Recovery of gold from ammonia-thiosulfate media with amberlite IRA-410 ionic exchange resin

Abstract

The adsorption and elution of gold in thiosulfate-ammonia media were studied at laboratory level using the Amberlite IRA-410 ionic exchange resin. Tests were carried out in a stirred reactor, maintaining constant temperature (25°C), with a volume of solution/mass of resin ratio of 833,3 ml/g and during 3 h. The variables tested were the following: pH (9-11), thiosulfate concentration (0-0,5 M), ammonia concentration (0-0,5 M) and selectivity in the presence of cupric ion. The obtained results indicate that gold adsorption was quick; the presence of thiosulfate decreased strongly the adsorption; and the presence of ammonia did not affect the adsorption mostly. The copper was in a certain measure a competitor of the gold, but its biggest negative effect was that acted as catalyst of the oxidizing reaction of thiosulfate (S 2O32-) to tetrathionate (S4O 62-) and trithionate (S3O62-), which can cause a partial elution of gold during the load stage. Also, the behavior of ClO4-, SO32- and ClO- as eluents was studied in both gold and copper elution. These tests were also carried out in a stirred reactor, to constant temperature (25°C), with a volume of aqueous solution/mass of resin ratio of 200 ml/g and for 3 h. Results demonstrated that the copper was eluted more quickly that the gold in all the cases.