Using Nickel as a Catalyst in Ammonium Thiosulfate Leaching for Gold Extraction

Abstract

The use of copper as a catalyst for gold leaching in ammonium thiosulfate solution might cause the high consumption of thiosulfate. Also, the high copper consumption is resulted in the zinc precipitation process for recovering the gold from the pregnant solution. In this investigation, nickel was used as a catalyst to minimize the reagent consumption. On a 100 mass%-75 mm of silicate type gold ore containing 16 g/t Au and 0.2 mass% of Fe and C, the nickel catalyzed ammonium thiosulfate solution could extract 95% of gold with the 1.2 kg/t-ore of ammonium thiosulfate consumption in 24 hours at the most favorable reagent combination of 0.0001 mol/dm 3 NiSO 4 , 0.05 mol/dm 3 (NH 4 ) 2 S 2 O 3 and 0.5 mol/dm 3 NH 4 OH at pH9.5, while the standard cyanidation at 0.02 mol/dm 3 (1.0 g/dm 3 ) NaCN consumed around 1.5 kg/t-ore NaCN. In the concentration range of 0:0001$0:005 mol/dm 3 Ni 2þ , the ammonium thiosulfate consumption was 1$5 kg/t-ore, while the ammonium thiosulfate consumption of copper catalyzed lixiviant was greatly increased from 3 kg/t-ore to 21 kg/t-ore as the increase of Cu 2þ concentration from 0.0001 mol/dm 3 to 0.001 mol/dm 3 . The feasibility of recycling barren solution was confirmed with zinc precipitation at nearly 100% of gold recovery. Nickel consumption on the cementation process was less than 50%. For extracting gold from the copper bearing sulfide ore, a higher ammonia and thiosulfate concentrations were required with 0.0001 mol/dm 3 of Ni 2þ . The ammonium thiuosulfate consumption with nickel as catalyst on the copper bearing sulfide ore was about 1$5 kg/t-ore less than that using copper as catalyst.

Lixiviación carbonato amoniacal: estimación del níquel disuelto en el efluente de destilación

“…A las condiciones de "sobre destilación", el área de estabilidad de la especie hexammina níquel (II) [Ni(NH 3 ) 6 ] 2+ es pequeña debido a la baja concentración de amoníaco, en consonancia con los resultados mostrados en la Fig. 3d; además, es posible la precipitación de óxidos de níquel y la formación del anión [Ni(S 2 O 3 ) 2 ] 2− en un amplio rango de potencial y estabilidad a pH inferior a 7,2 (Arima et al, 2004).…”

A Review of Thiosulfate Leaching of Gold: Focus on Thiosulfate Consumption and Gold Recovery from Pregnant Solution

“…Molleman and Dreisinger [43] proposed that the pH range of 9-10 is preferred to simultaneously stabilize thiosulfate and copper ammonia complex. Moreover, the concentration ratio of Cu(II) to Cu(I) is also a critical factor for both of thiosulfate consumption and gold dissolution because the ratio determines the oxidation potential of leach solution [16,44]. Oxygen plays an important role in changing the ratio by oxidizing Cu(I) to Cu(II).…”

“…Ninety-five percent of gold in a silicate-type ore was extracted by nickel-ammonia-catalyzed thiosulfate leaching, and thiosulfate consumption was only 1.2 kg/t-ore [44]. The dissolved gold in nickel-ammonia-catalyzed ammonium thiosulfate solution can be efficiently recovered by a strongly basic anion exchange resin, and the percentages of gold adsorption and elution are both over 99% because of the lack of interference of [Cu(S 2 O 3 ) 3 ] 5− [64].…”

Gold leaching by copper(II) in ammoniacal thiosulphate solutions in the presence of additives. Part I: A review of the effect of hard–soft and Lewis acid-base properties and interactions of ions

“…Yet, the non-suitability of cyanidation for some ores/concentrates and the growing concerns of toxicity and environmental issues related to the use of cyanide in some parts of the world have led to further interest and studies on leaching, separation and recovery of gold using solvent extraction, ionexchange, cementation, or precipitation in thiosulphate media (Zhao et al, 1997;Kejun et al, 2004;O'Malley, 2001, 2002;Choo and Jeffrey, 2004;Hiskey and Lee, 2003;Lee and Hiskey, 2008;Navarro et al, 2004;West-Sells and Hackl, 2005;Young et al, 2008, Jeffrey et al, 2010. Research activities related to non-ammoniacal and noncopper thiosulphate and mixed thiourea-thiosulphate leaching systems using iron(III) as the oxidant with oxalate or EDTA as the stabilising ligands, and anaerobic in-situ leaching operations, show continuing interest in developing a thiosulphate based gold extraction process (Ji et al, 2003;Arima et al, 2004;Chandra and Jeffrey, 2005;Heath et al, 2008;Feng and van Deventer, 2010b). …”