Hylke J. Glass

Reliability and reproducibility of mercury intrusion porosimetry

Precise interpretation of mercury intrusion data is only possible for cylindrical pores. Nevertheless reproducible data can be obtained which compare well with results on cylindrical pores from independent image analysis experiments. The effect of the compressibility correction is shown to be small.

Fractal characterization of the compaction and sintering of ferrites

A novel parameter, the fractal exponent DE, is derived using the concept of fractal scaling. The fractal exponent DE relates the development of a feature within a material to the development of the size of the material. As an application, structural changes during the compaction and sintering of ceramic materials have been characterized with the fractal exponent DE. Samples taken during the processing of (Mn,Zn)-ferrite, a soft magnetic ceramic material, were analysed with porosimetry. Results show that the fractal exponent DE provides additional insight into the processing.

Method for near infrared sensor-based sorting of a copper ore

Sorting of minerals based on near infrared (NIR) analysis is promising because many minerals have distinct “fingerprints” in the NIR region. An experimental system was customised in order to obtain accurate NIR reflectance spectra. As a test application, the NIR spectra of transects across pre-classified copper ore particles were measured. Matrices containing correlation coefficients of particle pixel–pixel spectra were subjected to principal component analysis. In addition to providing insight into the homogeneity of the particle surface, the results were used to identify key spectral features which could be used to sort product from waste particles. With a selected spectral range, it was found that the classification improved when two standard pixels relating to product and waste were inserted into the transects. While testing an equal number of particles from each rock type, it was found that a correct classification was made in 82% of all rocks. It was found that moisture had little to no effect on the sorting method.

Migration of arsenic from old tailings ponds—A case study on the King Edward Mine, Cornwall, UK

A methodology is presented to study the physico-chemical processes in old tailings ponds using an array of analytical-physical chemistry approaches. A case study was conducted on the sorption/desorption behaviour of arsenic in tailings pond 2406, at the King Edward Mine (KEM) in Cornwall, UK. The tailings pond was in operation from approximately 1907 to 1921. The methodology involves two principal stages: (1) sequential extraction followed by subsequent arsenic species determination to characterise the material with regards to the association of arsenic with soil phases and identification of As (III/V) in the easily accessible soil phase; (2) batch contacting/equilibrating the tailings pond material with As(III/V), followed by a similar procedure as in stage 1 to establish the materials As(III/V) phase distribution kinetics/thermodynamics. By extrapolating the data from present day samples we infer past and future elemental mobility. From this study it is concluded that adsorption and desorption from tailings material is a rapid process for the most unstable soil phases (non-specific and specific) and a slow process for the more stable phases (poorly crystalline and well crystalline). The hypothetical application of this conclusion to the tailings from dam 2406 is that, during the initial phases of the dams creation (ca. 100 years ago), when arsenic was both in solution and bound to mineralogical components, arsenic must have dispersed into the environment as a result of slow As(V) adsorption/phase distribution processes. Aging of the tailings material sees the movement of the arsenic to the more stable soil phases, producing a situation that is seen at present day.

Potential for near Infrared Sensor-Based Sorting of Hydrothermally-Formed Minerals

Dry processing of minerals is increasingly attractive in a mining environment where water is a scarce commodity. Sensor-based sorting has the potential to perform dry separation of ore from gangue at an early stage of the processing, also helping to reduce energy consumption due to downstream crushing. In order to develop a sensor-based sorting process, selection of a suitable sensor is of critical importance. In practice, a near infrared sensor can measure characteristic features of carbonate, hydroxyl and water groups contained in minerals and rocks. This paper examines the process of establishing the suitability of a near infrared sensor for distinguishing hydrothermally-formed minerals. It is concluded that characteristic absorption features in near infrared spectra offer a more robust route to separating out minerals than the level of absorption.

Soil geochemical signature of a calciner site, Cornwall, SW England

Abstract Historical mining activity has led to significant anthropogenic contamination of areas of Cornwall. Arsenic-rich polymetallic ores were processed by heat treatment to remove the arsenic leaving residues of metalloids and metals. To investigate the long-term impact of arsenic ore processing and refining a derelict calciner site in West Cornwall was subjected to a study by soil sampling to test for contaminant levels of elements other than arsenic and determine their spatial distribution. Within the soil profile, levels of Cu, Zn, Pb, Bi, W,U, Ga, and Cd are elevated above background concentrations. SEM examination shows that there are complex particulate grains of metals and metalloids. Statistical examination shows significant correlation between metals and arsenic as well as correlation between metals. The geochemistry of the residues indicates that the feedstock came predominantly from the Camborne–Redruth orefield. Contamination was mainly from fugitive dusts and a distinct geochemical signature is apparent in the soil surrounding the old industrial site.

Mechanics of coal spirals

Separation of liberated, organic contaminants from polluted soil has been simulated both numerically and experimentally. Simulation of the motion of the individual particles shows that the organic contaminants accumulate in the middle of the trough while soil particles move to the inner rim. The results suggest that the separation is determined by segregation in the first turn of the spiral. It was found that the separation is optimal when the spiral is operated close to the maximum capacity. Both a high slurry density and slurry flow rate are found to be beneficial.

Aqueous and solid-phase speciation of arsenic in Cornish soils

Abstract Cornwall (UK) has suffered extensive arsenic contamination due to the historic mining and processing of mineral ores. Standard procedures for contaminated land risk assessment (DEFRA and Environment Agency, 2002a) are probably unworkable in Cornwall, with a very large number of sites classified as contaminated by arsenic. Methods of measuring the speciation and mobility of arsenic are essential for effective and rapid risk assessments of arsenic contamination. Three clusters of lysimeters were installed in three different areas of an arsenic-contaminated Cornish site. A novel phosphoric acid microwave extraction technique was applied to the soils removed from the lysimeter holes; HPLC-HG-AFS analysis showed the majority of solid-phase arsenic to be arsenate (AsV). Pore waters obtained from the lysimeters showed variable, relatively low levels of arsenite (AsIII) and arsenate (AsV) to be present (<1 - 129 μg 1-1). Less toxic arsenate predominated in most pore waters, with the presence of minor amounts of arsenite suggesting heterogeneous redox conditions. Pore-water arsenic concentrations were strongly positively related to solid-phase arsenate concentrations. The use of techniques that assess the speciation of arsenic both in the solid and aqueous phases of a soil provides important information about the mobility of arsenic. The methodology presented in this paper may offer a novel basis for risk assessments of other contaminated sites.

Multinomial distributions applied to random sampling of particulate materials

When sampling a batch consisting of particulate material, the distribution of a sample estimator can be characterized using knowledge about the sample drawing process. With Bernoulli sampling, the number of particles in the sample is binomially distributed. Because this is rarely realized in practice, we propose a sampling design in which the possible samples have a nearly equal mass. Expected values and variances of the sample estimator are calculated. It is shown that the sample estimator becomes identical to the Horvitz–Thompson estimator in the case of a large batch-to-sample mass ratio and a large sample mass. Simulations and experiments were performed to test the theory. Simulations confirm that the round-off error due to the discrete nature of particles is negligible for large sample sizes. Sampling experiments were carried out with a mixture of PolyPropylene (PP) and PolyTetraFluorEthylene (PTFE) spheres suspended in a viscous medium. The measured and theoretical variations are in good agreement.

Assessment of physical leaching processes of some elements in soil upon ingestion by continuous leaching and modeling.

The physical processes controlling the desorption of some elements (B, Cd, Co, Mn, Ni, and Sr) from soils in a continuous leaching system representing the human stomach are investigated here by fitting experimental leaching data to a mathematical particle diffusion model. Soil samples (50 mg) from Cornwall, UK, contained in a flow-through extraction chamber (ca. 6.5 mL) were intimately contacted with artificial gastric solution at various flow rates (0.42-1.42 mL min(-1)) for up to ca. 4 h, followed by analysis of the fractions collected with inductively coupled plasma mass spectrometry (ICP-MS). The leaching profiles of the various elements were fitted to a mathematical model incorporating two mass transfer processes (liquid film diffusion and apparent solid phase diffusion) to determine the effective external mass transfer coefficient (beta) and the apparent intraparticle soil diffusion coefficient (D(a)). A system of partial differential equations was solved numerically with a finite difference discretization of the computational domain allowing the rate limiting physical desorption process(es) for each element to be determined. The (thermodynamic) driving force of the leaching process is defined by the distribution coefficient (K(d0)) between soil and leachant. Although the K(d0) values investigated are very similar (ca. 6-15 L kg(-1)) for the elements studied with the exception of B (ca. 2.7 L kg(-1)), the leaching profiles are very different due to diffusion-limited processes. The elements may be classified as limited by beta (B, Sr, and Cd), by D(a) (Co, and Mn) or by beta and D(a) (Ni). This results in quantifiable parameters for the liability of elements in soil upon ingestion which may be implemented in future risk assessment protocols.