The main chemical reactions in the leaching process of uranium , gold (and copper , silver ) ores occur in aqueous solution. These reactions may be related to the potential of the system and the pH of the solution, respectively, so the general formula is as follows:
make , then the formula (2) becomes:
-â–³G=RTlnKa-RTlnQa (3A)
Or â–³G=RTlnQa-RTlnKa (3B)
In each of the above formulas, the Ka-chemical reaction equilibrium constant;
R-gas constant, R = 8.315 J / (K · mol);
T-absolute temperature;
A-the activity of the substance;
Gibbs free energy change of ΔG-reaction;
Qa-reaction (activity) entropy.
The reaction proceeds spontaneously towards the reduction of the system Gibbs free energy ΔG (at constant temperature and constant pressure) when:
Qa<Ka, ΔG is a negative value, and the reaction proceeds to the right;
Qa>Ka, â–³G is a positive value, and the reaction cannot proceed to the right;
Qa = Ka, ΔG is zero, and the reaction is in equilibrium.
When the activity of the reactants and the product are both equal to 1, the temperature is 25 ° C, and the pressure is 0.1 MPa, the formula (3B) becomes ΔG = -RTlnKa. This ΔG is called the standard Gibbs free energy change and is generally referred to as ΔG φ .
When the electrode reaction is involved, the decrease in the Gibbs free energy change in the reaction is equal to the maximum useful electrical work done by the reaction, - ΔG = nFE according to the Nernst equation:
Where F is the Faraday constant, and in the standard state, equation (5) becomes:
Below, combined with the actual heap leaching, the thermodynamic relationship of the four main chemical reactions is discussed.
Redox reaction between ions
There is electron migration in this type of reaction, and the potential of the system is only related to the ion activity in the solution, regardless of the pH of the solution. The general formula for this type of reaction is:
Uranium leaching, manganese ore usually first soft oxidized to the Fe 2 + Fe 3 +, Fe 3 + and then by oxidation of the UO 2 UO 2 2 +, to leaching. The total response is:
It includes the redox reaction between the following two ions:
Copper oxide ore is often accompanied by hydrocobalt ore. When using sulfuric acid heap leaching, a reducing agent is often added to leaching cobalt. The reaction can be expressed as:
Its potential relationship is:
Steel strips is low price and is widely used. Quick link baling tie is used in construction, farming and plastic areas.
Quick Link Bale Tie,Galvanizing Baling Wire,Blue Steel Strip,Double Loop Wire Ties
Dovin limited , https://www.dovinmachine.com