Acid curing and agglomeration for heap leaching

Heap leaching method is known as cheap method for copper extraction. Presence of clay and acid consumer waste minerals are the most critical issues because they may bring out the process from economic mode. For reduce acid consumption and increasing copper extraction in heap leaching method, about 3 tons sample was taken randomly from different low grade zones. After homogenization and spelling into small parts, bottle roll tests were carried out to achieve maximum copper recovery and acid consumption in a short time at pH= 1, 1.1 and 1.2. Maximum copper recovery were 60.8, 60.2 and 60.1%, respectively. Also acid consumption were 107.30, 99.90 and 93.23 kg/t of ore, respectively. After diagnostic tests, nine columns with dimension 2m height and 15cm diameter were filled by 0.5, 1 and 1.5 inches ore. Columns were irrigated with 7, 9 and 11 g/l as acid solution concentration at flow rates of 7, 11 and 15 l/m2*h for 63 days. Results showed that there are high correlation between copper and iron recoveries. Copper recovery changed from 25.5% to 58.9% while iron recovery changed from 4.7% to 15.2%. Acid consumption were achieved between 18 to 54 kg per ton of ore. Acid solution concentration and irrigation flow rate are the most important parameters on the copper and iron recoveries. By increasing of leaching period Copper extraction will increase, but acid will be waste more. Copper and iron recoveries were increased with increasing the acid solution concentration and irrigation flow rate but Increasing in amount of acid consumption does not increase copper extraction inevitably. Irrigation flow rate of acid solution has significant effect on acid consumption. With decreasing the ore particle size, both of copper recovery and acid consumption were increased.

Atmospheric aerosol particles impact Earth's radiation balance by acting as seeds for cloud droplet formation. Over half of global cloud seed particles are formed by nucleation, a process where gas‐phase compounds react to form stable particles. Reactions of sulfuric acid (SA) with a wide variety of atmospheric compounds have been previously shown to drive nucleation in the lower troposphere. However, global climate models poorly predict particle nucleation rates since current nucleation models do not describe nucleation for systems containing tens to hundreds of precursor compounds. The nucleation potential model (NPM) was recently developed to model SA nucleation of complex mixtures by measuring an effective base concentration using a 1‐nm condensation particle counter. This technique for estimating particle nucleation rates can be deployed at a much higher spatial and temporal resolution than current methods which require detailed knowledge of all nucleation reactions and measurements, typically using a mass spectrometer, of all nucleation precursor gases. This work expands NPM by showing that this model can capture enhancement and suppression of SA nucleation rates within a complex mixture of organic and inorganic acids, ambient air, and across a range of atmospherically relevant relative humidities. In addition, an expression for calculating atmospheric nucleation rates was also derived from the NPM. Ultimately, NPM provides a simple way to measure and model the extent compounds in a complex mixture enhance SA nucleation rates using a condensation particle counter.

As a subnanometer thick platinum (Pt) film can have catalytic properties different from those of the Pt bulk, the research on the preparation and characterization of a Pt monolayer is fundamentally intriguing and may lead to cost-effective fuel cells. We devise an electroless deposition method to fabricate a Pt monolayer and use scanning tunneling microscopy (STM) to characterize its atomic structures. This method involves the use of carbon monoxide (CO) molecules as the reducing agent for PtCl62– complexes, yielding a CO-capped Pt film on an Au(111) substrate. The deposition of the Pt film stops at one atom thick. To expose the Pt film, the CO adlayer is stripped off by pulsing the potential to 0.96 V (vs hydrogen reversible electrode) for 3 s in H2-saturated 0.1 M H2SO4. Atomic resolution STM imaging shows that the Pt adatoms arrange in two hexagonal arrays with different atomic corrugation patterns and a notable difference (5.5%) in the Pt–Pt distance at 0.1 V. The Pt film with a larger interatomic spa...

Orientations of the phenyl group and the intramolecular hydrogen bond play prime roles in the packing patterns of three conformational polymorphs of an unsymmetrical thiourea derivative, 1-(5-methylthiazol-2-yl)-3-phenylthiourea (PTH1). Self-assembly of each polymorph is composed of hydrogen-bonded dimeric motifs held together in head-to-tail arrangement but packed in different manners. Each has an intramolecular N–H···N hydrogen bond between an amide N–H and the nitrogen atom of the 5-methylthiazole unit. The packing pattern of 1-(4-methylthiazol-2-yl)-3-phenylthiourea (PTH2) is composed of dimeric assemblies of PTH2 in head-to-tail fashion. PTH2 is monomorphic as there are intermolecular C–H···S interactions between a C–H bond of the phenyl ring of each molecule and the sulfur atom of the thiocarbonyl group of a neighboring molecule. Such interactions lock the orientation of phenyl group in the solid state. The syn–anti conformation across the thiourea group, originally present in the positional isomers PTH1 and PTH2, is invariably transformed to syn–syn conformation in their salts. The extent of hydration of anions in the salts of PTH1 or PTH2 is dependent on the cation as well as the anion. The chloride salt of PTH1 has a large difference in packing patterns in comparison with the corresponding chloride salt of PTH2; they also differ in the numbers of symmetry-nonequivalent molecules in their respective unit cells. The anhydrous salt of PTH1 with hydrogen bromide having a 1:1 ratio of cation and anion is formed, whereas the bromide salt of PTH2 is a hydrate of composition (HPTH2)2(Br)2·6H2O. This salt has bromide–water clusters in its crystal lattice. Nitric acid reacts with PTH1 under different conditions to form hydrated or anhydrous salts. The hydrated salt (HPTH1)2(NO3)2·H2O has anions bridged by water molecules. The anhydrous nitrate salts of PTH1 and PTH2 are structurally similar in having nitrate···nitrate interactions. The deprotonation of polyacids by PTH1 and PTH2 is selective. The ability to abstract a proton from sulfuric acid to form crystalline salts by PTH1 and PTH2 differs. The sulfate salt (HPTH1)2(SO4) is formed by reaction of sulfuric acid with PTH1, but PTH2 forms the bisulfate salt (HPTH2)HSO4·H2O. PTH1 forms the corresponding dihydrogen phosphate salt upon reaction with orthophosphoric acid; the dihydrogen phosphate anions are held together in the form of cyclic hydrogen-bonded hexameric assemblies in the lattice. Water loss from the assemblies of hydrated salt was determined by thermogravimetry and differential scanning calorimetry and showed that dehydration from anion-assisted assemblies was guided by the cationic host and the type of assembly.

The present study is concerned with the effectiveness of use of local Egyptian serpentine ore for production of magnesium sulfate. An investigation of the ore composition was carried out by means of X-ray diffractometry and chemical analysis. The reaction of sulfuric acid with the ore was studied at different leach parameters under laboratory conditions for the uncalcined and calcined ore. The dissolution rate constants of magnesia were determined by the analysis of the experimental data. The resultant activation energy of reaction between the acid and the studied ore was lower than the values reported previously. This result is discussed in terms of structural changes of serpentine during the calcination of ore which may affect its reactivity towards acids. The high yield of magnesia extraction from the ore emphasizes the possibility of exploitation of the ore in the preparation of sulfate salt with a lower price.

Bacterial leaching utilises bacteria, ubiquitous to sulphide mining environments to oxidise sulphide ores. The sulphide mineral chalcopyrite is the most common copper mineral in the world, comprising the bulk of the known copper reserves. Chalcopyrite is resistant to bacterial leaching and despite research over the last 20-30 years, has not yet been economically bioleached. Attempts have been made to use silver to catalyse the bacterial leaching of chalcopyrite since the early seventies. The majority of reported testwork had been performed on finely ground ore and concentrates in agitated batch reactors. This project used silver to catalyse the bioleaching of chalcopyrite in shake flasks, small columns and large columns. The catalytic effect was extensively studied and experimental parameters were varied to maximise copper recovery. Silver was also used to catalyse the ferric leaching of chalcopyrite at elevated temperatures. It was noted that the leaching performance of chalcopyrite in shake flasks compared to columns was markedly different. The specific differences between shake flasks and columns were qualified and separately tested to determine which parameter(s) affected the bioleaching of chalcopyrite. It was found that the ore to solution ratio, aeration, addition of carbon dioxide, solution distribution and small variations in the leaching temperature did not significantly effect the bioleaching of chalcopyrite ore in columns. The method of silver addition to columns did significantly affect the overall copper extraction. The ore in shake flasks was subjected to abrasion between ore particles and with the base of the flask. A test was designed to mimic the shake flask conditions, without the abrasion. The low abrasion test performed similarly to a column, operated with optimum silver addition. This indicated that the inherent equipment difference between shake flask and column operation largely accounted for the difference in leaching performance. Chalcopyrite ore was biologically leached in large columns. The ore crush size and other conditions were typical of those used in the field. The biological leach achieved 65% copper extraction in 160 days. This level of copper extraction is significantly higher than any previously reported results (typically /10% copper extraction) and represents a significant advance in the bacterial leaching of chalcopyrite ore. Due to the inherent high temperature within underground stopes, it was decided to investigate the possibility of separating the leaching and the bacterial oxidation stages. The concept of separate bacterial and ferric leaching has been previously suggested, however the application to a stope, and heat exchange between the process streams was a novel approach. Large column ferric leaches at 70 oC illustrated the technical feasibility of this process. Copper extraction was rapid and high (70% in 100 days of leaching), even when a reduced level of silver catalysis was used. After leaching in large columns, samples of ore were taken for analysis by optical mineralogy. The analysis gave valuable insights into the nature of reaction passivation on chalcopyrite ore. In particular, it was discovered that the precipitation of goethite was a major limiting factor in the bioleaching and ferric leaching of chalcopyrite in columns. In addition, reduced sulphide species were detected on the surface of residual chalcopyrite, giving an indication of the sequential nature of the chalcopyrite reaction chemistry. The bacterial population was characterised using DNA techniques developed during the project. Qualitative speciation was carried out and compared between the columns, down the columns and over time in a column. Comparison of these populations enabled greater mechanistic understanding of the role of bacteria in the leaching of chalcopyrite. This work was the most comprehensive attempt to date made to delineate the complex microbiological/mineral actions using analysis of population dynamics from a mixed inoculum. It was found that the iron oxidiser Thiobacillus ferrooxidans dominated within the columns and leach solutions. The sulphur oxidiser Sulfobacillus thermosulfidooxidans was also prevalent in the columns, particularly during the period of rapid chalcopyrite oxidation. The high temperature, ferric leaching of chalcopyrite was unexpectedly poor in the first round of large columns. The reason for the low extraction was attributed to an increase in pH down the column, resulting in excessive goethite precipitation. The solution flowrate (velocity) was increased by ten times in subsequent columns. There were no operational problems (e.g. break-up of ore agglomerates). The increase in flowrate resulted in a high yield of copper. The kinetics of extraction were faster than a corresponding bacterial leach, confirming the potential advantage of a high temperature leach. The small column studies highlighted that it was important to get an even distribution of silver down the stope to enable maximum catalytic effect. If the ore were agglomerated, silver would be added with acid at that point. However, it may not always be possible to agglomerate the ore. For example, the process may be used in-situ on a fractured ore body, or on an ore that has a low fines content, and hence does not require agglomeration. Various complexing agents were tested for their ability to distribute silver at the start of the leach and to recover silver at the end of the leach. For instance when silver was complexed with thiourea and then trickled through the ore, an even distribution of silver was achieved. After leaching was completed, a thiourea wash recovered a significant amount of the silver. These two techniques minimised the amount of silver required and thus significantly added to the economic viability of the process. The success of the technical work has led to an evaluation of the process in the field. A flowsheet was developed for the high temperature, in-stope ferric leach of chalcopyrite. An economic analysis was performed that illustrated the process would be viable in certain situations. An engineering study considered issues such as acid consumption, aeration, silver distribution, silver recovery and a heat balance of the stope.

The title compound, C10H28N2O10S2, was synthesized by the reaction of concentrated sulfuric acid with (R,S)-ethambutol. The zwitterionic amino–sulfate system, protonated at both N atoms, lies about a centre of symmetry. The asymmetric unit also contains a solvent water molecule. In the crystal structure, intermolecular O—H...N and N—H...O hydrogen bonds link the molecules into a three-dimensional network.

This study reports supportive evidence, from scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM) of bentonite cakes, of the textural effects caused by reaction of concentrated sulfuric acid on the bentonite component of geosynthetic clay liners (GCLs) and how these effects may influence observed bentonite hydraulic performance. SEM images revealed that changes to the natural micro-textures of bentonite were due to interaction with acidic leachate, the effects being greater with increased concentration. It was observed from high resolution TEM images that most of the effects detrimental to hydraulic performance were related to re-arrangement of smectite quasi-crystals, as expected for textural responses to increased ionic strength. Significant bentonite dissolution was also observed in both SEM and TEM images after reaction at room temperature for as much as 48 h with sulfuric acid. The observed changes in the microtexture of the bentonite component by both SEM and TEM provide a physical explanation to the bulk experimental results as well as a benchmark for the application of GCLs under acidic conditions.

The first four examples of organic‐inorganic hybrid lanthanide‐silver heterometallic frameworks, namely, [AgLn(μ5‐C2O4)(SO4)(H2O)2] [Ln = Eu (1) and Sm (2)] and [AgLn(μ4‐C2O4)0.5(μ6‐C2O4)0.5(SO4)(H2O)] [Ln = Tb (3) and Dy (4)] based on oxalate and sulfate anions were synthesized by hydrothermal reactions of lanthanide oxide, silver nitrate, oxalic acid and sulfuric acid. All structures contain ladder‐like inorganic lanthanide sulfato chains, which are further connected together through silver atoms by oxalate anions with different coordination behavior (μ5‐C2O4: 1 and 2, μ6‐C2O4 mixed μ4‐C2O4: 3 and 4) to generate two types of 3D networks. The luminescent properties of these compounds were also studied.

In this study, an efficient and facile technique for preparing graphene oxide in suspension and powder forms was presented based on a modification on Hummers' method followed by an additional ultrasonic process. The method involved the provision of graphene oxide from graphite by reaction of potassium permanganate and sulfuric acid with stabilizing the medium complex. Furthermore, this study evaluated the functionality of graphene oxide in powder form in comparison with suspension using Fourier transform infrared spectroscopy. In addition, prepared graphene oxide powder was characterized using X-ray diffraction method for investigating the exfoliation of graphite to graphene nanosheets. Moreover, transmission electron microscopy and atomic force microscopy techniques were employed to demonstrate the structure of resulting graphene oxide in suspension form. The presence of graphene oxide nanosheets including an average thickness of about 2-4 nm was proved via microscopy observation of the prepared nanosheets.

The reaction rate of methanol was measured in solutions of sodium chlorate and sulfuric acid at several levels of temperature and concentration, in the presence of mercuric nitrate. The progress of the reaction was monitored by proton NMR signals corresponding to methanol and formic acid. Chlorine dioxide formation was suppressed by adding mercuric nitrate, which was shown earlier to catalyze the disproportionation of the intermediate species, chlorous acid, and sequester chloride ions. The reaction is first order in methanol and chlorate concentration and in the Hammett acidity function. The reaction of formic acid, sodium chlorate and sulfuric acid was also studied using the same technique. Formic acid was stable and did not react with chlorate at a measurable rate, even at concentrations and temperatures of a commercial process. This study relates to commerical processes that produce chlorine dioxide by reducing chlorate ions with methanol.

The reaction of ReCl5 and fuming sulfuric acid (25 % SO3) in a sealed glass tube at 200 °C led to red, needle shaped single crystals of Re2O4Cl4(SO4) (monoclinic, C2/c, a = 1501.8(2) pm, b = 1545.9(2) pm, c = 945.18(8) pm, β = 98.761(9)°, Z = 8). In the crystal structure the [ReO2] moieties are linked by [SO4]2– tetrahedra to chains along the [101] direction. Each sulfate ion connects four rhenium atoms, additional two chloride ions complete the octahedral coordination sphere of each rhenium atom according to $\rm^1_\infty$[ReO2/1Cl2/1(SO4)2/4].

Extension of atmospheric dispersion models to incorporate fast reversible reactions

Establishment of a Fast Chemical Identification System for screening of counterfeit drugs of macrolide antibiotics

The enhancing effects of starch on the jelly strength of kamabokos made from lizard fish producing strong jelly and those of shark affording relatively weak one, have been compared. The jelly strength of non-starch kamaboko made from the latter was shifted by addition of water, but that of the former scarecely affected. When various amounts of starch were added to their ground muscles, the jelly strength of the products from lizard fish containing a small amount of water increased slightly with increasing starch, but in further addition of water rather decreased with increasing starch. It is probable that, although the strength of the products having a large amount of starch and a small amount of water was apparently intensive in strength owing to the hardness of starch paste, when a large amount of water was added, the own strength of fish muscle itself in place of starch paste should be shown. Lizard fish muscle having the higher jelly strength, therefore, seems to be decreased in its proper strength by the interference of starch paste. On the contrary, in the shark kamaboko which jelly strength largely depend upon the stiffness of starch paste, its strength was intensified with increasing addition of starch and decreased with increasing water. These facts seem to be attributable to the different content of soluble proteins in their fishes; lizard fish contains much soluble proteins and shark a less amount of them. Since ground lizard fish muscle may increase in amount of soluble proteins with increasing water, its strength would not be influenced so much by addition of starch and water, while in kamaboko from shark which may decrease in the concentration of soluble proteins in accordance with addition of water, its strength would be decreased and be influenced by starch paste with increasing water.