Council for Mineral Technology

1
Council for Mineral Technology
Oxidative Precipitation of Mn from Cobalt Leach
Solutions using Dilute SO2/air Mixtures Ndinanwi
Mulaudzi SAIMM Hydrometallurgy conference 24
26 February 2009
2
Contents

• Introduction
• Objectives
• Background
• Experimental
• Results
• Conclusions

3
Introduction

• Dilute SO2/air (or O2) gas mixtures have been
  used to oxidatively precipitate Mn from Zn(II),
  Co(II) and Ni(II) solutions.
• SO2/air (or O2) gas mixture is a cheaper oxidant
  compared to other strong oxidising agents such as
  O3 and H2O2.

4
Objectives

• Evaluate effects of
• SO2/air ratio
• pH
• temperature
• Minimum cobalt losses targeted (lt 1).

5
Thermodynamic considerations
6
SO3-/SO32- and SO5-/SO52- redox couples
(Das et.al, 1999).
7
S(IV) speciation
Distribution of sulphur(IV) oxide species (Brandt
et.al, 1994)
8
Reaction stoichiometry

• MnSO4 SO2 O2 2H2O ? MnO2 2H2SO4 (1)
• 2MnSO4 SO2 O2 3H2O ? Mn2O3 3H2SO4 (2)
• SO2 0.5O2 H2O ? H2SO4
  (3)
• H2SO4 Ca(OH)2 ? CaSO4 2H2O
  (4)
• SO2 flowrate
• - calculated from reaction 1 for a
  stoichiometric runtime of 5 hours actual runtime
  was 6 hours
• - was kept constant at 11 ml/l for all the
  tests

9
Experimental matrix
All initial solutions contained 2 g/L Mn(II) and
6.5 g/L Co(II) Moles of O2 used in SO2/air and
SO2/O2 mixtures the same
10
Experimental set-up
11
Effect of SO2/air ratio on kinetics
pH 3 30oC
12
Mn precipitation and Redox
pH 3 30oC 6 hours
13
SO2/air versus SO2/O2
pH 3 30oC 6 hours
14
Effect of pH on kinetics
3 SO2 30oC
15
Effect of pH on Mn and Co
3 SO2 30oC 6 hours
16
Redox O2 vs SO2/air
3 SO2 30oC 6 hours
17
Effect of temperature on kinetics
pH 3 3 SO2
18
Effect of temperature on Mn and Co
pH 3 3 SO2 6 hours
19
Gypsum phase
20
Mn phase
21
Conclusions

• For specific experimental set-up
• Efficiency increased with increased SO2/air ratio
  up to 3 SO2 in air
• O2 instead of air Mn precipitation improved
• SO2/air ratio affected redox potential
• Solution pH critical
• Temperature increased rate and extent of Mn ppt
• Redox potential not only parameter determining Mn
  removal rate and extent of removal
• Co losses to be improved

22
Thank you
www.mintek.co.za