Time resolved, in-situ diffraction can be of use in the set-up and optimisation of industrial processes by providing direct information about reaction mechanisms and kinetics.  This paper will discuss several examples of this type of work which required different experimental set-ups, but which all exploited the mineralogical information (including phase quantification) provided directly by diffraction.  It will present the results of both laboratory and synchrotron experiments and discusses the practice and perils of in-situ experimentation in general.

The first two examples are hydrometallurgical and use a novel experimental set-up employing a capillary reaction vessel, short wavelength radiation and a position sensitive detector to enable rapid, simultaneous collection of a wide range of diffraction data.  The industrial processes examined are (i) the high pressure acid leaching (HPAL) of nickel laterite ores and (ii) the Bayer process for the production of alumina from bauxite.  These systems have been examined using both laboratory and synchrotron X-radiation.  The third example is a preliminary study into scale formation on the surface of inert anodes within electrochemical cells and utilised the penetrating power of white radiation (synchrotron) energy dispersive diffraction (EDD). 

HPAL of nickel laterites

The majority of nickel is refined from sulphide ores but the oxide ores or laterites represent the largest reserves of this metal.  HPAL involves leaching of laterites in sulphuric acid under hydrothermal conditions, typically 250°C and 45 atmospheres pressure.  Components of the ore are known to undergo rapid changes upon cooling following HPAL thus making examination via traditional post-mortem techniques difficult.   

The Bayer process

The Bayer process is used for the production of alumina from bauxite, and involves dissolving the bauxite ore in a caustic solution at temperatures between 150 – 250ºC. The process is complicated by the presence of reactive silica phases, as these also react with the aluminium and sodium to form insoluble scales. Previous studies have concentrated on ex-situ studies of the long term evolution of the scales. This work concentrates on the initial formation of the scale phases by examining the systems during reaction rather than after cooling, washing, etc.

Light metal production via inert anodes

Inert anodes are a proposed replacement for traditional carbon anodes in the production of light metals.  The advantages of these metal oxide anodes over carbon are twofold: (i) they are not consumed during operation thus replacement is not necessary on the same timescale as carbon and (ii) they emit no greenhouse gases during operation unlike their carbon counterparts.  Scale formation on the anode surface during operation can be detrimental to its operation but may actually be favourable if the scale is sufficiently thick to protect the anode but sufficiently thin to allow conduction.  It is therefore vital in the development of this potentially important technology that the scale formation be characterised and understood.  To date, preliminary examinations have taken place on cycled and cooled cells using white radiation and EDD.  Results regarding the measurement of scales in this way will be discussed as will novel methodology for phase quantification of EDD data.

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1. Synchrotron powder diffraction study of ionic liquids during melting and crystallisation