Engineering closure of an open pit gold operation in a semi-arid climate

Along with material characteristics and geometry, the climate in which a mine is located can have a dramatic effect on the appropriate options for rehabilitation. The paper outlines the setting, mining, milling and waste disposal at Kidston Gold Mine's open pit operations in the semi-arid climate of North Queensland, Australia, before focusing on the engineering aspects of the rehabilitation of Kidston. The mine took a holistic and proactive approach to rehabilitation, and was prepared to demonstrate a number of innovative approaches, which are described in the paper. Engineering issues that had to be addressed included the geotechnical stability and deformation of waste rock dumps, including a 240 m high in-pit dump: the construction and performance monitoring of a “store and release” cover over potentially acid forming mineralised waste rock; erosion from the side slopes of the waste rock dumps; the in-pit co-disposal of waste rock and thickened tailings; the geotechnical stability of the tailings dam wall; the potential for erosion of bare tailings; the water balance of the tailings dam; direct revegetation of the tailings; and the pit hydrology. The rehabilitation of the mine represents an important benchmark in mine site rehabilitation best practice, from which lessons applicable worldwide can be shared.

Effects of polyunsaturated fatty acids on voltage-gated K+ and Na+ channels in rat olfactory receptor neurons

Although the polyunsaturated fatty acids arachidonic acid (AA) and docosahexaenoic acid (DHA) are enriched in the olfactory mucosa, their possible contribution to olfactory transduction has not been investigated. This study characterized their effects on voltage-gated K+ and Na+ channels of rat olfactory receptor neurons. Physiological (3-10 mum) concentrations of AA and DHA potently and irreversibly inhibited the voltage-gated K+ current in a voltage-independent manner. In addition, both compounds significantly reduced the inhibitory potency of the odorants acetophenone and amyl acetate at these channels. By comparison, the steady-state effects of both AA and DHA on the voltage-gated Na+ channel were relatively weak, with half-maximal inhibition requiring approximate to 35 mum of either compound. However, a surprising finding was that the initial application of 3 mum AA to a naive neuron caused a strong but transient inhibition of the Na+ current. The channels became almost completely resistant to this inhibition within 1 min, and a 2-min wash in control solution was insufficient to restore the strong inhibitory effect. These observations suggest that polyunsaturated fatty acids have the potential to strongly influence the coding of odorant information by olfactory receptor neurons.

ATP-dependent K+ channels in renal ischemia reperfusion injury

ATP-dependent K+ channels (K-ATP) account for most of the recycling of K+ which enters the proximal tubules cell via Na, K-ATPase. In the mitochondrial membrane, opening of these channels preserves mitochondrial viability and matrix volume during ischemia. We examined KATP channel modulation in renal ischemia-reperfusion injury (IRI), using an isolated perfused rat kidney (IPRK) model, in control, IRI, IRI + 200 muM diazoxide (a K-ATP opener), IRI + 10 muM glibenclamide (a K-ATP blocker) and IRI + 200 muM diazoxide + 10 muM glibenclamide groups. IRI was induced by 2 periods of warm ischemia, followed by 45 min of reperfusion. IRI significantly decreased glomerular filtration rate (GFR) and increased fractional excretion of sodium (FENa) (p < 0.01). Neither diazoxide nor glibenclamide had an effect on control kidney function other than an increase in renal vascular resistance produced by glibenclamide. Pretreatment with 200 muM diazoxide reduced the postischemic increase in FENa (p < 0.05). Adding 10 muM glibenclamide inhibited the diazoxide effect on postischemic FENa (p < 0.01). Histology showed that kidneys pretreated with glibenclamide demonstrated an increase in injure in the thick ascending limb of outer medulla (p < 0.05). Glibenclamide significantly decreased post ischemic renal vascular resistance (p < 0.05). but had no significant effect on other renal function parameters. Our results suggest that sodium reabsorption is improved by K-ATP activation and blockade of K-ATP channels during IRI has an injury enhancing effect on renal epithelial function and histology. This may be mediated through K-ATP modulation in cell and or mitochondrial inner membrane.

Tissue engineering for bone regeneration using differentiated alveolar bone cells in collagen scaffolds

Regeneration of osseous defects by a tissue-engineering approach provides a novel means of treatment utilizing cell biology, materials science, and molecular biology. In this study the concept of tissue engineering was tested with collagen type I matrices seeded with cells with osteogenic potential and implanted into sites where osseous damage had occurred. Explant cultures of cells from human alveolar bone and gingiva were established. When seeded into a three-dimensional type I collagen-based scaffold, the bone-derived cells maintained their osteoblastic phenotype as monitored by mRNA and protein levels of the bone-related proteins including bone sialoprotein, osteocalcin, osteopontin, bone morphogenetic proteins 2 and 4, and alkaline phosphatase. These in vitro-developed matrices were implanted into critical-size bone defects in skulls of immunodeficient (SCID) mice. Wound healing was monitored for up to 4 weeks. When measured by microdensitometry the bone density within defects filled with osteoblast-derived matrix was significantly higher compared with defects filled with either collagen scaffold alone or collagen scaffold impregnated with gingival fibroblasts. New bone formation was found at all the sites treated with the osteoblast-derived matrix at 28 days, whereas no obvious new bone formation was identified at the same time point in the control groups. In situ hybridization for the human-specific Alu gene sequence indicated that the newly formed bone tissue resulted from both transplanted human osteoblasts and endogenous mesenchymal stem cells. The results indicate that cells derived from human alveolar bone can be incorporated into bioengineered scaffolds and synthesize a matrix, which on implantation can induce new bone formation.

Sequencing batch reactor technology: the key to a BP refinery (Bulwer Island) upgraded environmental protection system - a low cost lagoon based retro-fit

BP Refinery (Bulwer Island) Ltd (BP) located on the eastern Australian coast is currently undergoing a major expansion as a part of the Queensland Clean Fuels Project. The associated wastewater treatment plant upgrade will provide a better quality of treated effluent than is currently possible with the existing infrastructure, and which will be of a sufficiently high standard to meet not only the requirements of imposed environmental legislation but also BP's environmental objectives. A number of challenges were faced when considering the upgrade, particularly; cost constraints and limited plot space, highly variable wastewater, toxicity issues, and limited available hydraulic head. Sequencing Batch Reactor (SBR) Technology was chosen for the lagoon upgrade based on the following; SBR technology allowed a retro-fit of the existing earthen lagoon without the need for any additional substantial concrete structures, a dual lagoon system allowed partial treatment of wastewaters during construction, SBRs give substantial process flexibility, SBRs have the ability to easily modify process parameters without any physical modifications, and significant cost benefits. This paper presents the background to this application, an outline of laboratory studies carried out on the wastewater and details the full scale design issues and methods for providing a cost effective, efficient treatment system using the existing lagoon system.

Exceptionally high-rate nitrification in sequencing batch reactors treating high ammonia landfill leachate

The nitrogen removal capacity of a suspended culture system treating mature landfill leachate was investigated. Leachate containing high ammonium levels of 300-900 mg N/L was nitrified in a bench scale sequencing batch reactor. Leachate from four different landfills was treated over a two year period for the removal of nitrogen. In this time, a highly specific nitrifying culture was attained that delivered exceptionally high rates of ammonia removal. No sludge was wasted from the system to increase the throughput and up to 13 g/L of MLSS was obtained. Settleability of the purely nitrifying biomass was excellent with SVI less than 40 mL/g, even at the high sludge concentrations. Nitrification rates up to 246 mg NI(L h) (5.91 g N/(L d)) and specific nitrification rates of 36 mg N/(gVSS h) (880 mg N/(gVSS d)) were obtained. The loading to the system at this time allowed complete nitrification of the leachate with a hydraulic retention time of only 5 hours. Following these successful treatability studies, a full-scale plant was designed and built at one of the landfills investigated.

Unsaturated diffusivity functions for concrete derived from NMR images

Deterioration of concrete or reinforcing steel through excessive contaminant concentration is often the result of repeated wetting and drying cycles. At each cycle, the absorption of water carries new contaminants into the unsaturated concrete. Nuclear Magnetic Resonance (NMR) is used with large concrete samples to observe the shape of the wetting profile during a simple one-dimensional wetting process. The absorption of water by dry concrete is modelled by a nonlinear diffusion equation with the unsaturated hydraulic diffusivity being a strongly nonlinear function of the moisture content. Exponential and power functions are used for the hydraulic diffusivity and corresponding solutions of the diffusion equation adequately predict the shape of the experimental wetting profile. The shape parameters, describing the wetting profile, vary little between different blends and are relatively insensitive to subsequent re-wetting experiments allowing universal parameters to be suggested for these concretes.

Selective entrainment of sediment graded by size and density under waves

The influence of near-bed sorting processes on heavy mineral content in suspension is discussed. Sediment concentrations above a rippled bed of mixed quartz and heavy mineral sand were measured under regular nonbreaking waves in the laboratory. Using the traditional gradient diffusion process, settling velocity would be expected to strongly affect sediment distribution. This was not observed during present trials. In fact, the vertical gradients of time-averaged suspension concentrations were found to be similar for the light and heavy minerals, despite their different settling velocities. This behavior implies a convective rather than diffusive distribution mechanism. Between the nonmoving bed and the lowest suspension sampling point, fight and heavy mineral concentration differs by two orders of magnitude. This discrimination against the heavy minerals in the pickup process is due largely to selective entrainment at the ripple face. Bed-form dynamics and the nature of quartz suspension profiles are found to be little affected by the trialed proportion of overall heavy minerals in the bed (3.8-22.1%).

Field hydraulic properties of an Alfisol under various fallow systems in southwestern Nigeria

The effects of various fallow management systems and cropping intensities on water infiltration were measured on an Alfisol at Ibadan in southwestern Nigeria. The objective was to determine the influence of the land use systems (a combination of crop-fallow sequences and intercropping types) on soil hydraulic properties obtained by disc permeameter and double-ring infiltration measurements. The experiment was established in 1989 as a split-plot design with four replications. The main plots were natural fallow, planted Pueraria phaseoloides and planted Leucaena leucocephala. The subplots were 1 year of maize/cassava intercrop followed by 3-year fallow (25% cropping intensity), or 2-year fallow (33% cropping intensity), or 1-year fallow (50% cropping intensity), or no fallow period (100% cropping intensity). Water infiltration rates and sorptivities were measured under saturated and unsaturated flow. Irrespective of land use, infiltration rates at the soil surface (121-324 cm h(-1)) were greater than those measured at 30 cm depth (55-144 cm h(-1)). This indicated that fewer large pores were present below 30 cm depth compared with 0-30 cm, depth. Despite some temporal variation, sorptivities with the highest mean value of 93.5 cm h(-1/2) increased as the cropping intensity decreased, suggesting a more continuous macropore system under less intensive land use systems. This was most likely due to continuous biopores created by perennial vegetation under long fallow systems. Intercropped maize and cassava yields also increased as cropping intensity decreased. The weak relationship between crop yields and hydraulic conductivity/infiltration rates suggests that the rates were not limiting.

Anomalous water absorption in porous materials

The absorption of fluid by unsaturated, rigid porous materials may be characterized by the sorptivity. This is a simple parameter to determine and is increasingly being used as a measure of a material's resistance to exposure to fluids (especially moisture and reactive solutes) in aggressive environments. The complete isothermal absorption process is described by a nonlinear diffusion equation, with the hydraulic diffusivity being a strongly nonlinear function of the degree of saturation of the material. This diffusivity can be estimated from the sorptivity test. In a typical test the cumulative absorption is proportional to the square root of time. However, a number of researchers have observed deviation from this behaviour when the infiltrating fluid is water and there is some potential for chemo-mechanical interaction with the material. In that case the current interpretation of the test and estimation of the hydraulic diffusivity is no longer appropriate. Kuntz and Lavallee (2001) discuss the anomalous behaviour and propose a non-Darcian model as a more appropriate physical description. We present an alternative Darcian explanation and theory that retrieves the earlier advantages of the simple sorptivity test in providing parametric information about the material's hydraulic properties and allowing simple predictive formulae for the wetting profile to be generated.