Acid dissolution and metal ion hydrolysis of metal oxides

Electromigration does not occur in such reactions, and the ionic activity in the solution is only related to the pH of the solution, regardless of the potential. Dissolved uranium ore heap leaching uranium oxide (hexavalent), the hydrolysis reaction of metal ions belong to such a reaction. Its general formula is as follows:

Since the enthalpy of this type of reaction is zero and the activity of water is l, the standard Gibbs free energy of the reaction becomes:

When the activity of the A ion and the B ion in the system are both equal to 1, the formula (2) becomes:

From the formula (4), the pH at this time is only related to the standard Gibbs free energy of the reaction. We call this pH the standard pH value, indicated by the pH _mark . Its physical meaning is: in the standard state, the pH of the reactants and the activity of the product are both 1. It is an important indicator of the degree of hydrolysis of metal ions. When the pH of the medium is greater than the standard pH, the metal ions are hydrolyzed, and the hydroxide of the metal precipitates; when the pH of the medium is less than the standard pH, the activity of the metal ions is greater than 1, that is, the metal hydroxide The precipitate dissolves. The equilibrium conditions for this type of reaction are:

When using sulfuric acid as the leaching agent or uranium ore heap leaching copper ores, are often higher than the bottom of the slag in the upper grade grade slag, when the individual slag grade ore leaching out of the bottom of the high grade is because even improper control of pH value Causing hydrolysis of the leached ions

The relationship between the concentration of UO ₂ ^{2 +} and the pH at the time of reaction equilibrium is as follows:

When uranium ore heap leaching, the dissolution and leaching reaction of UO ₃ in the ore is:

It is clear that the dissolution of UO ₃ depends on the acidity of the leach solution and its relationship is as follows:

The copper oxide ore (CuO) in copper ore, copper oxide ore such as chrysocolla (CuSiO ₂ · 2H ₂ O), and the reaction in the heap leaching of sulfuric acid can be expressed as:

Such leaching reaction equilibrium Cu ^{2 +} concentration and pH value of the relationship is as follows:

In the heap leaching process, in addition to valuable metals such as uranium, gold, copper, silver, etc., certain elements in the gangue minerals, such as iron , aluminum , calcium, magnesium, etc., are also compatible with the leaching agent (especially in the application). an acidic leaching agent) chemical reaction, and thus ^{Fe 2 +, Fe 3 +,} Al 3 +, Mg 2 +, Ca 2 + and other ions into the leach solution, wherein the high iron, aluminum ions often cause fouling, interfere with smooth production of get on. This type of fouling is closely related to the pH of the solution. For example, when uranium or copper ore is heap leached with sulfuric acid, a large amount of ferrous and high-iron ions are often introduced into the leachate. After several cycles, the ferrous iron is oxidized to high iron. The pH of Fe ^{3 +} is lower than Fe ^{2 +} due to hydrolysis ^. , thus causing a large amount of precipitation. The hydrolysis reaction of Fe ^{3 +} , Fe ^{2 +} and its relationship with pH are as follows:

Al ^{3 +} in the solution precipitates due to hydrolysis at a pH of 3.1, and the reaction is as follows:

then

When the content of biotite [H ₂ K(Mg,Fe) ₃ Al(SiO ₂ )3] and alkaline silicate mineral in the ore is high, the elements such as iron, aluminum and magnesium in the ore are easily dissolved by acid. If the infusion is leached, if no anti-fouling measures are taken, the scale of the heap is unavoidable.

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