A characteristic of this type of reaction is that the system potential is independent of pH and is only related to the ion activity in the solution. The general formula of the reaction is:
The greater the value of the E system, the system of larger ions are reduced to precipitate metals trend; the other hand, if the smaller the value of the system E, the greater the tendency of the metal is oxidized, the oxidation reaction if the final product is readily soluble Then the metal dissolves.
In heap leaching, the dissolution and leaching of copper , gold and silver and the dissolution of most metals belong to this type of reaction. For heap leaching with natural copper in the ore, when an oxidant is present, the reaction can be expressed as:
When replacing the scrap iron copper leaching solution to form a copper sponge, which reaction is as follows:
This reaction involves two simple metal electrode reactions. The copper dissolution reaction is as described above, and the other electrode reaction and its potential relationship are as follows:
Electric type of displacement reaction:
When a sufficient amount of iron is present, the reaction proceeds until almost all of the copper ions have been deposited. Because when ε = 0, aCu 2 + /aFe 2 + =10 - 26.3 .
For gold ore heap leaching, the gold in the ore is essentially natural gold, and its leaching reaction can be expressed as:
Its potential is: E=1.3+0.0591lgaAu + (9)
Such a high potential indicates that it is impossible to oxidize and leaching gold by using oxygen or other oxidizing agent in an aqueous solution. In the production practice, people use the complexation of gold with cyanide and chloride to reduce the concentration (activity) of metal ions in the solution, thereby reducing the potential of the system. The complexation reaction is as follows:
It can be seen from Table 1 and Table 2 that the standard reduction potential of the above reaction is -0.68 V, and the stability constant of the complex ion is 2 × 10 38 . It can be seen that when there is free CN - , the activity of metal ions in the solution can be significantly reduced. . At this time, the potential of the gold cyanide heap leaching is:
Table 1 Common monovalent gold complex formation potential
Complex ion | Electrode reaction | Reduction potential (V) |
Au(CN) 2 - | Au(CN) 2 - Au+2CN - | -0.686 |
Au(S 2 O 3 ) 2 3 - |
| -0.007 |
Au[CS(NH 2 ) 2 ] 2 + | Au[CS(NH 2 ) 2 ] 2 + +e Au+2CS(NH 2 ) 2 | +0.223 |
Au(SCN) 2 - | Au(SCN) 2 - +e Au+2SCN - | +0.72 |
AuBr 2 - | AuBr 2 - +e Au+2Br - | +1.02 |
AuCl 2 - | AuCl 2 - +e Au+2Cl - | +1.20 |
Table 2 Commonly used gold junction ion stability constants
Au+ complex ion | Stability constant | Au3+ complex ion | Stability constant |
Au(CN) 2 - | 2×10 38 | Au(CN) 4 - | ~1×10 56 |
Au(S 2 O 3 ) 2 3 - | 5×10 28 | AuI 4 - | 5×10 47 |
AuI 2 - | 4×10 19 | Au(SCN) 4 - | 1×10 42 |
Au(SCN) 2 - | 1.3×10 17 | AuBr 4 - | 1×10 32 |
AuBr 2 - | 1×10 12 | AuCl 4 - | 1×10 26 |
AuCl 2 - | 1×10 9 |
AuCl 2 - | 1×10 9 |
For the gold cyanide complex ions in the cyanide heap leaching solution, some of the heap leaching fields adopt a zinc replacement process, and the chemical reaction is as follows:
Another metal electrode reaction and its potential relationship included in this reaction are as follows:
It should also be pointed out that in the heap leaching process of gold, copper, silver and other ores, the extract of high-grade copper oxide ore is subjected to extraction-back extraction to obtain a stripping solution with high copper content (35-50 g/L); gold ore By the adsorption-desorption of carbon, a desorption liquid having a high gold content (0.3 to 8 g/L) is obtained, and these solutions are obtained by electrowinning to obtain electrolytic copper and gold mud, respectively. These electrowinning processes also belong to the metal electrode reaction.
Ammonium dihydrogen phosphate (NH4H2PO4) is a white crystalline solid that is soluble in water. It is commonly used as a fertilizer, flame retardant, and food additive. It is also used in the production of ceramics, pharmaceuticals, and detergents. Ammonium dihydrogen phosphate is a source of both nitrogen and phosphorus, two essential nutrients for plant growth. It is often used in combination with other fertilizers to provide a balanced nutrient supply to crops. Ammonium dihydrogen phosphate is also used as a flame retardant in plastics and textiles, as it releases ammonia when heated, which dilutes the combustible gases and inhibits combustion. In the food industry, it is used as a leavening agent in baking powders and as a pH regulator in soft drinks.
Ammonium dihydrogen phosphate (ADP) is a colorless, crystalline compound with the chemical formula NH4H2PO4. It is commonly used as a fertilizer and as a food additive. ADP is also used in the manufacturing of ceramics, electronics, and other products.
ADP is soluble in water and has a slightly acidic pH. It is a highly reactive compound and can react with strong bases to form ammonium phosphate. ADP is also a source of phosphorus and nitrogen, which are essential nutrients for plant growth.
In addition to its use as a fertilizer, ADP is used in the production of ammonium polyphosphate, which is used as a flame retardant and in the manufacturing of plastics. ADP is also used in the production of specialty glasses and in the preparation of buffer solutions for laboratory use.
ADP has been classified as a hazardous substance by the United States Environmental Protection Agency due to its potential to cause harm to human health and the environment. It can cause skin and eye irritation, and inhalation of the dust can cause respiratory problems. ADP can also contribute to eutrophication, which is the excessive growth of algae in water bodies, leading to oxygen depletion and harm to aquatic life.
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