A Mechanism of pressurized acid leaching
Pressure oxidation acid leaching is liquid, solid, heterogeneous reaction gas, the leaching effect of oxygen and oxidation action of acid soluble metal oxide of zinc sulfide concentrates, essentially traditional roasting zinc hydrometallurgy leaching two The processes are combined into one process. The mechanism of pressurized oxidizing acid leaching of zinc sulfide concentrate can be basically divided into two types, namely, electrochemical corrosion mechanism and adsorption complex mechanism.
a Electrochemical Corrosion Mechanism The dissolution of sulfides is similar to the electrochemical reaction of metal corrosion.
Cathodic reaction:
O ₂ +2H ⁺ +2e ==== H ₂ O ₂

H ₂ O ₂ +2H ⁺ +2e ==== 2H ₂ O
Anode reaction:
MeS ==== Me ²⁺ +S+2e

MeS+4H ₂ O ==== Me ²⁺ +SO ₄ ^2- +8H ⁺ +8e
Total response:
1
MeS+ - O ₂ +2H ⁺ ==== Me ²⁺ +H ₂ O+S
2
MeS+2O ₂ ==== MeSO ₄

S ² in the sulfide oxidizes and emits electrons at the anode portion of the ore, and transfers it to the cathode through the ore itself to reduce oxygen to complete a closed-circuit microbattery. The reduction of oxygen is carried out by a H ₂ O ₂ intermediate.
Zinc sulfide was subjected to an oxidative acid dissolution test at 100 ° C, and its kinetic curve is shown in the figure below. The relationship between the oxygen pressure in the solution and the amount of acid required is: the higher the oxygen pressure, the higher the required acid concentration; when the oxygen pressure is constant, the acid exceeds the limit content, and the reaction rate does not increase, maintaining a constant value. A similar curve was obtained when zinc sulfide was oxidized and dissolved at 130 ° C, confirming the electrochemical corrosion mechanism.

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b Adsorption complex mechanism It is assumed that the adsorption complex S·B is formed in the middle of the reaction between the solid phase S and the liquid phase B, and the reaction mechanism can be expressed by the following formula.

S _solid + B _liquid ==== S·B —→ product

The formation of the adsorption complex is the slowest phase of the process and is the control step of the process rate. The reaction kinetics of the process can be derived as follows:
Let Q be the part that participates in the reaction during the formation of the adsorption complex,
1 - Q = free part that does not participate in the reaction. The rate at which the complex is formed ξ ₁ is ξ ₁ = K ₁ (1-Q)[B] ⁿ
Let the rate of complex decomposition (component formation) ξ ₂ be ξ ₂ = K ₂ Q
Let the rate of complex decomposition (forming product) ξ ₃ be ξ ₃ = K ₃ Q
Wherein K ₁ , K ₂ , and K ₃ are rate constants.
When the reaction state of n=1 is stable, the following relationship can be established:

The test confirmed that the reaction rate of CuS oxidizing acid solution conformed to the above formula, and the test results are shown in the figure below. [next]

[B]
As can be seen from the figure, - is a linear relationship with [H ⁺ ] at a constant oxygen pressure value. It can be inferred that the oxidative acid dissolution of CuS may be as follows: ξ _Cu
get on.
K ₁
CuS+2[H ⁺ ] ← —→[CuS·2H ⁺ ]
K ₂

K ₃
CuS·2H ⁺ —→ Cu ²⁺ +H ₂ S

1 K
H ₂ S——O ₂ —→S+H ₂ O
2
Total reaction formula:
1
CuS+2H ⁺ +——O ₂ —→Cu ²⁺ +S+H ₂ O
2
The formation of CuS·2H ⁺ in the formula is the slowest stage.

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