The extractant No. 260 solvent naphtha is 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.
Metal extractants are mainly seven kinds of common 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.
Metal extractant extraction principle: 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 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. The structural formula is:
When is extracted, it can form a metal chelate with copper ions, so that copper is extracted and hydrogen ions are precipitated. The reaction can be expressed by the following formula: Cu2+ (aqueous phase) + 2RH (organic phase) = = CuR (organic phase) + 2H+ (aqueous phase)
The above-mentioned reaction is reversible. In a weakly acidic medium, due to the good stability of the metal chelate produced by the reaction, the reaction proceeds to the right, that is, the extraction reaction. In a strong acid medium, the above reaction proceeds to the left, that is, the metal ions of the chelate will be transferred from the organic phase to the water phase, and the organic phase can be regenerated. This is called the 'back extraction' reaction.