Kathryn C. Sole

Solvent Extraction Developments in Southern Africa

The largest solvent-extraction plant in the world at the time, the Nchanga Copper Operation, was in Zambia. The first commercial process using solvent extraction for the refining of the platinum-group metals was in South Africa. More recently, the Southern African region has seen the implementation of solvent extraction for other base metals, precious metals, and specialty metals. These include the world firsts of primary production of zinc at Skorpion Zinc in Namibia and the large-scale refining of gold by Harmony Gold in South Africa. Several other flowsheets that use solvent-extraction technology are currently under commissioning, development, or feasibility study for implementation in this part of the world, including those for the recovery of copper, cobalt, nickel, tantalum, and niobium.

Solvent Extraction and Ion Exchange Applications in Africa's Resurging Uranium Industry: A Review

Abstract During the past five years, there has been a global resurgence in the processing of uranium. This is particularly evident on the African continent where exploration for uranium is booming, several plants are being commissioned, and many more projects are in the pipeline, mainly in Malawi, Namibia, Niger, South Africa, and Tanzania. This article reviews recent African uranium developments with a focus on solvent-extraction, ion-exchange, and resin-in-pulp processes. The essential chemistry is outlined, followed by discussions of process choices and selected flowsheets.

Isothermal DSC study of the thermal decomposition of potassium permanganate

Abstract Potassium permanganate decomposes on heating in two stages. The first stage (−290 °C) is exothermic overall and the second (620 °C) is endothermic. The Prout-Tompkins model is often used to describe the kinetics of the first stage. Isothermal DSC studies show that the first stage of the decomposition does not give the symmetrical exotherm expected for the Prout-Tompkins model, but consists of several overlapping exotherms, as well as a final endothermic contribution when product oxygen is removed by an inert carrier gas. The effects of atmosphere, temperature and particle-size on the DSC curves are reported and electron micrographs reveal some details of the decomposition mechanism.

Ion Exchange in Hydrometallurgical Processing: An Overview and Selected Applications

Ion exchange has traditionally been employed for the purification of water and the removal of metal contaminants from dilute waste streams. More recently, its use in removing trace metallic impurities from hydrometallurgical process streams (with typical background metal concentrations of 50–100 g/L) has increased substantially. It is also used as a primary recovery and concentration unit operation for certain commodities, where both technical and cost advantages become apparent for complex flow sheets. This overview discusses selected modern applications of ion exchange in hydrometallurgical processes for uranium, precious metals, copper, cobalt, nickel and zinc, and identifies some opportunities for the future.

Aqueous processing in materials science and engineering

Reviews of aqueous processing in JOM have traditionally focused on hydrometallurgical process routes. This article, however, addresses the application of aqueous processing in materials engineering and presents some promising developments that employ aqueous-based routes for the manufacture of high-tech components and specialty products. Such applications include producing metallic and ceramic powders; etching; surface modification by electroplating and electroless plating; manufacturing jewelry and intricate components by electroforming; and producing advanced ceramics, composites, and nanophase materials by sol-gel and biomimetic processing.

Oxidation kinetics of chromium(III) chloride

The kinetic behaviour of anhydrous chromium(III) chloride pellets in oxygen in the temperature range 350–630 °C has been examined by isothermal and temperature-programmed thermogravimetry and scanning electron microscopy. The reaction starts at ca. 400 °C under non-isothermal conditions and exhibits a deceleratory rate. Cr2O3 is usually the only solid product detected, although CrO2Cl2 or CrOCl may form under extreme experimental conditions. Isothermal thermogravimetric curves are fitted to a number of kinetic expressions, and statistical analyses are used to identify the rate equation that best describes the experimental data. The examination, by scanning electron microscopy, of cross-sections of partially reacted samples supports the conclusion that the reaction is under chemical control, and occurs at a linearly advancing interface between the reactant and product. The reaction kinetics can best be described by a contracting-geometry rate expression.

Flowsheet options for cobalt recovery in African copper–cobalt hydrometallurgy circuits

ABSTRACT The price of cobalt has increased by some 450% in the past two years, mainly due to increasing demand for lithium–ion batteries. With an official 2017 production of 64 kt, the Democratic Republic of Congo produces more than half of the world’s cobalt. African Copperbelt operations have traditionally focused on copper production; however, it has now become imperative to also consider cobalt recovery from these ores. A plethora of processing routes is possible. Most hydrometallurgical flowsheets recover cobalt from the raffinate of the low-grade copper solvent-extraction circuit. Downstream purification processes include sequential precipitation with a variety of reagents, solvent extraction, and ion exchange. Product choices include hydroxide, carbonate, sulfate, and metal cathode. This study assesses technical and economic advantages and limitations of various approaches to the hydrometallurgical processing of cobalt in an African context.