Browsing by Author "Liebenberg, Cornelius Johannes"
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- ItemRecovery of base metals from a sulphate-based bioleach solution using commercially available chelating ion exchange resins and adsorbents(Stellenbosch : Stellenbosch University, 2012-12) Liebenberg, Cornelius Johannes; Dorfling, C.; Akdogan, G.; Bradshaw, S. M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Lonmin Plc. is currently investigating a hydrometallurgical process route for the recovery of base metals (BMs) and platinum group metals (PGMs) from a low grade PGM bearing ore originating from the Platreef deposit in the northern limb of the Bushveld Complex. The front-end of the flow sheet entails recovering the BM values from the ore in a heap bioleach carried out at a temperature of 65 C after which the PGMs are recovered from the solid residue of the bioleach in a second stage heap cyanide leach (Mwase et al., 2012; Mwase, 2009). Commercially available chelating ion exchange resins and chelating adsorbents, Dow M4195 (bispicolylamine functionality), Dow XUS43605 (hydroxypropylpicolylamine functionality), Amberlite IRC748 and Purolite S930 (iminodiacetic acid functionality), and Purolite S991 (mixed amine and carboxylic functionality), were investigated in this thesis for the recovery of copper, nickel and cobalt (metals of interest, or MOI) from the bioleach solution. Screening tests indicated that Dow M4195 and Dow XUS43605 were able to selectively adsorb copper to the preference of all other metals in the solution at pH 3 and 4, while the other resins only succeeded in this purpose at pH 4 in the presence of little ferric iron. Only Dow M4195 proved to be able to selectively recover nickel over other metals in the solution at pH 4. Dow M4195, Dow XUS43605 and Amberlite IRC748 were selected for further investigation. Batch kinetic and equilibrium studies were performed on these resins and they were compared on the basis of their metals uptake rate and equilibrium concentrations of the MOI. The rate of metal uptake equilibrium attainment was found to be the fastest for Dow XUS43605, followed by Amberlite IRC748 and Dow M4195. Langmuir and Freundlich isotherm models were tted to equilibrium data for copper adsorption with Dow XUS43605 and nickel adsorption with Dow M4195, and copper and nickel capacities of these two resins at pH 4 were found to be 26 g/L and g/L 30.86 g/L, respectively. Column adsorption experiments revealed that flow rate and temperature were the parameters that had the most significant effects on the copper loading achieved on Dow XUS43605 at copper breakthrough. A 36% increase in copper loading on Dow XUS43605 at copper breakthrough was observed when the temperature increased from 25 to 60 ºC, and the co-loaded nickel decreased proportionally. This increase was ascribed to the faster kinetics of copper adsorption at 60º C than at 25º C. Regarding nickel and cobalt recovery, the same trends were observed for increasing the flow rate and temperature. In addition to flow rate and temperature, an increase in initial solution pH also significantly increased metal adsorption, as would be expected. Elution studies revealed that a split elution could be performed to remove the majority of the nickel from the resin with 2 bed volumes (BV) of 20 g/L sulfuric acid to remove the majority of the co-loaded nickel, followed by 2-3 BV of 100 or 200 g/L sulfuric acid to elute the copper, thus a purer copper-rich eluate fraction could be obtained. The same was true for nickel and cobalt elution from Dow M4195. The effect of flow rate in the range of 2 to 10 BV/h did not signi cantly influence metal elution from either Dow XUS43605 or Dow M4195, whereas temperature was found to increase the rate of metal elution. Finally, two flow sheets were proposed for the recovery of the MOI. The overall recoveries of copper, nickel, cobalt and zinc for both flow sheets were 100%, but 14% nickel was lost to the copper eluate for both flow sheets, while the nickel lost to the cobalt rich effluent of the lag column was reduced from 8.3% for ow sheet option 1 to 5.6% for ow sheet option 2. By reducing the flow rate at which the process is carried out, these losses could be reduced. Also, by modifying flow sheet 2 and carrying out the copper recovery with Dow XUS43605 at a lower pH (pH 2 or 3), nickel losses to the copper eluate could be minimized as the resin's selectivity towards nickel is lower at lower solution pH values. It was further concluded that additional processing of the cobalt-rich eluate fraction of the lag column (in the lead-lag con guration of Dow M4195) is necessary to recover cobalt in a pure form.