Resin properties

Ion exchange resins are synthetic materials which consist of an inert matrix (e.g. polystyrene divinyl benzene co-polymers) and contain surface functional groups, such as amines and esters. Resins prepared without using a solvent diluant in the process have a gel type matrix structure, while those prepared with solvents have a more open, macroporous structure [4]. The latter are preferred for using in gold extraction systems since they provide high surface area for ion adsorption and have better mechanical strength than gel type resins.

The functional groups can exchange ions with other similarly charged ionic species in solution, depending on the preference of a particular functional group for a specific ion. This depends on the properties of the functional group and the charge, size, and polarizability of the ions in solution. Functional groups can be basic (anion exchangers) or acidic (cation exchangers) and can be further classified as having weak or strong base/acid properties, depending on their degree of dissociation in the solution. Alternatively, highly selective functional groups can be attached to a resin matrix, but these are of limited interest in gold extraction. The next table shows some resin types and their capacity for gold recovery from a cyanide solution.

Resins are produced as beads, ranging from 0.25 to 0.60 mm diameter. The physical strength of resins depends strongly on the matrix structure, and consequently different resins show variable attrition resistance. Resin structure is also susceptible to thermal and osmotic shock. The maximum recommended operating temperature for many commercially available resins is between 60^oC and 70 ^oC, and repeated exposure to acid and alkaline solutions can lead to a severe physical degradation.

Table 1. Gold in solution after extraction (mg/l). [5]

Resin	S.B. capacity (W.B. capacity) mol/l	Resin used in extraction
		25 mg	55mg	80 mg
1	1.40 (0.0)	0.45	0.15	0.12
2	0.80 (0.0)	0.84	0.37	0.26
3	0.125 (0.23)	0.23	0.03	0.00
4	0.30 (0.0)	22.4	0.46	0.17
5	0.47 (0.0)	0.51	0.14	0.07
6	0.21 (0.29)	1.46	0.02	0.00
7	0.17 (0.69)	11.8	0.06	0.00

Resin 1, Rohm & Haas; IRA 400.

• Resins 2 to 7, Mintek macroporous strong base resin.
• S.B. Strong Base, W.B. Weak Base.