versão On-line ISSN 2411-9717
versão impressa ISSN 0038-223X
J. S. Afr. Inst. Min. Metall. vol.109 no.6 Johannesburg Jun. 2009
Mixing system design for the Tati Activox® autoclave
M. NicolleI; G. NelII; T. PlikasIII; U. ShahIII; L. ZuntiIII; M. BellinoI; H.J.H. PieterseIV
IHatch Africa (Pty) Ltd, South Africa
IINorilsk Nickel Africa (Pty) Ltd, South Africa
IIIHatch (Pty) Ltd, Ontario, Canada
IVPieterse Consulting Inc., Arizona, USA
The Tati Activox® Project will be the first full-scale implementation of the patented Activox® process (The Tati Activox® project was deferred in 2008. Please refer to the Norilsk Nickel press issue on the topic for more info). The process was developed by Norilsk Process Technology and has been tested on Tati mine sulphide concentrates in laboratory, pilot and demonstration plant scales and demonstrated its viability. There are inherent risks to the final scale-up of the process from the demo plant and one of them will be investigated in this paper.
Compartment 1 is designed to leach approximately 77% of the total nickel leached. For this reason agitation requirements in the first compartment of the autoclave are reviewed. An attempt is made to minimize the process and mechanical risks associated in achieving oxygen mass transfer into the slurry solution. The agitator powers for oxygen mass transfer are calculated using empirical correlations and compared to demonstration plant testwork. The resulting gassed power per unit volume (P/V) is higher than most commercial autoclaves and raises uncertainty on the viability of using such high unit power inputs. Additionally, there is concern about the ability of the autoclave shell to withstand and support the higher loading of large agitators. An alternative solution to designing for the increased P/V is assessed in which the number of compartments within the autoclave is reduced from 5 to 4 by removing the compartment wall separating compartments 1 and 2. This results in an enlarged first compartment containing 3 agitators instead of 2. Therefore the compartment 1 oxygen demand is supplied through 3 agitators, which lowers the P/V per agitator.
The reduction in the number of autoclave compartments raises the potential for short-circuiting the mean flow pattern by slurry particles. Short-circuiting and low velocity zones could result in a lower recovery of metal and localized hot spots, respectively. A computational fluid dynamic (CFD) analysis was conducted to quantify these concerns and also to evaluate further design considerations. The results indicate that the proposed design change to 4 compartments affects short-circuiting. The impact of increased short-circuiting on the overall autoclave recoveries is not quantified, however; it is expected to be negligible based on testwork done in the Tati Demonstration Plant and similar modifications made to another operating autoclave. The CFD analysis also suggests that there will be no low velocity zones within the compartment.
“Full text available only in PDF format”
TROMANS, D. Temperature and Pressure Dependant Solubility of Oxygen in Water: A Thermodynamic Analysis. Hydrometallurgy, vol. 48, 1998. pp. 324-342. [ Links ]
TROMANS, D. Oxygen Solubility Modeling in Inorganic Solutions: Concentration, Temperature and Pressure Effects. Hydrometallurgy, vol. 50, 1998. pp. 279-296. [ Links ]
PIETERSE, H. Oxidation Autoclave Agitation Review. Pressure Hydrometallurgy 2004, 34th Annual Hydrometallurgy Meeting, Banff, Alberta, Canada. 2004. [ Links ]
BOWEN, R.L. Agitation Intensity: Key to Scaling Up Flow-Sensitive Liquid Systems. Chemical Engineering, March 18, 1985. [ Links ]
DAVIS, M.E. and DAVIS, R.J. Fundamentals of Chemical Reaction Engineering. Mcgraw-Hill Chemical Engineering Series, International Edition, July 2002. [ Links ]