Selective Reduction of Au(I) from a High-Concentration Thiosulfate Solution for Gold Recovery Using One-Step Heat-Treated High-Sulfur Coal

Abstract

It is challenging to economically, efficiently, and selectively recover Au(S 2 O 3 ) 2 3− from thiosulfate gold leaching solutions. This article reports an approach to effectively recover Au(S 2 O 3 ) 2 3− using a toxic material, high-sulfur coal (HSC). Calcined HSC (CHSC) obtained through the onestep calcination of HSC in an inert environment can effectively adsorb Au(S 2 O 3 ) 2 3− present in a high-concentration thiosulfate solution. While the adsorption process is dominated by chemical adsorption, the optimization of the adsorption conditions of Au(S 2 O 3 ) 2 3− suggested that pH and the concentration of thiosulfate can also exert influence on the adsorption process. The adsorption of Au(S 2 O 3 ) 2 3− by CHSC followed the Langmuir isotherm model, and the high correlation coefficient suggested that the reaction followed pseudo-second-order kinetics. X-ray diffraction (XRD) was conducted to characterize the phases of HSC before and after calcination. The XRD results indicated that the main phase of HSC changed from FeS 2 (pyrite) to Fe 8 S 9 (pyrrhotite) after calcination. The Fermi level and surface charge density of Fe 8 S 9 were greater than those of FeS 2 , which facilitated the extraction of electrons from the surface of Fe 8 S 9 during the reduction of Au(I). As a result of the formation of Fe 8 S 9 , the open-circuit potential is reduced from 0.08 V (HSC) to −0.023 V (CHSC). As such, CHSC has a greater reducing capability, which gives rise to the reduction of Au(I) present in the solution to elemental gold. These results were confirmed using an X-ray photoelectron spectrometer. This study not only converted toxic HSC to a valuable material but also provided a new method to adsorb Au(S 2 O 3 ) 2 3− from thiosulfate leaching solutions.

Core–Shell Structured Fe3O4@CuS for Effective Gold Capture and Recovery

“…The effective adsorption of gold on Fe 3 O 4 @CuS can be attributed to two primary factors: the strong affinity between sulfur and gold and the redox reaction between Au­(III) and CuS. Numerous studies have demonstrated that adsorbents with high sulfur content exhibit a strong affinity for gold complexes, ,− which enhances their selective recovery from aqueous solutions. Furthermore, high-resolution XPS analysis of Cu 2p reveals that a portion of Cu + undergo oxidation during gold adsorption.…”

“…On the other hand, adsorbents with high sulfur content have been proven to be very effective for capturing and recovering gold complexes. ,− Gold complexes are attracted to adsorbents with high sulfur content because they form strong chemical bonds with the sulfur atoms in the adsorbent. Thiol or mercaptan functional groups (−SH) on the adsorbents can form strong coordination bonds with gold complexes, allowing the gold to be effectively captured and retained by the adsorbent, and the attraction between sulfur-containing adsorbents and gold complexes is usually highly selective. ,,,, …”

“…Thiol or mercaptan functional groups (−SH) on the adsorbents can form strong coordination bonds with gold complexes, allowing the gold to be effectively captured and retained by the adsorbent, and the attraction between sulfur-containing adsorbents and gold complexes is usually highly selective. 9,13,16,18,19 In this study, we present a facile, easy, and economical approach to fabricate a magnetic adsorbent, which is a core− shell structured Fe 3 O 4 @CuS. The magnetic Fe 3 O 4 core provides high magnetism for easy separation, while the CuS shell is used for effective and selective gold capture and recovery.…”

Calcined High-Sulfur Coal for Highly Efficient Adsorption of Au(S2O3)23– from a Gold Thiosulfate Leaching Solution Using an External Reduction Potential

“…Because the Fermi level of Fe 8 S 9 was higher than that of FeS 2 , the reducibility of CHSC was higher than that of high-sulfur coal, and Au(S 2 O 3 ) 2 3− in solution can be reduced to elemental Au. 23 High-sulfur coal cannot be burned directly, and long-term stacking releases harmful gases, such as SO 2 , H 2 S, and NO 2 , 24,25 and pollutes the surrounding water and soil. Therefore, using high-sulfur coal as an adsorbent for Au(S 2 O 3 ) 2 3− broadens the utilization value of high-sulfur coal and provides a new method for recovering Au(S 2 O 3 ) 2 3− from thiosulfate solutions.…”

“…The phases of high-sulfur coal before and after calcination were characterized using X-ray diffraction, and it was determined that the primary phase changed from FeS 2 for high-sulfur coal to Fe 8 S 9 for CHSC. Because the Fermi level of Fe 8 S 9 was higher than that of FeS 2 , the reducibility of CHSC was higher than that of high-sulfur coal, and Au­(S 2 O 3 ) 2 3– in solution can be reduced to elemental Au …”