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Sulfide copper mineral, typically Chalcopyrite (CuFeS), is one of the most common minerals for producing metallic copper via the pyrometallurgical process. Generally, flotation tailings are produced as a byproduct of flotation and still consist of un‒recovered copper. In addition, it is expected that more tailings will be produced in the coming years due to the increased exploration of low‒grade copper ores. Therefore, this research aims to develop a copper recovery process from flotation tailings using high‒pressure leaching (HPL) followed by solvent extraction. Over 94.4% copper was dissolved from the sample (CuFeS as main copper mineral) by HPL in a HO media in the presence of pyrite, whereas the iron was co‒dissolved with copper according to an equation given as C = 38.40 × C. To avoid co‒dissolved iron giving a negative effect on the subsequent process of electrowinning, solvent extraction was conducted on the pregnant leach solution for improving copper concentration. The result showed that 91.3% copper was recovered in a stripped solution and 98.6% iron was removed under the optimal extraction conditions. As a result, 86.2% of copper was recovered from the concentrate of flotation tailings by a proposed HPL‒solvent extraction process.

This paper focuses on the synthesis of gold nanorods by a seeding growth approach in the presence of cetylthrimethylammonium bromide as a weak reducing agent. The pH value of the solution is an important factor in the formation and control the morphology of gold nanorods. In the pH-dependent range from pH 3.3 to pH 2.2, the main product that gold nanorods with the aspect ratio of 18.7 were produced. The effect of the pH value of the aqueous solution on the aspect ratio of gold nanorod was discussed.

Abstract. Iodine-iodide leaching and activated carbon adsorption processes for recovery of gold (Au) from waste printed circuit boards (WPCBs) were discussed in this paper. A pressure oxidative acid leaching (POAL) was carried out in an autoclave using diluted sulfuric acid (1 M H2SO4) solution in order to remove high concentrations of some base metals especially copper (Cu), aluminum (Al), iron (Fe) and zinc (Zn) due to their negative effects on gold dissolution from WPCBs. The factors affecting the performance and efficiency of the iodine-iodide leaching process; such as iodine/iodide concentration, pulp density, leaching time and leaching temperature were optimized in order to maximize the gold dissolution efficiency from the WPCBs in the iodine-iodide solution. Results indicated that the vast majority (> 99 %) of gold was dissolved in the solution from the WPCBs under the optimized leaching conditions. Adsorption tests were conducted on leach liquor solution resulting from the iodine-iodide leaching using activated carbon. Nearly 98 % of gold was adsorbed from the liquor solution onto the carbon under the conditions optimized in this study. The results obtained revealed that gold can be successfully recovered from this secondary resource, where the percent recovery amounts to nearly 97 % for gold.

The scope of this study was to improve the hydrometallurgical processes involving iodine-iodide leaching and precipitation for recovery of gold from waste printed circuit boards. Firstly, the influence of different precipitating agents, namely ascorbic acid, trisodium citrate and sodium hydroxide on the recovery of gold from gold-iodide leach liquor were investigated in order to define the most effective precipitating agent. The leach liquor was prepared by dissolving pure gold chips in 1:6 molar ratio of iodine-iodide solution at 40°C, 550 rpm for 12 h. The variables, which affect the efficiency of gold precipitation from the leach liquor, were the molar ratio of precipitating agents to gold, pH and redox potential of the solutions. The attained high gold precipitation efficiency from the leach liquor was more than 99% under the highly acidic (pH < 1.6) and alkaline conditions (pH > 13) induced by 0.1 M ascorbic acid and 0.1 M sodium hydroxide respectively, but 64.5% of gold at a weak alkaline condition (pH 8) with 0.1 M trisodium citrate. Secondly, physico-chemical properties of resultant colloidal solutions and prepared gold particles were examined. Finally, recycling of waste printed circuit boards (WPCBs) via iodine-iodide leaching followed by the ascorbic acid reduction was discussed. Results indicate that over 95% of gold extracted from WPCBs by two-step iodine-iodide leaching under the defined conditions, while the dissolution efficiencies of other precious metals (Ag, Pd) and metal impurities (Cu, Al, Fe, Ni, Pb and Zn) were less than 1% and 3%, respectively. The vast majority of Au (99.8%), Cu (95.6%) and Ag (76.8%) were precipitated from the pregnant leach solution by ascorbic acid reduction at ambient conditions.

: This paper deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Base metals present in WPCB ash were removed via HPOL using a diluted sulfuric acid solution at elevated temperatures. Effects of potassium iodide concentration, hydrogen peroxide concentration, sulfuric acid concentration, leaching temperature, and leaching time on gold extraction from pure gold chips with KI–H2O2–H2SO4 were investigated. The applicability of the optimized iodide leaching process for the extraction of gold from the leach residue obtained after HPOL were examined at different pulp densities ranging from 50 g/t to 200 g/t. Results show that the removal efficiency was 99% for Cu, 95.7% for Zn, 91% for Ni, 87.3% for Al, 82% for Co, and 70% for Fe under defined conditions. Under the optimal conditions, the percentage of gold extraction from the gold chips and the residue of WPCBs was 99% and 95%, respectively. About 99% of the gold was selectively precipitated from the pregnant leach solution by sequential precipitation with sodium hydroxide and L-ascorbic acid. Finally, more than 93% of gold recovery was achieved from WPCB ash by overall combined processes.

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The volatilization of arsenic (As) and antimony (Sb) impurities in a copper ore consisting of tennantite (Cu 12 As 4 S 13)/tetrahedrite (Cu 12 Sb 4 S 13) by roasting in both nitrogen and air atmospheres was investigated in this study. The roasting experiments were performed at different temperatures ranging from 500 to 1200°C and different retention times from 15 to 60 minutes while the nitrogen and air flow to a furnace chamber was same as 300 ml/min. The results showed that at 700°C, the maximum As volatilization in nitrogen and air atmospheres was reached over 90% and about 70%, respectively. Whereas the maximum Sb volatilization was about 90% at 1200°C in a nitrogen atmosphere and over 95% at 600°C in an air atmosphere. Meanwhile, copper and iron in the ore sample were not volatilized under the conditions. The contents of As, Sb and Cu in the residue obtained from roasting at 1200°C in a nitrogen atmosphere were 0.004 mass%, 0.75 mass% and 34.2 mass%, while their contents were 0.45 mass% As, 4.19 mass% Sb and 34.5 mass% Cu in the residue from roasting at 1000°C in an air atmosphere. Volatilization of arsenic from enargite, arsenic and antimony from tennantite/tetrahedrite sample containing chalcopyrite in a nitrogen atmosphere under the determined roasting condition were also discussed. It suggests that As and Sb can be selectively separated from each other/other metals by volatilization. On the other hands, high grade copper concentrate with lower As and Sb contents can be made by volatilization in a nitrogen atmosphere.