Fundamental studies into the formation of jarosite related precipitates

[摘要] Jarosites are a fascinating class of materials with broad relevance to a range of science areas including hydrometallurgy, acid mine drainage, novel (in-situ) minerals leaching processes and the environmental history of Mars. The phase formation of jarosites (nucleation and growth mechanisms) is not fully understood. This project was conceived in order to gain better understanding of its formation mechanisms which would contribute to being able to enhance or suppress its formation in a range of environments. The project has used a range of experimental and analytical techniques including both in situ and ex situ approaches. In this way new capability has been brought into the organisation along with the refinement of existing procedures and adaptation of methods to nucleation and crystallisation studies.The experimental programme for this project incorporated:1. In situ small angle X-ray scattering (SAXS) to examine the earliest stages of nucleation from solution.2. In situ X-ray and neutron diffraction to examine (i) the crystal growth characteristics and (ii) stability of a range of jarosite compositions.3. Kinetic studies based upon the in situ syntheses.4. Characterisation of thermal expansion properties via X-ray and neutron diffraction.5. Phase chemistry determination during dehydration and decomposition via heating in situ during diffraction experiments to determine stability.6. A parallel programme of ex situ syntheses to produce materials comparable to those produced in situ in order to have bulk specimens suitable for chemical and TGA/DTA analyses. These products were also the subject of detailed crystal chemistry analysis via synchrotron X-ray diffraction.The key outcomes from this project are:1. Development of in situ hydrothermal synthesis techniques which are applicable to anyhydrothermal/solvothermal system.2. The finding that jarosite forms via a single nucleation event which followed by crystal growth of the monodisperse particle population. The number of nuclei formed relates to the temperature of reaction.3. The initial particles formed are large and amorphous and gradually convert to jarosite. This conversion may be controlled by controlling the pH of the system which is critical for avoiding jarosite in bioleaching or promoting it in hydrometallurgical circuits.4. Iron vacancies within the jarosite structure may be ordered thus lowering its crystal symmetry Controlling this ordering controls the properties of the jarosite formed. This finding provides a solution to anomalies observed in magnetic studies of jarosites.5. Reaction kinetics have been determined showing the influence of temperature and composition within a specified range of conditions.These outcomes have been published in six fully refereed journal papers (four complete, two submitted with a further three in preparation), one experiment report to ISIS, three internal reports, six oral presentations nationally and internationally (plus five more internally to CSIRO and ANSTO), six posters at national and international conferences and thirteen successful proposals to advanced radiation sources locally and internationally.The technique development has been transferred to a joint CMSE/University of Melbourne Science Leader project and has resulted in the awarding and appointment of a dedicated OCE PDF to a project entitled “Informatic discovery of solvothermal TiO2 architectures”. This project will use very similar experimental and analytical methodology to the jarosite project and the materials developed will contribute to areas of National Priority in energy (photovoltaics), water (degradation of pollutants) and the environment.

[发布机构] CSIRO

[学科分类] 地球科学(综合)