I 2 -NaI-H 2 O system. When iodine is dissolved in NaOH, the following reactions occur:
3I 2 +6Na0H ==== NaI0 3 +5NaI+3H 2 0
When the iodine is excessive, a sodium iodate-sodium iodide-water system is formed. Excess iodine and a large amount of iodide ions in the system form stable polyiodide ions, and the following dynamic balance exists:
I 2 +I - +H 2 0; â†â†’ I 3 - ·H 2 0
3I 2 +I - +H 2 0 â†â†’ I 7 - ·H 2 O
The dissolution reaction of gold is based on the oxidation of polyiodide ions to form complex salts of Au(I) and Au(III):
2Au+I 3 - +I - ====2[AuI 2 ] -
2Au+I 7 - +I - ====2[AuI 4 ] -
The iodate in the system acts as an auxiliary oxidation during the dissolution of gold.
The gold dissolved in the system can be extracted by activated carbon adsorption, organic solvent extraction, metal replacement, reducing agent reduction, ion exchanger enrichment and the like. From the viewpoint of simplicity and economy, the use of zinc, iron or substituted saturated sodium sulfite powder can obtain a high recovery rate reduction, reduction reaction as follows:
2[AuI 2 ] - +Zn - ==== [ZnI 3 ] - +I - +2Au ↓
3[AuI 2 ] - +Fe - ====[FeI 4 ] - +2I - +3Au ↓
2[AuI 2 ] - +SO 3 2- +H 2 0 ==== SO 4 2- + 4I - +2H + +2Au ↓
Consider the recovery and reuse of iodine, reduce the recovery of gold impurities in iodine, and use sodium sulfite to reduce it. The iodine in the system after the recovery of gold can also be regenerated according to the fact that in the acidic solution of sulfuric acid, iodine ions are oxidized by potassium chlorate to precipitate iodine:
6I - +C10 3 - +6H + ==== 3I 2 +Cl - +3H 2 0
3I 2 +6Na0H ==== NaI0 3 +5NaI+3H 2 0
When the iodine is excessive, a sodium iodate-sodium iodide-water system is formed. Excess iodine and a large amount of iodide ions in the system form stable polyiodide ions, and the following dynamic balance exists:
I 2 +I - +H 2 0; â†â†’ I 3 - ·H 2 0
3I 2 +I - +H 2 0 â†â†’ I 7 - ·H 2 O
The dissolution reaction of gold is based on the oxidation of polyiodide ions to form complex salts of Au(I) and Au(III):
2Au+I 3 - +I - ====2[AuI 2 ] -
2Au+I 7 - +I - ====2[AuI 4 ] -
The iodate in the system acts as an auxiliary oxidation during the dissolution of gold.
The gold dissolved in the system can be extracted by activated carbon adsorption, organic solvent extraction, metal replacement, reducing agent reduction, ion exchanger enrichment and the like. From the viewpoint of simplicity and economy, the use of zinc, iron or substituted saturated sodium sulfite powder can obtain a high recovery rate reduction, reduction reaction as follows:
2[AuI 2 ] - +Zn - ==== [ZnI 3 ] - +I - +2Au ↓
3[AuI 2 ] - +Fe - ====[FeI 4 ] - +2I - +3Au ↓
2[AuI 2 ] - +SO 3 2- +H 2 0 ==== SO 4 2- + 4I - +2H + +2Au ↓
Consider the recovery and reuse of iodine, reduce the recovery of gold impurities in iodine, and use sodium sulfite to reduce it. The iodine in the system after the recovery of gold can also be regenerated according to the fact that in the acidic solution of sulfuric acid, iodine ions are oxidized by potassium chlorate to precipitate iodine:
6I - +C10 3 - +6H + ==== 3I 2 +Cl - +3H 2 0
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