Extraction principle of metal extractant Extractant is widely used in non-ferrous metal hydrometallurgy industry, such as copper, zinc, cobalt nickel, cadmium, gold and silver, platinum group metals, rare earth and other industries. (Sannuo Chemical) The metal extractant is mainly composed of some common seven kinds of hydrogen ions such as phosphoric acid, ammonium salt, benzene, etc., or the hydroxyl groups are replaced by some 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 principle of metal extractant extraction: The difference in solubility or partition coefficient between two immiscible and non-reactive (slightly soluble) solvents is used to transfer compounds from one solvent to another. After repeated extractions, most of the compounds are extracted. The author's understanding is that inorganic ions are generally soluble in the water phase, and organic matter is easily soluble in the organic phase. For example, chloride ions, calcium ions, etc. are easily soluble in water, and lipids are easily soluble in acetone or ethers (ethyl ether petroleum ether). The organic phase is soluble in alcohols, but the alcohols contain hydrogen bonds and are easily soluble in water. Solvent extraction is based on the fact that organic solvents dissolve different metal ions differently, so that the metal ions in the solution can be enriched and separated. For example, when the organic phase containing the organic agent and the solution phase containing metal ions (also called the water phase) are in contact with each other, the metal ions are redistributed due to the different solubility of the two phases, so as to realize the enrichment of a metal in the organic phase. And separated from other impurities. Now take the extraction of copper-containing solution with an extractant named N-510 as an example to illustrate the extraction mechanism. N-510 is a hydroxime-type extractant, its full name is 2 hydroxy-5 sec-octyl dimethyl ketone oxime, and its molecular weight is 325.
Most extractants in the industry are 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 increase 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 group 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 ions, purifying the metal ions, changing the types of anions, and so on.
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, lipophilicity of the extractant, etc. 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, the extractant is configured according to a certain ratio of the V/V of the extractant to the organic solvent. 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 into the water phase to ensure the purity of the organometallic ions.
6. Washing with water mainly considers the problem of phase separation and entrainment in extraction.
Seven, back extraction. With a certain acid, the metal is back-extracted from the organic to the water phase again.