Recovery of base metals from a sulphate-based bioleach solution using commercially available chelating ion exchange resins and adsorbents

[摘要] ENGLISH ABSTRACT: Lonmin Plc. is currently investigating a hydrometallurgical process route forthe recovery of base metals (BMs) and platinum group metals (PGMs) froma low grade PGM bearing ore originating from the Platreef deposit in thenorthern limb of the Bushveld Complex. The front-end of theflow sheet entailsrecovering the BM values from the ore in a heap bioleach carried out at atemperature of 65 C after which the PGMs are recovered from the solid residueof 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 (hydroxypropylpicolylaminefunctionality), Amberlite IRC748 and Purolite S930(iminodiacetic acid functionality), and Purolite S991 (mixed amine and carboxylicfunctionality), 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 toselectively adsorb copper to the preference of all other metals in the solutionat pH 3 and 4, while the other resins only succeeded in this purpose at pH 4in the presence of little ferric iron. Only Dow M4195 proved to be able to selectivelyrecover 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 theywere compared on the basis of their metals uptake rate and equilibrium concentrationsof the MOI. The rate of metal uptake equilibrium attainment wasfound to be the fastest for Dow XUS43605, followed by Amberlite IRC748 andDow M4195. Langmuir and Freundlich isotherm models weretted to equilibriumdata for copper adsorption with Dow XUS43605 and nickel adsorption with Dow M4195, and copper and nickel capacities of these two resins at pH4 were found to be 26 g/L and g/L 30.86 g/L, respectively.Column adsorption experiments revealed that flow rate and temperaturewere the parameters that had the most significant effects on the copper loadingachieved on Dow XUS43605 at copper breakthrough. A 36% increase in copperloading on Dow XUS43605 at copper breakthrough was observed when thetemperature increased from 25 to 60 ºC, and the co-loaded nickel decreasedproportionally. This increase was ascribed to the faster kinetics of copperadsorption at 60º C than at 25º C. Regarding nickel and cobalt recovery, thesame trends were observed for increasing the flow rate and temperature. Inaddition to flow rate and temperature, an increase in initial solution pH alsosignificantly increased metal adsorption, as would be expected.Elution studies revealed that a split elution could be performed to removethe majority of the nickel from the resin with 2 bed volumes (BV) of 20 g/Lsulfuric acid to remove the majority of the co-loaded nickel, followed by 2-3 BVof 100 or 200 g/L sulfuric acid to elute the copper, thus a purer copper-richeluate fraction could be obtained. The same was true for nickel and cobaltelution from Dow M4195. The effect of flow rate in the range of 2 to 10 BV/hdid not signi cantly influence metal elution from either Dow XUS43605 or DowM4195, whereas temperature was found to increase the rate of metal elution.Finally, two flow sheets were proposed for the recovery of the MOI. Theoverall recoveries of copper, nickel, cobalt and zinc for both flow sheets were100%, but 14% nickel was lost to the copper eluate for both flow sheets, whilethe nickel lost to the cobalt rich effluent of the lag column was reduced from8.3% forow sheet option 1 to 5.6% forow sheet option 2. By reducing theflow 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 withDow XUS43605 at a lower pH (pH 2 or 3), nickel losses to the copper eluatecould be minimized as the resin's selectivity towards nickel is lower at lowersolution pH values. It was further concluded that additional processing of thecobalt-rich eluate fraction of the lag column (in the lead-lag con guration ofDow M4195) is necessary to recover cobalt in a pure form.

[发布机构] Stellenbosch University