Chelating resin is a kind of cross-linked functional polymer material which can form multi coordination complex with metal ions. In its functional group, there are O, NSP, As and other atoms with unlinked lone pair electrons. These atoms can form coordination bonds with metals as a pair of lone pair electrons, forming stable structures similar to small molecule chelates. The dissociatable parts of some chelating resin functional groups can also form ion bonds with metal ions like ordinary ion exchange resins. The chelating resin with iminodiacetic group can form a very stable chelating structure with Cu2+.
Polyamine chelating resin belongs to N, N coordination agent, which complexes with metal ions only by the lone pair electrons of N atom. In fact, this kind of resin is also a kind of common anion exchange resin.
It can be seen from the above that, on the one hand, the chelating resin has its unique function, and on the other hand, it has certain similarities with the aforementioned ion exchange resin. Compared with the ion exchange resin, the bonding force between the integrated resin and metal ions is stronger and the selectivity is higher. Its synthesis method is basically similar to that of ion exchange resin. One is to polymerize low molecular compounds with coordination groups, and the other is to introduce coordination groups into cross-linked polymers through polymer reaction to obtain chelating resins of various structures.
Chelating resin is a very complex category. There are more than 200 varieties and structures reported in the literature. It is impossible to comprehensively and detailedly describe the synthesis methods of various chelating resins in this chapter. Small molecule integrators have two or more coordination atoms that can give the fox pair electrons, and these coordination atoms must be in proper positions (preferably separated by two or three other atoms). These principles also apply to chelating resins. Therefore, the following is an overview of grouping according to the type of coordination atoms.
1、 The most important strain of N, O coordination group chelating resin is amino carboxylic acid, among which iminodiacetic acid resin is the most important commercial chelating resin. In addition to amino carboxylic acids, amine (or ammonia) groups with hydroxyl and carboxyl groups nearby and oxime groups with hydroxyl and carbonyl groups nearby also belong to this category. It can be imagined that there are many kinds of them.
Iminodiacetic acid (IDA) resin has many brands. For example, domestic D401, foreign Dowex A-l, Diaion CR-10, AmberliteIRC-718, etc. There are many ways to synthesize IDA resin. Styrene series IDA resin can be synthesized with chloromethylated intermediate or its aminated product (weakly basic anion exchange resin with primary amine group) as starting material. The typical method is to add the resin with primary amine group to the aqueous solution of chloroacetic acid (the molar ratio of - NH to chloroacetic acid is 1:3~5). Under the condition of stirring, adjust and maintain the pH at 9 with Na. CO:, and react at 80 ℃ for 8~72h to obtain IDA resin. Under this condition, aminoacetic acid will be hydrolyzed, so the reaction with benzylamine group is not easy to complete, and there will be a considerable number of monoacetate groups. Only when a large amount of chloroacetic acid is used or an appropriate amount of chloroacetic acid is added for secondary reaction, the resin with high Cu2+adsorption can be obtained.
The resin with quaternary ammonium group reacts with iminodiacetic acid to obtain a "semi EDTA" based chelating resin without monoacetate group. The produced dimethylaniline can be recovered and used to prepare quaternary ammonium resin. The above reaction can be carried out almost quantitatively, and the performance of the product is also very good.
IDA resin can also be obtained by using chloromethylated cross-linked polystyrene as raw material, amination with nitrogen based acrylate or iminodiacetonitrile, hydrolysis, or amination with industrial amine diethanol, and oxidation with nitric acid.
Hydrophobic chloromethyl crosslinked polystyrene is difficult to react with water-soluble nucleophilic reagent amino carboxylic acid, so it cannot be aminated with such reagent to directly obtain IDA resin. However, the chloromethylation intermediate is partially aminated with trimethylamine first, and then iminodiacetic acid can be used for direct amination to obtain IDA resin with an exchange capacity of 1.9mmol/g for Cu2+.
When IDA resin is prepared by the above methods, the chlorocarboxylic acid used can be B-chloropropionic acid, r-chlorobutyric acid, etc. in addition to chloroacetic acid; The amino carboxylic acid ester used can be methylamino acetate, amino triacetate, iminodipropionate, etc.
There are other methods for preparing imine carboxylic acid resin. But the styrene IDA is still the most important. The selection order of metal ions is:
Cu2+>Pb2+>Fe3+>A13++>Ni2+>Zn2+>Co2+>Cd2+>Fe2+>Ba2+>Ca2+>Na+
However, in many synthesis methods, the structure of the group obtained is not very clear, so its performance may not be completely the same as that of the "semi EDTA" group with double five membered ring structure.
8-hydroxyquinoline resin is also a N, O coordination chelating agent, and there are many synthetic methods. The simplest is to polycondensate 8-hydroxyquinoline with formaldehyde under acidic conditions.
Spherical chelating resin can be obtained by chloromethylation of 8-hydroxyquinoline and reaction with primary amine resin for 1h at 100 ℃.
Using 5-chloromethyl-8-hydroxyquinoline to react with macroporous crosslinked polystyrene under the catalysis of SnC14, 8-hydroxyquinoline resin can also be obtained. The exchange capacity of Cu2+reached 2.16meq/g.
Schiff bases are also a large class of N, O chelating resins. Basically, it is formed by condensation of primary amine and aldehyde. In structure, it is required to have a coordination group such as 0H or SH near the Sifo bond to form a chelate structure.
This kind of chelating resin includes polyamines, pyridines, oximes, pyrazole, imidazole, guanidine, schiff bases and many other varieties.
Polyamine chelating resin is also an anion exchange resin, which has many types of styrene, acrylic and polycondensation structures. Such resins are complexed with metal ions by primary or secondary amine groups.
The corresponding chelating resin can be obtained by the reaction of guanidine and pyrazole compounds with chloromethylated crosslinked polystyrene.
When a large number of metal ions are splashed on the resin, the adsorption recovery rate of Au3+is still more than 90%, and the adsorption rate of Au is 100% in the range of 0.2~6molHCI.
When the degree of crosslinking was 8, the conversion of the reaction was 65% at 8 h. Resin to Au (III) The adsorption capacity of Ag (I) is 170 and 177mg/g.
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