An electrochemical study of the dissolution of gold in thiosulfate solutions. Part II. Effect of Copper

Thiosulfate has been considered as one of the most promising of the non-toxic alternatives to cyanide for the leaching of gold and much work has been carried out with the aim of understanding and improving the ammoniacal thiosulfate leaching process. In particular the behaviour of gold in thiosulfate solutions containing copper in the absence of ammonia has received little attention. It has been shown in this study involving electrochemical and leaching tests that copper ions catalyze not only the oxidation of thiosulfate but also the dissolution of gold in alkaline thiosulfate solutions. Electrochemical studies have shown that copper has a positive effect on the anodic dissolution of gold with increasing concentrations of copper resulting in higher dissolution rates of gold at a potential of 0.3V. Studies on the dissolution of gold powder in alkaline oxygenated thiosulfate solutions containing low concentrations of copper have shown that the role of copper in enhancing the dissolution rate of gold is possibly associated with the formation of a copper–thiosulfate–oxygen intermediate which is more reactive in terms of cathodic reduction than dissolved oxygen. The electrochemical experiments have been complemented by a leaching study which has shown that milling of gold powder in the presence of copper (added as ions, metal, or oxide) assists with the dissolution of gold in thiosulfate solutions.     

Effect of randomization on the oxidative stability of corn oil

Randomized corn oil TAG oxidized much faster than natural oil, but after purification with alumina, they oxidized at the same rate. We showed that this effect could not be attributed to a difference, in total tocopherols in the randomized and natural oils. Polar material recovered from the alumina treatment was fractionated by TLC, and a pro-oxidant effect was found in the fractions containing MAG and DAG. However, MAG and DAG, although mild pro-oxidant could not account for the pro-oxidant effect generated by randomization. No other compounds could be detected in the MAG fraction by MS. The pro-oxidant effect of randomized oil disappeared when EDTA or citric acid was added in sufficient amounts. The pro-oxidant effect of randomized corn oil was increased by the incorporation of additional copper or iron at a concentration that did not catalyze oxidation of the purified oil. Treatment of corn oil with ascorbic acid, ascorbyl-6-palmitate, ethyl acetoacetate, ethyl diacetoacetate, and acetylacetone did not reproduce the effect of the unknown pro-oxidant. Although the identity of the pro-oxidant is still unknown, we have confirmed that it is produced during randomization; it does not have pro-oxidant activity alone, but it facilitates the catalytic activity of the transition metal ions.     

Retardation of volatile aldehyde formation in the exhaust of frying oil by heating under low oxygen atmospheres

Volatile aldehydes were generated in the exhaust of high-oleic safflower oil during heating at 180°C by spraying water into atmospheres with four levels of oxygen concentrations (2, 4, 10, and 20%). These aldehydes were quantitatively analyzed by HPLC after the conversion to 2,4-dinitrophenyl hydrazones. Ten alkanals (C₂ through C₁₀), eight 2-alkenals (C₃ through C₁₀) and three 2,4-alkadienals (C₇, C₉, and C₁₀) were found. These aldehyde levels were found to be positively correlated with both the heating time and the atmospheric oxygen concentration. The total amounts of aldehydes were the lowest in the oil heated in an atmosphere with 2% O₂, and corresponded to 1/10 of those in the atmosphere with 20% O₂. Acrolein was not found in oils heated in the atmosphere with 2% oxygen. These results suggest that frying in atmospheres with low oxygen levels can effectively decrease the generation of volatile aldehydes in the exhaust.     

Dependence of oil stability index of fatty compounds on their structure and concentration and presence of metals

During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous materials such as metals on oxidative stability.     

Ethanol combustion over strontium- and cerium-doped LaCoO3 catalysts

Ce- or Sr-doped LaCoO₃ bulk perovskites were prepared by citric acid method as well as 10 wt.% of LaCoO₃ was deposited on alumina carrier stabilized with lanthanum. Properties of prepared materials were characterized by determination of surface area, acid-basic properties and XRD, XPS, TPDO₂, H₂-TPR measurements as well as catalytic activity and selectivity for ethanol combustion was tested. It was found that substitution of La in LaCoO₃ with either Sr or Ce has only small effect on its activity in ethanol combustion. Strontium inserted into LaCoO₃ structure increases basic character of the perovskite surface as well as selectivity to acetaldehyde (ACA). Substitution of La with cerium has no effect on the concentration of basic sites and does not affect the selectivity to ACA. Activity of LaCoO₃-based catalysts in ethanol combustion and their selectivity to ACA formation can be explained on the basis of the presence of both -oxygen species and sites with basic character on the material surface.

Acid-basic properties of supported LaCoO₃ are dominated by acidic character of the carrier. Results of XPS and H₂-TPR measurements of LaCoO₃ supported on La–Al₂O₃ suggest that perovskite remains in strong interaction with carrier and probably is partially decomposed. Deposition of perovskite on stabilized carrier significantly increases the rate of ethanol combustion.     

Geographic Variation in Alkaloid Production in <Emphasis Type="Italic">Conium maculatum</Emphasis> Populations Experiencing Differential Herbivory by <Emphasis Type="Italic">Agonopterix alstroemeriana</Emphasis>

Conium maculatum, a Eurasian weed naturalized in North America, contains high concentrations of piperidine alkaloids that act as chemical defenses against herbivores. C. maculatum was largely free from herbivory in the United States, until approximately 30 yr ago, when it was reassociated via accidental introduction with a monophagous European herbivore, the oecophorid caterpillar Agonopterix alstroemeriana. At present, A. alstroemeriana is found in a continuum of reassociation time and intensities with C. maculatum across the continent; in the Pacific Northwest, A. alstroemeriana can cause severe damage, resulting in some cases in complete defoliation. Studies in biological control and invasion biology have yet to determine whether plants reassociated with a significant herbivore from the area of indigeneity increase their chemical defense investment in areas of introduction. In this study, we compared three locations in the United States (New York, Washington, and Illinois) where C. maculatum experiences different levels of herbivory by A. alstroemeriana to determine the association between the intensity of the interaction, as measured by damage, and chemical defense production. Total alkaloid production in C. maculatum was positively correlated with A. alstroemeriana herbivory levels: plants from New York and Washington, with higher herbivory levels, invested two and four times more N to alkaloid synthesis than did plants from Illinois. Individual plants with lower concentrations of alkaloids from a single location in Illinois experienced more damage by A. alstroemeriana, indicative of a preference on the part of the insect for plants with less chemical defense. These results suggest that A. alstroemeriana may act either as a selective agent or inducing agent for C. maculatum and increase its toxicity in its introduced range.     

Adsorption of aroma chemicals on cotton fabric from aqueous systems

The adsorption of aroma chemicals on cotton fabric was studied relative to the surfactant concentration, surfactant type, water solubility, and fiber morphology. The adsorption increased with increasing surfactant concentration to a maximum near the critical micelle concentration, then decreased with further increases in surfactant concentration. The adsorption also was found to be highly dependent on the fiber surface area and pore structure; dramatic differences were observed between untreated and mercerized cotton fabric and are believed to be due to morphological differences. Cationic and anionic surfactants increased the aroma chemical adsorption, which varied with surfactant type, with cetyltrimethylammonium chloride (CTAC)>sodium dodecyl sulfate (SDS)>H₂O. Water solubility also influenced adsorption; in most cases, adsorption increased with water solubility. In addition, adsorption was also influenced by chemical structure and hydrophobic interactions. The adsorption of aroma chemicals on cotton fabric can be attributed to the aqueous solution being physically held in capillaries and pore structures within the fibular structure of cotton fiber and also to molecular interactions among the aroma chemical molecules, surfactants, and cotton substrate.     

Clinical trial results support a preference for using CLA preparations enriched with two isomers rather than four isomers in human studies

CLA mixtures are now commercially available. They differ from each other with respect to their content of CLA isomers and their degree of purification. As a group of natural FA, CLA have been widely assumed to be safe. However, the suspected presence of both impurities and particular isomers might induce undesirable side effects. Despite this potential health risk, only a few CLA preparations have been tested under rigorous conditions for clinical efficacy and safety. Based on the limited results available, it is possible to suggest that preparations enriched in c9,t11 and t10,c12 isomers are preferable for human consumption compared to preparations containing four isomers, in terms both of safety and efficacy.     

Extraction of 2-hydroxyphenol by surfactant coated nanosized magnetic particles

A colloidal suspension of magnetic particles coated with double layer surfactant molecules was prepared, characterized and used for separation of some chemicals. The aqueous magnetic fluid was prepared by chemical precipitation method and characterized by total organic carbon analyzer (TOC), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The TOC and TGA measurements indicate that the prepared magnetic particles are coated with surfactant molecules in double layers. The outer surfactant layer has free polar heads. TEM measurement results show that magnetic particles are nanosized. A mixture of 2-hydroxyphenol (strong polar) and 2-nitrophenol (weak polar) was chosen as the target system. Results show that the magnetic fluid can selectively adsorb 2-hydroxyphenol from the mixture, whereas the adsorption of 2-nitrophenol is insignificant. For 2-hydroxyphenol, the adsorption equilibrium can be described well by Langmuir isotherm, and the adsorption kinetic can be fitted well by a linear driving force mass transfer model.