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In the regeneration non-ferrous metallurgy, the application of hydrometallurgical method increasingly widespread, fairly efficient. Compared with pyrometallurgy, its main advantages are:
(1) The recovery rate of major metals and associated metals is higher;
(2) The process is more flexible;
(3) The energy consumption is relatively small;
(4) It is easier to solve environmental protection problems;
(5) Metallurgical processes are easy to mechanize and automate.
Hydrometallurgical treatment of recycled materials has its outstanding characteristics. These characteristics are first manifested in the ingredient stage. Metal scrap has various oily grease deposits, various emulsions, dirt agglomerates, and the like on its surface. The large size of the scrap is very detrimental to hydrometallurgy. Fine-grained residues, salt, silicon carbide and other materials contain many non-metallic inclusions, making it difficult to handle these materials.
In order to obtain high technical indicators of the hydrometallurgical treatment process, raw materials must be prepared.
Modern method for preparing recycled materials for hydrometallurgy
In terms of size, meaning maximum hydrometallurgical copper-based alloy.
There are several methods of preparing metal scrap for hydrometallurgy in current practice. The simplest and most common method of removing the most annoying organic acrobatics is to be calcined in a tube-type rotary furnace in an oxidizing environment of 700 to 900 °C. Short kiln lengths of 10 to 15 meters and diameters of 1.5 to 2.0 meters are usually used. Furnace lined with brick and clay brick. The stove is heated with natural gas or heavy oil. The fuel consumption is 10 to 15% of the total amount of the calcining charge.
This method has substantial shortcomings: a large amount of odor is emitted, and the loss of copper and other non-ferrous metals is large. The metal is odorized by the formation of a volatile compound (chloride). However, this method can remove not only organic impurities but also chlorine and fluorine in the sublimate ( zinc dust).
In order to actually evaluate this process, not only data on chloride saturated vapor or fluoride saturated vapor pressure at various temperatures, but also gas phase components having suitable furnace characteristics are required.
The following is a list of saturated vapor pressures for copper chloride:
Temperature (°C) 401.4 459.8 499.3 52.1
CuCl 2 pressure (kPa) 0.198 0.882 3.375 7.733
The melting point of copper chloride is 630 ° C; in the temperature range of 335 to 400 ° C, the heat of sublimation is 65.16 kJ / mol.
There is a significant difference in the nature of cuprous chloride. Cuprous chloride has a boiling point of up to 1367 to 1490 ° C and a melting point of 430 ° C. At the calcination temperature, the saturated vapor pressure is only 0.756 kPa in total. That is to say, there is not much copper chloride transferred into the gas phase. However, cuprous chloride is a poorly soluble compound. Therefore, in hydrometallurgy, such compounds are undesirable in ash.
In the standard state, the change of Gibbs free energy is calculated. The ΔG o 298 of cuprous chloride is 118.4 kJ/mol; the ΔG o 298 of copper chloride is 95.18 kJ/mol; cuprous chloride It can be obtained by hydrogen reduction of copper chloride:
2CuCl 2 +H 2 =2CuCl+2HCl (1)
Equilibrium constant at 400 °C:
1gK flat = P 2 HCl /PH 2 =0.67 (2)
The lack of reliable data on the heat of cuprous chloride and chlorine copper makes thermodynamic calculations difficult to accomplish.
In an oxidizing environment, the oxidation of copper chloride is divided into two phases:
2CuCl 2 +1/2O 2 =CuO·CuCl 2 +Cl 2 (3)
CuO·CuCl 2 +1/2O 2 =2CuO+Cl 2 (4)
Equilibrium concentrations should be obtained for both reactions. At 452 ° C, the logarithm of the equilibrium constant of the equation (124) (1 g K level ) is equal to 2.68. Therefore, at the time of oxidative baking, copper chloride is oxidized with the formation of a stable compound copper oxide, and a relatively stable compound, cuprous chloride, is formed in a reducing environment. Part of the copper chloride is lost with the flue gas.
For other non-ferrous metal chlorides, high saturated vapor pressure is also a major feature. For example, zinc chloride has a saturated vapor pressure of 0.1 MPa at 732 °C. Oxidation of the chloride reduces the loss of the metal with the gas.
The fluoride of non-ferrous metals has a higher boiling point: lead fluoride is 1239 ° C, and zinc fluoride is 1500 ° C. Fluorine can be transferred to the gas phase in the form of hydrogen fluoride during calcination. In the rotary kiln oxidative roasting, arsenic present in some different types of recycled raw materials and non-metallic scraps ( arsenic bronze, dust particles, low-quality nickel sulfate) is removed and enters the gas phase. In order to remove arsenic, it is necessary to convert it to arsenic trioxide having a high saturated vapor pressure at the time of baking. To this end, the gas has an excess of oxygen. In the presence of excess oxygen, dipotassium pentoxide is formed and interacts with other metal oxides to form a stable arsenate:
MeO+As 2 O 5 =MeO·As 2 O 5 (5)
In order to destroy the arsenate, it is necessary to carry out reduction calcination or to reduce the agent in the oxidizing roasting charge.
It should be noted that separation of arsenic from non-ferrous metals, particularly nickel and cobalt , is complicated under pyrometallurgical process conditions.
The final product of the oxidative calcination is an oxide of a metal. They are readily soluble in industrial solvents, especially in sulfuric acid solutions.
It is unreasonable to directly treat non-standard grade recycled raw materials by hydrometallurgy because these recycled raw materials have chemical heterogeneity and particle size heterogeneity. A suitable preparation method for these raw materials is pre-oxidation baking in an electric furnace or a combustion furnace. In this case, most of the acrobatic slag (oxides of aluminum , iron , silicon, etc.), organic impurities are burned off, and zinc, lead, cadmium , and tin are transferred into the gas phase. The liquid copper gradually collects in the furnace and is then broken or atomized with a large amount of water. Water shredding is a process that is widely spread in metallurgical processes unlike atomization.
The Institute of Materials Science of the Ukrainian Academy of Sciences attaches great importance to the atomization of liquid copper. Industrial equipment including melting equipment and atomizing components has been developed. Induction furnaces are recommended as melting equipment. The electrical diagram of the device consists of a high frequency current converter operating at 750 volts (frequency 2500 Hz), a high frequency capacitor bank, a console and an induction furnace. The inductors of the capacitor and the furnace are connected in parallel by means of a busbar establishing an oscillating circuit.
The atomizing component consists of a metal liquid receiver, a nozzle, and a spray chamber with a material reservoir. The liquid copper is atomized and reaches the necessary temperature and then enters the metal liquid transformer and then enters the nozzle along the metal liquid conduit. Atomization can be carried out using compressed air or water at a pressure of 0.4 to 0.7 MPa. The gas stream (water flow) and the atomized copper enter a chamber that separates the copper powder into separate phases. By varying the ultimate velocity of the gas (water) flow, the geometry of the nozzle, the size of the cooling plug, and the environment filled with the gas (water) chamber, it is possible to influence the properties and granulation composition of the resulting copper powder.
The powder of copper powder obtained by atomization of copper melt by water from Ala Verde Mining and Metallurgical Company has a weighted average diameter of 57 μm, a specific gravity of 3.88 g/cm 3 , and a density of 8.3 g/cm 3 at a high temperature. It is 0.013 m 2 /g, with a flow of 50 g in 26 seconds, and the shape is a twisted sphere.
The particle size composition is (micron): +200, 3.7%, ; -200, +160, 4.5%; -160, +100, 13.7%; -100, +63, 41.1%; -63, +50, 5.3%; -50, 30.3% . Air atomization is used in this company.
In the process of dispersing the melt with an oxygen-containing gas, a strong copper oxide film is formed on the surface of the spherical particles to prevent the copper particles from continuing to oxidize. When a film having protective properties is formed on a metal, particularly when the composition of the scale is more than that calculated in the oxide middle school, the oxidation rate (including copper) is rarely related to the concentration (pressure) of oxygen. For example, at 1000 ° C, the concentration of oxygen (proportional increase in pressure) only increases by 0.143. The amount m of copper oxidized by oxygen conforms to the law of parabola.
m 2 =KF 2 τexp(—3770/RT) (6)
Wherein, F-surface area (m 2 ); τ-oxidation time (hours); constant of K-reaction rate, equal to 975 g 2 · cm -4 · hour -1 .
According to the formula (127), the time required for a large amount of oxidation of the spherical copper particles at 1200 ° C is about 13 seconds. The oxidation duration τ = δ / 4D is calculated according to the partial form of Hooke's second law (where δ = 20 μm, D = the coefficient of copper self-diffusion into copper oxide, equal to 1.16 × 10 -7 cm 2 / sec) The result is τ = 10 seconds. The actual oxidation time is much shorter. [next]
From the perspective of hydrometallurgy, it is not desirable to form an oxidized protective film on the surface of the copper powder because the oxide layer dissolves quickly (the first dissolution stage), and the second layer, the metal layer dissolves slowly, with respect to the kinetics of the process. It must be judged based on the solubility rate of metallic copper, not the dissolution rate of copper oxide.
Preparing recycled copper for hydrometallurgical processing is a complex, expensive, and expensive process. At the same time, the preparation cost can be considerably compensated in the next step of hydrometallurgical treatment. The advantages of this method are:
(1) The waste rock can be separated from the slag containing the metal part in one operation;
(2) Since the metal may be equally distributed in the gas phase and the liquid, the comprehensive utilization of the raw materials is easily solved;
(3) The work of removing copper impurities (after copper dissolution) is simplified.
(4) Improved conditions for copper melting.
Through the study of the dissolution process of copper compared to copper, the relationship between the dissolution rate and the surface ratio of copper powder was determined (air consumption 44 m 3 /m 3 · hour, 85 ° C, Re = 92000, liquid: solid = 20):
Size (micron) - 63 - 100, +63 - 160, +100 - 315, +160
Specific surface (m 2 /g) 0.0168 0.0165 0.0104 0.09
Dissolution rate (g/dm 3 · hour) 35.2 31.9 28.8 20.5
The dissolution rate of atomized copper is 5 to 6 times higher than that of water-crushed copper, under the same dissolution conditions.
The method of pre-stocking for the next atomization should be considered as the most promising high-pressure leaching of copper powder with specified characteristics from recycled copper, because the value of copper powder is much higher than that of primary copper or recycled copper. The production of copper sulphate and other copper salts (copper halides) from recycled copper powder has a broad future.
The simplest and simplest method of preparing a raw material for hydrometallurgy is considered to be a method that is carried out at relatively low temperatures and in aqueous solution. For example, tin and zinc are removed from the surface of the scrap with a boiling caustic soda solution (a melting point of NaOH of 318 ° C and a boiling point of 1388 ° C), and then tin and zinc are recovered from the solution by fatty acid extraction. Was added tin and zinc nitrate waste (NaNO 3) or chromate (Na 2 CrO 4) with an oxidizing agent such as sodium hydroxide (caustic soda) to process.
With an aqueous solution to prepare regenerated metal hydrometallurgical process materials, a predetermined 20 to 25 g / dm 3 sodium carbonate solution and a solution containing 10 g / dm 3 with a base to remove the oil Hanbaoyufang metal. The temperature of the alkali solution is 70 to 80 ° C, and the operation duration is 20 to 30 minutes. Except for the oily metal at a temperature of 60 to 70 ° C, the alkali is washed away with hot water and completed in 10 to 15 minutes. Domestic companies have not adopted this law.
A block or loosely regenerated metal is placed in a metal bucket in a stainless steel bucket and treated with an alkali solution. The loading amount is 0.3 to 0.5 tons at a time. The solution is heated to a specified temperature with strong steam.
Preparing various non-metallic scraps for hydrometallurgical processing is fairly straightforward. Most of these non-metallic scraps are compounds that are relatively easy to dissolve in industrial solvents. However, some simple preparation steps are necessary. In order to increase the dissolved surface area, the waste should be ground; in order to remove the iron inclusions, magnetic separation is required; in order to separate the mixed wastes by density, heavy medium (liquid) sorting must be performed. In recent years, the relevant units have developed a sorting process, a regenerating apparatus, a washing liquid, and a magnetic fluid sorting apparatus for removing a ferromagnetic liquid product from a beneficiation product and a non-magnetic non-ferrous metal for separating the magnetic liquid in a magnetic field by density.
The essence of this process is that under the interaction of the ferromagnetic liquid and the external non-uniform magnetic field, various driving forces generated in the ferromagnetic liquid act on solid particles of different densities. It is well known that as the strength of the magnetic field changes, the quasi-density of the separation medium also changes.
The equilibrium state of the non-magnetic particles in the ferromagnetic liquid under the action of the thrust and the tensile force can be expressed by the following formula:
(P particle-P liquid) g=
M
dH
(7)
4Ï€
dZ
P particle - the density of non-magnetic particles (kg / m3 ); P liquid - liquid density (kilograms 3 ); g - the speed of free fall (m / s 2 ); M - in the particle distribution The average magnetization of the liquid (A/m); dH/dZ - the gradient of the magnetic field strength in the direction of the thrust (A/m 2 ).
From equation (128), the effect of the repulsive force is mainly determined by the nature of the magnetic fluid and the strength of the magnetic field.
Studies have shown that magnetic fluid static separation can separate materials with a density of 1.5×10 3 to 2.0×10 3 kg/m 3 ; in heavy media, the separable density ranges from 1.5×10 3 to 5×10 3 kg. / meter 3 material.
As the magnetic fluid, using a dispersion medium (coal oil, diethyl ether), and phase pulverized - finest colloidal solution magnetic particles (about 10% by weight of liquid) thereof. These finest magnetic particles are surrounded by a film of a surface active material (glycerol trioleate). The viscosity of the colloidal solution is about 30 MPa·sec. The magnetic hydrostatic separation method separates the binary and ternary mixtures. For example, pure aluminum and copper concentrates can be obtained by separating impurities composed of aluminum, copper and lead, and lead products containing no more than 2% of copper and lead.
When using a sorting machine and separating granular impurities with a particle size of 1.2 to 4.5 mm (containing 58.5% of aluminum, 14.8% of zinc, 19.7% of copper, and particles of lead, silica and tin), the aluminum-containing 83.8 was separated. % and copper + lead 5.5% light components, containing 11.4% aluminum industrial products, consisting of copper, lead, tin and containing 1.6% of heavy components of aluminum.
The magnetic fluid separation method is used to enrich the tin ore and potassium ore, and to refine the diamond concentrate and gold-bearing concentrate. In regenerative non-ferrous metallurgy, this method has not exceeded the limits of the type industry test.
In order to separate heavy non-ferrous metals, a magnetohydrostatic separator was used (Fig. 93). Raw materials consisting of heavy non-ferrous metals (copper, zinc, tin, lead) (package 20-40 mm) are placed in a feed tank with a capacity of 1.5 to 2 m3 , and then the raw materials are evenly distributed by a vibrating feeder. Ground supply points. The bulk material enters the sorting chamber and is placed on the surface of the ferromagnetic liquid. The effective density value of the ferromagnetic liquid (which is the median of the density values ​​of the various separated materials) can be determined based on the current in the coil of the electromagnet. For example, in the treatment of copper-lead (cable waste), the effective density of the ferromagnetic liquid should be greater than 9 × 10 3 and less than 11 × 10 3 kg / m 3 . Therefore, the light component (copper) moves toward the discharge direction on the surface of the ferromagnetic liquid, and the lead sinks into the ferromagnetic liquid and is removed by the lower portion of the separator. The technicality of the sorting machine is listed below:
Production capacity (kg / s) 0.8
Block size (mm) of separated material 2~10
Density of separated material (kg/ m3 ) (4~22)×10 3
Required power (watts) 5000
Magnetic field strength along the gap axis (kA/m) 380
Dimensions (mm) (length × width × height) 1400 × 1100 × 2500
Sorting machine weight (kg) 5000
The raw material to be crushed next is usually cooled before the sorting.