What is an acidic extractant

Release time:

2023-08-04

Source:

Acid extractants are named after their ability to ionize hydrogen ions in water. Due to the exchange of hydrogen atoms with metal cations in water during extraction, it is also known as a liquid cation exchanger. According to the ionization constant Ka, acidic extractants can be divided into strong acidic extractants (dissociation constant Ka>1) and medium strong acidic extractants (Ka ≈ 10). And weak acidic extractant (Ka ≈ 10). Carboxylic acids and acidic phosphorus extractants are the most important acidic extractants.

carboxylic acid

Carboxylic acids are an important type of acidic extractants that typically exist in the form of dimers due to intermolecular association. Because K2 is a constant generated by dimerization reaction, it is called the dimerization constant. Carboxylic acids are usually weak acids, with less acidity than general inorganic acids and greater acidity than carbonates. They can react with bases to form carboxylates (metal soaps). As the pH value of the aqueous solution increases, the solubility of carboxylic acids in water increases. During extraction, carboxylic acids undergo cation exchange reactions with metal ions.

Acidic phosphorus extractant

Acidic phosphorus extractants are also the main acidic extractants, which can be regarded as the products of one or two hydroxyl groups in phosphoric acid molecules being esterified or replaced by hydrocarbon groups. This type of extractant, like carboxylic acids, can also undergo intermolecular association and exist as dimers. It has strong acidity and belongs to the category of strong acidic extractants. Cation exchange reactions also occur when extracting metals. The extraction process of alkyl phosphate (phosphonic acid) is relatively complex, and there are four forms depending on the extraction conditions: (1) when the concentration of metal ions in the aqueous phase is low and the organic phase loading is small, only one hydrogen ion in the dimeric alkyl phosphate molecule participates in the reaction; (2) If the concentration of metal ions in the aqueous phase is high, alkyl phosphoric acid exchanges with metal ions in the form of monomers; (3) When a certain anion in the aqueous phase has strong coordination ability with metal ions, the extractant anion can form a mixed complex with the metal cation to be extracted; (4) Due to the correlation between the acidic ionization of alkyl phosphate and the acidity of the solution, under high acidity conditions, the ionization of alkyl phosphate is inhibited. At this time, alkyl phosphate mainly acts as a phosphoryl group, similar to neutral phosphorus containing extractants.

Phosphoric (phosphonic) acid extractants containing P (O) OH groups are the same as carboxylic acids. As their acidity increases, their extraction ability increases. The order of extraction ability is: (RO) 2POOOH>(R) (RO) POOH>R2POOH. As the carbon phosphorus bonds in these extractant molecules increase, the alkoxy groups decrease, and the electron absorption effect weakens, resulting in an increase in pKa, a decrease in acidity, and a decrease in extraction ability.

Key words:

What is an alkaline extractant

The Use and Application Fields of Cobalt

What is an alkaline extractant

The Use and Application Fields of Cobalt