60 research outputs found
The dissolution of gold colloids in aqueous thiosulfate solutions
No full textThe kinetics of the dissolution of gold and silver colloids in ammoniacal thiosulfate solutions has been studied using oxygen, copper(II) or oxygenated copper(II) as oxidants at pH 9 - 11 and temperature 22oC to 48oC. The effects of the concentration of the main reagents such as copper(II), ammonia and thiosulfate as well as various background reagents have been investigated. Gold and silver colloids have characteristic absorption peaks at 530 nm and 620 nm respectively. Thus, the extent of gold or silver dissolution in different lixiviant systems was monitored using an ultraviolet-visible spectrophotometer. A comparison of the behaviour of gold colloids and powders has also been made. The beneficial or detrimental effects of silver colloid, and background reagents such as silver nitrate, and sodium salts of nitrate, carbonate, sulfite, sulfate, trithionate, tetrathionate anions have also been investigated.
Experimental results show that the relative rates and the extent of gold colloid dissolution at 25ºC in different lixiviant systems in a given time interval are in the order: oxygen-cyanide > copper(II)-ammonia-thiosulfate ≈ oxygen-copper(II)- ammonia-thiosulfate > oxygen ammonia-thiosulfate ≥ oxygen-ammonia > copper(II) ammonia. The analysis of electrode potentials shows that Au(S2O3)23- is the predominant gold(I) species in the lixiviant solutions containing oxygen or copper(II) as oxidant and thiosulfate or mixed ammonia-thiosulfate as ligands. During the reaction of copper(II) with thiosulfate in ammoniacal solution without oxygen, the measured potential using a platinum electrode represent the redox couple Cu(NH3)n2+/Cu(S2O3)m1-2m (n = 4 or 3, m = 3 or 2) depending on the concentrations of thiosulfate and ammonia.
The initial dissolution rates of gold colloid by oxygen in copper-free solutions show a reaction order of 0.28 with respect to the concentration of dissolved oxygen, but independent of the concentration of ammonia and thiosulfate. The reaction activation energy of 25 kJ/mol in the temperature range 25°C to 48°C indicated a diffusion controlled reaction.
The initial dissolution rates of gold colloid by oxidation with copper(II) in oxygenfree solutions show reaction orders of 0.41, 0.49, 0.60, 0.15 and 0.20 with respect to the concentrations of copper(II), thiosulfate, ammonia, chloride and silver respectively. The presence of silve (I) or chloride ions enhances the rate of gold dissolution, indicating their involvement in the surface reaction, possibly by interfering with or preventing a passivating sulfur rich film on gold surface. An activation energy of 40-50 kJ/mol for the dissolution of gold by oxidation with copper(II) in the temperature range 22°C to 48°C suggests a mixed chemically/diffusion controlled reaction. The dissolution of gold by oxidation with copper(II) in oxygen-free solutions appears to be a result of the reaction between gold, thiosulfate ions and the mixed complex Cu(NH3)p(S2O3)0. The half order reactions support electrochemical mechanisms in some cases.
The initial dissolution rates of gold colloid, massive gold and gold-silver alloys by oxygenated copper(II) solutions also suggest a reaction that is first order with respect to copper(II) concentration. High oxygen concentration in solutions has a negative effect on the initial rate of gold dissolution and overall percentage of gold dissolution, indicating that oxygen affects the copper(II), copper(I) or sulfur species which in turn affects the gold dissolution. The surface reaction produces Au(NH3)(S2O3)- and Cu(NH3)p+. The mixed complexes Au(NH3)(S2O3)- and Cu(NH3)p+ re-equilibrate to the more stable complexes Au(S2O3)23- and Cu(S2O3)35- in solution.
The dissolution of gold powder by oxidation with copper(II) in oxygen-free solutions shows the same trends as that of gold colloid. The presence of silver(I) or chloride ions enhances the initial rate and percentage dissolution of gold colloid and powder. The dissolution kinetics of gold powder and colloid follow a shrinking sphere kinetic model in solutions of relatively low concentrations of thiosulfate and ammonia, with apparent rate constants being inversely proportional to particle radius.
The best system for dissolving gold based on the results of this work is the copper(II)-ammonia-thiosulfate solution in the absence of oxygen or in the presence of oxygen. In the absence of oxygen, copper(II) 1.5-4.5 mM, thiosulfate 20-50 mM, ammonia 120-300 mM and pH 9.3-10 are the best conditions. The presences of carbonate and sulfite have a significant negative effect on the dissolution of gold. The presence of sodium trithionate shows a beneficial effect in the first two hours, while sodium tetrathionate or lead nitrate have a small negative effect and sodium nitrate showed no effect on the dissolution of gold. Silver nitrate and sodium chloride also show beneficial effects. In the presence of oxygen, copper(II) 2.0-3.0 mM, thiosulfate 50 mM, ammonia 240 mM and pH 9.3-9.5 are the best conditions
Catering to Domain (Genomics) specific eResearch needs
No full textProviding eResearch capability and training catered to a specific domain such as
Genomics presents its own set of challenges and opportunities. The advancement of
sequencing technologies and decreasing cost is responsible in creating an avalanche of
genomics data across multiple sub-domains. This data deluge demands an
interdisciplinary approach to face the associated challenges such as data storage,
parallel and high-performance computing solutions for data analysis, scalability, security
and data integration. Ability to deliver solutions to these needs will result in converting
highly granular, unstructured genomics data into real scientific insights which will
accelerate the advances being made in genomics assisted precision medicine,
eukaryotic conservation programmes, etc. Also, implementing eResearch training tools
such as genomics virtual labs will assist beginners’ level bioinformaticians/computationalbiologists to acquire advance skills within an interactive environment which will assist
them in their search to understand the rules of life. ABOUT THE AUTHOR(S)Nooriyah Lohani
- A background in bioinformatics and past roles as a bioinformatician at Pacific Edge in
Dunedin and the Bioinformatics Institute at the University of Auckland has exposed me to
both the commercial and academic research spaces. Currently as NeSI’s Research
Communities Advisor, my aim is to help bring the right digital tools to meet researchers
needs.Dinindu Senanayake
- An Applications Support Specialist at NeSI with a particular interest in Genomics and
Bioinformatics. Joined NeSI following half a decade of research experience gained in the
field of Cancer Genetics, Chemical Genetics and Bioinformatics. </div
HPC for life sciences: handling the challenges posed by a domain that relies on big data
No full textThe advancement of sequencing technologies, proteomics, microscopy (High throughput
high content), etc. and decreasing cost is responsible in creating an avalanche of data across
multiple sub-domains that fall under life sciences. This data deluge demands an
interdisciplinary approach to face the associated challenges such as data storage, parallel
and high-performance computing solutions for data analysis, scalability, security and data
integration. Ability to deliver solutions to these needs will result in converting highly
granular, unstructured data into real scientific insights which will accelerate the advances
being made assisted precision medical treatment based on an individual’s genetic makeup,
developing drugs with minimum side effects, species conservation programmes, etc.New Zealand eScience Infrastructure (NeSI) is focused on delivering these tools that are
required by our researchers who might need a “huge” amount of memory to assemble a
large genome, simulate the Newtonian equations of motion in biochemical molecules like
proteins, nucleic acids in parallel, facilitate the ever increasing requirement of data storage
(from day to day to “Sensitive”) and deploying efficient methods for end-to-end data
transfers. Also, NeSI’s partnership with Genomics Aotearoa had been instrumental in
introducing training tools such as virtual machines and an extensive number of workshops
hosted on these machine which are proving to assist beginners’ level
bioinformaticians/computational biologists to acquire advance skills within a short period to
be used in their search to understand the rules of life.ABOUT THE AUTHOR(S) Dinindu Senanayake is an Applications Support Specialist at NeSI with a particular interest in Bioinformatics
and Computational Biology. Joined NeSI following half a decade of research
experience gained in the field of Cancer Genetics, Chemical Genetics and
Bioinformatics </div
Intrathyroid Abscess Formation with Multiple Necrotizing Cervical Lymphadenitis due to Meticillin Resistant Staphylococcus aureus (MRSA); A Case Report with Literature Review
No full textA review of chloride assisted copper sulfide leaching by oxygenated sulfuric acid and mechanistic considerations
No full textThe beneficial effect of chloride on sulfide leaching in sulfuric acid has been widely reported over the last 3-4 decades but the reasons have not been resolved. A review of recent literature shows that sulfide leaching is complex due to alternative reaction paths, competitive reactions and interim compounds formed on solid surfaces or in solutions. This study focuses on analysis of rate data for covellite leaching by oxygenated sulfuric acid in the presence of sodium chloride and comparison with the leaching data of chalcocite. The published results for initial copper leaching from covellite are analysed on the basis of a shrinking particle kinetic model to determine the apparent rate constants and reaction orders with respect to the concentrations of chloride, dissolved oxygen, and hydrogen ions. The first stage leaching of chalcocite to an intermediate CuS appears to be controlled by the mass transport of oxygen to the sulfide surface. A comparison has been made between the second stage leaching of chalcocite and the initial leaching of pure covellite to produce elemental sulfur by considering the effect of temperature on dissolved oxygen concentration and apparent rate constants. The Arrhenius plots gave comparable values for activation energy for covellite (101 kJ mol- 1) and second stage leaching of chalcocite (96 kJ mol- 1). A linear correlation of stability constants was used to determine equilibrium constants for the formation of CuS2 and Cu(OH)(Cl). The peak potentials of voltammograms of covellite are in reasonable agreement with the predicted potentials based on thermodynamics of a range of solid phases including CuS, CuS2, Cu(OH)Cl, and Cu2Cl(OH)3. These observations are used to propose a reaction mechanism via mixed-ligand complex species
Characterization and leaching kinetics of ilmenite in hydrochloric acid solution for titanium dioxide production
No full textA kinetic study of ilmenite in hydrochloric acid (HCl) leaching in the presence of reducing agent has been investigated. The effect of temperature ranging from 60 °C to 80 °C and HCl concentrations (4-9 M) on titanium and iron dissolution has been reported. The chemical and mineralogical studies of ilmenite samples was also performed using scanning electron microscopy with an energy disperse X-Ray (SEM-EDX), X-ray diffraction (XRD) and X-ray fluorescence techniques (XRF). From XRD analysis, ilmenite was found to be the main mineral phase in the presence of associated minerals such as rutile and hematite. SEM micrograph indicated that ilmenite before leaching has a homogenous and angular shape. After leaching for 3 hours, a few particles have reduced its particle sizes due to structural disruption during chemical attack by HCl, but some still retain their shapes. From chemical analysis of leached product, it is indicated that 85.6% of titanium dioxide with low iron content. The dissolution of ilmenite leaching in HCl is reasonably agreed well with a shrinking core kinetic model. The apparent activation energy for iron and titanium is 71.9 kJ mol-1 and 90.1 kJ mol-1 respectively
Spread of the h-index for each manipulative and non-manipulative author (as absolute values) in the first simulation scenario.
No full text<p>For authors of similar seniority, the ‘manipulative’ author group has a clear advantage.</p
Thermal treatment of spodumene (LiAlSi2O6) for lithium extraction
No full textThis work provides a detailed description of the qualitative and quantitative mineralogical, dynamic, as well as kinetic aspects for the structural transformation of α-spodumene (α-LiAlSi2O6), and advances the industrial processing of spodumene by introducing two novel alternative technologies that are relatively straightforward and potentially cost-effective. Spodumene, the most abundant lithium-containing mineral, usually undergoes calcination at an extreme temperature of about 1100 ºC and strong-acid digestion during industrial processing. The calcination process stimulates the structural transformation of spodumene from its naturally occurring pyroxene-framework α-phase into the relatively more reactive β-spodumene of the keatite (SiO2) structure. On the other hand, the acid digestion approach facilitates the production of water-soluble lithium compounds (mainly lithium sulfate Li2SO4). This study resolves the technical obstacles associated with cheaper (and safer) processing of spodumene concentrates.
The project incorporated intensive experiments to analyse the thermally-activated changes during the calcination of spodumene. The combination of hot-stage and high-temperature synchrotron X-ray diffractometry (XRD) enabled in-situ mineralogical analysis of the transformation processes, identifying (and quantifying) the resulting phases at various temperatures. Each of the diffractometry techniques complements the heating rate and temperature limitations of each other. Likewise, accurate calorimetric and thermogravimetric analyses yielded the corresponding thermodynamic and kinetic functions, allowing the precise determination of the minimum energy required for the heat treatment process. Distinctly, the project also involved detailed investigation on roasting of spodumene with the most effective additives, CaO and Na2SO4, for better extraction of lithium. The addition of these chemicals resulted in the formation of water-soluble lithium compounds via the roasting process at a relatively low temperature (800 – 900 ºC). Set of experiments determined the best condition for minimising these additives and maximising the productivity of lithium. Atomic absorption spectrometry (AAS) quantitated the recovered lithium from the roasted spodumene concentrate. Techniques, such as X-ray fluorescence (XRF) and AAS, attested the chemical analyses of the raw spodumene concentrate. The Match! Software allowed phase identification, while HSC 7.1 software facilitated the estimation of energies.
The results of this thesis have demonstrated that the transition reaction of spodumene occurs via different pathways, depending on the amorphicity and the thermal history of the mineral. The results have also identified the intermediate species and clarified their appearance as a function of temperature and heating rate, and particle size, relative to the final phase of β-spodumene. For instance, the formation of the recently reported γ-spodumene is initiated by crystallisation of minuscule amorphous materials in the concentrated sample at slow heating conditions, while fast initial heating to 800 ºC prompts the emergence of a newly-identified phase of β-quartzss, at low temperatures of less than 900 ºC. Requiring an operating temperature of above 1000 ºC, the calcination of spodumene concentrate has been elucidated to adopt slow kinetics, with a high activation energy of more than 800 kJ mol-1 and significant dependency on the degree of conversion.
The combined outcomes of this study are instrumental in optimising the energy cost of lithium extraction from spodumene mineral in practical operations. In particular, this thesis reveals that, the roasting of spodumene concentrate with a small amount of CaO reduces the transformation temperature by 150 – 200 ºC as determined by in-situ XRD, which translates into important energy saving during the calcination of spodumene in the first step of the commercial acid digestion process. Roasting of spodumene with CaO and Na2SO4 at 882 ºC for 2 h results in producing a water-leachable lithium compound of LiNaSO4 with 94 % lithium recovery. Thus, the roasting of spodumene concentrate with these two additives eliminates the aggressive acidic treatment and decreases the operating temperature of the kiln
Infrastructure facilities for deep-sea and off-shore fishing
No full textThe author presents a brief account of the infrastructure facilities required for the fishing industry. He describes those facilities presently available in Sri Lanka, and those that are under construction, and gives a few suggestions indicating the nature of infrastructure facilities that are vital to the local situation at its present stage of development. The principal facilities discussed are (1) fish landing places; (2) unloading handling facilities; (3) vessel servicing facilities; and (4) navigation aids
Refractory calculation-induced idiopathic generalized epilepsy: A case report and review of the literature
No full textWe report a case with calculation-induced idiopathic generalized epilepsy (IGE) that, unlike most patients with IGE, was refractory to medications. This patient had a family history of (1) a similar condition in a relative of hers who, however, did not have identical manifestations, and (2) a mother who had migraine. Our observations illustrate that the occurrence of IGE in families usually follows rather complex patterns of inheritance and that some of them can be refractory to therapy. © 2005 International League Against Epilepsy.Andermann F., 1987, MIGRAINE EPILEPSY, P3; Berg AT, 2001, EPILEPSIA, V42, P1553, DOI 10.1046-j.1528-1157.2001.21101.x; Berg AT, 2000, EPILEPSIA, V41, P1269, DOI 10.1111-j.1528-1157.2000.tb04604.x; Choueiri RN, 2001, PEDIATR NEUROL, V24, P37, DOI 10.1016-S0887-8994(00)00231-9; Gelisse P, 2001, J NEUROL NEUROSUR PS, V70, P240, DOI 10.1136-jnnp.70.2.240; GOOSSENS LAZ, 1990, NEUROLOGY, V40, P1171; INGVAR DH, 1962, NEUROLOGY, V12, P282; Inoue Y, 1994, EPILEPTIC SEIZURES S, P81; SENANAYAKE N, 2000, HDB CLIN NEUROLOGY, V73, P183; SENANAYAKE N, 1989, EPILEPSY RES, V3, P167, DOI 10.1016-0920-1211(89)90045-4; Senanayake N, 1994, Ceylon Med J, V39, P67; WIEBERS DO, 1979, NEUROLOGY, V29, P1499; WOLF P, 2000, EPILEPTIC SEIZURES P, P609; YAMAMOTO J, 1991, EPILEPSIA, V32, P39, DOI 10.1111-j.1528-1157.1991.tb05608.x; YAMAMOTO S, 1992, JPN J PSYCHIAT NEUR, V46, P44022
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