Ammonium Thiosulfate Solution Research Articles

Thermodynamic evaluation of gold oxidation and reduction mechanisms in ammonium thiosulfate solution

The copper-catalyzed gold oxidation and reduction mechanisms in ammonium thiosulfate solution were investigated by Eh-pH diagram based on the optimum reagent combination for a 60% (by weight) -75-μm silicate ore containing 16-g/t Au with the maximum gold extraction of 92% and the minimum ammonium thiosulfate consumption of 23 kg/t for 24-hours of leaching at ambient temperature. The gold recovery by cementation was nearly 100% using Zn and Al powders at metal/Au mass ratios of 30 and was around 95% using Cu powder at a Cu/Au + mass ratio of 50. To oxidize the gold efficiently with less thiosulfate consumption, the stable region of [Cu(NH 3 ) 4 ] 2 + should be as wide as possible in the region where [Cu(S 2 O 3 ) 2 ] 3 - is more stable than [Cu(NH 3 ) 2 ] + in the Eh-pH diagram. To recover gold using Zn, Cu or Al powder efficiently, the solubility of [Cu(S 2 O 3 ) 2 ] 3 - should be higher than [Cu(NH 3 ) 2 ] + on copper precipitation. Zinc powder may recover gold more efficiently than copper powder with a similar trend on the effect of ammonia, copper and thiosulfate. However, the large amount of copper will be co-precipitated along with gold because the stability of zine ammine and thiosulfate complexes are higher than that of copper's. Aluminum may reduce gold efficiently at higher thiosulfate concentration and pH. These results were confirmed and compared to the optimum reagent combination for a finer-ground, 100% (by weight) - 75-μm, sample. It was concluded that the optimum reagent combination was 0.5-mol/dm 3 NH 4 OH, 0.0001-mol/dm 3 CuSO 4 .5H 2 O and 0.05-mol/dm 3 (NH 4 ) 2 S 2 O 3 , which resulted in 94% gold extraction and an ammonium thiosulfate consumption of 3 kg/t. Gold and copper stabilities agreed with the thermodynamic rule found on a coarser ground ore (60% by weight -75 μm). The lower reagent combination will reduce gold oxidation power, but significantly minimizes reagent consumption. From this pregnant solution, nearly 100% of the gold was successfully recovered by zinc precipitation at a Zn/Au + mass ratio of 30. Aluminum and copper precipitations resulted in less than 40% gold recoveries at metal/gold mass ratios of 30. The thiosulfate oxidation mechanism is believed to be in agreement with the Belousov-Zhavotinsky reaction.

Scaling of Roughness in Silver Electrodeposition

The electrodeposition of silver from thiosulfate solutions and its surface roughness are studied using scaling methods. Although silver electrodeposition from photographic fixing baths containing thiosulfate has been done successfully for many years, the vast majority of information about this process remains empirical. A comparison is made between plating silver from ammonium- and sodium-thiosulfate-containing solutions. Atomic force microscopy is used to study surface roughness, which is then analyzed by scaling methods. Silver electrodeposition from sodium-thiosulfate-containing solutions was found to be smoother than from ammonium-thiosulfate-containing solutions. The obtained scaling exponents, found after correction for local effects, depend strongly on the nature of the electrolyte; the growth exponents β are 0.13 and 0.71 for sodium and ammonium thiosulfate solutions, respectively. Local effects are observed only for the sodium but not for the ammonium thiosulfate solution. © 2003 The Electrochemical Society. All rights reserved.

Gold Recovery from Nickel Catalyzed Ammonium Thiosulfate Solution by Strongly Basic Anion Exchange Resin

Copper catalyzed ammonium thiosulfate leaching process has been proposed as an alternative gold extraction process to cyanidation. In order to recover gold from the ammonium thiosulfate solution, ion exchange process has been proposed as a gold recovery method using strongly basic anion exchange resin. However, the co-adsorption of copper along with gold causes difficulty in separating gold and copper at the gold elution stage. Our previous study has demonstrated that nickel catalyzed ammonium thiosulfate solution for gold extraction has the advantage of reducing thiosulfate consumption. In this study, the results also demonstrated the advantage of gold recovery from the nickel catalyzed ammonium thiosulfate solution by strongly basic anion exchange resin. The optimal gold loading conditions on a 1 g/dm 3 strongly base anion exchange resin (wet base value) are investigated in several ion concentrations and 95 kg-Au/t-resin has been obtained. The alternative gold eluant was investigated as the gold loaded resin cannot be eluted by conventional hydrochloric acid. Results showed that the elution efficiency was in the order of OH � < Cl � � NO3 � < Br � � I � < ClO4 � . The maximum gold recovery by using 2.5 mol/dm 3 ClO4 � was around 98% with the stripped resin assayed as 0.2 kg/t Au. The feasibility of resin recycling has demonstrated that there was no deterioration in gold adsorption and desorption for four cycles.

The treatment of copper–gold ores by ammonium thiosulfate leaching

The application of ammonium thiosulfate for the treatment of copper–gold ores has been investigated. Copper minerals and copper–gold samples were leached in an ammonium thiosulfate solution under varying experimental conditions, i.e. aeration, temperature and reagent addition. The behaviour of thiosulfate, tetrathionate and sulfate in solution was studied using ion chromatography. Experiments showed that both gold extraction and thiosulfate stability are affected by a combination of aeration and cupric ions in solution. It is important to establish a balance between providing sufficient air and cupric ions for fast gold dissolution, and at the same time minimize the amount of air in the presence of cupric ions to prevent excessive thiosulfate degradation. Promising results, i.e. high gold extractions and low thiosulfate consumption, were obtained during a 24-h leach without forced aeration.

The adsorption of gold and copper onto ion-exchange resins from ammoniacal thiosulfate solutions

The recovery of gold and copper from ammonium thiosulfate (ATS) solutions using anion-exchange resins has been investigated using batch studies. Strongly basic resins are preferred to weakly basic resins because of their greater range of operational pH and higher loading. The kinetics and isotherms for the adsorption of gold and copper were measured. Individually, gold and copper could be loaded onto resins at high concentrations. The presence of copper was found to greatly lower the stability of the ammonium thiosulfate solution due to copper-catalyzed thiosulfate oxidation and formation of copper sulfides or hydroxides, depending on the conditions. Tetrathionate, as the product of thiosulfate oxidation, strongly poisoned the resins. The effect of thiosulfate and ammonia concentrations on the adsorption was also studied. In the simultaneous loading, good selectivity for gold over copper was obtained. The metals were eluted with a mixed solution of Na 2SO 3 and NH 3.

Gold Cementation from Ammonium Thiosulfate Solution by Zinc, Copper and Aluminium Powders

Gold cementation test was conducted without de-aeration by using zinc, copper and aluminium powders from an ammonium thiosulfate solution contained 8 mg/l Au. The amount of metal powder was varied in the range of 30–450 Metal/Gold mass ratio. The solution composition was 1–5 mol/l NH4OH, 0.01–0.05 mol/l CuSO4 ∗ 5H2O, 0.2–0.4 mol/l (NH4)2S2O3 and pH 9.5–10.5. The results indicated that the gold was effectively recovered from a solution of lower ammonia and copper concentrations and higher thiosulfate concentration. The optimum reagent composition for the gold cementation from the ammonium thiosulfate solution was founded to be 1 mol/l NH4OH, 0.01 mol/l CuSO4 ∗ 5H2O and 0.4 mol/l (NH4)2S2O3 at pH 9.5. 100% of gold was recovered by zinc and aluminium powders at a Metal/Gold mass ratio of 30. Copper powder recovered 93% of gold at a Metal/Gold mass ratio of 50. Zinc might re-generate thiosulfate concentration and precipitate most of copper in the solution. Aluminium precipitation might recover gold with less amount of copper deposition and some thiosulfate reduction. Copper precipitation reduced a small amount of thiosulfate concentration and greatly increased copper concentration. Ammonia concentration stayed constant during cementation process.

チオ硫酸アンモニウムによる金の浸出

The sponge gold (99.92 % pure) has been leached with ammonium thiosulfate solution. In this investigation, the gold leaching rate (extraction rate) and the thiosulfate oxidation rate (consumption rate) have been studied on the effects of CuSO4, (NH4)2S2O3, (NH4)2SO4, NH4OH, stirring speed and retention time. The copper ion acts as a catalyst in gold dissolution, on the other hand, it also accelerates oxidation of thiosulfate (consumption). It was found that the best gold extraction was obtained at 12 hours under following optimum conditions:0.8 ∼ 1.0 mol / l (NH4)2S2O3, 0.03 mol / l CuSO4, 2.0 ∼ 3.0 mol / l NH4OH, 0.4 ∼ 0.5 mol / l (NH4)2SO4, pH 10 ± 0.2 and 150 rpm. The thiosulfate oxidation is about 15 % of the initial concentration.

Separation of Gold from Other Metals in Thiosulfate Solutions by Solvent Extraction

The extraction of gold, silver, copper, zinc, and nickel present in thiosulfate solutions with or without the presence of ammonia was studied. Results show that neither a primary amine nor the mixed extractants of a primary amine with tributyl phosphate or trialkyl amine oxide can separate gold from other metals in the absence of ammonia in aqueous solutions. In the case of ammonium thiosulfate solutions, the percent extraction of gold is increased tremendously in comparison with other metals, and thus gold can be separated from them. The pH50 of gold extraction for a mixed solvent of primary amine with amine oxide is about 9.0, which is very close to the pH of the actual leaching solutions. By using the mixed solvent to extract gold in the solutions from leaching of gold-containing sulfide concentrate, the separation factors of Au to Ag and Au to Cu could reach as high as 15 and 1695, respectively, for a pH less than 8.

Solubilities in the ammonium thiosulfate-urea-ammonium nitrate-water system at 0�C

Solubilities in the system CO(NH2)2-NH4NO3-(NH4)2S2O3-H2O were obtained at 0°C and pH values between 6.12 and 7.33. The new composition of matter, (NH4)6(S2O3)2(NO3)2·CO(NH2)2, was identified and characterized chemically and microscopically. Stable high-analyses solution fertilizers can be produced at 0°C utilizing waste ammonium thiosulfate solutions with standard ammonium nitrate and urea fertilizer materials. A 31-0-0-5.6S grade (%N-%P2O5-%K2O-Other) fertilizer solution can be formed at 0°C when NH4NO3/CO(NH2)2 is about one. Stable 30% total nitrogen solutions containing up to 10% sulfur can be produced at other NH4NO3/CO(NH2)2 ratios.