Development of an iodine generator for reclaimed water purification in manned spacecraft applications

A successful 30-day test is described of a prototype Iodine Generating and Dispensing System (IGDS). The IGDS was sized to iodinate the drinking water nominally consumed by six men, 4.5 to 13.6 kg (10 to 30 lb) water per man-day with a + or - 10 to 20% variation with iodine (I2) levels of 0.5 to 20 parts per million (ppm). The I2 treats reclaimed water to prevent or eliminate microorganism contamination. Treatment is maintained with a residual of I2 within the manned spacecraft water supply. A simplified version of the chlorogen water disinfection concept, developed by life systems for on-site generation of chlorine (Cl2), was used as a basis for IGDS development. Potable water contaminated with abundant E. Coliform Group organisms was treated by electrolytically generated I2 at levels of 5 to 10 ppm. In all instances, the E. coli were eliminated

Mars aqueous chemistry experiment

The Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. Progress for the first year MACE PIDDP is reported in two major areas of effort: (1) fluids handling concepts, definition, and breadboard fabrication and (2) aqueous chemistry ion sensing technology and test facility integration. A fluids handling breadboard was designed, fabricated, and tested at Mars ambient pressure. The breadboard allows fluid manipulation scenarios to be tested under the reduced pressure conditions expected in the Martian atmosphere in order to validate valve operations, orchestrate analysis sequences, investigate sealing integrity, and to demonstrate efficacy of the fluid handling concept. Additional fluid manipulation concepts have also been developed based on updated MESUR spacecraft definition. The Mars Aqueous Chemistry Experiment Ion Selective Electrode (ISE) facility was designed as a test bed to develop a multifunction interface for measurements of chemical ion concentrations in aqueous solution. The interface allows acquisition of real time data concerning the kinetics and heats of salt dissolution, and transient response to calibration and solubility events. An array of ion selective electrodes has been interfaced and preliminary calibration studies performed

An electrochemical model for the leaching kinetics of gold ore in cyanide solutions

This project consisted of a literature and a laboratory study to investigate the applicability of an electrochemical model, to the leaching kinetics of gold ore. The procedure was to get an approximate measurement of the gold surface potential and then, to use only this potential and an area term in a two parameter rate expression. The potential measurements in a pulp, with a gold and gold-silver electrode, were attempted but, the electrodes became passive. The results showed that the rate controlling mechanism was a combination of the rate of both oxygen and cyanide diffusion and it was concluded that the applicability of an electrochemical model to the leaching kinetics of gold ore, could not be ruled out. It was found that the leaching kinetics could be modelled very accurately by using the solution redox potential, however, no theoretical basis could be found to explain this observation

The application of deep eutectic solvent ionic liquids for environmentally-friendly dissolution and recovery of precious metals

publisher: Elsevier articletitle: The application of deep eutectic solvent ionic liquids for environmentally-friendly dissolution and recovery of precious metals journaltitle: Minerals Engineering articlelink: http://dx.doi.org/10.1016/j.mineng.2015.09.026 content_type: article copyright: Copyright © 2015 The Authors. Published by Elsevier Ltd.© 2015 Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

How to preserve lead artifacts for future generations

This paper discusses the advantages and disadvantages of different conservation treatments that have been developed over the years to protect the lead cultural heritage. The chemical and aesthetic points of view are looked at

An investigation into the ferric leaching of chalcopyrite : a sub-process in the bioleaching of chalcopyrite

Bibliography: leaves 70-79.The current focus of research in the UCT Minerals Bioprocessing Research Unit is to develop an understanding of the chalcopyrite bioleaching sub-processes. This thesis forms part of the greater study on bioleaching, investigating the ferric leaching subprocess. The objective of this thesis was two-folds. Firstly, a detailed literature review was undertaken to develop a better understanding of the ferric leaching of chalcopyrite and the cause of passivation during chalcopyrite leaching. Secondly, leach experiments on pyrite were used to establish the applicability and reproducibility of measuring the rate of ferric leaching at a constant redox potential, using the methodology developed by Kametani and Aoki (1985). Following this, chalcopyrite ferric leach experiments were conducted to obtain the redox potential range where chalcopyrite leaching occurs. The rate of chalcopyrite leaching in a sulfate media decreases with time due to the formation of a passivating layer. This has been described by many researchers as parabolic kinetics (Dutrizac, 1982; Beckstead et al., 1976; Munoz et al., 1979 and Dutrizac and Mac Donald, 1974). The nature of the passivating layer is still under considerable debate. Current theories of passivation include either the formation of jarosite, ferric hyroxy sulfate, sulfur or iron deficient polysulfide like covellite (Klauber et al. , 2001 , Parker et al., 1981 , Munoz et al, 1976, Warren et al., 1985 and Parker et al., 1981). Recent research has suggested that different passivating layers are formed during the various stages of chalcopyrite leaching. These include a ferric hydroxy sulfate layer followed by jarosite over extended period of time (Klauber etal., 2001 and Parker et al., 2001 ). Current investigations are underway to establish whether semiconductor properties of the mineral affects the type of passivating layer formed. To date, most of the work has been performed at temperatures higher than those at which chalcopyrite bioleaching occurs and with varying pH and redox potentials. There has been little consideration of the potential difference between the suspended particles surface and the solution. This problem can be overcome by conducting experiments at a constant solution redox potential. Kametani and Aoki (1985) first presented a method of maintaining a constant redox potential by using potassium permanganate as an oxidant to continuously re-oxidise ferrous-iron to ferric-iron. This method was then adopted by our research group to determine the initial rates of chalcopyrite leaching. Preliminary rates of chalcopyrite leaching were presented in the thesis by Furamera (2000). Further work was required to firmly establish the rates of chalcopyrite leaching and the optimal redox potential range within which chalcopyrite leach occurs. This involved optimising the redox potential control system to obtain better redox potential control during the chalcopyrite leach experiment

Fundamentals of Chalcopyrite Dissolution in Alkaline Glycine Solutions

The slow leach rate of copper from chalcopyrite in acid solutions has often been attributed to the formation of a poorly soluble “passive” layer on the surface. For this study, it has been shown that no such passive layer exists in alkaline glycine solutions. Surface analyses have shown these species exist, but are not passivating. The leach rate is instead determined by the electronic structure of chalcopyrite

Polarization and potentiometric studies of cobalt and copper oxidised ores in ammonium chloride medium

This research study was conducted to evaluate the dissolution and electrochemical behaviour of low grade Cu-Co oxide ore (0.4% Cu; 3% Co) in ammonium chloride media (NH4Cl) by means of polarization and potentiometric measurements. Polarization measurements were carried out to evaluate the electrochemical behaviour as well as the leaching and re-passivation behaviour of the ores at pH of 9.5, 9.6, 9.7 and 9.8 in NH4Cl solution. In all the pH tested, the potential changed from negative to electropositive values suggesting formation of passive film on the surface of the ore which lowered the dissolution rates. Stable behaviours as were as high dissolution rate were observed at pH of 9.5. Potentiometric measurements were carried out at constant current and varying potential to study the reactivity of Cu-Co oxide ores in 0.25M, 0.5M and 1M of NH4Cl solution. In this test the dissolution rates increased with increasing concentration and the pH decreased with increasing concentration and time suggesting production of acid as oxidation reaction takes place, the ranges of pH are depicted in the Pourbaix diagrams. Stable behaviours were observed in 1M of solution. All observations made in these measurements are confirmed by AAS, XRF, SEM and XRD analysis

The Development of Sustainable Hydrometallurgical Processes for the Recovery of Precious Metal

The study investigates the utilization of cedar wood bark as bioadsorbent for the adsorption and simultaneous precipitation of gold as flakes. This is with a view to establishing the electrochemical study of the adsorption and evaluate pre-treated cedar wood bark as possible adsorbent for gold in various solutions. The research plan for this project is divided into two parts. Part one focuses on understanding the adsorption of gold using the cedar wood bark as adsorbent. The second part focuses on the electrochemical study of the redox reaction during adsorption process using cyclic voltammetry technique. Synthetic solution of gold is prepared with dissolution of gold (III) chloride in hydrochloric acid, sodium thiosulfate and sodium thiourea lixiviants. Cedar wood bark is pre-treated with dilute and concentrated sulfuric acid under various experimental conditions to obtain three bioadsorbents, dilute-air dried (D-AD), concentrated washed-air dried (CW-AD) and concentrated not washed-oven dried (CNW-OD). The gold solutions are electrochemically tested for redox reaction using cyclic voltammetry (CV) techniques. One-point adsorption test is carried out on the various gold solutions to determine the suitable samples for the research. The outcome of the CV experiment indicates that redox reaction of gold in hydrochloric acid medium is easily measured through the anodic and cathodic peak formation. The one-point adsorption test favors the use of D-AD as adsorbent in acidic gold solution with percentage adsorption of 99.999%. Hence, the research is narrowed down to the use of D-AD adsorbent and acidic gold solution. Solid/liquid ratio and hydrochloric acid concentration tests indicate that 1.5 and 0.5 M, respectively, are the best suitable for the research. For the kinetic study of the adsorption process at temperatures of 298, 303 and 313 K in 96 hours, pseudo-second order model has determination coefficients of 0.988, 0.996 and 0.998, respectively, while the pseudo-first order model has determination coefficients of 0.91, 0.77 and 0.62 at those three different temperatures. Hence, the adsorption process follows the pseudo-second order model. The activation energy from the pseudo-second order rate constant indicates that the process is chemisorption with a value of 59.86 kJ/mol. The adsorption isotherm is found to follow Freundlich isotherm model, which might have favored the formation of gold flakes on the adsorbent. The CV experiment shows the disappearance of anodic peaks as the adsorption of gold progresses, which is an indication of reduction reaction synonymous to adsorption process. X-ray diffractometer (XRD) and Fourier transform infrared (FTIR) instruments were used to determine the presence of gold precipitates and the spectra obtained from the two experiments confirm the presence of gold. In conclusion, the study established cedar wood bark as a potential source of biomass for adsorption of gold (III) ions from acidic chloride solution, and that cyclic voltammetry (CV) technique was successfully used to examine the adsorption process