Gordon Parkinson

Evidence on the structure of synthetic schwertmannite

Abstract Evidence from transmission electron microscopy (TEM) and electron nanodiffraction (END) provides a new understanding of schwertmannite, an iron oxyhydroxysulfate mineral. The ball-and-whisker, or “hedge-hog,” morphology of schwertmannite particles makes a complete structural interpretation difficult, but no evidence for a “modified” akaganeite structure was found in this study. END analyses suggest that most schwertmannite whiskers have a structure consistent with the maghemite-like structural component previously described by Janney et al. (2000a) for ferrihydrite. Some sections of whiskers also contain the previously described highly disordered ferrihydrite structural component (Janney et al. 2000a), and more amorphous regions. Under certain conditions in an electron microscope, schwertmannite particles transformed to crystalline cubic and hexagonal phases. During this process, sulfate and OH/H2O were ejected from the structure, confirming sulfate to be structurally incorporated. The existence in schwertmannite whiskers of such structural components may seem unlikely, as it contradicts previous conclusions concerning the octahedral coordination of Fe3+ and the location of sulfate in the structure. It has been hypothesized, however, that the incorporation of OH/ H2O and sulfate may permit an octahedral coordination of Fe3+ in a cubic-close-packed arrangement. Unfortunately, the thickness of the schwertmannite aggregates precludes determination of whether they consist solely of whiskers (containing the maghemite-like/highly disordered/amorphous structural components) radiating from a central point or if a structurally distinct material resides within the core of these aggregates. This study provides a new perspective of the schwertmannite structure, and its relationship to ferrihydrite, as both contain similar structural components.

Investigation into the effect of phosphonate inhibitors on barium sulfate precipitation

The effect of a series of phosphonate molecules on barium sulfate precipitation was tested. While an increase in the number of phosphonate groups generally resulted in increased inhibition of barium sulfate precipitation, two notable exceptions showed that a relatively high number of phosphonate groups does not guarantee inhibition while a relatively low number of phosphonate groups does not imply no inhibition. Increasing the pH showed an increased effect of additives on barium sulfate precipitation up to pH 8. However, on increasing from pH 8 to 12, a loss of inhibition in the additives was observed which appears to be due to the barium sulfate surface changing with pH. r 2002 Elsevier Science B.V. All rights reserved.

Delamination and re-assembly of surfactant-containing Li/Al layered double hydroxides

Exchange of the chloride anion intercalated in [LiAl2(OH)6]Cl.nH2O with a range of surfactants is reported. Attempts to delaminate (or exfoliate) the surfactant-exchanged intercalates, where the surfactant was an alkyl sulfate, were unsuccessful. In contrast, delamination of the layered double hydroxides [LiAl2(OH)6][C12H25C6H4SO3.nH2O] and [LiAl2(OH)6][C8H17C6H4SO3.nH2O] was successful. The necessity of the alkyl chain of the surfactants was demonstrated by the failure of [LiAl2(OH)6][CH3C6H4SO3.nH2O] to delaminate. The delamination of the unique Li/Al LDH is thus found to be dependent on the guest surfactant structure in terms of both chain length and head group moiety.

The role of phosphonate speciation on the inhibition of barium sulfate precipitation

Abstract The inhibition of barium sulfate precipitation in the presence of phosphonate containing molecules was investigated experimentally and speciation curves were used to elucidate the interactions involved. Inhibition of precipitation was found to be pH dependent and loss of inhibition was observed at both very high and low pHs. Maximum inhibition for all the inhibitor molecules occurred at pH 8. While speciation curves showed that inhibition could be improved by the presence of 2 or more fully de-protonated phosphonate groups (for pure aminophosphonates) on the molecule at pH⩽8, at pH 12 inhibition was insensitive to the number of de-protonated phosphonate groups. It is, therefore, suggested that surface charge repulsion affects inhibition at very high pH. For molecules which are not pure aminophosphonates, stereochemistry, functional groups and the ionisation state appear to play a significant role in inhibition at 3

Iron oxy-hydroxide crystallization in a hydrometallurgical residue

In some hydrometallurgical operations, the removal of iron from process liquors can be critical, with the method of choice commonly being crystallization (precipitation). It has been recently discovered that if the removal of iron occurs at pH 3, ferrihydrite, a complex and disordered compound, will generally be precipitated. A laboratory scale, computer controlled, continuous crystallizer was constructed to investigate the removal of iron from low pH solutions (precipitation). The significance of ferrihydrite precipitation and the effect of pH and silica concentration on the properties of the precipitate were investigated. Considerable insight has been gained concerning the crystallization and growth mechanisms under these conditions, including the unusual limit of ferrihydrite crystal growth. The use of in situ focussed beam reflectance measurement (FBRM) analysis has allowed the particle size differences experienced at low pH in ferrihydrite precipitation to be studied. The improved understanding of the crystallization of iron from hydrometallurgical process liquors has resulted in a methodology for more effective removal of iron.

Atomistic modelling of gibbsite: surface structure and morphology

We have developed interatomic potentials that fit multiple hydroxide systems, including gibbsite. These potentials have been used to compute the equilibrium and growth morphologies of gibbsite. The results compared favourably to experimental data, reproducing all observed faces. In addition, the configuration and coordination of surface aluminium atoms were found to exert a major influence on the morphology.

Microstructure control of oxygen permeation membranes with templated microchannels

Microchanneled ceramic membranes have been prepared by a templated phase-inversion process, and the effects of coagulant and slurry properties on the microchannel structure were investigated in order to control membrane microstructure for achieving highly-efficient oxygen permeation. Microchannels are formed by the rapid convection of coagulant and solvent during the phase-inversion, using a mesh as a template. The membrane microstructure is greatly affected by the method of applying coagulant, coagulant solubility and phase-inversion time. Polymer concentration and solid loading influence slurry viscosity, and long and uniform microchannels are formed from the slurries with low slurry viscosities. The membrane with long and uniform microchannels achieved high oxygen permeation fluxes because of short oxygen ion diffusion distances and large membrane surface area located within the numerous microchannels. The formation mechanism of the microstructure was also proposed on the basis of the experiment results.

A microchanneled ceramic membrane for highly efficient oxygen separation

A microchanneled ceramic membrane has been developed for oxygen separation. Numerous parallel microchannels traverse the ceramic membrane with one open end and another end terminating with a thin dense layer. Compared with conventional dense membranes, the new membrane substantially increases oxygen permeation flux by a factor of greater than 5.

The effect of zinc sulfide on phase transformations of ferrihydrite

Abstract The addition of ZnS particles to suspensions of ferrihydrite promotes the formation of the more crystalline phases goethite [α-FeO(OH)] and hematite (α-Fe2O3) at pH ~ 2.3 and 85 °C. This previously undocumented effect appears to arise from surface-mediated reduction of Fe3+ species to Fe2+ with associated dissolution of ZnS.

Identifying nanoscale ferrihydrite in hydrometallurgical residues

The identification of a disordered nanoscale material such as ferrihydrite in a heterogeneous sample environment, as is typically the case in a hydrometallurgical residue, requires a rigorous multifaceted characterization approach. An example of this is the identification of ferrihydrite in paragoethite process residues generated in zinc refining. In a pure-form ferrihydrite, a poorly crystalline iron(III) oxyhydroxide possesses a characteristic powder x-ray diffraction profile consisting of very broad low-intensity reflections. However, in coexistence with crystalline material, the diffraction profile may be masked, lost in the background noise, and easily overlooked. By using several characterization approaches in combination, ferrihydrite can be identified in a hydrometallurgical residue with a higher degree of confidence than can be achieved by the application of a single technique.