The basic principle of the decomposition process of tungsten mineral hydrochloric acid

First, the main reaction and its thermodynamic conditions

White tungsten ore: (1)

Black tungsten ore: (2)

(3)

The equilibrium constant of the above reaction at 25 ° C and the concentration equilibrium constant Kc (Kc = [CaCl ₂ ] ∕ [HCl] ² ) are shown in Table 1.

Table 1 Equilibrium constants for some reactions

Second, the reaction mechanism and factors affecting the decomposition rate

Reaction mechanism. Zheng Changqiong and other studies have shown that when the stirring speed is fast enough, the diffusion of the solid H ₂ WO ₄ membrane is a control step of the decomposition process, and the number of stages in the process and the H ₂ WO ₄ film formed with the concentration of hydrochloric acid The properties are not completely the same. When the concentration of hydrochloric acid is 1-4 mol ∕L, the membrane has the greatest inhibitory effect on the diffusion process, while the inhibition is smaller at about 8 mol ∕L. For artificial white tungsten, the relationship between the decomposition fraction (x) and time (t) is subject to the following equation:

The apparent activation energy (40-98 ° C) of the reaction is 37.93 kJ ∕ mol, which is controlled by a solid phase membrane (ie, H ₂ WO ₄ membrane). For scheelite concentrates, the apparent activation energy was measured to be 43.61 kJ ∕mol.

Factors that affect the rate of decomposition. Increasing the decomposition temperature, increasing the amount of hydrochloric acid and prolonging the time are all beneficial to increase the decomposition rate. In the case of a certain amount of acid, changing the acid concentration changes the solid-liquid ratio. On the one hand, the concentration of the reactant is large, which is favorable for the reaction; on the other hand, the solid-liquid ratio becomes large, which is not conducive to the liquid phase. Quality, in general, it is generally believed that the use of high concentrations is beneficial to increase the decomposition rate. Since the process is controlled by diffusion of the H ₂ WO ₄ film, reducing the particle size of the ore, correspondingly reducing the thickness of the H ₂ WO ₄ film, is advantageous for increasing the decomposition rate, for example, 2.5 times the theoretical amount of hydrochloric acid. The hydrochloric acid concentration was 29.75%, 100 ° C, and stirring for 1.5 h. When the particle size was 58-74 μm and less than 58 μm, respectively, the decomposition rates were 87.3% and 95.1%, respectively.

Since the diffusion by the H ₂ WO ₄ film is a rate controlling step, decomposition at the same time as ball milling is advantageous for increasing the decomposition rate. Further, since the mine wolframite reaction with HCl, so that the iron-containing raw material (wolframite) is high, the decomposition rate decreases.

Impurity behavior. The behavior of impurities when decomposed with hydrochloric acid is shown in Table 2.

Table 2 Impurities scheelite hydrochloric acid decomposition process

(Continued Table 2)

Table 3 Solubility of H ₂ WO ₄ and H ₂ MoO ₄ in hydrochloric acid (g∕L)

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