Capacity and mechanisms of uptake of silver by jarosite family minerals

Cogram, Peter Frank (2017) Capacity and mechanisms of uptake of silver by jarosite family minerals. Doctoral thesis, Birkbeck, University of London.

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Abstract

Jarosite is a family of iron-hydroxysulphate minerals that commonly occur in acidic, sulphate-rich environments and in ore processing wastes. Jarosite precipitation is used in hydrometallurgy to control Fe and other impurities. End-member jarosite sensu stricto contains potassium and has the chemical formula KFe3(SO4)2(OH)6, but extensive element substitution takes place in the crystal structure. Silver can be taken up by jarosite minerals and, in theory, Ag can form solid-solution series with K, Na and Pb in jarosite. This study carried out synthesis experiments, using a variety of sulphate starting solutions and temperatures, to form K-jarosite, Na-jarosite and Pbjarosite minerals and determined their capacity for Ag by investigating them using powder X-ray diffraction (XRD), Rietveld refinement, electron microprobe analysis and inductively coupled plasma-atomic emission spectroscopy. Solid solution was found between Ag-jarosite and separately K-jarosite, Na-jarosite and Pb-jarosite, but with substantial hydronium (H3O) content and vacancies in the Fe site. The average relative partitioning coefficients for Ag were 0.9 in K-jarosite, 1.3 in Na-jarosite and 1.17 in Pb-jarosite. Powder XRD analysis showed that, in the K-Ag-H3O and Pb-Ag- H3O-jarosite series, d-spacing values for the hkl 003 and 006 peaks indicated the unitcell c-axis parameter decreased as Ag content increased. Rietveld refinement showed that, in K-Ag-H3O-jarosite and Na-Ag-H3O-jarosite, there were trends of increasing unit-cell a-axis parameters and decreasing c-axis parameters as Ag content increased. Rietveld refinement indicated decreasing K,Ag-O2 and K,Ag-O3 bond lengths as Ag content increased in K-Ag-H3O-jarosite. Raman spectroscopic analysis showed the assigned v1SO4 and v3SO4 vibrational modes in some K-Ag-H3O-jarosite series had higher wavenumbers (cm-1), indicating higher bonding energies, as Ag content increased. The XRD, Rietveld refinement and Raman data from this project will inform the evaluation of the Ag composition of jarosite minerals in complex natural mineral assemblages using these same techniques.

Item Type: Thesis (Doctoral)
Copyright Holders: The copyright of this thesis rests with the author, who asserts his/her right to be known as such according to the Copyright Designs and Patents Act 1988. No dealing with the thesis contrary to the copyright or moral rights of the author is permitted.
School/Department: School of Science > Earth & Planetary Sciences
Depositing User: ORBIT Editor
Date Deposited: 07 Aug 2017 14:18
Last Modified: 07 Aug 2017 14:18
URI: http://bbktheses.da.ulcc.ac.uk/id/eprint/262

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