Nickel extracting industries have been facing challenges reflecting, inter alia, low recoveries of Ni and Co, high acid consumption and inadequate knowledge of dissolution kinetics. In oxic laterite, Ni is mostly associated with goethite. Consequently, for effective extraction of Ni and Co from oxic Ni laterites, a clear understanding of their chemistry, mineralogy and mechanism of sorption in goc;!thite during laterite ore formation is essential. The result from experiment of Ni sorption on goethite revealed that at surface loadings of 0.003 to 0.2 wt. % Ni, only the >Fe(OH)2Ni complex was needed to, fit the data whereas both >Fe(OH)2Ni and (FeOH)2Ni complexes were invoked to fit surface loadings of >0.2 to 0.35 wt. % Ni. At 0.75 wt. % Ni and above, however, the polynuclear complex (FeOH)3Nh was required to fit the data. Similar results were obtained for Co sorption and co-sorption of Ni and Co on goethite. EXAFS results support the existence of Ni surface precipitate or extended polynuclear Ni complex in the Ni-sorbed goethite and Ni laterite. In all the samples, Ni and Co dissolve incongruently with iron. However, there exist disparities in their dissolution and desorption kinetics as a function of aging and concentration, which indicate differences in chemical structure. Modelling of Ni laterite using PHREEQC and equilibrium constants obtained from EQLFOR provides information on the processes of Ni laterite formation and the zones of supergene Ni enrichment as well as prediction of the weathering profile. The solubility product (Ksp) of Ni or Co substituted goethite increases with increasing metal substitution. Similar results were obtained for bi-metal substituted goethite. In general, leaching with dilut~ 2.75 M aqua regia is best for Ni laterites formed at low loading as well as those formed via surface precipitation with Fe content less than 33 wt. % Fe whereas 2.75 M HCI is effective for those formed at high loading containing> 33 wt.% iron.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:691177 |
| Date | January 2015 |
| Creators | Ugwu, Ifeoma Mary |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0018 seconds