Leaching of copper sulfide ore in sulphate solution

The leaching of sulfide ore must use oxidants to oxidize sulfur to elemental sulfur or sulfate to dissolve copper . Therefore, leaching chemistry should study oxidants on the one hand.
And the oxidation - reduction of sulfur, while also analyzing the various intermediates produced by the reaction. Sulfate solution is the most important copper sulfide mineral leaching body
Because it is more compatible and consistent than other systems and leaching products. Sulfur can be oxidized by means of an oxidizing agent under normal pressure. The most commonly used oxidizing agent is Fe ³⁺ , which can be regenerated by oxidation in the air and returned to use.
The figure below shows the E _h -pH diagram of the Cu-Fe-SH ₂ 0 system, indicating the stable regions of various copper and iron sulfide minerals. These figures are instructive for selecting the leaching conditions of the sulfide ore and understanding the potential and pH ranges for the presence of various compounds and ions.

The following figure   25 °C Eh-pH diagram of Cu-Fe-S-H2O system (the total sulfur content in solution is 0.1mol/L , and the activity of Cu ²⁺ is 0.01mol/L )

    Copper sulphide minerals are mostly semiconductors, and minerals with different dissolution and restoring potentials are in close contact. When an oxidation - reduction reaction occurs, a galvanic cell is produced.
use. The table below shows the rest potentials for various copper sulfide minerals and other common minerals.
Pyrite is the most stable, so it is in contact with other sulfide minerals to form a primary battery, which is always at the anode and is not oxidized. Minerals at the cathode lose electrons and are oxidized.

    Chalcopyrite leaching
    Early studies have shown that when leaching natural chalcopyrite, a series of intermediate minerals are produced: Cu ₂ S → Cu _1.8 S → Cu _1.2 S → CuS . From the standpoint of the resting potential, it should be increased in the above order, and thus the stability is increased. But actually 30 ° C And at lower ferric ion concentrations, CuS is not produced. The reaction proceeds as follows: [next]
First stage A : 5Cu ₂ S → 5Cu _1.8 S + Cu ₂₊ + 2e
First stage B : 5/3Cu _l.8 S → 5/3Cu _l.2 S + Cu ₂₊ + 2e
The second _{stage: 5 / 6Cu l.2 S → 5} / 6S + Cu 2+ + 2e
in 30 ° C Next, the first stage reaction is related to the ore particle size, while the second stage reaction is independent of the ore particle size. However, the second stage reaction oxidizes to form elemental sulfur, which must be reacted at a higher temperature to complete. The study of the reaction kinetics of the electrode shows that 90 ° C The reason for the slow reaction under normal pressure is not because the elemental sulfur may form a film to block the diffusion, but because the electrons are slowly transmitted on the surface of the sulfide ore. This is an electrochemical point of view.
Using 0.5 mol/L Fe ³⁺ and 0.001 mol/L Fe ²⁺ as the leachant, the 0.1 mol/L copper ore was leached , and the initial potential Eh of the Fe ³⁺ /Fe ²⁺ pair was 917 mV . At the end of the first phase, it is 781mV , and finally it is reduced to 735mV at the end of the second phase. in 90 ° C Next to 0.5mol / L of ferric ions as the lixiviant second stage leach, the ore particle size of 210 ~ 297 μ m (48 ~ 65 mesh), dried over 2h, the copper leaching rate reached 90%. The results are consistent with the shrinking kernel model.
The activation energy measured by the first stage leaching of the copper ore leaching is relatively low, so it is considered that there are many researchers in the diffusion control. The activation energy measured by copper blue leaching is generally higher, so it is considered that there are more reaction controllers.
Bornerite leaching
    The porphyrite is often symbiotic with chalcopyrite and chalcopyrite. The study using rotating electrodes shows that at 30~ 70 ° C Under the same conditions, the leaching speed of the porphyrite is only about half of that of the feldspar. The dissolution is divided into two stages, and the sir becomes a non-metering mineral. The reaction is as follows.

Cu ₅ FeS + xFe ₂ ( S0 ₄ ) ₃ ==== Cu _5-x FeS ₂ + 2xFeS0 ₄ + xCuS0 ₄

In the second stage, the non-metering mineral is converted to chalcopyrite and produces elemental sulfur.

Cu _5-x FeS +( 4-x ) Fe ₂ ( S0 ₄ ) ₃ ==== CuFeS _{2 +} ( 8-2x ) FeS0 ₄ +( 4 − x ) CuS0 ₄ + 2S

When in 35°C When the following leaching of the porphyrite, the reaction kinetic curve is parabolic, and the reaction stops in the first stage, producing a non-measured porphyrite. At high temperatures, chalcopyrite continues to be leached and the kinetics are in a straight line equation.
Another study, at 101.3 kPa oxygen partial pressure, 90 ° C The 0.1mol / L sulfuric acid leaching 8h, bornite natural particle size of -45 + 38 μ m copper leaching rate of only 28%. The outside of the particles is copper blue, and the core is still copper. The elemental sulfur produced by the copper-blue reaction may form a retardation film, making the reaction difficult to proceed.
Chalcopyrite leaching
A passivation phenomenon
The relationship between the rate of oxygen oxidation and leaching of chalcopyrite and temperature is shown in the figure below. 180 ° C In the following cases, the chalcopyrite leaching rate expressed by oxygen consumption is very slow, and the leaching process can be expressed by the following total reaction formula:

CuFeS ₂ + 4H ⁺ + O ₂ ==== Cu ²⁺ + Fe ²⁺ + 2S + 2H ₂ 0

200 ° C The above reaction rate is obviously accelerated, and the main reaction is:

CuFeS ₂ + 40 ₂ ==== Cu ²⁺ + Fe ²⁺ + 2S0 ₄ ^{2- _[next]}

A similar phenomenon occurs when leaching with ferric sulfate. Most researchers believe that membranes that produce elemental sulfur block further responses. Some also believe that the formation of a retardation film due to hydrolysis of iron salts, which is especially important in bacterial leaching, because the pH of the solution is between 1.5 and 2 . This phenomenon is called " passivation " .

    In some experiments, the generated elemental sulfur was dissolved with an organic solvent, which effectively accelerated the leaching and restored to the original leaching speed. However, there are also different experiments, and it has been found that the dissolution rate does not accelerate the leaching rate.
In recent years, electrochemical and surface analysis (such as Auger spectrum , X -ray photoelectron spectroscopy) and other new methods have been used to confirm that some Fe ^{2+ is} first leached when oxidizing and leaching of chalcopyrite CuFeS ₂ , Fe and Cu The dissolution ratio is 4 to 1 . This led to the formation of copper disulfide, which in turn produced copper polysulfide intermediates. Therefore, the overall leaching speed is considered to be determined by the slow decomposition of copper sulphide to the rate of elemental sulphur and copper ions. This speed is slower, which reduces the leaching speed.
Whether it is the use of high pressure oxygen or high iron as an oxidant, or bacterial oxidation, passivation occurs under certain conditions. Overcoming the passivation and increasing the reaction rate have become the central issues in the study of chalcopyrite leaching. [next]
B leaching kinetics
    The activation energy of chalcopyrite leaching is generally high, so it is considered that chemical or electrochemical reactions are more controlled. However, some researchers believe that high activation energy is caused by diffusion in the pores.
C non-oxidative dissolution
    Pure chalcopyrite ore in 95 °C The leaching of 3mo1/L HCl and 0.4mo1/L NaCl solution for 14.5h , copper was not leached, but the iron leaching rate reached 11.45% . It is believed that the following reaction may occur:

CuFeS ₂ + 2H ⁺ ==== CuS + Fe ²⁺ + H ₂ S

D ferrous ion effect
In many experiments, it has been observed that the addition of ferrous ions to a solution of iron sulfate leached chalcopyrite results in a decrease in the rate of the leaching reaction. It may be that the potential of the Fe ( III ) /Fe ( II ) pair is affected by the concentration of ferrous ions and decreases with the increase of Fe ( II ).
However, in recent years, Japanese scholars reported ^[4] that a dilute sulfuric acid solution containing 0.04 mol1/L ferrous sulfate was used as the leaching agent. 30 °C Under the air, the chalcopyrite is leached, and the leaching speed is even faster than that of the air containing 0.2 mol/L of ferric sulfate solution. Moreover, the leaching speed increases with the concentration of ferrous iron added. However, if nitrogen is supplied, it does not react. The reaction mechanism they proposed was that with the participation of ferrous iron, the following reactions occurred:

CuFeS ₂ + 3He ²⁺ + 3Cu ²⁺ ==== 2Cu ₂ S + 4Fe ³⁺

Cu ₂ S is leached by air oxidation or high-iron ion oxidation to form copper ions and elemental sulfur. such as:

Cu ₂ S +4Fe ³⁺ ==== 2Cu ²⁺ + 4Fe ²⁺ + S

In the first step of the reaction, the ferrous ion acts as a reducing agent. In the past, there have been many studies to reduce chalcopyrite first, and then leaching. If someone is used in the presence of copper ions, the chalcopyrite is reduced with sulfur dioxide to form chalcopyrite and porphyrite, and then leached.

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