1,352 research outputs found
Applications and Preparation Methods of Copper Chromite Catalysts: A Review
No full textIn this review article various applications and preparation methods of copper chromite catalysts have been
discussed. While discussing it is concluded that copper chromite is a versatile catalyst which not only catalyses
numerous processes of commercial importance and national program related to defence and space
research but also finds applications in the most concerned problem worldwide i.e. environmental pollution
control. Several other very useful applications of copper chromite catalysts are in production of clean energy,
drugs and agro chemicals, etc. Various preparation methods about 15 have been discussed which depicts
clear idea about the dependence of catalytic activity and selectivity on way of preparation of catalyst.
In view of the globally increasing interest towards copper chromite catalysis, reexamination on the important
applications of such catalysts and their useful preparation methods is thus the need of the time. This
review paper encloses 369 references including a well-conceivable tabulation of the newer state of the art.
Copyright © 2011 by BCREC UNDIP. All rights reserved.
[How to Cite: R. Prasad, and P. Singh. (2011). Applications and Preparation Methods of Copper Chromite
Catalysts: A Review. Bulletin of Chemical Reaction Engineering & Catalysis, 6 (2): 63-113
The role of collectors in the flotation of partially oxidised copper ores
No full textThe effects of xanthates, dithiophosphates, dithiocarbamates and mixtures of these collectors on the froth flotation performance of partially oxidised and oxidised copper sulphide ores were investigated in this study. More specifically, the role of the functional groups of the collectors, their dosages and the effect of collector mixtures and their dosages were investigated. Batch flotation tests were used to assess the performance in terms of mass-water recovery, sulphur grade-recovery, copper grade-recovery and acid soluble copper grade-recovery relationships and the Klimpel rate constant for copper recovery. Flotation characteristics of bornite rich Carolusberg copper sulphide ore from Okiep Copper Company (1.8% copper) and bornite and chalcopyrite rich ore from Palaborwa Mining Company (0.58% copper) were compared
The thermodynamic chemistry of the aqueous copper-ammonia thiosulfate system
No full textA fundamental thermodynamic study was undertaken in order to establish the speciation of copper(I) and copper(II) during the leaching and recovery of gold from thiosulfate-copper-ammonia solutions. Despite considerable research into this complex leaching system, the lack of important fundamental chemistry has delayed the implementation of the thiosulfate process as an alternative to cyanidation. Over the last two decades, research in this field has focused on the kinetics and electrochemistry of leaching, which involves the use of copper(II) as an oxidant. However, the fundamental thermodynamic data for copper(I) and copper(II) in this system is limited.
Ion association was found to significantly affect the dissociation constant of the ammonium ion in solutions containing sodium sulfate and/or sodium thiosulfate, thus influencing the free ammonia concentration in solution. These findings highlight the importance of using the correct dissociation constant value in thermodynamic studies that involve ammonia in order to obtain precise stability constants.
It has been established that the mixed-ligand complexes Cu(NH3)(S2O3)23- and Cu(NH3)(S2O3)- exist in solution and they are more stable than the other species Cu(S2O3)35-, Cu(NH3)2+ and Cu(NH3)3+ at high concentrations of ammonia and/or thiosulfate. The relative proportions of each two species is dependant on the [NH3]:[S2O32-] ratio in solution. This is reflected in two- and three- dimensional speciation diagrams that have been constructed for typical leaching and recovery processes using the stability constants obtained in this study. The 3-dimensional diagrams reveal subtle speciation trends that are not easily discernable from the 2-dimensional diagrams.
An investigation into the effect of high sulfate and chloride concentrations showed that these anions are not involved in the complexation with copper(I)-ammonia or copper(I)-ammonia-thiosulfate species under the experimental conditions studied. However, these anions and perchlorate formed relatively stable species with the copper(II)-ammine complexes in the absence of thiosulfate. Stability constants were obtained for the species Cu(NH3)4SO40, Cu(NH3)4Cl+ and Cu(NH3)4ClO4+ and it is suggested that these anionic ligands form outer-sphere complexes with the Cu(NH3)42+ ion.
Various methods of predicting stability constants for mixed-ligand complexes from those for the corresponding single ligand systems have been evaluated for this copper(I) system. Although the results have not been quantitatively accurate, the trends suggest that an appropriate method may serve as a useful qualitative tool to predict the possible existence of mixed-ligand complexes.
The combined application of 2- and 3-dimensional speciation and potential diagrams could be used as a hydrometallurgical tool in the design, optimization and control of possible future processes for the extraction of gold using thiosulfate in the presence of copper ions and ammonia. The work presented in this thesis adds to our understanding of the chemistry of copper(I) and copper(II) in this leaching system
A new role for carbonic anhydrase 2 in the response of fish to copper and osmotic stress: Implications for multi-stressor studies
No full textCopyright @ 2014 de Polo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article was made available through open access by the Brunel Open Access Publishing Fund.The majority of ecotoxicological studies are performed under stable and optimal conditions, whereas in reality the complexity of the natural environment faces organisms with multiple stressors of different type and origin, which can activate pathways of response often difficult to interpret. In particular, aquatic organisms living in estuarine zones already impacted by metal contamination can be exposed to more severe salinity variations under a forecasted scenario of global change. In this context, the present study aimed to investigate the effect of copper exposure on the response of fish to osmotic stress by mimicking in laboratory conditions the salinity changes occurring in natural estuaries. We hypothesized that copper-exposed individuals are more sensitive to osmotic stresses, as copper affects their osmoregulatory system by acting on a number of osmotic effector proteins, among which the isoform two of the enzyme carbonic anhydrase (CA2) was identified as a novel factor linking the physiological responses to both copper and osmotic stress. To test this hypothesis, two in vivo studies were performed using the euryhaline fish sheepshead minnow (Cyprinodon variegatus) as test species and applying different rates of salinity transition as a controlled way of dosing osmotic stress. Measured endpoints included plasma ions concentrations and gene expression of CA2 and the α1a-subunit of the enzyme Na+/K+ ATPase. Results showed that plasma ions concentrations changed after the salinity transition, but notably the magnitude of change was greater in the copper-exposed groups, suggesting a sensitizing effect of copper on the responses to osmotic stress. Gene expression results demonstrated that CA2 is affected by copper at the transcriptional level and that this enzyme might play a role in the observed combined effects of copper and osmotic stress on ion homeostasis
Ecotoxicology and ecophysiology of mysids, with special reference to copper toxicity in Praunus flexuosus
No full textToxicity of dissolved copper was examined in a common coastal mysid population {Praunusflexuosus}. The life cycle and ecophysiology were studied under natural conditions throughout the year, and responses to dissolved copper were determined in the laboratory. Pronounced and ontogenic seasonal differences in copper toxicity for the mysid Praunusflexuosus were observed. Sublethal and lethal parameters (mortality, behaviour, metabolism, reproduction, and bioaccumulation) showed seasonal variation in response to copper toxicity, being highest toxicity in summer. Changes in the form of dissolved copper were measured during toxicity testing, using the chelating resin method to provide a measurement of total and labile (Chelex-available) dissolved copper in the natural seawater used in the toxicity tests. Labile dissolved copper did not show significant variations in the test seawater, confirming that organisms were exposed to constant labile copper concentrations during the toxicity test. The total dissolved copper concentration was significantly higher than the labile form, as organic complexation occurred in natural seawater and during toxicity tests. The labile fraction could be less than 50% of the total fraction. The total dissolved copper concentration decreased significantly when the organism was under stress. While the mortality of the population was insignificant after 10 days of copper exposure (0, 5,25, 75 and 200µg 1-1) in winter, lethal effects occurred at every copper exposure level after 24 hours (96h LC50 =30.8 µg 1-1) in summer. The effects of copper on metabolism (respiration and excretion) were very sensitive indicators of sublethal toxicity, which resulted in lethal effects with a prolonged time of exposure. Metabolism shifted to a greater reliance on protein catabolism under copper exposure in both seasons, demonstrating a stronger effect in summer. Total copper content accumulated in the organism increased with increasing copper concentration in solution. Copper accumulation rate was higher in summer. than in winter, increasing to rates of 7.9µg g-1 dry weight day per day. Reproductive processes were severely disrupted at any copper treatment. Production of juveniles was reduced to zero, because of the high abortion rate, reduction on brood survival and damage to fertilisation processes
A multi criteria analysis and comparison of primary copper processing options
No full textIn the present study a methodology and a spreadsheet model were developed with the aim of integrating techno-economic and environmental objectives simultaneously during decision making. The model was developed specifically for the copper industry, mainly due to the wide array of different processing technologies and operational synergies that exist in this industry
Were burnt moulds derived from prehistoric copper production activities?
No full textBurnt mounds and copper arrived on the scene in the British Isles at about the same time, at the beginning of the Neolithic to Bronze Age transition in the mid-3(^rd) millennium BC. Burnt mounds disappeared from that scene when iron was in process of replacing copper as the pre-eminent metal of the British Isles by about 500BC. Are burnt mounds and copper, then, directly related? Specifically, were burnt mound sites locations where some or all of the stages of the earliest forms of copper production took place? The research described in this paper is an initial attempt to find out. The first three chapters review and examine what is known both of burnt mounds in the British Isles and of the earliest copper production, the latter mainly from other pans of the world, since so few early copper processing sites have yet been discovered in the British Isles. Chapter 3 also compares features found at burnt mound sites with the requirements of early copper production, as far as they are known. In Chapters 4 and 5 attempts are made to test, by geochemical and geographic means, whether there is a direct relationship between burnt mounds and copper production. In Chapter 4, EDXRF is used to determine concentrations of copper and other elements in three burnt mounds, and in Chapter 5 known locations both of burnt mounds and copper sources are mapped and compared to find out whether burnt mounds are grouped close to copper sources. Chapter 6 evaluates the overall results and recommends a variety of additional types of research to more closely approach an answer to the title of this paper
Very high cycle fatigue of copper: Evolution, morphology and locations of surface slip markings
No full textThe surfaces of commercially pure polycrystalline copper specimens subjected to interrupted 20 kHz fatigue tests in the very high cycle fatigue regime were investigated. The stress amplitude needed to form the early slip markings was found twice lower than the stress amplitude required to fracture which confirmed the results obtained by Stanzl-Tschegg et al. (2007). Three types of slip markings were classified according to their morphology and their location in the polycrystalline material. They are compared to slip markings observed during fatigue tests at frequencies lower than 100 Hz and numbers of cycles lower than 107. For 20 kHz fatigue tests, stress amplitudes ranging from 45 MPa to 65 MPa produce straight and long early persistent slip markings located along twin boundaries. Stress amplitudes lower than 45 MPa produce clusters of fine early persistent slip markings mainly located at triple junctions
Prehistoric copper production and technological reproduction in the Khao Wong Prachan Valley of central Thailand
No full textEmploying a technological approach derived from the ‘Anthropology of Technology’
theoretical literature, this thesis concerns the identification and explanation of change in
prehistoric extractive metallurgical behaviour in the Khao Wong Prachan Valley of central
Thailand. The ‘Valley’ metallurgical complex, amongst the largest in Eurasia, constitutes
Southeast Asia’s only documented industrial-scale copper-smelting evidence. The two
smelting sites investigated, Non Pa Wai and Nil Kham Haeng, provide an interrupted
but analytically useful sequence of metallurgical consumption and production evidence
spanning c. 1450 BCE to c. 300 CE. The enormous quantity of industrial waste at these
sites suggests they were probably major copper supply nodes within ancient Southeast
Asian metal exchange networks.
Excavated samples of mineral, technical ceramic, and slag from Non Pa Wai and Nil Kham
Haeng were analysed in hand specimen, microstructurally by reflected-light microscopy
and scanning electron microscopy (SEM), and chemically by polarising energy dispersive
x-ray fluorescence spectrometry ([P]ED-XRF) and scanning electron microscopy with
energy dispersive x-ray fluorescence spectrometry (SEM-EDS). Resulting analytical data
were used to generate detailed technological reconstructions of copper smelting behaviour
at the two sites, which were refined by a programme of field experimentation.
Results indicate a long-term improvement in the technical proficiency of Valley
metalworkers, accompanied by an increase in the human effort of copper production. This
shift in local ‘metallurgical ethos’ is interpreted as a response to rising regional demand
for copper in late prehistory
Copper-NHC complexes in catalysis
No full textThe authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.) for funding.Although the chemistry of copper has a long history [1a-d], the relatively recent discovery of N-heterocyclic carbene (NHC) as transition-metal supporting ligands has permitted novel vistas to be explored in copper reactivity and catalysis [1e,f]. Shortly after the seminal discovery of Arduengo, Raubenheimer reported a neutral copper carbene complex [1] and [2]. However, the field remained dormant for almost ten years. In the early 2000s, new breakthroughs were achieved: first, the synthesis of NHC–copper using Cu2O was reported by Danopoulos and followed by the first application in catalysis by Woodward [3] and [4]. The work by Buchwald and Sadighi appeared next, where the first catalysis using a well-defined complex was described [5]. The first reports in this field were based on systems used to mimic their phosphine relatives. NHCs have become ligands of significant interest due to their steric and electronic properties [6], [7] and [8]. Combining the NHC ligand family and copper became, for some, an obvious and productive area [6]. Over the last decade alone, numerous systems have been developed. Copper–NHC complexes can be divided into two major classes: neutral mono-NHC and cationic bis-NHC derivatives: [Cu(X)(NHC)] [9] (X = halide, acetate, hydroxide, hydride, etc.) and [Cu(NHC)(L)][Y] (L = NHC or PR3; Y = PF6, BF4) [10]. The neutral-halide-bearing complexes have been widely used in catalysis, mainly due to their ease of synthesis [9]. In addition to halide-bearing complexes, notable important related compounds have been reported: Nolan and co-workers disclosed the first hydroxide derivative [Cu(OH)(IPr)] (IPr = N,N’-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene) and Sadighi published alkoxides, hydrides and borate species, which permitted novel reactivity to be explored [9g-i]. With respect to cationic derivatives, homoleptic and heteroleptic bis-NHC complexes have been reported and have been efficiently used in catalysis allowing important improvements [10]. In this review, an overview of the two classes and their respective catalytic performance will be presented.Peer reviewe
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