Large particle effects in chemical/biochemical heap leach processes - A review

The application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12-25 mm top size for crushed and agglomerated ores and larger for run-of-mine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.     

Making concrete with saline well-water

Permitted limits of salt concentrations in water used for making mortar and plain concrete differ from one country to another, but in any event geographical conditions prevent this guidance being applied directly to Saudi Arabia. Comparing the effects on compressive strength of saline well-water and drinking quality water, scientists at the Department of Building Research in the Saudi Arabian Standards Organisation show in this article that well-water with total dissolved salts (TDS) concentrations up to 4500 ppm can be suitable for mixing and curing mortars and plain concrete.     

Tea and coffee consumption in relation to vitamin D and calcium levels in Saudi adolescents

ABSTRACT: BACKGROUND: Coffee and tea consumption was hypothesized to interact with variants of vitamin D-receptor polymorphisms, but limited evidence exists. Here we determine for the first time whether increased coffee and tea consumption affects circulating levels of 25-hydroxyvitamin D in a cohort of Saudi adolescents. METHODS: A total of 330 randomly selected Saudi adolescents were included. Anthropometrics were recorded and fasting blood samples were analyzed for routine analysis of fasting glucose, lipid levels, calcium, albumin and phosphorous. Frequency of coffee and tea intake was noted. 25-hydroxyvitamin D levels were measured using enzyme-linked immunosorbent assays. RESULTS: Improved lipid profiles were observed in both boys and girls, as demonstrated by increased levels of HDL-cholesterol, even after controlling for age and BMI, among those consuming 9--12 cups of coffee/week. Vitamin D levels were significantly highest among those consuming 9--12 cups of tea/week in all subjects (p-value 0.009) independent of age, gender, BMI, physical activity and sun exposure. CONCLUSION: This study suggests a link between tea consumption and vitamin D levels in a cohort of Saudi adolescents, independent of age, BMI, gender, physical activity and sun exposure. These findings should be confirmed prospectively.     

Investigations of the Failure in Boilers Economizer Tubes Used in Power Plants

In this study, failure of a high pressure economizer tube of a boiler used in gas-Mazut combined cycle power plants was studied. Failure analysis of the tube was accomplished by taking into account visual inspection, thickness measurement, and hardness testing as well as microstructural observations using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Optical microscopy images indicate that there is no phase transformation during service, and ferrite-pearlite remained. The results of XRD also revealed Iron sulfate (FeSO₄) and Iron hydroxide sulfate (FeOH(SO₄)) phases formed on the steel surface. A considerable amount of Sulfur was also detected on the outer surface of the tube by EDS analysis. Dew-point corrosion was found to be the principal reason for the failure of the examined tube while it has been left out-of-service.     

Non-invasive monitoring of water content and textural changes in clay-rocks using spectral induced polarization: A laboratory investigation

Seven well-characterized clay-rocks have been taken from three test sites to perform spectral induced polarization (SIP) measurements during desiccation of these samples. These test sites include (1) the Tournemire site (IRSN) located in south of France, (2) The Bure test site (ANDRA) located in west of France, and (3) the Super-Sauze earthflow located in south western of France. We dried the samples at ambient temperature followed by heating between 65 °C and 105 °C. The quadrature conductivity, at very low-frequency, was able to discriminate between the loss of free water from the macropores and the loss of water in the micropores associated with textural changes. The calcite and quartz grain size distributions had a significant effect on the low-frequency spectrum. The inversion of our SIP data demonstrated that the generalized Cole–Cole model is an appropriate empirical and practical model for monitoring changes in water content of clay-rocks.     

Adaptive fuzzy semi‐decentralized control for a class of large‐scale nonlinear systems with unknown interconnections

In this paper, a general method is developed to generate a stable adaptive fuzzy semi‐decentralized control for a class of large‐scale interconnected nonlinear systems with unknown nonlinear subsystems and unknown nonlinear interconnections. In the developed control algorithms, fuzzy logic systems, using fuzzy basis functions (FBF), are employed to approximate the unknown subsystems and interconnection functions without imposing any constraints or assumptions about the interconnections. The proposed controller consists of primary and auxiliary parts, where both direct and indirect adaptive approaches for the primary control part are aiming to maintain the closed‐loop stability, whereas the auxiliary control part is designed to attenuate the fuzzy approximation errors. By using Lyapunov stability method, the proposed semi‐decentralized adaptive fuzzy control system is proved to be globally stable, with converging tracking errors to a desired performance. Simulation examples are presented to illustrate the effectiveness of the proposed controller. Copyright © 2006 John Wiley & Sons, Ltd.     

Putting labs online with Web services

This paper describes an online experiment system that is based on Web services designed to support interoperable, machine-to-machine interaction over a network, and can also integrate heterogeneous resources. A service-oriented architecture was devised for online experiment systems, enabled by Web service protocols, and a methodology for wrapping the operations of the instruments into Web services. Although these methods aren't suitable for time-critical missions or applications that need real-time control, they do work for controlling standard commercial instruments over low-speed or unreliable communication networks. Using this framework, an online experiment system for students can be created that incorporates a great variety of instruments and that users can access without installing special software.     

Homo‐oligomerization of maleic anhydride in nonpolar solvents: A kinetic study of deviations from nonlinear behavior

Deviation from nonlinear first order polymerization kinetic models is usually observed for cases where steric effects are dominant. A kinetic model was developed for the homo‐oligomerization of bulky maleic anhydride units. Factors affecting the kinetics of homo‐oligomerization of maleic anhydride have also been studied using two different initiators, azoisobutyronitrile (AIBN) and benzoyl peroxide, at 10 mol % concentrations in two different solvents o‐xylene and toluene. Maleic anhydride polymers having a number average molecular weight by SEC, between 300 and 900, and a polydispersity of between 1.0 and 2.0 were observed, and data were justified by the model. The molecular weight of the polymers increased with the conversion, and steric effects dominated at higher molecular weight as observed from the decrease in magnitude in the corresponding termination rate constants. The model values of conversion were compared with experimental data and cross verification of the model was done using molecular weight calculations. The present model represents the data with an average error of less than 5% over the entire experimental range. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3404–3412, 2006     

Dietary cholestyramine reduces ochratoxin A-induced nephrotoxicity in the rat by decreasing plasma levels and enhancing fecal excretion of the toxin

Ochratoxin A (OTA) is a mycotoxin that may contaminate animal feed (oat, barley, and rye) and food (wheat, rice, coffee, beer, pig meat), leading to major health problems (e.g., nephropathy) in several animal species including humans. Several methods have been tested to reduce the toxicity of OTA in animals but with limited success. In rats, the effect of cholestyramine (CHA), a bile acid-binding resin, was investigated on OTA-induced nephrotoxicity and bioavailability. Animals were fed semisynthetic diets containing two levels of OTA: 1 or 3 ppm. At each level of OTA, the diets were enriched with 0.1, 1, and 5% of CHA. The results showed that CHA decreased the concentration of OTA in plasma. At 1 and 3 ppm of OTA in the diet, CHA is effective at a level of 0.1% and 5%, respectively. The excretion of OTA and its metabolites (ochratoxin alpha and hydroxylated ochratoxin A) in bile and urine was also decreased by addition of 5% CHA in the diet. This was associated with an increase of OTA excretion in feces. Enzymuria and renal morphology revealed that dietary CHA can decrease OTA-induced nephrotoxicity, probably by reducing renal exposure to the toxin. In conclusion, CHA can reduce OTA concentrations in plasma as well as reducing nephrotoxicity, which may be attributed to a decrease of bioavailability and/or enterohepatic circulation of the toxin.     

Release of chylomicrons by isolated cells of rat intestinal mucosa

Fat-laden mucosal cells were isolated by flotation from fed male rats after digesting scrapings of washed jejunum with collagenase in bicarbonate buffer. About 50–60 million cells were obtained per preparation, which were 95–100% viable as assessed by Trypan Blue. The isolated cells were capable of effective incorporation of labeled fatty acids and glucose into triglycerides and phospholipids, and of labeled leucine and glucosamine into the protein envelope of the released chylomicrons. The secretion of the labeled protein paralleled the release of the labeled fat, both of which were linear with the concentration of the albumin in the incubation mixture. About 80% of the total fat of the cell was released as chylomicrons within 30 min when incubated in the presence of albumin-bicarbonate buffer. Injection of puromycin 24 hr prior to harvesting of cells led to a complete inhibition of chylomicron release. Addition of puromycin to the incubation medium gave 50–80% inhibition of release. No inhibition of release of chylomicrons resulted from a treatment with ethionine. The released chylomicrons were separated from the cells by Millipore filtration. Presented in part at the AOCS Meeting, Chicago, September 1970.