A Case Study of Rock-Fluid Interaction in the Enhanced Geothermal System in Cooper Basin, South Australia

This study was undertaken to observe mineral dissolution with replacing circulating fluid with fresh water every 24 hours. This was an attempt to accelerate the dissolution rate and to mimic the condition of a geothermal site when fresh water or treated water from a precipitation tank is reinjected to the fracture. The experiments were carried out in a titanium flow through cell for 1, 7, and 28 days at 250°C and 40 bars. Water analysis was performed using ICP-MS, and rock analyses were conducted using SEM, XRD and XRF. The experimental results revealed a linear correlation of mineral (element) dissolution at the early stages of the experiment. However at later stages, the mineral dissolution proceeds at a slower rate. This may have been caused by the exhaustion of a more soluble mineral phase in the sample. Therefore, this may cause the pore size in the fracture path size to enlarge. SEM observations showed evidence of etching of the mineral surfaces consistent with partial dissolution. SEM backscattered images reveals that mostly quartz phase (SiO₂) remains after 28 days of circulation. XRD results complement these finding, that quartz was stable throughout the experiment, and that the albite-feldspar (NaAlSi₃O₈) and microcline (KALSi₃O₈) in the rock had partially dissolved. As well, ICP-MS analysis of water samples confirmed that some mineral dissolution occurred. XRF study was used to generate an elemental mass balance. Determination of the dissolution kinetics of the various minerals phase is being undertaken.Gideon Kuncoro, Yung Ngothai, Brian O'Neill, Allan Pring, Joël Bruggerhttp://www.chemeca2010.com/abstract/270.as

Use of in-situ flow-through reactors to study mineral replacement reactions and associated permeability changes in hydrothermal systems

GeoCat; 74874D. Brautigan, B. Etschmann, A. Pring, B. O'Neil and Y. Ngotha

Thermodynamic modeling of poorly complexing metals in concentrated electrolyte solutions: an X-ray absorption and UV-Vis spectroscopic study of Ni(II) in the NiCl(2)-MgCl(2)-H(2)O system

Knowledge of the structure and speciation of aqueous Ni(II)-chloride complexes is important for understanding Ni behavior in hydrometallurgical extraction. The effect of concentration on the first-shell structure of Ni(II) in aqueous NiCl2 and NiCl2-MgCl2 solutions was investigated by Ni K edge X-ray absorption (XAS) and UV-Vis spectroscopy at ambient conditions. Both techniques show that no large structural change (e.g., transition from octahedral to tetrahedral-like configuration) occurs. Both methods confirm that the Ni(II) aqua ion (with six coordinated water molecules at RNi-O = 2.07(2) Å) is the dominant species over the whole NiCl2 concentration range. However, XANES, EXAFS and UV-Vis data show subtle changes at high salinity (> 2 mol∙kg(-1) NiCl2), which are consistent with the formation of small amounts of the NiCl+ complex (up to 0.44(23) Cl at a Ni-Cl distance of 2.35(2) Å in 5.05 mol∙kg(-1) NiCl2) in the pure NiCl2 solutions. At high Cl:Ni ratio in the NiCl2-MgCl2-H2O solutions, small amounts of [NiCl2]0 are also present. We developed a speciation-based mixed-solvent electrolyte (MSE) model to describe activity-composition relationships in NiCl2-MgCl2-H2O solutions, and at the same time predict Ni(II) speciation that is consistent with our XAS and UV-Vis data and with existing literature data up to the solubility limit, resolving a long-standing uncertainty about the role of chloride complexing in this system.Ning Zhang, Joël Brugger, Barbara Etschmann, Yung Ngothai, Dewen Zen

Rheological Sensitivity Analysis of Polystyrene Latex Dispersed in Gelatin Solution

The theoretical results produced by the Hone and Howe Phenomenological Model for the low shear viscosity of polystyrene latex-gelatin dispersions were compared to experimental data. Polystyrene latex particles were used as a model to analyse the rheological behaviour of the photographic (colour coupler) dispersions. The polystyrene latex particles analysed were 70 nm in diameter and were suspended in 10% (by weight) gelatin solution. An adsorbed gelatin layer of 28 nm was determined from previous work and was assumed for this study. As the temperature was increased, the accuracy of the rheological model also increased. A sensitivity analysis was performed (by varying the scaling factor) on the Hone and Howe Model across changing temperatures and latex volume fractions. A linear relationship was observed between the scaling factor and temperature for a constant latex volume fraction. However, a correlation between the scaling factor and the two latex volume fractions (8 and 5%) was not apparent. Further experimentation could be used to identify such a correlation. Rheological results for four latex particle diameters were also analysed (70, 380, 660 and 1094 nm). It was shown that at larger particles sizes (>100 nm) the scaling factor was independent of temperature. Furthermore, for larger latex particles, the hard sphere and Hone and Howe models produce results relatively close to one another. This was expected as such particle sizes can be treated as hard spheres with little compressibility of the gelatin layer. Lastly, the rheology of two colour coupler dispersions (supplied by Kodak Australasia Pty. Ltd.) was also analysed. Clear linear relationships were observed between temperature and scaling factor for these substances.http://www.icms.com.au/chemeca2005/abstract/75.ht

Implementation and analysis of a Chemical Engineering Fundamentals Concept Inventory (CEFCI)

An effective understanding of fundamental concepts in Chemical Engineering can have an enduring affect on the ability of students to achieve success in their degree. Concept inventories are tools implemented to analyse students understanding of the fundamental concepts in their learning programs. A study at a large University in Australia has facilitated the development and implementation of a Chemical Engineering Fundamentals Concept Inventory (CEFCI). This concept inventory provides a quantitative means to predict areas in which course development can be focused. The purpose of this paper is to illustrate the results from the CEFCI implemented at our institution, which follows similar research at the University of Melbourne (Shallcross, 2010). An outline of the development of the CEFCI questions is provided, showing the thorough methodology implemented to ensure a strong foundation for the CEFCI. Results from implementation of the CEFCI, along with the implications and limitations of these results are provided. Unlike previous research, rigorous analysis of the results through implementation of statistical methods has been completed. This provided a novel approach through which to analyse the effectiveness of both the inventory and the teaching of foundational concepts in the School of Chemical Engineering. The results of the implementation and analysis of the inventory displayed areas for constructive development in areas of synthesis and instruction of key concepts. Furthermore we believe a longitudinal study will facilitate improved understanding and implementation of the CEFCI. A similar tool could be utilised for other engineering disciplines, providing broad appeal for this current research. © 2011.Y. Ngothai and M.C. Davi

South Australian Geothermal Research Centre

M. Hand and Y. Ngothaihttp://trove.nla.gov.au/work/3847269

An investigation of the effect of surfactant on the rheology of polystyrene latex-gelatin dispersions

http://www.chemengcongress2005.co.uk/pdf/programme_book.pd

Preparation of monodisperse functionalised superparamagnetic nanoparticies

Copyright © 2007 Inderscience Enterprises Limited. All rights reserved.Monocrystalline iron oxide nanoparticles were synthesised by a one-pot procedure using iron salts in benzyl alcohol and functionalised with dopamine and carboxylmethylated dextran. Dextran macromolecules with low and high carboxyl contents were synthesised and grafted onto the dopamine-functionalised nanoparticles. The particles were characterised using X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), transmission electron microscopy (TEM) and dynamic light scattering (DLS). Monodisperse functionalised nanoparticles were obtained with a hydrodynamic diameter of 20-50 nm. The functionalisation also provided excellent colloidal stability in phosphate buffered saline, even at high salt concentration. Copyright © 2007 Inderscience Enterprises Ltd

Formation and stability of n-dodecane nanoemulsions produced by the PIT method: effects of oil concentration and type of surfactant

In this paper, the effects of sodium chloride on the formation and stability of n-dodecane/surfactant/NaCl/water nanoemulsions are discussed in terms of oil concentration (R) and the type of surfactant. Nanoemulsions, widely used in cosmetics and pharmaceuticals industries, are a dispersion system consisting droplets with sizes ranging from 20 to 200nm. Among the low energy methods, phase inversion temperature (PIT) method was used to prepare nanoemulsions by heating an emulsion system to a temperature close to PIT point followed by a quenching process as it works with the changes in affinity of a non-ionic surfactant with temperatures. Phase inversion process was determined by plotting the conductivity of emulsions versus temperatures. The change of the phase inversion process and the decrease of the PIT temperature, with increasing oil concentration, were more significant in brine system especially at high salt concentration. At low surfactant concentration, the nanoemulsions were monodispersed in either pure water or brine system, when R was 0.2 to 0.4. More sodium chloride was needed to produce stable nanoemulsions when the oil concentration was increased, viz. 0.001M NaCl in R=0.3 and 0.01M NaCl in R=0.4. When the oil concentration was increased, there was partial reversible system in low salt systems but irreversible system in high salt systems. In both pure water and brine system, nanoemulsions formed with mixed surfactant (Span80/Brij30) were polydispersed and had larger droplet size compared to n-dodecane/Brij30 systems. The mixed surfactant system was extremely unstable and there was no reversibility ability.Jeffery Liew, Dzuy Nguyen and Yung Ngotha

Biodiesel production from recycled grease trap waste: a case study in South Australia. Part 2: optimization of the transesterification process

This study aimed to investigate the conversion of the pre‐treated oil, which was originally extracted from grease trap waste (GTW), to biodiesel via a transesterification reaction. The pre‐treated oil, which consists of approximately 80% free fatty acid ethyl esters (FAEEs) and 18% of glycerides, was obtained through the esterification of GTW reported in a previous study. Response Surface Methodology (RSM) based on Central Composite Design (CCD) was applied to determine the optimum conditions for the transesterification reaction through four process variables, these being: the molar ratio of ethanol to oil, reaction time, reaction temperature, and base catalyst loading. A set of 30 experiments were conducted in duplicate to study the interactive effects of the above parameters on the ester yield. A maximum ester yield of 96.7% was obtained at the optimum conditions, which were: 4:1 ethanol to oil molar ratio, 1 hr reaction time, 65 °C reaction temperature, and 1 wt% KOH loading per oil weight. In order to reduce the excess ethanol used, a modification was applied to the experimental design of the transesterification reaction, resulting in a 30% reduction in ethanol used, while the same ester yield could be obtained.Nghiep N. Tran, Edward J. McMurchie and Yung Ngotha