Kristian E. Waters

Measurements of Interactions between Particles and Charged Microbubbles Using a Combined Micro- and Macroscopic Strategy

We report the use of atomic force microscopy (AFM) to study the interactions between silica glass colloidal probes and charged microbubbles created using one of two different surfactants: anionic sodium dodecyl sulfate (SDS) and cationic dodecyl trimethylammonium bromide (DTAB) in an aqueous environment. On close approach between the glass probe and a SDS microbubble, an appreciable repulsive force was observed prior to contact. This was not observed when using a DTAB microbubble, where only attractive forces were observed prior to contact. zeta-potential analysis showed that silica surfaces are negatively charged across the pH range of 3-10 when surfactant is not present. Addition of SDS did not alter the zeta-potential significantly, indicating that adsorption onto the particle surface did not occur. Conversely, the addition of DTAB decreased the negativity of the zeta-potential, reversing the sign, indicating that adsorption had occurred. This analysis was used in the removal of fine particles from suspension using charged microbubbles. Silica particles were recovered using positively charged microbubbles from DTAB but not when using negatively charged microbubbles generated from SDS. Taken together, the data suggest that repulsive long-range interactions were responsible for the selective attachment of silica particles to microbubbles in a charge-dependent manner.

Characterization of aqueous interactions of copper-doped phosphate-based glasses by vapour sorption.

Owing to their adjustable dissolution properties, phosphate-based glasses (PGs) are promising materials for the controlled release of bioinorganics, such as copper ions. This study describes a vapour sorption method that allowed for the investigation of the kinetics and mechanisms of aqueous interactions of PGs of the formulation 50P2O5-30CaO-(20-x)Na2O-xCuO (x=0, 1, 5 and 10mol.%). Initial characterization was performed using (31)P magic angle spinning nuclear magnetic resonance and attenuated total reflectance-Fourier transform infrared spectroscopy. Increasing CuO content resulted in chemical shifts of the predominant Q(2) NMR peak and of the (POP)as and (PO(-)) Fourier transform infrared absorptions, owing to the higher strength of the POCu bond compared to PONa. Vapour sorption and desorption were gravimetrically measured in PG powders exposed to variable relative humidity (RH). Sorption was negligible below 70% RH and increased exponentially with RH from 70 to 90%, where it exhibited a negative correlation with CuO content. Vapour sorption in 0% and 1% CuO glasses resulted in phosphate chain hydration and hydrolysis, as evidenced by protonated Q(0)(1H) and Q(1)(1H) species. Dissolution rates in deionized water showed a linear correlation (R(2)>0.99) with vapour sorption. Furthermore, cation release rates could be predicted based on dissolution rates and PG composition. The release of orthophosphate and short polyphosphate species corroborates the action of hydrolysis and was correlated with pH changes. In conclusion, the agreement between vapour sorption and routine characterization techniques in water demonstrates the potential of this method for the study of PG aqueous reactions.

Physicochemical aspects of allanite flotation

Abstract This paper investigated the physicochemical properties of allanite, a RE-silicate, by measuring zeta potential in the absence and presence of three different flotation collectors (benzohydroxamic acid, sodium oleate and dodecylamine). This data was then verified by microflotation experiments and with bubble-particle attachment pictures. The investigated properties of allanite were compared to those of quartz, a common gangue mineral in many RE deposits. The results of this work indicated that only dodecylamine was able to achieve a selective separation of allanite and quartz. This was accomplished by lowering the dodecylamine dosage so that only quartz was recovered by microflotation.

Ionic liquid-based observation technique for nonconductive materials in the scanning electron microscope: Application to the characterization of a rare earth ore.

A new approach for preparing geological materials is proposed to reduce charging during their characterization in a scanning electron microscope. This technique was applied to a sample of the Nechalacho rare earth deposit, which contains a significant amount of the minerals fergusonite and zircon. Instead of covering the specimen surface with a conductive coating, the sample was immersed in a dilute solution of ionic liquid and then air dried prior to SEM analysis. Imaging at a wide range of accelerating voltages was then possible without evidence of charging when using the in‐chamber secondary and backscattered electrons detectors, even at 1 kV. High resolution x‐ray and electron backscatter diffraction mapping were successfully obtained at 20 and 5 kV with negligible image drifting and permitted the characterization of the microstructure of the zircon/fergusonite‐Y aggregates encased in the matrix minerals. Because of the absence of a conductive layer at the surface of the specimen, the Kikuchi band contrast was improved and the backscatter electron signal increased at both 5 and 20 kV as confirmed by Monte Carlo modeling. These major developments led to an improvement of the spatial resolution and efficiency of the above characterization techniques applied to the rare earth ore and it is expected that they can be applied to other types of ores and minerals. Microsc. Res. Tech. 77:225–235, 2014.

A systems approach to mineral processing based on mathematical programming

ABSTRACT Mathematical programming (MP) is fundamental to systems engineering and operations management, but has not been widely adopted by mineral processors. The current paper presents an interdisciplinary approach, using MP to incorporate basic notions of mass balancing into an optimisation framework. The optimisation is typically related to economic profitability. Two- and three-product formulas are extended to give formal descriptions of alternate modes of operation, and a global representation of the concentrator. At this global level, the framework may assist plant managers to make tactical decisions based on incoming feed data. The MP framework is demonstrated through sample calculations describing a lead–zinc concentrator.

Surface characterisation of fergusonite

Abstract There is currently very little information on the physico–chemical properties of rare earth element bearing minerals, or on their processing. With the increasing demand for rare earths, this is something that needs to be addressed. This paper introduces some surface chemistry analysis of fergusonite (YNbO4), and the bubble particle attachment. Zeta potential measurements indicate adsorption of sodium oleate and, to a lesser degree, potassium amyl xanthate onto the surface, and an increase in attachment to an air bubble is observed at pH 4·5 and 6·5. At a pH of 10·5, no attachment is observed, whether in the presence of the reagents or not. This analysis, although initial, will be used to initiate flotation tests, in order to facilitate the selective recovery of fergusonite. Two extensively characterised minerals, one hydrophilic (quartz) and one hydrophobic (galena) were also investigated as a comparison. Il y a présentement très peu d’information concernant les propriétés physico-chimiques des minéraux porteurs d’élément de terre rare, ou de leur traitement. Avec l’augmentation de la demande des terres rares, on a besoin d’examiner cette question. Cet article introduit une certaine analyse de la chimie de surface de la fergusonite (YNbO4) et de l’attachement de bulle-particule. Des mesures du potentiel zêta indiquent l’adsorption d’oléate de sodium et, à un degré moindre, du xanthate amyle de potassium à la surface. On observe également une augmentation de l’attachement à une bulle d’air à un pH de 4·5 et de 6·5. À un pH de 10·5, il n’y a pas d’attachement, que ce soit avec ou sans agents réactifs. Cette analyse, bien qu’initiale, sera utilisée pour initier des essais de flottation afin de faciliter la récupération sélective de la fergusonite. On a également examiné, à titre de comparaison, deux minéraux caractérisés considérablement, soit un hydrophile (quartz) et un hydrophobe (galène).

Characterisation of rare earth minerals with field emission scanning electron microscopy

Abstract Rare earth elements are becoming increasingly in demand, due to their prevalence in both renewable energy devices and high end electronics. The characterisation of the composition and morphology of the various phases that have valuable rare earth elements in the ores are needed in conjunction with the study of their physicochemical properties to optimise industrial process to extract the minerals containing the rare earth elements. Rare earth bearing minerals contain many elements with overlapping X-ray peaks (L- and M-lines) with an energy dispersive spectrometry detector, requiring a high degree of X-ray energy resolution. A program was developed to obtain the intensity of each peak by deconvolution of the X-ray spectrum. Low accelerating voltage of less than 5 kV and small beam diameter of less than 10 nm of a cold field emission scanning electron microscope allow x-ray microanalysis on the nanometre scale. A 100 nm wide phase was observed at 4 kV on a backscattered electron micrograph. Furthermore, a small beam diameter of less than 10 nm was used for identification of small phases of a few micrometres. Les éléments de terre rare sont de plus en plus en demande, grâce à leur prévalence tant dans les dispositifs d’énergie renouvelable que dans l’électronique de haute gamme. On a besoin de caractériser la composition et la morphologie des différentes phases qui contiennent des terres rares de valeur dans les minerais, en combinaison avec l’étude de leurs propriétés physico-chimiques, afin d’optimiser le procédé industriel d’extraction des minéraux contenant les terres rares. Les minéraux porteurs de terre rare contiennent plusieurs éléments ayant des pics de rayons x qui se chevauchent (lignes L et M) avec un détecteur de spectroscopie à dispersion d’énergie, nécessitant une haute résolution énergétique. On a développé un programme visant à obtenir l’intensité de chaque pic par déconvolution du spectre de rayons x. Un faible voltage d’accélération de moins que 5 kV et un faisceau à faible diamètre de moins que 10 nm d’un microscope électronique à balayage par cathode froide permettent la microanalyse des rayons x à l’échelle du nanomètre. On a observé une phase de 100 nm de largeur à 4 kV sur une micrographe d’électrons rétrodiffusés. De plus, on a utilisé un faisceau de faible diamètre de moins que 10 nm pour l’identification de petites phases de quelques μm.

X-ray Microanalysis Phase Map on Rare Earth Minerals with a Conventional and an Annular Silicon Drift Detector

Rare earth elements (REEs) have become important components in over 200 products across an extensive range of applications, causing the demand for these elements keeping rising and the rare earth industry keeping flourishing [1]. The Nechalacho rare earth deposit, located in the Northwest Territories in Canada, is one of the most important REE sources in the world [2]. The aim of this work is to use one high spatial resolution and high count rate scanning electron microscope/x-ray energy dispersive spectrometry (SEM/EDS) system to characterize rare earth minerals (REMs) in this deposit using phase maps. The Xray microanalysis was achieved by a conventional silicon drift detector (SDD) with 60 mm collecting area located on the side of specimen and an annular SDD with a same collecting area inserted below the objective lens. The position of the annular detector provides the shortest working distance and the largest solid angle, allowing the X-ray microanalysis with a count rate as high as 2,000,000 cps and short acquisition time. Because of the high count rate, the relatively low accelerating voltage can be used, providing a high spatial resolution, making the characterisation of small features in micron-scale possible. The traditional EDS elemental map shows distribution of elements, but it cannot provide enough information for phase identification. The problem is more obvious in geological materials, where the samples have numerous micro phases with unknown composition. In order to overcome that, we develop a phase map method using the traditional EDS map and the f-ratio method [3]. The method was applied to acquire the compositional information of REM and to show their distribution.

Break-up in formation of small bubbles: an energy consideration

ABSTRACT The formation of small bubbles in flotation is usually accomplished by the use of frothers, or sometimes is due to the presence of inorganic salts in the process water. The effective mechanism associated with the presence of these solutes is generally considered to be coalescence inhibition. However, recent work has demonstrated that the presence of frothers and salts also reduces the size of bubble at the initial formation stage. In this paper, we adapt the same experimental setup to investigate the time that it takes for a bubble to form; for a known system power input, the energy to form a bubble can then be estimated from the time. The hypothesis is that the presence of frother and salt will reduce the time for a bubble to form, which can be interpreted as an added energy component being derived from the solute. Testing different types and concentrations of frothers and salts, the hypothesis is supported: the mechanical energy required to form a bubble decreases by about 10% in the presence of these solutes.

Characterization of Rare Earth Element Ores with High Spatial Resolution Scanning Electron Microscopy

Rare earth elements (RREs) include the fifteen lanthanides plus scandium and yttrium [1]. Because of their prevalence in renewable energy devices and high-end electronics, REEs become increasingly significant for the advancement of technology and energy saving devices [2]. The goal of this project is to estimate the economical values of rare earth elements and to find the optimal extraction process through charactering composition and morphology of REEs-bearing minerals. Typically, the quantitative evaluation is achieved by automated scanning electron microscope and mineral liberation analyzer, but the results are limited by the low spatial resolution and global chemical analysis of these methods. High spatial resolution imaging and x-ray microanalysis are needed to correctly characterize the REEs-bearing minerals.