scholarly journals Mineral Transformations in Gold–(Silver) Tellurides in the Presence of Fluids: Nature and Experiment

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 167 ◽  
Author(s):  
Jing Zhao ◽  
Allan Pring
Keyword(s):  
Bulk Solution ◽  
Hydrothermal Conditions ◽  
Gold Silver ◽  
Silver Telluride ◽  
Substantial Progress ◽  
Mineralization Processes ◽  
Oxidative Leaching ◽  
Mineral Transformations ◽  
Kinetics Of ◽  
Competing Pathways

Gold–(silver) telluride minerals constitute a major part of the gold endowment at a number of important deposits across the globe. A brief overview of the chemistry and structure of the main gold and silver telluride minerals is presented, focusing on the relationships between calaverite, krennerite, and sylvanite, which have overlapping compositions. These three minerals are replaced by gold–silver alloys when subjected to the actions of hydrothermal fluids under mild hydrothermal conditions (≤220 °C). An overview of the product textures, reaction mechanisms, and kinetics of the oxidative leaching of tellurium from gold–(silver) tellurides is presented. For calaverite and krennerite, the replacement reactions are relatively simple interface-coupled dissolution-reprecipitation reactions. In these reactions, the telluride minerals dissolve at the reaction interface and gold immediately precipitates and grows as gold filaments; the tellurium is oxidized to Te(IV) and is lost to the bulk solution. The replacement of sylvanite is more complex and involves two competing pathways leading to either a gold spongy alloy or a mixture of calaverite, hessite, and petzite. This work highlights the substantial progress that has been made in recent years towards understanding the mineralization processes of natural gold–(silver) telluride minerals and mustard gold under hydrothermal conditions. The results of these studies have potential implications for the industrial treatment of gold-bearing telluride minerals.

scholarly journals Single entity electrochemistry and the electron transfer kinetics of hydrazine oxidation

Nano Research ◽  
2021 ◽  
Author(s):  
Ruiyang Miao ◽  
Lidong Shao ◽  
Richard G. Compton
Keyword(s):  
Electron Transfer ◽  
Bulk Solution ◽  
Relative Contribution ◽  
Rate Determining Step ◽  
Multistep Process ◽  
Ph Range ◽  
Electro Catalytic Oxidation ◽  
Single Particle Impact ◽  
The Impact ◽  
Kinetics Of

AbstractThe mechanism and kinetics of the electro-catalytic oxidation of hydrazine by graphene oxide platelets randomly decorated with palladium nanoparticles are deduced using single particle impact electrochemical measurements in buffered aqueous solutions across the pH range 2–11. Both hydrazine, N2H4, and protonated hydrazine N2H5+ are shown to be electroactive following Butler-Volmer kinetics, of which the relative contribution is strongly pH-dependent. The negligible interconversion between N2H4 and N2H5+ due to the sufficiently short timescale of the impact voltammetry, allows the analysis of the two electron transfer rates from impact signals thus reflecting the composition of the bulk solution at the pH in question. In this way the rate determining step in the oxidation of each specie is deduced to be a one electron step in which no protons are released and so likely corresponds to the initial formation of a very short-lived radical cation either in solution or adsorbed on the platelet. Overall the work establishes a generic method for the elucidation of the rate determining electron transfer in a multistep process free from any complexity imposed by preceding or following chemical reactions which occur on the timescale of conventional voltammetry.

scholarly journals Green approach in gold, silver and selenium nanoparticles using coffee bean extract

2020 ◽  
Vol 5 (1) ◽  
pp. 761-767
Author(s):  
Reiyhaneh Abbasian ◽  
Hoda Jafarizadeh-Malmiri
Keyword(s):  
Spherical Shape ◽  
Coffee Bean ◽  
Hydrothermal Conditions ◽  
Ag Nps ◽  
Au Nps ◽  
Stabilizing Agents ◽  
E Coli ◽  
Green Approach ◽  
Gold Silver ◽  
Ft Ir

AbstractGreen fabrication of metal nanoparticles (NPs), using natural reducing and stabilizing agents existed in plants and their derivatives, due to their unique properties, has gained more attention. The present study focuses on the synthesis of gold (Au), silver (Ag) and selenium (Se) NPs using coffee bean extract under hydrothermal conditions (1.5 atm and 121°C, for 15 min). Coffee bean extract obtained in 2 h processing using Clevenger apparatus and Fourier transform-infrared (FT-IR) spectroscopy indicated five highlighted peaks, namely, hydroxyl, amide, aromatic, alkane and ring groups. Dynamic light scattering analysis revealed that among three different NPs formed, fabricated Ag NPs had small particle size (153 nm) and high zeta potential value (16.8 mV). However, synthesized Au NPs had minimum polydispersity index (0.312). Results also indicated that fabricated Au, Se and Ag NPs had low antioxidant activity with values of 9.1, 8.9 and 8.7%, respectively. Morphological and antibacterial activity assessments, demonstrated that synthesized Ag, Au and Se NPs had spherical shape and high bactericidal activity against E. coli and S. aurous. Obtained results indicated that the synthesized NPs, can be utilized in various areas.

Kinetic model for calcium sulfate α-hemihydrate produced hydrothermally from gypsum formed by flue gas desulfurization

2015 ◽  
Vol 48 (3) ◽  
pp. 827-835 ◽  
Author(s):  
Mingliang Tang ◽  
Xuerun Li ◽  
Yusheng Shen ◽  
Xiaodong Shen
Keyword(s):  
Flue Gas ◽  
Calcium Sulfate ◽  
High Performance ◽  
Transformation Process ◽  
Flue Gas Desulfurization ◽  
Synthesis Process ◽  
Stable Phase ◽  
Hydrothermal Conditions ◽  
Simple Method ◽  
Kinetics Of

Modeling of the kinetics of the synthesis process for calcium sulfate α-hemihydrate from gypsum formed by flue gas desulfurization (FGD) is important to produce high-performance products with minimal costs and production cycles under hydrothermal conditions. In this study, a model was established by horizontally translating the obtained crystal size distribution (CSD) to the CSD of the stable phase during the transformation process. A simple method was used to obtain the nucleation and growth rates. A nonlinear optimization algorithm method was employed to determine the kinetic parameters. The model can be successfully used to analyze the transformation kinetics of FGD gypsum to α-hemihydrate in an isothermal batch crystallizer. The results showed that the transformation temperature and stirring speed exhibit a significant influence on the crystal growth and nucleation rates of α-hemihydrate, thus altering the transformation time and CSD of the final products. The characteristics obtained by the proposed model can potentially be used in the production of α-hemihydrate.

scholarly journals In situ monitoring of hydrothermal reactions by X-ray diffraction with Bragg–Brentano geometry

2020 ◽  
Vol 53 (4) ◽  
pp. 1163-1166
Author(s):  
Karsten Mesecke ◽  
Winfried Malorny ◽  
Laurence N. Warr
Keyword(s):  
Quantitative Information ◽  
In Situ Monitoring ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
X Ray ◽  
Saturated Vapour Pressure ◽  
Concrete Production ◽  
Aerated Concrete ◽  
Kinetics Of

This note describes an autoclave chamber developed and constructed by Anton Paar and its application for in situ experiments under hydrothermal conditions. Reactions of crystalline phases can be studied by successive in situ measurements on a conventional laboratory X-ray diffractometer with Bragg–Brentano geometry at temperatures <483 K and saturated vapour pressure <2 MPa. Variations in the intensity of X-ray diffraction reflections of both reactants and products provide quantitative information for studying the reaction kinetics of both dissolution and crystal growth. Feasibility is demonstrated by studying a cementitious mixture used for autoclaved aerated concrete production. During a period of 5.7 h at 466 K and 1.35 MPa, the crystallization of torbermorite and the partial consumption of quartz were monitored.

scholarly journals Oxidative Leaching Kinetics of Vanadium from the Vanadium-Chromium-Reducing Residue with K2Cr2O7

ACS Omega ◽  
2020 ◽  
Vol 5 (15) ◽  
pp. 8777-8783 ◽  
Author(s):  
Hao Peng ◽  
Qian Shang ◽  
Ronghua Chen ◽  
Yumeng Leng ◽  
Jing Guo ◽  
...  
Keyword(s):  
Leaching Kinetics ◽  
Oxidative Leaching ◽  
Kinetics Of

Chelating agents in high temperature aqueous chemistry. 1. The kinetics of the thermal decomposition of aqueous nitrilotriacetate (NTA), iminodiacetate (IDA), and N-methyliminodiacetate (MIDA)

1977 ◽  
Vol 55 (10) ◽  
pp. 1762-1769 ◽  
Author(s):  
Meindert Booy ◽  
Thomas Wilson Swaddle
Keyword(s):  
Chelating Agents ◽  
Nuclear Reactors ◽  
Rate Coefficients ◽  
Aqueous Mixtures ◽  
Hydrothermal Conditions ◽  
Good Thermal Stability ◽  
First Order ◽  
First Order Kinetics ◽  
Kinetics Of ◽  
Thermal Stability Of

Aqueous H3NTA, H2MIDA, H2IDA, and their anions decompose under hydrothermal conditions (400–580 K) according to first order kinetics by successive decarboxylations, oxidation by O2 being unimportant except at the highest temperatures. In the presence of added H+, the species H4NTA+ and, to a lesser extent, H3MIDA+ (but not H3IDA+), provide significant decomposition pathways through elimination of a —CH2COO— group (deacetylation). For HnNTA(3−n)−, first order rate coefficients kn for decomposition are k0 = 4.5 × 10−7, k1 ∼ 1 × 10−6, k2 ∼ 7 × 10−5, k3 = 2.1 × 10−4, and k4 = 1.0 × 10−2 s1, at 503 K and ionic strength 2.0 m, the spread in rates being due to differences in ΔS* rather than ΔH*. H2MIDA and H2IDA are comparable in reactivity to H3NTA, while their anions are much less reactive than the NTA species of the same charge. The good thermal stability of aqueous NTA commends it as a reagent for boiler servicing and for decontamination of water-cooled nuclear reactors. A potentiometric method for the estimation of mono-, di-, and tribasic aminoacids in aqueous mixtures of these is described.

Reaction Kinetics of Organic Aerosol Studied by Droplet Assisted Ionization: Enhanced Reactivity in Droplets Relative to Bulk Solution

2020 ◽  
Vol 32 (1) ◽  
pp. 46-54
Author(s):  
Yao Zhang ◽  
Michael J. Apsokardu ◽  
Devan E. Kerecman ◽  
Marcel Achtenhagen ◽  
Murray V. Johnston
Keyword(s):  
Reaction Kinetics ◽  
Organic Aerosol ◽  
Bulk Solution ◽  
Kinetics Of
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