Examination of multiple sources of selenium release from coal wastes and strategies for remediation.

Selenium (Se) has been mobilised by leaching from coal and associated waste rock exposed by mining activities in Western Canada, with deleterious impact on aquatic wildlife. Waste rock characterisation indicates that up to 7% of the Se, as Se(IV), may be associated with organic matter, with ≈9%, as Se(0), associated with euhedral pyrite. Small 1-2 µm mineral particles with average Se concentration of 1.

Passivation of pyrite for reduced rates of acid and metalliferous drainage using readily available mineralogic and organic carbon resources: A laboratory mine waste study.

Acid and metalliferous drainage (AMD) is a major environmental issue resulting largely from exposure to weathering of mine wastes containing pyrite (FeS). At-source strategies to reduce the rate of formation of AMD have potential to be more cost-effective and sustainable than post-generation downstream treatments. The objective of this study was to examine the efficacy of geochemical and microbial treatments for at-source control through pyrite surface passivation.

Oxidative Dissolution of Sulfide Minerals in Single and Mixed Sulfide Systems under Simulated Acid and Metalliferous Drainage Conditions.

Chalcopyrite, galena, and sphalerite commonly coexist with pyrite in sulfidic waste rocks. The aim of this work was to investigate their impact, potentially by galvanic interaction, on pyrite oxidation and acid generation rates under simulated acid and metalliferous drainage conditions. Kinetic leach column experiments using single-minerals and pyrite with one or two of the other sulfide minerals were carried out at realistic sulfide contents (total sulfide <5.

Unexpected Non-acid Drainage from Sulfidic Rock Waste.

Most rock extraction sites, including mine sites and building construction sites, require a plan to assess, and mitigate if present, the risk of acid mine drainage (AMD). AMD is typically the major environmental concern where sulfide minerals are present in the excavated material and AMD prediction and remediation is based on internationally-accepted acid-base accounting (ABA) tests of representative field samples. This paper demonstrates that standardized ABA tests may not always be provide the correct AMD classification for commonly occurring waste rocks containing low-pyrite and -carbonate due to mineralogic assumptions inherent in their design.

Formation of Aluminum Hydroxide-Doped Surface Passivating Layers on Pyrite for Acid Rock Drainage Control.

The aim of this study was to test the performance of a novel method for acid rock drainage (ARD) control through the formation of Al(OH)-doped passivating surface layers on pyrite. At pH 2.0 and 4.

The Effects of Galvanic Interactions with Pyrite on the Generation of Acid and Metalliferous Drainage.

Although the acid generating properties of pyrite (FeS) have been studied extensively, the impact of galvanic interaction on pyrite oxidation, and the implications for acid and metalliferous drainage, remain largely unexplored. The relative galvanic effects on pyrite dissolution were found to be consistent with relative sulfide mineral surface area ratios with sphalerite (ZnS) having greater negative impact in batch leach tests (sulfide minerals only, controlled pH) and galena (PbS) having greater negative impact in kinetic leach column tests (KLCs, uncontrolled pH, >85 wt% silicate minerals). In contrast the presence of pyrite resulted consistently in greater increase in galena than sphalerite leaching suggesting that increased anodic leaching is dependent on the difference in anodic and cathodic sulfide mineral rest potentials.

The Formation of Silicate-Stabilized Passivating Layers on Pyrite for Reduced Acid Rock Drainage.

Acid and metalliferous release occurring when sulfide (principally pyrite)-containing rock from mining activities and from natural environments is exposed to the elements is acknowledged as a major environmental problem. Acid rock drainage (ARD) management is both challenging and costly for operating and legacy mine sites. Current technological solutions are expensive and focused on treating ARD on release rather than preventing it at source.

Method for distinctive estimation of stored acidity forms in acid mine wastes.

Jarosites and schwertmannite can be formed in the unsaturated oxidation zone of sulfide-containing mine waste rock and tailings together with ferrihydrite and goethite. They are also widely found in process wastes from electrometallurgical smelting and metal bioleaching and within drained coastal lowland soils (acid-sulfate soils). These secondary minerals can temporarily store acidity and metals or remove and immobilize contaminants through adsorption, coprecipitation, or structural incorporation, but release both acidity and toxic metals at pH above about 4.

The role of the Auger parameter in XPS studies of nickel metal, halides and oxides.

The critical role of the Auger parameter in providing insight into both initial state and final state factors affecting measured XPS binding energies is illustrated by analysis of Ni 2p(3/2) and L(3)M(45)M(45) peaks as well as the Auger parameters of nickel alloys, halides, oxide, hydroxide and oxy-hydroxide. Analyses of the metal and alloys are consistent with other works, showing that final state relaxation shifts, ΔR, are determined predominantly by changes in the d electron population and are insensitive to inter-atomic charge transfer. The nickel halide Auger parameters are dominated by initial state effects, Δε, with increasing positive charge on the core nickel ion induced by increasing electronegativity of the ligands.

Effect of surface structure of kaolinite on aggregation, settling rate, and bed density.

The flocculation and solid/liquid separation of four well-characterized kaolinites (2 well, 2 poorly crystallized) have been studied for comparison of surface structure (SEM), aggregate structure during flocculation (cryo-SEM), settling rate, and bed density (with raking). It is shown that major differences in these properties are largely due to crystallinity and consequent surface structure of the extensive (larger dimension "basal") face. Well-crystallized kaolinites, with higher Hinckley indices and lower aspect ratios, have relatively smooth, flat basal surfaces and thicker edge planes promoting both effective initial bridging flocculation (largely edge-edge) and structural rearrangement to face-face during the raking process.

In situ calcite formation in limestone-saturated water leaching of acid rock waste.

The result of leaching of a 75% acid rock/25% limestone column with limestone-saturated solution has shown that the pH of the effluent recovered from 2.5, after apparent loss of acid neutralizing capacity after 4 years with water leaching, to pH 7 in less than 3 years. Bulk assay results, XRD and SEM/EDS analyses of samples from the column at 384 weeks (pH 3.

Sonochemical destruction of chloroform by using low frequency ultrasound in batch and flow cell.

Ultrasound assisted environmental remediation is emerging as a viable technology to remove organic pollutants. In this study, the potential of low frequency ultrasound (20 kHz) to remediate chloroform contaminated waters (demineralised water and groundwater) in batch and flow cell treatment was evaluated. The results show that approx.

Methods for estimation of long-term non-carbonate neutralisation of acid rock drainage.

In the long-term phase of an acid rock drainage (ARD) evolution profile, after any short-term neutralisation capacity provided by carbonate minerals is exhausted, the net acid release is a product of a declining acid generation rate (AGR) and a slower, long-term acid neutralisation rate mainly provided by gangue silicate minerals. At some point, the AGR and the non-carbonate acid neutralisation rate (ANRnc) will be similar. Matching of the AGR and ANRnc near 10mg H(2)SO(4)/kg/week is demonstrated in data from 10-year columns.

Observation of gaseous films at solid-liquid interfaces: removal by ultrasonic action.

The critical role of dissolved gas nano-bubbles at solid surfaces in particle association, aggregation, adsorption and flotation has been recognised in the recent literature. The principles of mineral processing, fine particle separation, and water recovery depend upon changing the surface properties at the solid-liquid interface. It has been assumed that the solid surfaces are either in direct contact with the liquid or may have nano-bubbles attached only at hydrophobic surfaces.

Application of high frequency ultrasound in the destruction of DDT in contaminated sand and water.

High frequency ultrasound, as an alternative to high cost incineration, has been investigated to remediate DDT from sand and soil slurries. In this study, low power high frequency ultrasound (1.6 MHz; 150 W/L), with operating costs much lower than low frequency ultrasound, has been used to remediate DDT in liquid solution and in sand slurries.

Kaolinite flocculation structure.

Effective flocculation and dewatering of mineral processing streams containing colloidal clays has become increasingly urgent. Release of water from slurries in tailings streams and dam beds for recycle water consumption, is usually slow and incomplete. To achieve fast settling and minimization of retained water, individual particles need to be bound, in the initial stages of thickening, into large, high-density aggregates, which may sediment more rapidly with lower intra-aggregate water content.

Plasma enhanced chemical vapour deposition of silica onto Ti: Analysis of surface chemistry, morphology and functional hydroxyl groups.

Previously, we have developed and characterised a procedure for the deposition of thin silica films by a plasma enhanced chemical vapour deposition (PECVD) procedure using tetraethoxysilane (TEOS) as the main precursor. We have used the silica coatings for improving the corrosion resistance of metals and for enhancing the bioactivity of biomedical metallic implants. Recently, we have been fine-tuning the PECVD method for producing high quality and reproducible PECVD-silica (PECVD-Si) coatings on metals, primarily for biomaterial applications.

A simplified method for estimation of jarosite and acid-forming sulfates in acid mine wastes.

In acid base accounting (ABA) estimates of acid mine wastes, the acid potential (AP) estimate can be improved by using the net carbonate value (NCV) reactive sulfide S method rather than total S assay methods but this does not give recovery of potentially acid producing ferrous and ferric sulfates present in many wastes. For more accurate estimation of AP, an effective, site-specific method to quantify acid sulfate salts, such as jarosite and melanterite, in waste rocks has been developed and tested on synthetic and real wastes. The SPOCAS (acid sulfate soils) methods have been modified to an effective, rapid method to speciate sulfate forms in different synthetic waste samples.

Adsorption of bisphosphonate onto hydroxyapatite using a novel co-precipitation technique for bone growth enhancement.

Premature bone resorption and remodeling by osteoclasts can limit the longevity of implant fixation and recovery time. Orally administered bisphosphonates (BPs) have been used to inhibit osteoclast action at the implant/bone interface. Ideally, these should be delivered at the interface with the osteoblast-active hydroxyapatite (HA) for maximum effect.

Kinetics of adsorption of high molecular weight anionic polyacrylamide onto kaolinite: the flocculation process.

The adsorption kinetics of anionic polyacrylamide flocculant onto kaolinite clay are examined as a function of flocculant dosage and pH. Special attention has been given to the flocculation effect during the adsorption process and the resulting inhibition of further adsorption. At pH 8.

Thin calcium phosphate coatings on titanium by electrochemical deposition in modified simulated body fluid.

Adherent and optically semitransparent thin calcium phosphate (CaP) films were electrochemically deposited on titanium substrates in a modified simulated body fluid at 37 degrees C. Coatings deposited by using periodic pulsed potentials showed better adhesion and better mechanical properties than coatings deposited with use of a constant potential. Scanning electron microscopy was used to study the morphology of the coatings.

Influence of aluminum doping on titania pigment structural and dispersion properties.

The influence of aluminum concentration on the structural properties and rheological behavior of aqueous suspensions of aluminum-doped titania pigment from the chloride process was investigated. The variation in rheological properties correlates with the change in the pigment surface properties, determined from electrophoresis measurements and atomic surface concentrations. Pigment suspensions exhibited a maximum yield stress and viscosity at or near the isoelectric point (iep).

Direct measurement of interactions between adsorbed vitronectin layers: the influence of ionic strength and pH.

Vitronectin (Vn) is an adhesive protein in the plasma serum and plays an important role in cell attachment, spreading, and proliferation. The interactions between protein bovine vitronectin layers adsorbed onto a silica probe and a mica surface have been investigated with the use of atomic force microscopy (AFM). Adsorption of vitronectin was confirmed by XPS surface analysis.

Vitronectin adsorption on surfaces visualized by tapping mode atomic force microscopy.

Vitronectin (Vn) is an abundant glycoprotein present in plasma and the extracellular matrix of most tissue and is an important medium required for bone cells to attach and spread on biomaterial surfaces. Hence, Vn adsorption is an initial and key step in implantation. In this study, adsorption of Vn molecules on mica and oxidized titanium substrates in Milli-Q water (pH 5.