I. Thermodynamic analysis of the alkaline negative potential region of Sb-S-H 2 O system
The Sb-S-H 2 O system is a complex complex system. In addition to the single-ligand complex ions (SbS 2 - , SbS 3 3 - , SbS 4 3 - ) with a single ligand, there is a single coordination. Complex polynuclear complex ions (Sb 2 S 4 2 - , Sb 2 S 5 4 - , Sb 2 S 6 6 - ) and complex ions of a partial oxo ligand, such as SbSO - , SbSO 2 - , the latter SbO + , SbO 2 - , SbO 3 3 - , SbO 3 - , SbO 4 3 - . As the ligand, S 2 - also has a plurality of variable ions (S 2 2 - , S 2 O 3 2 - , SO 4 2 - , SO 3 2 -, etc.) and variant ions (HS - ).
According to the principle of simultaneous balance and the principle of electrical neutrality, the computer-based solution equation was used to calculate the potential-pH value of Sb-S-H 2 O system, and [Sb] T =1mol∕L and [S] were drawn at 25 °C. T is equal to the potential-pH diagram of 2 mol ∕L and 3 mol ∕L Sb-S-H 2 O system, respectively (Fig. 1 and Fig. 2). In the figure, [Sb] T and [S] T are the total equilibrium concentrations of ions containing strontium and sulfur, respectively.
Figure 1 Sb-S-H 2 O system potential-pH diagram
[Sb] T =1mol∕L, [S] T = 2mol∕L
Figure 2 Sb-S-H 2 O system potential-pH diagram
[Sb] T =1mol∕L, [S] T = 3mol∕L
It can be seen from Fig. 1 that on the solid-liquid equilibrium line, as the pH increases, the potential moves negatively, and the ruthenium-containing complex ions in the solution are mainly composed of a complex ion (SbS 2 - ) with a small coordination number ( pH<13.6) transitions to complex ions (SbS 3 3 - , Sb 2 S 6 6 - ) with a large coordination number (pH = 13.6 to 14.2); at the same time, the number of oxygen atoms replaced by ruthenium complex anions increases, for example At pH > 14.2, SbO 3 3 - is predominant.
As can be seen from Figures 1 and 2, the stable region of the solution, especially the simple coordination complex ion stable region, is narrow. That is, as the potential increases, the number of oxo ligands increases, so that eventually all of the oxo SbO 4 3 - or SbO 3 - and SbO 3 3 - or SbO 2 - plasmas are replaced by oxygen. S 2 - is oxidized to S 2 O 3 2 - and the like, which shows leachate easily oxidized, generate various sodium salts (Na 2 S 2 O 3, Na 2 SO 3, Na 2 SO 4 , etc.).
It can also be seen from Fig. 1 and Fig. 2 that as the ratio of [Sb] T ∕ [S] T decreases, the solid phase and the Sb 2 S 3 solid phase stable region shrink, and the solution stable region expands. When [Sb] T /[S] T =1∕2, the solid phase stability area of ​​Sb 2 S 3 is large. When [Sb] T /[S] T =1∕3, Sb 2 S 3 solid phase The stable zone is shrunk into a narrow strip. The calculations show that when [Sb] T /[S] T ≤1∕4, the Sb 2 S 3 solid phase stable region in the figure disappears. This indicates that the suitable leaching conditions for the strontium sulfide concentrate are [Sb] T /[S] T ≤1∕4.
Thermodynamic analysis of the basic negative potential region of Sb-Na-S-H 2 O system
The alkaline wet refining process is actually a more complex Sb-Na-S-H 2 O system with Na + , in which there are solutions and Na 3 SbO 4 crystals, solution and NaSbS 2 crystals and solid 锑Balance with solid NaSbS 2 . Figure 3 and Figure 4 are drawn by solving the exponential equation by an electronic computer.
Figure 3 Sb-S-Na-H 2 O system potential-pH diagram
25 ° C, [Sb] T = 0.5 mol ∕ L, [S] T = 2.0 mol ∕ L
Figure 4 Sb-S-Na-H 2 O system potential-pH diagram
25 ° C, [Sb] T = 0.5 mol ∕ L, [S] T = 3.0 mol ∕ L
It can be seen from Fig. 1 and Fig. 2 that Na 3 SbO 4 and NaSbS 2 have a wide stable region, that is, the actually present large solution stable region is covered by the two solid phase regions, which is related to the electrolysis with high strontium content. The crystallization occurs when the liquid cools. Since the stable region of Na 3 SbO 4 is wide, it is easy to prepare Na 3 SbO 4 crystals from Na 3 SbS 3 in an alkaline solution. This has a certain guiding significance for the research of a new product, sodium citrate. The new process for the direct preparation of sodium citrate is completed under the guidance of this theory.
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