FIG components shown to be more useful substances in solution all metals and anions, and their change with metal ligand, or a charged anion. Such a graph can be calculated and drawn by computer.
The basis of all computer models for calculating chemical equilibrium is the association between ions or ions and molecules generated by different materials, and the degree of association is described by equilibrium constants. There are many such balances to be considered in a solution containing multiple components, each of which is described by a mass action expression based on chemical equations and equilibrium constants. The following two conditions must be met when using these equations to calculate the substance in solution:
(1) Mass balance conditions. The sum of the calculated simple components and the associated components should be equal to the number of moles of metal or anion present in a certain amount of water in the initial state, and these molar effects result in charge neutrality.
(2) Chemical equilibrium conditions. It is required to make the system under consideration in the most stable state.
This most stable condition can be determined by the equilibrium constants of all mass modes in the system, or by the Gibbs free energy of all the components and the associations derived therefrom. From thermodynamics, the two methods are equivalent, but the numerical methods used to process them are different.
In the equilibrium constant method, the mass action formula and the equilibrium constant are substituted into the mass balance condition, and a nonlinear equation group is obtained for solving. In the Gibbs free energy method, the variables are transformed by the thermodynamic relationship of the reaction:
â–³G=â–³G r +RTlnK=0
Then the total free energy of the system is minimized. Regardless of the thermodynamic method used, the problem lies in solving nonlinear equations. Thermodynamic forms and mathematical models that can be used can be found in the relevant literature.
Since these calculations utilize thermodynamic relationships using activity rather than concentration, combining the Pieter ion model with the equations formed by the complexes yields a large amount of data for the calculation of major cations, trace cations, and various anions. The activity coefficient can be applied to a solution having an ionic strength of 1 mol ∕L.
In the field of chemical and physical metallurgy, there are now a number of Integrated Thermochemical Data hase (ITD) open to the public, providing detailed thermodynamic data and powerful software. The calculation of chemical equilibrium and phase diagrams for multicomponent and multiphase phases can be performed using these thermochemical databases. Due to the application of chemical thermodynamics in pyrometallurgy, thermochemical data of very large quantities of materials at high temperatures were determined. Therefore, ITD is widely used to calculate and map the dominant and phase diagrams of systems at high temperatures, which can be applied to very complex inorganic chemistry problems of interest to hydrometallurgy. In some cases, the process solution contains multiple elements. When applying thermodynamics to these solutions, the main difficulty is that the concentration of at least one of them is usually high, and the theory for calculating the activity coefficient of the mixed electrolyte solution is not mature. . The use of the Pice method may overcome these difficulties, especially with the computer for a large number of simple calculations. Such complex solution composition maps are particularly useful in studying the behavior of groundwater or various elements of sewage discharged from hydrometallurgical plants or other plants. A detailed discussion can be found in the literature.
Figures 1 and 2 are examples of several complex component maps. FIG 1 is a water-containing copper component 3 to pH = 8. The total amount of copper is 10 -5 mol, expressed as lgn Cu = -5.00. All copper-containing materials and anions considered for selection are numbered in the legend. The oxidation potential used for the plot calculation is indicated by the electronic standard pe, lga e -1 (aq). The E h of the river water is +0.500 V, so 0.500 = 0.05917 pe, and pe = 8.45 is obtained.
Fig.1 Composition of Cu in the range of pH=3～8 under river water conditions
1-Cu(s); 2-Cu + (aq); 3-Cu 2 + (aq); 4-Cu(OH) + (aq); 5-Cu(OH) 2 (aq); 6-Cu ( OH) 3 - (aq); 7-Cu(OH) 4 2 - (aq);
8-Cu(OH) 2 (s); 9-Cu 2 O(s); 10-CuO(s); 11-CuCl 2 - (aq); 12-CuCl 3 2 - (aq); 13-CuCl + ;14-CuCl 2 (aq);
15-CuCl(s); 16-CuSO 4 (aq); 17-CuSO 4 · 2Cu(OH) 2 (s);
18-CuSO 4 ·3Cu(OH) 2 ·H 2 O(s); 19-CuP 2 O 7 2 - (aq);
20-Cu(P 2 O 7 ) 2 6 - (aq); 21-Cu 2 P 2 O 7 (s); 22-Cu 3 (PO 4 ) 2 (s);
23-Cu 3 (AsO 4 ) 2 (s); 24-CuHCO 3 + (aq); 25-CuCO 3 (aq);
26-Cu(CO 3 ) 2 2 - (aq); 27-CuCO 3 (s); 28-Cu(OH) 2 ·CuCO 3 (s);
29-Cu(OH) 2 ·2CuCO 3 (s);
The total amount of copper is 10 -5 mol, which is recorded as lgn Cu =-5.00; lg|H 2 O|=0.00; lg|Cl - (aq)|=-2.30; lg|SO 4 2 - (aq)|=-2.92 ;lg|H 2 PO 4 - (aq)|
=-5.36;lg|H 2 AsO 4 - (aq)=-5.80;lgp CO2 (g)=-3.52;lg|e(aq)|=-8.50
In the range of pH = 3 to 6, the unnumbered curve drawn at the top of the line is thicker than the other lines, indicating the total amount n of Cu in the solution. Since all copper-containing species in the pH range are in solution, the value of n is 10 -5 . At pH = 6 to 6.5, substance 10, CuO(s), precipitates, and at pH = 8, it appears to contain all of the copper in the solution. However, the thick line shows that the solution still contains 10 - 7.5 mol of various forms of Cu at this pH, mainly including: Cu(CO 3 )(aq), Cu(OH) + (aq) and Cu 2 + (aq) .
Fig. 2 is a composition diagram of river water containing the same amount of Cu and an anion amount other than Cl - as in Fig. 1, except that lga H + is set to -5.00 and lga Cl - is changed from -5 to 0. A set of such graphs of |Cl - | changes at different pH can be plotted if desired. As |Cl - | increases the amount of CuCl + (aq) and CuCl 2 (aq) steadily increases, Cu + becomes the main copper-containing substance at a higher |Cl - | value. It is worth noting that even at an E value of about 500 mV, a large amount of Cu I chloride, such as CuCl 2 - (aq) and CuCl 3 2 - (aq), is formed in the solution when the value of |Cl - | is high.
Figure 2 The compositional conditions of Cu as a |Cl - | function are the same as in Figure 1.
lgnCu=-5.00; lgaH 2 O=0.00; lga (aq) = -2.92;
Lga (aq)=-5.36;lga (aq)=-5.80;
Lgp CO2 (g)=-3.52;lga e - (aq)=-8.50;lga H + (aq)=-5.00
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