's liquid internal friction law. According to Newton's law, the interaction between two layers of liquid in relative flow:
DÏ…
τ = μ——
Dy
Where Ï„ - shear stress (Pa);
DÏ…/dy - velocity gradient (s-1);
μ - viscosity (Pa·S).
The viscosity is numerically equal to the shear force per unit area of ​​the liquid level when dυ/dy is 1.
The suspension used in the beneficiation process, when the solid content is low, its properties are similar to those of Newtonian liquid. The rheological properties of the suspension can be explained by the above formula; when the solid content is high, the suspended solid particles will affect the viscosity of the whole system and change To express the law of this phenomenon, Bingham's law can be used to describe its rheological properties:
DÏ…
τ = τ 0 + μ P1 ——
Dy
Where τO——the ultimate shear stress;
μ P1 - plastic viscosity.
Thus, in order to illustrate the internal friction properties of Bingham liquid, it is necessary to know two parameters, viscosity μ P1 and ultimate shear stress τ O . Since the measurement of μ P1 and τ O is complicated, the ratio of shear stress to velocity gradient is also commonly used in practice to measure the rheology of the suspension. This value is called the apparent viscosity or apparent viscosity μ a .
  τ
μ a =  Dυ
Dy
There are many types of instruments for measuring viscosity, and they are still evolving. Commonly used according to its principle can be divided into: (1) capillary viscometer, according to the pressure and flow of the liquid flowing through the capillary to determine its viscosity; (2) concentric cylinder, limited by the shear stress and flow gradient of the liquid in the annular space The viscosity thereof; (3) the drop viscometer measures the viscosity according to the relationship between the speed at which the object falls freely in the liquid and the viscosity of the liquid; (4) vibrating viscometer, which mainly depends on the acoustic vibrating body or the ultrasonic vibrating body The principle works by the damping of liquid damping. Only a few special viscometers that can be used to determine the viscosity of a resuspension are described below.
The determination of the viscosity of the suspension is more difficult than that of a conventional homogeneous liquid because the stirring device must be installed in the viscometer to prevent the deposition of solids, but the reliability of the measurement due to agitation is avoided. [next]
(1) Capillary viscometer The earliest instrument for measuring the viscosity of resuspension is a capillary viscometer designed by Devoni and Schell. The instrument consists of a capillary with a pore size of 2.64 mm and a stirring device connected to it. The composition of the container. The apparent viscosity (viscosity) of the liquid is determined by the time required for each 100 ml of liquid to flow out, while the viscosity values ​​corresponding to different times can be calibrated with Newtonian liquid of known viscosity. The main disadvantage of this method is that the parameters τ O and μ P1 which characterize the full rheological properties of the suspension are not given, and the results of different instruments cannot be compared with each other, but since it can give results quickly and easily, it still remains In practical applications, many improvements have been made to capillary viscometers to make them more suitable for determining the viscosity of suspensions. In order to determine μ P1 and τ O of the Bingham plastic liquid, a vacuum capillary viscometer can be used. Figure 3 shows the vacuum capillary viscometer used by the Soviet Institute of Mineral Processing. The main difference from the conventional vacuum capillary viscometer is that the slurry is circulated by a sand pump to prevent sedimentation and delamination of the suspension.
Figure 3 Vacuum capillary viscometer
1—capillary; 2—capacity of circulating suspension; 3—storage tank of pump; 4—buffer bottle;
5—Viscometer reservoir; 6—three-way switch; 7—suspension surface elevation indication scale; 8—pressure gauge
Ultimate shear stress
3rP c
τ 0 = ————(Pa)
8L
Where r - capillary radius (m0);
P C ——Q=f(P) intercept on the abscissa (Pa);
L - capillary length (m).
Plastic viscosity
λ(P - P c )
μ P1 = ———————
Q
[next]
Where λ - the capillary constant, which can be calibrated with a liquid of known viscosity;
Q - the flow rate (m 3 /s) corresponding to the pressure P.
This method was used to determine the rheological properties of galena (S V = 5.7 * 10 5 m 2 /m 3 ) suspension. It was found that when the volume concentration of galena was 15.6%, Ï„ O =0. The nature of the suspension is close to Newtonian liquid; when the concentration is greater than 15.6%, Ï„O>0, obeying the rheological law of Bingham plastic liquid.
The capillary flow method measures the rhythmic viscosity under laminar flow conditions and cannot be extrapolated to high velocity gradients, such as those in mud pumps and heavy medium cyclones.
(2) Concentric cylinder viscometer This is the most widely used type of viscometer for studying the rheological properties of suspensions. The main part is a cylindrical container (outer cylinder) with another cylinder concentrically placed inside ( Inner cylinder), the annular space between the two cylinders is filled with the liquid studied. In order to obtain the corresponding relationship between flow velocity gradient and shear stress, the following three different methods have been used to design the viscometer:
â‘ The tumble the outer cylinder viscometer at a certain angular speed, causing the relative movement of the liquid layer in the annular space, and relying on shear force to twist the metal wire is suspended on the inner tube, according to its rotation angle, can be The rotational moments at different rotational speeds are calculated (correspondingly, the corresponding relationship between the flow velocity gradient and the shear stress is found), as shown in Fig. 4, which is a schematic diagram of such a viscometer.
Figure 4 External drum viscometer
1—Tachometer; 2—outer drum; 3—suspension; 4—twisted wire;
5—protractor; 6—motor