Copper sulfide ore hydrometallurgy in chloride solution

    Oxidation - reduction potential
Both Cu ⁺ and Cu ²⁺ form a complex with chloride ions, which causes the oxidation - reduction potential to change. And because stable cuprous ions with chloride anions, thus constituting the Cu (I) / Cu (II ) electrically pair. The relationship between Cu ( II ) /Cu ( I ) and Cu ( I ) /Cu ( 0 ) electrical pairs and chloride ion concentration is shown in the figure below. The pH-E _h diagram is also different from the sulfate system due to the change in potential. The lower graph is the pH-E _h diagram of copper in the chloride system.

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    Oxidant in chloride system
Since chloride ions have a strong depolarization, plus heavy metal chloride solubility is generally higher than the corresponding sulfate, chloride ion and a stable coordination compound with many metal ions, these factors increase the sulfide ore The driving force for leaching in the chloride system. Therefore, the same mineral tends to have higher leachability and leaching speed in the chloride solution than in the sulfate solution. The oxidizing agent used in the chloride system may be chlorine gas, iron chloride or copper chloride, or may be directly subjected to electrochlorination in an electrolytic cell, but chlorine gas is hardly used in copper chloride leaching.
Iron leaching
The FeCl ₃ —FeC1 ₂ electric pair has a stable potential and can oxidize a stable mineral such as chalcopyrite to oxidize sulfur to elemental sulfur. The reaction equation for the leaching of chalcopyrite by ferric chloride can be written as:

CuFeS ₂ +( 4—x ) FeCl ₃ ===xCuCl +( 1—x ) CuCl ₂ +( 5—x ) FeCl ₂ + 2S ^O

Obviously, the value of x in the formula depends on the amount of ferric chloride added, and the amount of addition is large, that is, x is small, and more copper ( II ) is formed. Adding less people, that is, x is large, and more copper ( I ) is generated. It can be seen from the above reaction formula that no H ⁺ participates in the reaction, and the acidity of the reaction system is maintained such that the high iron ions do not hydrolyze.
Copper chloride leaching
Since copper (I) is stable in the formation of CuCl ₂ ^- in a high concentration chloride solution, a Cu(II)/Cu(I) pair is formed, and its oxidation potential is lower than Fe(III)/Fe(II) , but The total reaction of various sulfide ores that can also oxidize copper, such as oxidized leachite, can be expressed as:

Cu ₂ S + 2CuCl ₂ ==== 4CuCl + S ⁰

In order to increase the chloride ion concentration and improve the stability of the cuprous chloride complex anion, an alkali or alkaline earth metal chloride is often added. Obviously, its advantage is that after the leaching, there is not a large amount of iron in the system, and the purification of the solution is relatively easy, for example, the method of adjusting the pH and hydrolyzing the precipitate can be used to remove heavy metal impurities. American copper processing companies use this method to produce copper powder with a purity of 99.9% .
Electrochlorination leaching
The chlorine, ferric chloride and copper chloride leaching agents are in a reduced state after use, and both need to be oxidized to an oxidized state before being reused. The method of oxidative regeneration can use air oxidation for cuprous and ferrous iron. However, the recovery of copper is mostly made by electrowinning. Therefore, it is most reasonable to use electro-oxidation regeneration. At the same time, it also inspired people to design an electrochemical reactor, continuously regenerating the leachant with electricity, and leaching in situ, which is called “ electrochlorination leaching ” .
Chloride leaching of copper sulfide ore
Chalcopyrite leaching
In the presence of chloride ions, the oxygen leaching of the copper ore is also divided into two stages. The first stage, as Cu ⁺ diffuses to the surface of the particle, undergoes several intermediate copper sulfides, which can be called copper-deficient copper. The final change is copper blue CuS . At this stage, no elemental sulfur is produced. Due to the presence of Cl ^- , chlorine complex ions such as CuCl ⁺ and CuCl ₂ are formed.
The second stage CuS oxidizes to form copper ions and elemental sulfur, forming a sulfur layer on the surface of the particles, and the inner layer is an unreacted mineral. Although the same as the first stage
It happens, but it is much slower. Scanning electron micrographs show that when there is chloride ion, the elemental sulfur produced is relatively large crystalline sulfur, and there are pores between the crystals, allowing the solution to pass, and the retardation of the reaction is relatively small. Only when the sulfur layer accumulates to a certain thickness, the reaction is blocked. At this time, the sulfur layer is dissolved in an organic solvent, and the reaction rate can be increased as shown in the following figure. In the pure sulfate solution, amorphous or cryptocrystalline sulfur is formed, which is relatively dense, and the solution is difficult to pass, so that the reaction is greatly blocked. This may be due to the fact that the “ passivation ” phenomenon is not obvious when chloride is present. The effect of the formation of copper chloride ions is only the second factor. [next]

    Copper blue leaching
Copper blue leaching is actually the second stage of leaching of the aforementioned chalcopyrite. The correlation between the leaching speed and oxygen partial pressure, temperature and chloride ion concentration is very similar. Due to the oxidation of copper blue CuS to form elemental sulfur and copper ions, the reaction process consumes acid:

CuS + 0.50 ₂ + 2H ⁺ + C1 ^- = CuCl ⁺ + H ₂ 0 + S

Therefore, the initial leach solution needs to contain a certain acidity.
Chalcopyrite
The leaching of the chalcopyrite from the chloride solution does not result in the passivation of the sulphate solution. Even if the mineral powder having a relatively large particle size is leached below the melting point of sulfur, a high leaching rate can be achieved. This is a great advantage of the chloride solution.
Although at 100 ° C Left and right, in the chloride or sulfate, the oxidized leaching products of chalcopyrite are elemental sulfur, and copper ions and ferrous ions are also formed in the same way. Of course, it is also possible to form a copper ion of chlorine in the chloride. Anion. In the solution of 0.1mol/LFeC1 ₃ and 0.3 mol/L HCI , the electrochemical dissolution test of the chalcopyrite turntable electrode found that the dissolution rate of chalcopyrite ( mg/cm ² ) was almost linear with time. 1- ( 1 - α ) ^1/3 is a straight line with the reaction time, that is, the chemical reaction control mechanism conforming to the shrinkage nucleus model, where α is the reaction fraction. As mentioned above, the leaching speed in 0.05 mol1/L Fe ₂ ( S0 ₄ ) ₃ and 0.3 mol/L H ₂ SO ₄ is parabolically related to time, which may be due to the formation of a compact membrane due to the formation of elemental sulfur. The diffusion in the membrane is a limiting step in the rate of reaction. That is, the sulfur layer blocks the reaction. It reflects the difference in reaction mechanism between the two solutions.
A reaction activation energy
The activation energy of the leaching reaction in the chloride was 41.9 kJ/mol and ΔH = 47.2 kJ/mol . And the activation energy sulphate solution is 74.9 kJ / mol, △ H = 36kJ / mol.
The influence of B iron and ferrous ions
High-iron ions are oxidants, and increasing the concentration of high-iron ions increases the leaching speed, which is consistent with the effect of increasing the partial pressure of oxygen when oxygen is used as the oxidant. When high-iron ions and oxygen are present simultaneously, the high-iron ions react directly with the ore, and the ferrous ions are oxidized and regenerated in the solution. The reaction rate is also linear with the oxygen partial pressure, at which point the actual oxidant consumed is still oxygen. [next]
C acidity effect
Due to the presence of high iron ions, a certain acidity must be maintained, otherwise the iron ions are hydrolyzed. The lowest acidity varies with temperature, and the higher the temperature, the higher the acidity is required. 45 °C When leaching, the reaction rate is very slow, and the effect of acidity on speed is small; 85 °C When the impact is better than
More obvious.
D copper ion effect
Copper ions also have an oxidizing effect in chloride solutions and can even oxidize chalcopyrite

CuFeS ₂ + 3CuCl ₂ ==== 4CuCl + FeCl ₂ + 2S ⁰

Obviously increasing the concentration of copper ions in the starting leachate is beneficial to the leaching of chalcopyrite, as shown in the following figure.

Effect of E chloride ion concentration
When the concentration of chloride ions in the leachate is 1 mol/L or less, the leaching speed is remarkably increased as the concentration thereof increases. After that, it gradually became smaller, and the effect after 2mo1/L was very gentle. Sometimes a large amount of chloride is added to the leachate, mainly to ensure the stability of the cuprous ion chlorine complex anion, or to increase the solubility of lead , silver, etc., or to increase the boiling point of the solution, rather than increasing the leaching speed.
F chloride - sulfate mixed system
In 0.1 mol / LFeC1 ₃ and 0.3mol / LHCI solution, plus magnesium sulfate, observe the effect of sulfate on the rate of chalcopyrite leaching. As a result, as shown in the figure below, as the concentration of magnesium sulfate increases, the leaching speed gradually decreases, and a complicated curve shape appears. When the concentration of magnesium sulfate is increased to 1~2mo1/L , the relationship between the leaching speed and time is very similar to that in sulphate leaching. [next]

Electrochemistry of G leaching process
The battery reaction indicates that the process of leaching the chalcopyrite by ferric chloride is as shown in the figure below. The reduction of ferric chloride occurs in the cathode region, and the chalcopyrite is oxidized in the anode region.

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