Chalcopyrite leaching

These authors observed that the leach solutions of chalcocite become more and more depleted in Cu and that this depletion is accompanied by a decrease of the Cu/S ratios of the solution from 2 to 1, which these authors ascribe to fractionation between diversely coordinated Cu in the different minerals. In contrast to chalcocite, chalcopyrite leaching produces no isotope fractionation. These authors also conclude from a comparison between columns seeded with bacteria and sterile columns that bacterial mediation had little if any influence on Cu isotopic fractionation in this specific experiment, which simply reflects that bacteria do not store signiflcant amounts of metal. 

Hiroyoshi N., Hirota M., Hirajima T., and Tsunekawa M. (1997) A case of ferrous sulfate addition enhancing chalcopyrite leaching. Hydrometallurgy 47, 37-45. 

In this chapter, the use of computational methods to study the sulfide mineral surfaces will be discussed with the focus in the chemical reactivity. In section 2, some technical aspects related to calculations will be presented and their applications and limitations will be highlighted. In section 3, the focus will be AMD and the use of DFT to study pyrite and arsenopyrite surfaces. The last topic, in section 4, the chalcopyrite leaching and advances obtained by molecular modeling of this system will be discussed. 

Fig. 9 Copper recover rate from a chalcopyrite leaching. Reprinted from Ref. 102 with permission from Elsevier.

Another process, which also generates elemental sulfur as a by-product, has been patented by Envirotech Research Center in Salt Lake City (29). In the Electroslurry process, a ball mill finely grinds a chalcopyrite concentrate, which reacts with an acidic copper sulfate solution for iron removal. The Hquor is electrolyzed and the iron is oxidized to the ferric form. This latter step leaches copper from the copper sulfide for deposition on the cathode. Elemental sulfur is recovered at the same time. 

Sulfide Ores ores. In the Zairian ores, cobalt sulfide as carroUite is mixed with chalcopyrite and chalcocite [21112-20-9]. For processing, the ore is finely ground and the sulfides are separated by flotation (qv) using frothers. The resulting products are leached with dilute sulfuric acid to give a copper—cobalt concentrate that is then used as a charge in an electrolytic cell to remove the copper. Because the electrolyte becomes enriched with cobalt, solution from the copper circuit is added to maintain a desirable copper concentration level. After several more steps to remove copper, iron, and aluminum, the solution is treated with milk of lime to precipitate the cobalt as the hydroxide. 

Copper ore minerals maybe classified as primary, secondary, oxidized, and native copper. Primaryrninerals were concentrated in ore bodies by hydrothermal processes secondary minerals formed when copper sulfide deposits exposed at the surface were leached by weathering and groundwater, and the copper reprecipitated near the water table (see Metallurgy, extractive). The important copper minerals are Hsted in Table 1. Of the sulfide ores, bornite, chalcopyrite, and tetrahedrite—teimantite are primary minerals and coveUite, chalcocite, and digenite are more commonly secondary minerals. The oxide minerals, such as chrysocoUa, malachite, and azurite, were formed by oxidation of surface sulfides. Native copper is usually found in the oxidized zone. However, the principal native copper deposits in Michigan are considered primary (5). 

Ni is found in many ores in combination with S, As Sb, the chief sources being the minerals chalcopyrite, pyrrhotite and pentlandite. Ni ores are of two types, sulfide and oxide, the former accounting for two-thirds of the world s consumption. Sulfide ores are refined by flotation and roasting to sintered Ni oxide, and either sold as such or reduced to metal, which is cast into anodes and refined electrolytically or by the carbonyl (Mond) process. Oxide ores are treated by hydrometallurgjcal refining, eg, leaching with ammonia. Much secondary Ni is recovered from scrap (Refs 6 7) 1... 

It can be seen, therefore, that ferrous iron and chalcopyrite oxidation are acid-consuming reactions, while pyrite oxidation and iron hydrolysis are acid-producing reactions. Thus, whether the overall reaction in a dump is acid producing or acid-consuming depends on the relative proportions of chalcopyrite and pyrite and on the pH conditions. In practice, sulfuric acid additions to the leach solution applied to the dump are usually required to overcome the acid consuming reactions of the gangue minerals and to keep the pH in a suitable range, typically 2 to 2.4, to optimize bacterial activity and minimize iron hydrolysis. 

Puvvada, G. V. K. Murthy, D. S. R. Selective precious metals leaching from a chalcopyrite concentrate using chloride/hypochlorite media. Hydrometallurgy 2000, 58, 185-191. 

Sherritt-Cominco A process for extracting copper from chalcopyrite, CuFeS2. The ore is reduced with hydrogen, the iron leached out with sulfuric acid, the residual Cu5FeS4 dissolved in concentrated sulfuric acid, and the copper isolated by electrowinning or hydrogen reduction. Pilot testing was complete in 1976. 

Treadwell A process for extracting copper from chalcopyrite by leaching with the stoichiometric quantity of sulfuric acid ... 

We now discuss in detail setting up the partial equilibrium model for a particular case. The dissolution of chalcopyrite, CuFeS2, has been studied extensively in the laboratory ( 3,4 5) and we have been interested in it because of its importance in dump leaching. Under dump leaching conditions, two dissolution reactions have been identified for this mineral (3,4 5) ... 

The solid sulfur product need not be chosen as an unknown. Near room temperature, only a small percentage of it is oxidized to soluble sulfur-containing anions(4). It can be assumed, therefore, that none of the sulfur atoms originally present in the solid chalcopyrite enter the solution. The sulfur product is not recovered in the leaching process and does not affect the solution chemistry. 

Liddell, K. C., A Mathematical Model of the Chemistry of the Dump Leaching of Chalcopyrite, 1979, Ph.D. Thesis, Iowa State University, Ames, Iowa. 

Baur, J. P. Gibbs, H. L. Wadsworth, M. E., Initial-Stage Sulfuric Acid Leaching Kinetics of Chalcopyrite Using Radiochemical Techniques, 1974, United States Bureau of Mines Report of Investigations 7823, Washington, D.C. 

Young et al. (in press) conducted related experiments. They examined the Cu isotope compositions of the solutions produced during acid sulfate leaching experiments aimed at extracting Cu from ore minerals (chalcopyrite, chalcocite, djurleite, bomite). The leaching experiment for chalcopyrite reads ... 

Despite the conflicting evidence, Heyes and Trahar (1984) believe there is sufficient evidence to confirm the presence of sulphur on mineral surface. They leached the surface of floated pyrrhotite from a typical test with cyclohexane and have examined the leach solution in a UV spectrophotometer. They found that sulphur could be extracted from the surface of pyrrhotite, which had been floated in the absence of collector. As can be seen from Fig. 2.26, the spectrum from the leached pyrrhotite was compared with the spectrum of sulphur dissolved in cyclohexane indicating that sulphur was present at the siuface. Kelebek and Smith (1989) used UV spectrophotometer to determine sulphur in the ethanol extract from the surface of floated galena and chalcopyrite showing that the amount of sulphur on the minerals can be correlated with their flotation rate which was found to be first order within the critical surface tension range. 

Leach caps have a significantly lower amount of Cu than in enrichment blankets due to downward migration and precipitation of leached copper in the form of chalcopyrite (CuFeS2) chalcocite (CU2S) and cuprite (CuO). 

In the leach cap, the Cu isotopes are lighter than those in the enrichment blanket. Near the surface, the isotopes are extremely low, to about -14%o. Deeper in vertical profile at about 300 feet, the enrichment blanket contains a heavier isotope signature around 8%o. This pattern is observed throughout the drill core. The hypogene mineralization is near 0%o and therefore, there has been fractionation of copper isotopes in the chalcopyrite during dissolution. This fractionation is seen because the hypogene ores are distinctly different than leach cap and enrichment minerals. 

Samples included hematite (Fe203), goethite (FeO(OH)), and jarosite (KFe " 3(0H)6(S04)2) from the leach cap and chalcopyrite (CuFeS2), chalcocite (CU2S), and cuprite (CU2O) from the enrichment blanket. 

Case-1 Porphyry-type Cu assays and mineral abundances were measured at 3 meter intervals through a Cu-Au porphyry. Figure 1 displays the sample depth vs. the total clay content vs. the Cu-Sulfide content (chalcopyrite and secondary Cu-sulfides such as bornite and covellite). Based on the mineral abundances, three distinct zones are recognized leached, supergene and hypogene zones, each... 

The CLEAR process is designed to completely leach the copper values from a copper concentrate consisting of any combination of copper sulphide or copper iron sulphide mineralization. The most abundant copper mineral is chalcopyrite whose composition is... 

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