Gold Leaching With IODINE

Iodine at very low concentrations leaches gold. If the ore or pulp has to be washed with a lot of water to recover the lixiviant, iodine can be recovered from the resulting dilute solution using a simple ion exchange technique. When recovered in that manner, iodine is readily eluted by hot water, with leaves it in a recyclable form.

When iodine attacks a gold ore where there is pyrite or other reducing agents, gold is solubilized as iodize complex AuI₂^- and AuI₄^-, and pyrite and other minerals are oxidized by iodine forming iodide. For an economical process iodine must be recycled, thus iodine must return to its oxidizing state and the gold have to be removed. These requirements are difficult and expensive. The difficulty is on the fact that iodine and gold-complex behave very similar in the presence of reducing materials such as resins or activated carbon which are employed to recover gold from liquors. Ergo, gold cementation with iron or zinc dust results in solubilization of big amounts of these elements because iodine and gold will be oxidized. Recovery by resins or activated carbon has a problem, gold and iodine competes for the same places at the same time.

In this process gold is leaches by iodine which is complexed by iodide. The oxidation of sulphide minerals produces iodide as a reaction product. The latter is combined with iodine favoring its dissolution because iodine has a low solubility (0.3 g/l). Oxidants are no necessary to be added. Iodine concentration must be in the range 2 to 10 gr/l.

The reactions are:

FeS₂ +I₂ = Fe²⁺ + 2S + 2I^-

Au + I^- + I₂ = AuI₂^-

Iodine penetrates gold particles particularly well and, above pH 8, it does no complex iron and attacks sulphides weakly. Below pH 7, iodine does attack sulphides, at which time is converted in iodine ions rather than combining with sulphur. Iodine can be regenerated to I₂ electrolytically in a diaphragm cell. During this electrolytical process iodide is reduce to iodine in the anode and gold is deposited in the cathode. Thus, iodine can be recycled and gold can be recovered. 

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