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Revealing the structure and relationship of Ca(II)-Fe(III)-AsO4 minerals: arseniosiderite and yukonite
No full textA sustainable light-chargeable two-electrode energy storage system based on aqueous sodium-ion photo-intercalation
No full textDirect photo-to-chemical energy conversion realized through photocatalysis could provide the ultimate solution to the intermittency problem of solar energy. Among different designs of photocatalytic solar energy storage systems, the two-electrode system offers the simplest configuration for enabling highly integrated solar energy conversion and storage in one electrode and on-demand electrocatalytic discharge in the other. In this study, a novel type of visible light chargeable two-electrode Na-ion energy storage system has been developed, to the best of our knowledge, for the first time. It consists of a WO3-(TiO2)-CdS photo absorbing, energy storing bi-functional electrode, a Pt foil counter electrode, and a sacrificial hole scavenging electrolyte. This device delivered a discharge capacity of 12.3 μA h cm-2 (or 18.1 mA h g-1) after 10 min light charging without exhibiting signs of photo/chemical corrosion on the chalcogenide sensitizer. Further by controlling the working voltage window, structure distortion due to overcharging was avoided, thereby leading to an improvement of cyclability (discharge capacity retention after 5 working cycles) from 36% to 64%, and this was eventually elevated to ∼90% upon optimizing the discharging rate. A stable overall solar-to-electrical energy efficiency of ∼0.3% has been achieved for the system. Moreover, a modified photo-rechargeable two-electrode system was developed by replacing the sacrificial hole scavenger and Pt with polysulfide aqueous electrolyte and Cu2S electrocatalytic electrode, respectively. In this way the issue of non-regenerable hole scavenger consumption and instability of Pt in sulfide electrolyte was resolved, establishing a new design, highly promising towards the development of an all-sustainable photo-rechargeable system
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Production of hematite in acidic zinc sulphate media
No full textIn this work, the kinetic and equilibrium profiles of each individual reaction step involved in the production of hematite at 200°C via oxydrolysis of ferrous sulphate in concentrated zinc sulphate media were established. Crystallization of ferrous sulphate was found to play a crucial role in the overall process due to its relatively low solubility and fast crystallization kinetics at elevated temperatures. In fact, the overall kinetics of the oxydrolysis process were found to be limited by the re-dissolution of ferrous sulphate. Pre-crystallization of ferrous sulphate prior to oxidation was found to result in enhanced overall kinetics, cutting down the required retention time from 3 to 2 hours. Enhanced kinetics were also achieved by performing oxydrolysis in two-temperature stages: a low temperature (T = 180°C) first stage with retention time >20 min and an elevated temperature (T = 200°C) second stage with retention time >100 min.The typical composition of the hematite material produced in this work was 64.3% Fe, 1.3% S (as SO4), 0.6% Zn, and 4.6% H2O. The sulphur content was found to be predominantly (0.6--0.8%) due to formation of sodium jarosite with the remaining (0.3--0.5%) attributed to SO4 chemisorption, and (to less extent) basic ferric sulphate formation. In the absence of zinc sulphate, the majority of sulphate contamination was due to basic ferric sulphate formation. Hematite was found to form via a predominantly homogeneous nucleation mechanism with sub-micron crystallites clustered together as aggregates of 5--10 mum size and around 7 m 2/g specific surface area. In contrast, hematite produced by direct hydrolysis of ferric sulphate possessed one order of magnitude higher specific surface area. As for the industrial hematite product, its composition was found to be 52.6% Fe, 4.6% S, 1.0% Zn, and 8.8% H2O. The sulphur contamination in the industrial product was mainly due to co-precipitation of jarosite and basic ferric sulphate compounds. Hydrothermal trans-formation of the industrial hematite product at elevated temperatures (>200°C) and retention time of >60 min with solids loading as high as 16 wt.% proved to be effective in reducing the sulphur content to less than 1%
Novel activators in cobalt removal from zinc electrolyte by cementation
No full textIn the electrolytic production of zinc, cobalt is removed from zinc electrolyte by cementation with zinc dust Prior to electrowinning. Although the thermodynamics for this reaction are favourable, kinetic barriers to cobalt reduction render the method impractical unless activators such as antimony or arsenic in conjunction with copper are used. There is a large body of work studying the effect of these additives, yet the mechanism by which they act is still poorly understood. Moreover, regardless of the beneficial effect of the activators, from time to time the process fails to meet the target level of 0.1 mg/L cobalt in the purified electrolyte, with negative consequences in the electrowinning operation. Even when the target conditions are met, zinc dust consumption is excessively high: satisfactory operation requires up to 300 times the stoichiometric amount of zinc dust.In the present work the role of the antimony/copper activators was investigated in a batch cementation process using synthetic electrolyte. The objectives were to study the fundamentals of cobalt cementation in zinc sulfate electrolyte with conventional additives, to clarify the action of additives and their role in cementation, and to identify and test novel additives. (Abstract shortened by UMI.
Impurity uptake duting gypsum crystallisation in wastewater treatment
No full textA common wastewater treatment process practised in zinc production plants is the single stage mixing of acidic wastewaters with slaked lime, inducing the reactive precipitation of fine (∼1 mum) gypsum (CaSO 4·2H2O) and other solids with a solids density of less than 10%. These solids report to tailings ponds for containment.The solid-liquid separation step would be more efficient if the size and density of the precipitated solids were increased. Tailings pond life would be increased if the solids density of the precipitated solids was improved. It is the scope of this thesis to report on how high density and clean gypsum may be produced by implementing staging and product recycling. According to this work a staged neutralisation process (each neutralisation reactor operating at different pH) leads to production of large sized gypsum crystals with a high solids density. A continuous lab scale circuit run with synthetic zinc plant effluent produced large (∼100 mum) gypsum crystals with a solids density of 35%.The effect of various metal impurities (such as Zn, Mn, Mg, Fe(II), Cd, Na) in concentrations ranging from 0.1 g/l to 10 g/l on the morphology of gypsum and their uptake by gypsum is investigated with the view of ultimately controlling gypsum contamination. By implementing staging and product recycling gypsum was produced containing less than 0.025% zinc and minor quantities of other elements hence meeting all industrial specifications for synthetic gypsum
High solids density gypsum production through an improved neutralization process for zinc plant effluent
No full textA common wastewater treatment process practiced by zinc production facilities is the single-stage mixing of acidic wastewaters with slaked lime, inducing the reactive precipitation of fine (∼1 mum) gypsum (CaSO4.2H 2O) and other solids with a solids density less than 10%. These solids report to a tailings pond for containment.Tailings pond life would be increased if the solids density of the precipitated solids was improved. Previous work at McGill University suggested that a staged neutralization process with solids recycle and seeded with gypsum would produce large-sized gypsum crystals with a high solids density. A continuous lab-scale process run with synthetic zinc plant effluent produced large (∼100 mum) gypsum crystals with a solids density of 50 +/- 3%.Meissner's method of calculating mean activity coefficients allowed for the calculation of gypsum solubility in mixed, strong sulphate electrolyte solutions
Mathematical modelling of an exothermic pressure leaching process
No full textNote:The object of the present thesis was the development of a mathematical model suitable for computer simulation of hydrometallurgical processes. The model formulation was made for a strongly exothermic three-phase reaction system, namely the pressure oxidation process as applied to the treatment of refractory gold ores and concentrates. The steps followed during the course of this work involved first, the experimental identification of the intrinsic kinetics of the two principal refractory gold minerals, arsenopyrite and pyrite, and second, the development of reactor models describing the isothermal and non-isothermal behaviour of batch and multi-stage continuous reactors at steady state. Emphasis was given to the identification of feed conditions for autothermal operation.The key features of the developed model are the coupling of both mass and heat balance equations, the description of the non-isothermal performance of a multistage continuous reactor, and the treatment of a two-mineral mixture concentrate. In addition, continuous functions are used to describe the size distribution of reacting particles and gas-liquid mass transfer rate limitations are assessed.The model predictions were in good agreement with pilot-plant scale industrial data. Simulation runs of alternative reactor configurations and feed compositions elucidated the impact of the size of the first reactor stage, the rate limiting regime, and the sulphur content of the feed on the attainment of autogenous performance.Le but de cette etude etait de developper un modele mathematique pour la simulation par ordinateur des processus hydrometallurgiques. La formulation du modele a ete faite pour un systeme de reaction de trois phases fortement exothermique, Ie processus d'oxidation sous pression applique au traitement des minerais et des concentres refract aires d'or. Les etapes suivies au cours de cette etude necessitaient premierement l'identification experiment ale de la cinetique intrinseque des deux principaux mineraux d'or, l'arsenopyrite et la pyrite, et par la suite, Ie developpement de modeies de reacteurs decrivant Ie comportement isothermique et non-isothermique de reacteurs en discontinu et de reacteurs en sene continus a Petat d'equilibre. L'emphase a ete donnee al'identification des conditions d'alimentation pouvant produire une operation autothermique.Les principales caracteristiques du modele developpe sont: la combinaison de deux equations d'equilibre de la masse et de la chaleur, la description de la performance non-isothermique de reacteurs en serie continus, Ie traitement d'un con centre d'unmeiange des deux mineraux, l'emploi de fonctions [...
Separation of iron(III) from zinc sulphate-sulphuric acid solutions using organophosphoric acid extractants
No full textIron(III) solvent extraction removal from zinc process solutions by OPAP (octylphenyl acid phosphate) and D2EHPA (di-(2-ethylhexyl)phosphoric acid) was studied within the context of stripping with strong HCl such that a saleable waste-free iron product could be generated downstream. Operated under ambient extraction and HCl stripping conditions, 0.95 F OPAP was found to be a highly suitable extractant for the removal of iron(III) from strong synthetic ZnSO 4-H2SO4 solutions and for the preparation of concentrated iron chloride strip solutions. Its major advantages included: very low sulphate co-extraction; reasonable zinc co-extraction; very low chloride back-extraction; and sufficient iron build-up and acid balance when a 'moderate strength' HCl-FeCl2 strip feed (3.38 N HCl-58.5 g/L Fe(II)-9.7 g/L Fe(III)) was used. Certain advantages were exhibited by 1.25 F D2EHPA over 0.95 F OPAP. These included a greater relative stability in aqueous streams, slightly better Fe3+/Zn2+ selectivity, and a comparable iron(III) loading capacity (∼20 g/L) when operated at 50°C. However, major drawbacks with D2EHPA were identified which included significant sulphate co-extraction (approximately twenty times greater than 0.95 F OPAP) and ineffective stripping and hence poor iron build-up ( < 100 g/L) with the 'moderate strength' strip feed
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