Study on improving the flotation effect of polymetallic ores

Multi-metal ore flotation production practice confirmed that the existing beneficiation process there are some shortcomings, thereby reducing the effect of this type of ore flotation. These shortcomings also make the process used not meet modern requirements, especially environmental requirements. This paper analyzes some technical solutions to overcome these shortcomings.

First, adjust the flotation slurry and make the flotation agent reach the optimal concentration

From an ecological point of view, the vast majority of currently used flotation reagents are unsafe. The amount of the agent measured per ton of ore consumed in the flotation process often fails to reach the optimum concentration in the flotation slurry of a certain process, and thus does not produce the necessary chemical reaction. Since the metal content in the treated ore is constantly fluctuating, the ratio of surrounding rock to metal minerals having different absorption capacities in these ores, and the residual agent concentration in the flotation pulp also vary. These conditions can cause periodic or inadequate medicine, or excess medication. In both cases, the pharmaceutical system is deviated and the flotation effect is greatly reduced. In addition, excessive amounts of unreacted chemicals entering the sewage will also worsen the ecological environment of the area where the company is located.

A series of physico-chemical parameters of the flotation system (mineral solubility product, oxidation-reduction potential and electrochemical potential value, oxygen, sulfide ion, concentration of sulfur hydride ion and elemental sulfur, wet contact of mineral surface) Angle values, pH, etc., it is possible to create optimized conditions that limit the chemical reaction and adsorption process of the agent used to the mineral surface. Only when some of the above parameters related to the concentration of the agent reach the optimum value can the flotation agent be effectively utilized and the high-technical-economic index can be obtained in the beneficiation process. The free energy at the interface between the bubble and the ore is reduced, which is related to the crystal lattice of the ore. In the ore preparation before flotation, elemental sulfur is formed on the mineral, resulting in the reconstruction of the crystal lattice in the surface layer of the particle, causing the lattice energy to increase (in the pulp preparation stage) and the energy of the system to decrease (in the flotation process). in).

The degree of adhesion of the bubbles on the ore particles determines the flotation activity of the ore particles.

The amount of adhesion can be measured by the work W required to cause the bubble to fall off from the unit contact area: W = σ liquid gas (1-cos θ) (1) where: σ liquid gas - surface tension at the liquid-vapor interface ; θ-wetting contact angle, the value of which is included in Newton's law expression.

This angle can be determined at the vector balance of the surface tension at the three-phase interface.

In the simplest case, the above equilibrium conditions have the form of the following equation: σ gas-solid = σ liquid-solid + σ liquid gas cos θ, or cos θ = (σ gas-solid σ liquid solid) / σ liquid gas (2) Medium: σ gas-solid, σ liquid-solid and σ liquid-gas - correspondingly the surface tension at the gas-solid, liquid-solid and liquid-gas phase interfaces. A notable feature of the θ angle is that its value is independent of the size of the finite interface phase (if their size exceeds 1 μm), mutual position, gravity, and other factors that do not affect the σ value. If the σ value is not regarded as a unit force and is regarded as the specific energy of the interface phase, equation (2) can also be obtained, and a supplementary information is obtained - the angle θ corresponds to the minimum free surface energy of the system. Non-polar oil droplets can also be used in place of bubbles or gases. In this case, by measuring the contact angle of selective wetting, the surface can be classified into hydrophobic (90° < θ < 180°) and hydrophilic (0° < θ < 90°). Forces acting on molecules close to the surface layer can be broken down into tangential and normal forces, or surface tension and molecular pressure. The mechanical work σ is consumed when the surface changes, and is released when the surface is reduced. The amount is determined by the change in surface tension and can be expressed by the change in surface free energy (erg/cm2 or dynes/cm2).

The total energy of the surface layer U = σ - T9T where: σ - is also the free energy represented by the G value below. Б1А1Шишковский proposed an equation that can determine the relationship between surface tension and surfactant concentration: Σ = σ water - b (aC + 1) where: σ - corresponds to the surface tension of the active substance concentration C; b and a - coefficient . Solubility of sulfide ore LMeS, solubility of metal hydroxide LMe (OH), partial pressure of oxygen in gas mixture in equilibrium with liquid phase, concentration of sulfur-containing ion CP due to sulfur oxidation of sulfide, system The relationship between the reduction of free energy ΔG, ΔG0 and pH can be described by the following formula: ΔG(K·Cal)=ΔG0-1.36lgLMeS/LMe(OH)m-1.36lgPnO2+1136n1lgC1-1.36n2pH(3) where: n , n1 and n2 - stoichiometric coefficients in the sulfur oxidation equation; m-metal valence. The work W consumed to cause the ore particles to fall off the bubble is proportional to the free energy reduction value ΔG due to oxidation of the ore particles, because in both cases, whether W or ΔG determines the flotation activity of the mineral. The reduction in free energy is proportional to and is equivalent to the standard free energy (ΔGp) of the reaction on the mineral surface.

The following equations are applied regardless of the equilibrium relationship between the concentration of the ionic and molecular reagents in the solution, or the thermodynamic analysis of possible reactions on the mineral surface:

1. The equation of the reaction equilibrium constant K. If the standard reaction free energy ΔGp is ​​known, the reaction equilibrium constant K value can be calculated because they have the following correspondence ΔGp=RTlnK. Where: R-general gas constant; T-absolute temperature. At 25 ° C and a total pressure of 105 Pa, ΔGh = 1.364 lgK. The reaction equilibrium constant illustrates the relationship between the activity (concentration) of the reactants and the activity (concentration) of the reaction product. It is only in a particularly dilute solution like flotation pulp that the activity of the dissolved material is equal in value to its concentration.

2. The relationship between the standard free energy of the reaction and the standard electrode potential E°. This relationship can be expressed by the following equation: ΔG°p=E°nF where: n-number of electrons participating in the reaction; F-farad constant, equal to 96485 k·Cal/mol. At this time, the standard reaction free energy changes, and the oxidized half-cell completely does not consider the electron formation energy (assuming it is equal to zero). When analyzing the reduced half-cell, the potential value E° remains "negative". The standard free energy of the reaction is the total free energy ΔG product of the reaction product formed in their standard state, minus the standard state free energy sum ΔG reactant of the reactant (ΔG°p=ΣΔG product-ΣΔG reactant), and It can be simplified to the reaction free energy of generating 1 mol of a substance from a stable element in a standard state. The standard free energy values ​​for the generation of various substances have been included in some relevant manuals. In an aqueous solution of an elementally stable form, the standard free energy of hydrogen ions formed under standard conditions is equal to zero. For convenience, as a standard or reference condition, a temperature of 25 ° C and a pressure of 105 Pa are employed. Under these conditions, the standard free energy (isometric isotherm) is equal to the ΔG° value (isostatic isotherm) that has been included in most manuals for reactions involving no gaseous species.

3. The relationship between the measured reaction potential, the standard potential and the reaction constant. If the activity of the participating reaction substance aA+bB=cC+dD is not equal to 1, then it can be obtained under normal conditions: ΔGp=ΔG°p+RTln([C]c[D]d/[A]a[ B]b) The potential E measured by means of a standard hydrogen electrode is: E=E°+RT/(nF)ln([C]c[D]d/[A]a[B]b) at 25°C , E=E°+0.059/[nlg([C]c[D]d)/([A]a[B]b)] For ease of calculation, always write the half-cell reaction like this, oxidize the product and release The electrons are placed at the right end of the chemical reaction equation. Water and hydrogen ions are considered when writing reactions. Their activity is easily determined by modern experimental methods. The steady state of sulfide ions on the surface of sulfide minerals determines their flotation activity, and this is one of the main problems in the theory of sulfide ore flotation. Let the right ends of equations (1) and (3) stand in parallel, and considering that the value of the wet contact angle is a criterion for the flotation activity of the sulfided mineral, and the value of the electrode potential E is expressed as the value of ΔG, we obtain A very important equation for flotation:

Some of the agents used in the flotation process will affect some of the parameters in equation (4) to some extent, and finally directly control the oxidation-reduction state of the mineral surface. For example, oxygen dissolved in water, when reacting with the surface of sulfide minerals, first produces elemental sulfur according to the following reaction: MeS+1/2O2+H2O=Me(OH)2+S°(5) According to the above calculation method, The potential of this reaction was obtained as follows. As an example, CuS is used instead of MeS minerals. Two electrons (n=2) participate in the reaction (5). Start by first determining ΔG°p: ΔG°p=(-85.3+0)-(-11.7+0-56.69)=16.91k·Cal The potential sought: E°=-16.91/(nF)=-87.6mV ( n = 2) The actual reaction is carried out in a pH range in which the metal hydroxide is stable. Considering the difference in density between sulfur and hydroxide (e.g., Fe(OH)2) (correspondingly 2.0 and 3.4 g/cm3), it is expected that the surface of the sulfide mineral will be covered with a mixture of metal hydroxide and sulfur. film. In the case of increasing the oxygen concentration and prolonging the contact time of oxygen with sulfur, the sulfur is further oxidized to the +6 valence state and is detached from the mineral surface at a rate determined by the pH: S+1.5O2+H2O= 2H++SO2-4(6) When the pH is lowered, the oxidation rate of sulfur may also decrease. In order to increase the flotation efficiency of sulfide minerals, it is highly desirable to reduce the rate of oxidation of elemental sulfur on the surface of the mineral, since the flotation activity of the mineral depends on the sulfur content on its surface. Obviously, the values ​​of W and G should also be a function of these values ​​W = K(υ1-υ2) 2(7) where: υ1 and υ2- correspond to the velocities of oxidizing or sulfides and elemental sulphur. In the relatively long contact time τ, the sulfur will achieve the greatest degree of filling in the ore particle surface, after which it will by oxidation, the hydrophilic ferric hydroxide has been reached completely cover the entire surface, And thus reduce the filling of sulfur. For each mineral, it has its own value of τ, at which the sulfur can reach its maximum filling on its surface. And the faster the reaction rate of the sulfide mineral surface to elemental sulfur, the smaller the value of τ. From this, it can be concluded that the importance of the adjustment process of the flotation slurry is first used before the flotation is started. For selective flotation, the duration of the slurrying process can be found between the τ values ​​of the separated minerals, and preferably at a value close to the τ of the mineral that is recovered into the foam product. The selective oxidation of sulfide minerals affects the order in which they are separated into the foam product and determines the choice of the beneficiation process. Using equation (4), the relative flotation activity of minerals under various practical conditions can be calculated, and thus the results of their surface hydrophobic effects can be predicted.

Second, with the help of foaming agent to ensure the best bubble size in the flotation machine

The reduction in the free energy of the mineral surface is closely related to their ability to adhere to the bubble wall in the flotation cell. The process of fixing the particles to the bubbles is also related to the decline of the free energy of the mineral-bubble system. For an effective flotation bubble-mineral aggregate, the relationship between the above energies and their optimum values ​​plays a decisive role. The testament is that this process has not been fully studied yet, so it is not yet a criterion for selecting an effective method to selectively adjust the fixing force of the particles toward the bubbles during the flotation process. Tests have shown that the ratio of bubble diameter to mineral particle size often determines the effect of flotation.

Therefore, the authors specially selected foaming materials capable of producing smaller-sized bubbles as foaming agents for mineral particles having a certain size. Appropriate bubble sizes can be obtained by applying different combinations of these blowing agents. For example, certain carboxylic acid amides have certain process advantages in the flotation circuits of lead and zinc compared to the foaming agents of terpineol and terpene alcohol. Diethyl toluamide and diethylbenzamide can achieve higher metal recovery in concentrates at lower levels than in the currently used foaming agents.

They have the ability to form microbubbles in flotation pulp, which is of particular importance for the useful minerals that effectively float finely divided particles. At the concentration of the foaming agent of 30 mg / L, according to the order of decreasing the number of microbubbles (-0155 mm) in the solution, several new foaming agents tested were arranged as follows: dioctyl phthalate Formate, dibutyl phthalate, dimethyl phthalate, diethyl phthalate, hexyl amide, dibutyl amide of hexanoic acid, diethyl toluamide, Azacyclohexylamide. None of these foaming agents produce stable foams, so there is little risk of "running" when using them as a foaming agent. A foaming agent, pine oil, which is well known to everyone, is in the middle of this arrangement (between hexylamine and dibutylamide). Among these foaming agents, only dimethyl phthalate (Д-3 foaming agent) which has a stable component and is well suited to ecological requirements has been industrially applied.

Third, the use of vacuum flotation process to ensure the best bubble size

The size of the bubble can be adjusted by making a flotation machine with a special structure inflator. According to the author, vacuum flotation machines are the most effective. In such a flotation machine, bubbles of a desired size can be produced by controlling the vacuum value. In addition, the closed flotation machine space will not damage the ecological condition of the surrounding area. From the perspective of maintenance and management of the flotation process, this is also very important. It is completely unaffected by automation and is still a skill of flotation workers in many aspects. One of the main advantages of this type of flotation machine is that it has no moving inflation system. In some of the flotation machines currently in use, those moving aeration systems over-saturate the oxygen in the flotation slurry. This will cause the mineral surface to be excessively oxidized, and thus it is impossible to stably stabilize the elemental sulfur required for the effective flotation mineral on the mineral surface.

4. The separation of qualified concentrates at the beginning of the flotation operation, including rough selection, sweeping and selection operations, often takes a long time, especially in the case of intermediate mining cycles during the flotation process. During this period, a considerable amount of oxygen supersaturation in the flotation slurry resulted in excessive oxidation of the mineral surface. As already pointed out, this is an undesirable phenomenon from the standpoint of maintaining optimal flotation conditions. Therefore, it is advantageous to first separate the flotation process of the easily floatable sulfide mineral at the beginning of the flotation process. The part of the mineral that is easy to float does not require the use of collectors because elemental sulfur is already fixed on their surface. In the case of flotation gold, it is also important to prevent it from muddy.

In the Almarich copper plant and many other concentrators, many successful experiences have been achieved in the separation of fast flotation concentrates from flotation.

V. Improving the accuracy and sensitivity of the method for determining the element content in the liquid phase of minerals and flotation pulp

There are many different elements in the mineral lattice. Therefore, the electrochemical potential value of the mineral surface is not likely to have a single value relationship with the flotation performance of the mineral. Because the number of heterogeneous elements in a mineral in different deposits may be very different, their electrochemical potential values ​​will also vary greatly, which will affect the correct estimation and calculation of a certain mineral float. Sex.

In order to perform the corresponding calculations, the accuracy of determining the impurity content in the mineral lattice must be greatly improved. By correlating the electrochemical potential values ​​with these measured data, a corresponding correction factor can be obtained for calculating the true mineral potential.

Mass spectrometry is currently the most promising method for detecting various elements in mineral crystal lattices. This method is now widely used because it is possible to record virtually all of the elements at the same time. It can detect elements in the Mendeleev periodic table almost, the detection limit is very low, and the analysis signal is very reproducible. Carrying out some scientific research and popularization work in the above direction can not only help deepen the research of flotation theory, but also improve the production process indicators of the concentrator.

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