Resin adsorption mechanism (2)

Due to the progress of the side reaction, some of the reactive groups are occupied by the anions of the impurities, which lowers the operating capacity of the resin to adsorb gold . In fact, the saturated AM-2 bismuth resin discharged from the adsorption leaching process contains no more than 20% of the total amount of metals and impurities contained therein.
It has been found that in the ion exchange resin phase, there is a multi-charged silver cyanide complex ion Ag(CN) ₃ ^2- , Ag (CN) ₄ ^3- . This is because a large number of simple adsorption resin of CN ^- ions, which further complex ions of silver cyanide entangled occur.
If gold, silver and impurity metal cyanide complex ions coexist, their order of adsorption on AM-2Б anion exchange resin is: Au(CN) ₂ ^- >Zn(CN) ₄ ^2- >Ni(CN) ₄ ^{2 -} >Ag(CN) ₃ ^2- >Cu(CN) ₄ ^3- >Fe(CN) ₆ ^4- . This sequence indicates that the resin has the highest affinity for Au(CN) ₂ ^- and can be substituted for other anions located thereafter.
3. Gold resin selection
1) The basic reaction of resin adsorption of gold, whether it is a strong basic resin, a weakly basic resin or a bifunctional resin containing a strong base and a weak base, when they adsorb gold from a cyanidation medium, they are all carried out by a typical ion exchange reaction. .
A strong basic resin adsorbs gold. The reaction of quaternary amine groups to adsorb gold and silver cyanide complex anions is as follows:

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2 tertiary amine resin adsorbs gold. The tertiary amine resin has a structure of R ₃ N and is a free base type. Protonation can be carried out in a certain pH solution, ie.
R ₃ N+HX=====[R ₃ NH]+·X ^- (abbreviated as R ₃ N ⁺ H·X ^- )
A series of ion exchange reactions similar to those described above are then carried out in the form of R ₃ N ⁺ H·X ^- . It can be seen that the ion exchange capacity of the tertiary amine resin is closely related to its protonation ability (ie, formation of R ₃ N ⁺ H). The protonation of the tertiary amine resin is closely related to the internal structure of the resin in addition to the pH of the solution it is in contact with, and its pK. value can be used to indicate its protonation ability, since R3N+H can be used. The extent of existence is seen as the extent to which cationic acids dissociate in water:

pKa is defined as the pH at which 50% of the resin functional groups are protonated. At present, most commercial weakly basic resins have a pKa value of 6-8. Therefore, gold can only be adsorbed in a cyanide solution having a pH of about 8 or lower. It is worth noting that the cyanide complex anion of gold reacts with a weakly basic resin to lower the acidity of the resin, that is, the pKa value. This allows the weakly basic resin to adsorb the gold cyanide complex in a higher pH solution. In recent years, some special structures of weakly basic resins have been developed, which have large pKa values. Therefore, gold can be adsorbed efficiently in a slightly alkaline or even cyanide solution having a pH of 9-10. This type of resin not only has high adsorption selectivity for gold, but also desorbs gold by removing its protonation with a NaOH solution. Therefore, for a long time, people have been paying close attention to the development of such resins. Further developments have recently taken place.
3 bifunctional resin adsorbs gold. Various experiments have shown that tertiary amine resins containing appropriate amounts of quaternary amine groups, i.e., bifunctional resins, such as AM-2, and China's 353E and modified 353E, still mainly utilize their quaternary amine groups to adsorb gold. The introduction of the tertiary amine group only greatly increases the adsorption selectivity of the resin, as if the quaternary amine group is dispersed, so that the adsorption of the cyanide complex anion having a high charge number is reduced because these ions require two or more A positively charged functional group is combined with it to satisfy electrical neutrality to be adsorbed.
2) Selection of gold-plating resin When the former Soviet Union raised the gold from the cyanide medium by the resin method, it gradually turned to the macroporous bifunctional resin from the test of the ordinary strong basic resin AB-17, as shown in Table 2, and finally developed. AM-2 resin with special advantages has been widely used in the gold extraction industry. [next]

These resins contain (mg/L):Au 0.6, Cu 1.5, Ni 1.2, Zn 0.6, Fe 1.1, CN ^- 200 from the liquid phase, and the isotherm of gold adsorbed in the cyanide slurry at pH=10.6 is shown in Fig. 2. Show.

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The results fully demonstrate that the gold capacity of all bifunctional resins is significantly higher than that of strongly basic resins, while in bifunctional resins, AM-2 is the highest gold capacity. When these resins are adsorbed and saturated from the above slurry, the adsorption amounts of various metals are shown in Table 3.

The results in Table 3 show that the macroporous strong basic resin not only has a very low gold capacity, but also has a high adsorption capacity for ruthenium metal, especially for Cu and Fe; the gold capacity of all tested bifunctional resins is compared. High, however, only AM-2 bismuth resin has the highest gold capacity and the lowest adsorption capacity for bismuth metal, the most prominent of which is its significantly lower adsorption capacity for copper . Further studies have shown that for AM-2Б type resin, the adsorption gold capacity is the highest when the pore diameter is 5~6nm, and the amount of adsorbed base metal is the lowest. Therefore, the performance of AM-2 resin used in the gold extraction industry is the best, which is the result of its strong base group and divinylbenzene content as well as suitable specific surface area and pore diameter.
In addition, a series of De-Acidite H resins (also belonging to the bifunctional resin type) with different base groups content, the gold capacity when gold is adsorbed from the cyanide solution with higher gold content and relatively lower base metal content. The relationship between the total adsorption amount of the impurity metal and the strong base group content of the series of resins is shown in FIG. The results also indicate that too high a strong base group content in the resin causes the resin to adsorb a large amount of base metal, while the capacity of gold is little increased, that is, the adsorption selectivity of the resin to gold is deteriorated. [next]