Selectivity of slurry electrolysis

When the slurry electrolysis, minerals (mainly sulphide ore) is oxidized in the anode region leached, the reduction of metal ions deposited on the cathode occurs. The oxidation potentials of different metal sulfides are different, and the reduction potentials of different metal ions are also different. The existence of this difference makes the slurry electrolysis, a new hydrometallurgical process, can achieve selective leaching of minerals to some extent. Selective extraction of metal ions. Since the slurry electrolysis process is generally selected as a chlorine salt system, many metal ions can form a complex with Cl ^- , resulting in a change in its redox potential. Therefore, only the standard electrode potential value is used to judge that different metal sulfides are at the anode. The order of oxidative leaching and the order of reduction and precipitation of different metal ions at the cathode are clearly inappropriate. Calculating the electrode potential values ​​of redox reactions of some metal sulfides and metal ions under different Cl ^- concentrations, and then analyzing the selectivity of slurry electrolysis from thermodynamics, has certain guiding significance for the study of slurry electrolysis process.

The cumulative production constant values ​​for metal ions and Cl ^- forming complexes are listed in Table 1.

The redox reaction formula of the metal sulfide Me _x S _y can be written as:

Its equilibrium equation is:

Where: [Me] _T - the total concentration of metal Me in the solution, mol ∕ L;

;

β _{Me , i} -Me and Cl ^- form a cumulative formation constant of the complex, β _{Me , 0} =1.

Table 2 Cumulative constant values ​​of various metal complexes

Zhang Yingjie calculated the redox reaction formula of common metal sulfides and their equilibrium equations, as shown in Table 2. The E-Cl ^- relationship curve of the metal sulfide oxidative decomposition reaction is shown in Fig. 1.

Table 2 Redox reaction formula of metal sulfide and its equilibrium equation

Figure 1 Sulfide anodic reaction E-[Cl ^- ] relationship

At pH=0, the concentration of each metal ion is 10 ^-1 mol∕L, Cl ^- = 3mol∕L (close to the actual conditions of slurry electrolysis), and each sulfide is based on its standard plate potential E ₂₉₈ ^Θ and potential The order of E ₂₉₈ from large to small is shown in Table 3.

Table 3 Orders of sulfides E ₂₉₈ ^Θ and E ₂₉₈ from large to small

It can be seen that there is a significant difference between the standard electrode potential of each sulfide and the equilibrium potential under the conditions of slurry electrolysis. Of course, the calculation results only show the possibility of hot schooling. Under specific conditions, the leaching process of minerals has a great relationship with its kinetic properties.

Increasing electrolyte Cl ^- in general reduces the concentration potential, advantageously anodic oxidation of sulfide.

In the cathode region, metal ions are reduced and precipitated on the cathode, and the reaction formula is:

Its equilibrium equation is

Zhang Yingjie calculated equilibrium equation common reduction reaction of the metal cation, while Table 4.298K various metal cations in [Me] _T = ^10-2 when the equilibrium potential of the Cl ^- concentration curve shown in Figure 2.

Figure 2 Me ^{x +} cathode reduction potential E-[Cl ^- ] relationship

Table 4, shown in the cathodic reaction can be seen that, Fe ^{3 +} is reduced at the cathode Fe ^{2 +} is inevitable, which will reduce the cathode current efficiency of the electrolysis process slurry.

Table 4 Reduction reaction and equilibrium equation of metal ions

(Continued from Table 4)

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