The two liquids are incompatible with each other, and the material that needs metal extraction can be extracted when the solubility of the two liquids is very different. If carbon tetrachloride is added to bromine water, the elemental bromine will be dissolved into carbon tetrachloride from the water.
The principle of selecting metal extractant:
① Incompatible with the solvent in the original solution;
② The solubility of the solute is much greater than that of the original solvent;
③ Not easy to volatilize;
④ The metal extractant cannot react with the solvent of the original solution. Separation funnel metal extraction Separation funnel metal extraction Common metal extractants: benzene, carbon tetrachloride, alcohol, kerosene, straight-run gasoline, ethane, cycloethane... Don’t forget that water is the cheapest and most readily available metal extractant.
The above metal extractants are mainly physical metal extractants. In the current industry, especially the metallurgical industry, a large number of chemical metal extractants are used, which are widely used in the processes of impurity removal, purification, separation, and product preparation.
Most of the metal extractants in the industry are dissolved in organic solvents, and the common organic solvent is sulfonated kerosene. Because it is easily available and cheap, and has a synergistic extraction effect on metal extractants because it contains a small amount of aromatic hydrocarbons. Soluble in organic solvents can also increase the metal extraction ability of the metal extractant, enhance the solubility of its metal extract compound, reduce its viscosity, reduce its volatility, and reduce its solubility in water.
Metal extractants are mainly used in non-ferrous metal hydrometallurgy industries, such as copper, zinc, cobalt nickel, cadmium, gold and silver, platinum metals, rare earths and other industries.
Application of metal extractant Compared with other methods of separating solution components, metal extraction has the advantages of normal temperature operation, energy saving, no solids, gas, and convenient operation. Metal extraction is usually beneficial in the following situations:
① The boiling points of the various components of the feed liquid are similar, and even form azeotropes, which are difficult for rectification, such as the separation of alkanes and aromatics in petroleum fractions, and the dephenolization of coal tar;
②The separation of low-concentration and high-boiling components requires high energy consumption by distillation, such as the dehydration of dilute acetic acid;
③Separation of multiple ions, such as the separation and purification of mineral extracts. If chemicals are added for partial precipitation, not only the separation quality is poor, but there is also a filtering operation, and the loss is also large;
④Isolation of unstable substances (such as heat-sensitive substances), such as the preparation of penicillin from fermentation broth. The application of metal extraction is still under development. Most of the elements in the periodic table can be extracted and separated by metal extraction methods. The selection and development of metal extraction agents, the determination of process and operating conditions, and the design and calculation of processes and equipment are all subjects of development of metal extraction operations. 
Metal extraction operations The operations of metal extraction 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 metal extraction agent, according to a certain ratio of metal extraction agent and organic solvent V/V, to configure the metal extraction agent. For example, P204 metal extractant, generally P204 metal extractant and sulfonated kerosene organic solvent V/V=4:1 are used to configure metal extractant.
3. Metal extraction of metal ions. Industry generally uses countercurrent metal extraction process. That is, the organic and water phases flow in opposite directions. Generally there will be metal extraction stages. This can ensure the yield of metal extraction.
Fourth, washing, this is mainly from the consideration of impurity removal, washing the metal ions with the subsequent metal extraction sequence to the water phase to ensure the purity of the organic metal ions.
Five, water washing, mainly consider the problem of metal extraction and entrainment.
Sixth, back extraction. Use a certain acid, alkali or salt solution to transfer the metal from the organic to the water phase again.