Microbial generation of highly magnetic iron sulphide for heavy metal recovery

Marius, Merissa S (2006) Microbial generation of highly magnetic iron sulphide for heavy metal recovery. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Biosorption of heavy metals using microbial biomass sorbents has been extensively studied in the laboratory with the view, to eventual commercial application. Microbially produced iron sulphide biosorbents are known to have a high affinity for heavy metals and magnetic properties which have the potential for use in biomagnetic separation processes. However, unwillingness to change from conventional methods, combined with the poor economic viability of the biomass separation has stalled commercial exploitation. This study examined the use of a mixed sulphate reducing bacteria population to produce a highly magnetic sulphide to enable easy, magnetic separation recovery. Sorption/desorption behaviour of the microbially produced sulphide on typical heavy metals found in commercial effluents was also investigated. low cost Culturing of the magnetic biosorbent using a mixed iron, ferrous rich modified Postgate growth medium and an alternating batch-continuous growth cycle produced a material with a magnetic susceptibility an order of magnitude greater than previously documented. and x-ray diffraction tests indicated the presence of iron, sulphur (elemental and sulphide) and phosphate. Mackinawite (FeSi-x) was inferred as the magnetic iron sulphide. Characterisation using chemical metals to the sulphide followed the Langmuir isotherm model Sorption of suggesting the occurrence of monolayer binding. uptake affinity followed the order Cd>Zn>Cu>Ni, with the maximum calculated sorption capacity being an order of magnitude greater than other commercially tested biomasses, indicating its efficiency on a single application and suitability for commercial applications. Ethylenediamine-tetra-acetic acid (EDTA) was found to eluting 30-90% of the bound metal. be the most However the biomass oxidised during the process and subsequent sorption efficiency was poor. effective desorbing agent The studied metal In summary, this thesis describes a pathway to produce a highly magnetic iron sulphide and characterises its biosrobent properties. The work has demonstrated the potential of this material to be applied to heavy metal pollutant recovery.

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