Organic addittives in zinc electrowinning and electrodeposition of Fe-Mo-P alloys as cathodes for chlorate production

Ce projet de travail est divisé en deux études principales: (a) l’influence des certains additifs organiques sur la consommation d’énergie et la pureté du métal de zinc déposé dans le processus d’extraction électrolytique, et (b) l’électrodéposition des alliages binaires et ternaires de Fe-Mo et Fe-Mo-P sur des substrats d’acier doux afin d’agir comme cathodes pour la production de chlorate. (a) Parmi les sept différents additifs organiques examinés, les sels des liquides ioniques ont réussi à augmenter le rendement du courant jusqu’à 95,1% comparé à 88,7% qui a obtenu à partir de l’électrolyte standard en présence des ions de Sb3+. La réduction maximale de la consommation d’énergie de ~173 kWh tonne-1 a été obtenue en ajoutant de 3 mg dm-3 du chlorure de 1-butyl-3-méthylimidazolium dans le même électrolyte. La teneur en plomb dans le dépôt de zinc est réduite de 26,5 ppm à 5,1-5,6 ppm en utilisant les sels des liquides ioniques. (b) Des différents binaires Fe-Mo et ternaires Fe-Mo-P alliages ont été électrodéposés sur des substrats d’acier doux. Les alliages préparés ont une tenure en Mo entre 21-47 at.% et une tenure en P de 0 à 16 at.%. L’activité électrocatalytique de ces alliages vers la réaction de dégagement d’hydrogène (RDH) a été étudiée dans des solutions de chlorure de sodium. La réduction maximale de la surtension de RDH de ~313 mV a été obtenue par l’alliage ternaire préparé Fe54Mo30P16 par rapport à celle obtenue pour l’acier doux. La rugosité de surface et l’activité intrinsèque des revêtements de Fe-Mo-P peuvent être l’origine du comportement prometteur de ces électrocatalyseurs vers la RDH.

The Electrowinning of Copper from Roasted Sulphides

A hydrometallurgical process for the recovery of copper from flotation concentrates has long been con­sidered an attractive possibility. The object of such a method is to produce electrolytic copper without resorting to expensive matte smelting and converting.

The Electrowinning of Manganese from Rhodochrosite

Manganese is commonly known to be a metal of great strategic importance. It is essential in the production of all steels, first as a scavenger to remove oxygen and sulfur, and second as an alloying element in wear-resis­tant steels.

Continuous electrowinning of plutonium metal : progress report /

"RL-SEP-30"--Cover.

Electroleaching of Zinc leach residues

A room-temperature cathodic electrolytic process was developed in the laboratory to recover zinc from industrial leach residues. The various parameters affecting the electroleaching process were studied using a statistically designed experiment. To understand the mechanisms behind the electrode processes, cyclic voltammetry and galvanostatic studies were carried out. The role of Einh measurements in monitoring such an electroleaching procedure is also shown. Since significant amounts of iron were also present in the leach liquor, attempts were made to purify it before zinc recovery by electrowinning. Reductive dissolution and creation of anion vacancies were found to be responsible for the dissolution of zinc ferrite present in the leach residue. A flow sheet of the process is given.

Studies on the ignition behaviour of boron powder

The ignition behaviour of boron powder, prepared through electrowinning process, was studied by using thermogravimetry coupled with simultaneous differential thermal analysis (TG-SDTA). The dependence of the inception of the ignition reaction on the partial pressure of oxygen, particle size of the boron powder and heating rate was investigated. It was observed that all these factors affect the ignition temperature. Boron powder with a mean particle size of about 10 mu m was found to be susceptible to ignition in oxygen even at 783K. In general, the susceptibility to ignition was found to vary inversely with the degree of crystallinity. Presence of carbon was found to retard the oxidation of boron and raise the ignition temperature. These results are useful in safe handling and storage of finely divided boron powder and in the subsequent production of boron carbide from it. (C) 2009 Elsevier B.V. All rights reserved.

Introduction

As liquid media at a temperature less than 100 °C that possess some level of ionic conductivity, it is immediately of interest to consider the use of ionic liquids (ILs) as electrolytes to carry out electrochemical processes. This has of course the origins of the modern era of interest in ionic liquids via the work of Wilkes and coworkers in the 1990s [1]. Applications in electrowinning and electrodeposition have developed including processes for a range of metals from copper and zinc to lithium and aluminium [2]. Some metals such as titanium remain, however, stubbornly difficult to electrodeposit [3]. A range of applications in electrochemical devices, including batteries, fuel cells, and solar cells have also emerged and are being thoroughly discussed in Volume 2 (Electrochemistry in ionic liquids. Applications). In parallel to this, there has emerged the need to understand more in detail some important fundamental concepts of electrochemistry as well as the interest on fundamental electrochemical process taking place in an ionic liquid medium and in identifying the ways in which the processes differ, or not, from conventional solvent systems as a result of the highly charged medium [4–6]. Thereby, in this book, special emphasis is placed on showing which aspects of electrochemistry in ionic liquids are different from electrochemistry in conventional solutions. Furthermore, new electrochemical concepts and theories are presented. The book commences with a deep and comprehensive discussion on electrode/electrolyte interface reactions, interface structure, and its critical properties for all electrochemical applications. Chapter 2 discusses these fundamental concepts along with some in situ techniques, such as electrochemical impedance and Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical quartz crystal microbalance, suitable for the characterization of electrode/IL interfaces.