In industry, especially in the metallurgical industry, a large number of chemical extractants are used, which are widely used in the processes of impurity removal, purification, separation, and product preparation.
The extraction agents in the industry are mostly dissolved in organic solvents. Common organic solvents are sulfonated kerosene, 260 solvent oil, and 406# environmentally friendly solvent oil. And it has a synergistic effect on the extractant because it contains a small amount of aromatic hydrocarbons. Soluble in organic solvents can also improve the extraction capacity of the extractant, enhance the solubility of its metal extract compound, reduce its viscosity, reduce its volatility, and reduce its solubility in water.
Extractants are mainly used in non-ferrous metal hydrometallurgical industries, such as copper, zinc, cobalt nickel, cadmium, gold and silver, platinum metals, rare earths and other industries.
The main functions of the extractant are: separating the main metal and impurity metal ions, enriching the concentration of the main metal ion, purifying the metal ion, and changing the type of anion.
Metal extractants are mainly seven kinds of common hydrogen ions such as phosphoric acid, ammonium salt, benzene, etc., or hydroxyl groups are replaced by long-chain alkyl groups. When the metal is combined with these extractants, it becomes a metal organic compound and dissolves in an organic solvent. Due to the different binding abilities of various metals with these extractants, the sequence of extracting metals by these extractants is different, thereby separating these metal ions.
The main factors affecting the extraction sequence of metal ions are: the valence state of the metal ion, the size of the metal ion radius, the hydration energy of the metal ion, the stabilization energy of the d electron, and the coordination number. For the extractant: acidity, steric hindrance, and lipophilicity of the extractant all affect the extraction sequence of metal ions.
The extraction operations mainly include 1. Adjust the pH of the feed liquid. For example, in cobalt-nickel metallurgy, the general material liquid is adjusted to pH 3.4-4.0.
2. The configuration of the extractant, according to a certain ratio of V/V of the extractant to the organic solvent, the extractant is configured. For example, P204 extractant, generally P204 extractant and sulfonated kerosene organic solvent V/V=4:1 are used to configure the extractant.
3. Saponification, mainly for acidic extractants. That is, a certain extractant reacts with alkali. The main purpose is to stabilize the pH of the feed liquid and enhance the extraction capacity of the extractant.
4. Extract metal ions. Industry generally uses countercurrent extraction process. That is, the organic and water phases flow in opposite directions. Generally there will be extraction stages. This can ensure the efficiency of extraction.
5. Washing. This is mainly from the consideration of impurity removal, washing the impurity metal ions with the subsequent extraction sequence to the water phase to ensure the purity of the organic metal ions.
Sixth, water washing, mainly considers the problem of extraction phase entrainment.
Seven, back extraction. Use a certain acid to strip the metal from the organic to the water phase again.