Kenneth N. Han

The Principles and Applications of Ammonia Leaching of Metals—A Review

Abstract An extensive literature survey on the principles and applications of ammonia leaching processes in hydrometallurgy is presented in this paper. The combination of ammonia anal ammonium salts is known to be a powerful lixiviant used in hydrometallurgical processes. Many metals can be extracted using the mixture of ammonia/ammonium. The thermodynamics and kinetics of the dissolution of various metals in ammonia/ammonium salts have been reviewed. The solubility, volatility, and complexation ability of various metals with ammonia have been reviewed and discussed. Eh-pH diagrams of various metal-ammonia-water systems are presented. Also presented is a comprehensive literature survey on the leaching behavior of metals in ammoniacal solutions. The metals considered in this paper are copper, cobalt, nickel, zinc, cadmium, silver, gold and palladium.

Metallurgy and Processing of Marine Manganese Nodules

This paper reviews the state of the art in processing and extraction of ocean floor manganese nodules. It briefly reviews the mining sites where the abundant rich nodules occur and also discusses the metal distribution in nodules in view of economical processing and extraction of these metal values. The paper discloses in a detailed manner the physical and chemical characteristics of nodules, including porosity, surface area, water content and the effect of temperature on crystal structure of major constituents of nodules. In the extraction aspect of nodules, the paper reviews two different extraction schemes revealed in the literature, namely hydrometallurgical treatment and pyrometallurgical treatment. The hydrometallurgical treatments include acid leaching, ammonia leaching, leaching with reducing agents and leaching after high temperature pre-treatments such as in sulfating rousting, while the pyrometallurgical processes include smelting, chlorination-vaporization and segregation. The paper also cover...

Electrochemical behavior of the dissolution of gold-silver alloys in cyanide solutions

AbstractThe dissolution behavior of gold and silver from Au/Ag alloys in aerated cyanide solutions has been investigated using rotating disc electrodes. The variables studied included concentration of cyanide, oxygen partial pressure, and rotating speed of the disc. The dissolution potential and the rate of dissolution were obtained in view of the anodic and cathodic current-potential relationships. The results were discussed in terms of the mixed potential theory. The results showed that the dissolution rate of gold and silver from the alloys was partially controlled by chemical reaction but largely controlled by transport of either oxygen or cyanide, depending on their relative concentrations under the experimental conditions employed in this study. The diffusion coefficient of free cyanide, Dcn−, was found to be (1.25 ± 0.05) X 10−5 cm2/s. The diffusion coefficient of oxygen,

The surface characteristics and flotation behavior of anglesite and cerussite

D_{O_2 }

An electrochemical study on the dissolution of gold and copper from gold/copper alloys

, was calculated to be (1.29 ± 0.02) X 10−5 cm2/s.

Opportunities and challenges for treating rare-earth elements

A leaching investigation of galena with ferric chloride has been carried out as a function of concentration of ferric chloride and sodium chloride, temperature, and particle size. Three size fractions were considered in this investigation, namely, 48 × 65, 35 × 48, and 28 × 35 mesh. The concentration ranges of ferric chloride and sodium chloride used in this investigation were 0 to 0.25 M and 0 to 3 M, respectively. The reaction rate mechanism has been discussed in terms of a shrinking core model developed for cubic systems. Mass transport of ferric chlorocomplex through the product sulfur layer appears to be responsible for establishing the overall leaching rate under most of the conditions used in this investigation. The apparent activation energy for the leaching of 28 × 35 mesh galena with 0.1 M FeCl3, 1 M HC1, and 3.0 M NaCl was found to be about 8.05 kcal/mol (33.7 kJ/mol), which was partially contributed by diffusion and partially by the heat of reaction of the formation of ferric chlorocomplexes. Rate of dissolution at both 50° and 90 °C is greatly affected by ferric chloride concentration up to 0.2 M and is essentially constant with ferric chloride concentration above this value.

The dissolution behavior of metals from Ag/Cu and Ag/Au alloys in acidic and cyanide solutions

Abstract The flotation behavior of anglesite and cerussite has been studied as a function of additions of amyl xanthate, primary amine, sodium carbonate and sodium sulfide as well as pH. Both cerussite and anglesite exhibit points-of-zero-charge at pH 4. Furthermore, since anglesite is metastable, its surface is easily amenable to phase transformation into lead oxide or lead carbonate depending on the presence of carbonate in solution. In general, cerussite exhibits better flotation response than anglesite with xanthate and amine. Flotation recovery of both minerals is affected significantly with additions of sulfide and carbonate.

The effect of concentration and temperature on diffusivity of metal compounds

Abstract The leaching behavior of galena in the presence of Thiobacillus ferrooxidans was investigated. In acidic media, at about pH 2.8, galena was oxidized to form lead sulfate. It was observed that the addition of 0.4% ferrous sulfate increased the initial rate of galena leaching and a higher concentration of iron did not appear to inhibit the rate of reaction. The final amount of galena oxidized, approximaiely 92%, was found to be independent of various leaching conditions applied. The physiological behavior of bacteria during the galena leaching has also been studied by monitoring the enzyme activities of sulfide oxidase in the cell fractions of the sphaeroplast and cytoplasm. It was observed that the sulfide oxidase activity was present in the cytoplasm and there was a periplasmic protein unique to galena oxidation.