Zinc sulfide as a solid phase additive for improving the processing characteristics of ferrihydrite residues

The effect of ZnS powders as additives for improving the physical and chemical properties of ferrihydrite residues has been studied in both kinetic and batch experiments. Four ZnS samples were compared: two industrial ZnS concentrates, high purity ZnS pieces, and a sample of synthetic ZnS nanoparticles. The industrial ZnS concentrates were found to be the most effective for promoting the transformation of ferrihydrite to hematite, and this effect was found to be due to their lower surface charge at pH 3, which promotes formation of mixed ZnS/ferrihydrite aggregates. For the high purity ZnS samples, aggregation was not favoured, and only goethite formation was promoted. The effect of particle size of the ZnS additive was also studied, and it was found that samples of smaller average particle size were more effective in promoting phase transformation. Measurement of filtration times and moisture content of ferrihydrite residues precipitated in the presence of ZnS showed only minor improvement in physical handling and indicated that better control of surface properties of the additive would be needed to optimise its effect on phase transformation

The dissolution behaviour of titanium oxide phases in synthetic Bayer liquors at 90 C

Many of the bauxites currently being processed to alumina contain titanium minerals, yet little fundamental knowledge is available regarding their dissolution behaviour in Bayer liquors. In this paper the dissolution of various titanium oxide phases (anatase, rutile, sodium titanate and calcium titanate) are presented. It is shown that rutile, calcium titanate and sodium titanate have the expected dissolution behaviour, which increases with free caustic concentration. Anatase, too, generally increases in dissolution with free caustic concentration. However, anatase is shown to have an anomalous behaviour when gibbsite co-precipitates. In this case, the dissolution of anatase does not follow the expected free caustic trend. According to the data presented, the most probable cause is an impervious aluminium/sodium titanate surface layer hindering further dissolution

The effect of zinc sulfide on phase transformation of ferrihydrite

The addition of ZnS particles to suspensions of ferrihydrite promotes the formation of the more crystalline phases goethite [a-FeO(OH)] and hematite (a-Fe2O3) at pH ~ 2-3 and 85 deg. C. This previously undocumented effect appears to arise from surface-mediated reduction of Fe3+ species to Fe2+ with associated dissolution of ZnS

Characterization of Iron III Oxyhydroxides in Hydrometalllurgical Residues

The characterization of iron iii oxyhydroxides arising from neutralization (removing dissolved iron and/or impurities), or precipitation in storage ponds, mine drainage and waste streams (oxidization of dissoved Fe ii) can prove difficult. The low solubility of iron iii inherently creates a high supersaturation environment favoring the formation of nanoscale, poorly crystalline, and metastable phases. These often have poor physical properties - controlling the properties of the residue - and contain high loadings of important adsorbed components. In this manuscript we provide examples of iron iii oxyhydroxide characterization from hydrometallurgical residues and more synthetic-based studies. We detail techniques to help delineate differences between poorly crystalline iron iii oxyhydroxides (2- and 6-line ferrihydrite, schwertmannite, akaganeite and goethite), and more combinational approaches for when admixed in heterogeneous residues. Generally, identification and even quantification can be achieved with a higher degree of confidence than by use of a single technique such as X-ray diffraction (XRD