The generation of waste from electrical and electronic devices is imminent due to the excessive increase in the production and disposal of them. This is a worldwide environmental problem since many of them have toxic materials that must be disposed properly. Nevertheless, e-waste may be a source of base metals like copper, zinc and precious metals like gold and silver. In the last decade, several methods have been proposed to recover precious metals, cyanide being the most used leaching agent despite being highly toxic. Therefore, in the present work the use of sodium thiosulfate is proposed, which is an environmentally friendly leaching agent that can improve on the kinetics of dissolving precious metals in comparison to cyanide. In the first instance, a preliminary treatment of material conditioning was carried out, which consists of subjecting the printed circuit boards to crushing, roasting and pulverizing. Subsequently, acid leaching was carried out with a 4 M HNO_3 solution for 6 hours at 40 °C obtaining 93 % copper removal. Gold leaching was carried out at room temperature with a 0,7 M Na_2S_2O_3 solution, using NH3 to adjust the pH to 10.5 over 24 hours. Under these conditions, it was possible to dissolve 80 % of the gold in 6 hours and only 30 % of the copper. Then, adsorption tests were carried out with the Purogold MTA5011 resin with a resin:leachate ratio of 100 g/L over 24 hours. The results indicated that it was possible to recover 87.4 % of the gold from the leachate and 29.3 % of the copper was adsorbed on the resin.
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