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Managed aquifer recharge (MAR) is increasingly used as a water management tool to enhance water availability and to improve water quality. Until now, however, the risk of fluoride release during MAR with low ionic strength injectate has not been recognised or examined. In this study we analyse and report the mobilisation of fluoride (up to 58 µM) and filterable reactive phosphorus (FRP) (up to 55 µM) during a field groundwater replenishment experiment in which highly treated, deionised wastewater (average TDS 33 mg/L) was injected into a siliciclastic Cretaceous aquifer. In the field experiment, maximum concentrations, which coincided with a rise in pH, exceeded background groundwater concentrations by an average factor of 3.6 for fluoride and 24 for FRP. The combined results from the field experiment, a detailed mineralogical characterisation and geochemical modelling suggested carbonate-rich fluorapatite (CFA: Ca10(PO4)5(CO3,F)F2) to be the most likely source of fluoride and phosphate release. An anoxic batch experiment with powdered CFA-rich nodules sourced from the target aquifer and aqueous solutions of successively decreasing ionic strength closely replicated the field-observed fluoride and phosphate behaviour. Based on the laboratory experiment and geochemical modelling, we hypothesise that the release of fluoride and phosphate results from the incongruent dissolution of CFA and the simultaneous formation of a depleted layer that has hydrated di-basic calcium phosphate (CaHPO4·nH2O) composition at the CFA-water interface. Disequilibrium caused by calcium removal following breakthrough of the deionised injectate triggered the release of fluoride and phosphate. Given the increasing use of highly treated, deionised water for MAR and the ubiquitous presence of CFA and fluorapatite (Ca10(PO4)6F2) in aquifer settings worldwide, the risk of fluoride and phosphate release needs to be considered in the MAR design process.

Managed aquifer recharge (MAR) is increasingly used as a water management tool to enhance water availability and to improve water quality. Until now, however, the risk of fluoride release during MAR with low ionic strength injectate has not been recognised or examined. In this study we analyse and report the mobilisation of fluoride (up to 58 µM) and filterable reactive phosphorus (FRP) (up to 55 µM) during a field groundwater replenishment experiment in which highly treated, deionised wastewater (average TDS 33 mg/L) was injected into a siliciclastic Cretaceous aquifer. In the field experiment, maximum concentrations, which coincided with a rise in pH, exceeded background groundwater concentrations by an average factor of 3.6 for fluoride and 24 for FRP. The combined results from the field experiment, a detailed mineralogical characterisation and geochemical modelling suggested carbonate-rich fluorapatite (CFA: Ca10(PO4)5(CO3,F)F2) to be the most likely source of fluoride and phosphate release. An anoxic batch experiment with powdered CFA-rich nodules sourced from the target aquifer and aqueous solutions of successively decreasing ionic strength closely replicated the field-observed fluoride and phosphate behaviour. Based on the laboratory experiment and geochemical modelling, we hypothesise that the release of fluoride and phosphate results from the incongruent dissolution of CFA and the simultaneous formation of a depleted layer that has hydrated di-basic calcium phosphate (CaHPO4·nH2O) composition at the CFA-water interface. Disequilibrium caused by calcium removal following breakthrough of the deionised injectate triggered the release of fluoride and phosphate. Given the increasing use of highly treated, deionised water for MAR and the ubiquitous presence of CFA and fluorapatite (Ca10(PO4)6F2) in aquifer settings worldwide, the risk of fluoride and phosphate release needs to be considered in the MAR design process.

This paper investigates the influence of barium sulfate scaling and scaling inhibitors on the electrochemical behaviour of stainless steel. The results of a synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) and electrochemical impedance spectroscopy (EIS) study on stainless steel shows that different scaling inhibitors interact uniquely with the substrate when barium sulfate is precipitated on the electrode surface. The main effect of the substrate in the presence of inhibitor is a tendency to form smaller barium sulfate particles. The SR-GIXRD patterns obtained in the presence of the two inhibitors were different to each other and to the control, with the carboxylate showing greater amounts of barite solids precipitated together with iron(III) and (II) sulfate, while the phosphonate showed low amounts of barite solid were precipitated. The presence of iron sulfates on the electrode surface as detected by SR-GIXRD, in the case of NTA, suggests that scaling inhibitors are not alwaysbenign, and can promote the dissolution of iron species from the substrate.

Global biosecurity threats such as the spread of emerging infectious diseases (i.e., avian influenza, SARS, Hendra, Nipah, etc.) and bioterrorism have generated significant interest in recent years. There is considerable effort directed towards understanding and negating the proliferation of infectious diseases. Biosensors are an attractive tool which have the potential to detect the outbreak of a virus and/or disease. Although there is a host of technologies available, either commercially or in the scientific literature, the development of biosensors for the detection of emerging infectious diseases (EIDs) is still in its infancy. There is no doubt that the glucose biosensor, the gene chip, the protein chip, etc. have all played and are still playing a significant role in monitoring various biomolecules. Can biosensors play an important role for the detection of emerging infectious diseases? What does the future hold and which biosensor technology platform is suitable for the real-time detection of infectious diseases? These and many other questions will be addressed in this review. The purpose of this review is to present an overview of biosensors particularly in relation to EIDs. It provides a synopsis of the various types of biosensor technologies that have been used to detect EIDs, and describes some of the technologies behind them in terms of transduction and bioreceptor principles.

An in situ surface study of the iron chalcogenide glass membrane ion-selective electrode (ISE) in aqueous media has been undertaken using a tandem technique of mixed potential/synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) and atomic force microscopy (AFM). This work has simultaneously monitored the mixed potential and in situ surface diffraction patterns of this crystalline glassy material, showing that the observed gradual shift of the electrode potential in the anodic direction is linked to the preferential dissolution of the GeSe (1 1 1), GeSe (1 0 1) and GeSe (1 4 1) and/or Sb2Se3 (0 1 3), Sb2Se3 (2 2 1) and Sb2Se3 (0 2 0) surfaces. Expectedly, these observations are internally consistent with preferential oxidative attack of the crystalline regions of the membrane comprising GeSe and/or Sb2Se3, as evidenced by AFM imaging of the electrode surface. Clearly, this work corroborates the results of previous ex situ surface studies on the iron chalcogenide glass ISE, whereby it was shown that alkaline saline solutions have a tendency to alter the surface chemistry and concomitant response characteristics of the ISE.

There is considerable interest in the development of electroanalytical sensors (i.e., potentiometric, amperometric, electrochemical biosensors) for the detection of a wide range of analytes. The success of many of these sensors is governed by the condition and stability of the membrane/electrode surface. In fact, the response mechanism is dictated primarily by the surface structure and a considerable amount of work has been undertaken to characterize the interfacial region. Consequently, electrochemical impedance spectroscopy (EIS) has played a pivotal role in the characterization of many types of sensors. EIS has been used to provide information on various fundamental processes (i.e., adsorption/film formation, rate of charge transfer, ion exchange, diffusion, etc.) that occur at the electrode electrolyte interface. Understanding and manipulating these interfacial processes has assisted in the development of membranes/electrodes with new and improved response characteristics. This paper reviews some of the work that has been undertaken using EIS over the past 35 years. More importantly, it evaluates the power of EIS in characterizing a wide range of electrochemical sensor systems.

The corrosion of steel grinding balls is a major recurrent cost for mill operators concerned with the production gold. Subsequently, the use of corrosion inhibitors in production fluids, which is typically at pH >9, is an attractive and economical option. This study reports on the corrosion wear of steel grinding balls under alkaline/oxygen conditions and in presence of cyanide. A fundamental study on the influence of several inorganic-based inhibitors (i.e., nitrite, chromate, silicate, hexametaphosphate) on the corrosion rate of carbon steel was undertaken. Subsequently, the corrosion performances of various inhibitors were evaluated in stirred vessels. Corrosion rates were determined via mass loss and electrochemical methods (i.e., linear polarisation, Tafel). It was observed that inhibitors based upon chromate provide superior protection under the conditions investigated in this study. In lime treated, high chloride waters, chromate gave over 80% protection at levels of 10 100 ppm with no evidence of pitting.

An in situ surface study of the carbon dioxide corrosion of mild steel has been undertaken using the tandem technique of mixed potential/synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD). Long-term monitoring of the mixed potential showed there was an initial shift toward cathodic potentials attributable to preferential suppression of the cathodic half-reaction (viz., the reduction of carbonic acid), probably due to the formation of an adlayer of corrosion product physically blocking the cathodic reaction sites during the uniform corrosion of mild steel. Subsequently, the mixed potential displayed a gradual shift to anodic potentials, symbolizing the preferential suppression of the anodic half-reaction as the primary corrosion products [viz., Fe2(OH)2CO3, Fe2O2(CO3), Fe6(OH)12(CO3), and Fe6(OH)12(CO3).2H2O] acquired a sufficient thickness to physically block the interface against further corrosion. Nevertheless, the corrosion product continues to grow over time, indicating that the corrosion product is discontinuous and porous, allowing the ingression of electrolyte to enable the further corrosion of the mild steel. This research has important ramifications for the field of corrosion research; it should enable researchers to develop improved methods of chemical inhibition by using compounds that can actually bind to the newly postulated corrosion products on mild steel.

This paper presents a fundamental study of the influence of carbon steel microstructure on the corrosion rate. Subsequently , the corrosion performance of various grades of carbon steels were evaluated in stirred autoclaves under elevated carbon dioxide and temperature conditions. Corrosion and penetration rates were determined via mass loss and optical microscopy, respectively. It was found that the corrosion rate of carbon steel line pipe is influenced by microstructure. More specifically, a relationship between localized corrosion susceptibility and the presence of pearlite bands in the steel microstructure was found. However, no correlation was evident between minor elemental concentrations (i.e., Ni, Cr, Mo) and corrosion resistance. It has been proposed that the corrosion stability of the various microstructures may arise from variations in the distribution of carbon bearing phases within the steel. In the banded ferrite/pearlite structure, the carbon-bearing phase (pearlite) is distributed in layers whereas in the other structures the carbon-bearing phases are much more evenly distributed. This study reports on the corrosion resistance of carbon steels in relation to their chemical and physical properties

This paper presents a fundamental study of the influence of various chemical inhibitors on the corrosion rate of mild steel in brine electrolyte under carbon dioxide conditions. The corrosion inhibitors were fitted to a Temkin adsorption isotherm, and various fundamental constants of adsorption ~i.e., adsorption equilibrium constants and molecular interaction constants! have been obtained. The inhibitor adsorption mechanism has been discussed in terms of thermodynamics ~i.e., DH, DG, and DS), and this revealed that some compounds chemisorb onto the steel electrode. In addition, molecular modeling was undertaken using PCSSPARTAN Plus and HyperChem Professional, and the various molecular parameters have been correlated with the thermodynamic adsorption properties of the inhibitors. Three-parameter and four-parameter fits for both negative and positive models are discussed. Multiple linear regression was performed on various combinations of molecular descriptors to describe the enthalpies and entropies of adsorption. Similarly, principal component analysis ~PCA! was employed to corroborate the scientifically based selection of molecular descriptors used in the multivariate regression models.

X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), rotating disc electrode - electrochemical impedance spectroscopy (RDE-EIS) and synchrotron radiation - grazing incidence X-ray diffraction (SR-GIXRD) have been used to study the response mechanism of the mercury(II) chalcogenide ion-selective electrode (ISE) in saline media. XPS and SIMS have shown that the chalcogenide surface is poisoned by silver chloride, or a mixture of silver halides, on continuous exposure to synthetic and real seawater. Significantly, the in-situ SR-GIXRD study demonstrated that electrode fouling in synthetic seawater is linked to the formation of poorly crystalline or amorphous silver chloride, and that the low level of free mercury(II) in a calibration buffer (i.e., 10-14 M) is able to undergo metathesis with silver(I) sulfide in the membrane generating mercury(II) sulfide. Significantly, the results of this detailed surface study have shown that silver chloride fouling of the electrode is ameliorated in real seawater comprising natural organic ligands, and this has been attributed to the peptization of silver chloride by the surfactant-like nature of seawater ligands at pH 8. RDE-EIS aging studies have revealed that the chalcogenide membrane experiences a sluggish charge transfer reaction in seawater, and contrary to a previous report for a static electrode, the seawater matrix does not passivate the RDE. The results of this XPS, SIMS, RDE-EIS and SR-GIXRD study have elucidated the response mechanism of the mercury(II) ISE in saline media.