Laterite Leach Tests

ANSTO Minerals Report C1206 to Lagoon Creek Resources – Westmoreland Deposits
4.2.4 Comparison of Oxidants
For ease of control, sodium permanganate was used in most leach test. Base case leaches for
Junnagunna and Redtree were also carried out using pyrolusite to demonstrate that both
oxidants gave equivalent results. The base case leach data for the two oxidants are compared
in Table 4.7. The oxidation equations for the two oxidants are given below, and show that
differences in acid consumption for the Fe 2+ oxidation reaction need to be considered:
4H + + MnO2 + 2Fe 2+ → Mn 2+ + 2Fe 3+ + 2H2O (1)
8H + + MnO4 - + 5Fe 2+ → Mn 2+ + 5Fe 3+ + 4H2O (2)
When pyrolusite is used as an oxidant, for every mole of Fe 2+ oxidised one mole of H2SO4 is
consumed. As the ratio is 0.8 moles of H2SO4 consumed for every mole of Fe 2+ for
permanganate, acid additions due to Fe 2+ oxidation are 20% lower when this oxidant is used.
Thus for a sodium permanganate addition of 1.6 kg/t, the acid saving compared to MnO2
would be 1.1 kg/t. As shown in Table 4.8, acid requirements for pyrolusite were in fact
slightly less for pyrolusite after 24 h, but about 0.6 kg/t greater on average at 12 h when
oxidant addition was stopped. For pyrolusite containing 75% reactive MnO2, the equivalent
addition to 1.6 kg/t sodium permanganate is 3.3 kg/t. This predicted requirement is close to
the experimental data.
The results show that essentially the same extractions of uranium were obtained for the two
oxidants after 24 h. Figure 4.18 also indicates that the rate of leaching was almost identical
for the samples, but noting that the initial rate for pyrolusite with Junnagunna was slower than
permanganate, probably resulting from the additional time to reach ORP set-point with
pyrolusite at the start of the leach. (as pyrolusite reacts relatively slowly, care is taken not to
overdose at the start of leaching).
TABLE 4.8
Comparison of Leaching Data for Different Oxidants*
Exp. ID Acid
Addition
(kg/t)
Oxidant ORP at 24 h
Addition (mV)
(kg/t)
Junnagunna
Residue Grade
(ppm U3O8)
Uranium
Extraction*
(%)
LC3 A 20.6 1.6 485 34 97.5
LC12 A 20.0 2.9 # 481
Redtree
38 97.2
LC3 B 17.1 1.6 477 59 96.5
LC12 B 17.0 2.8 # 472 53 96.9
* pH 1.5, 40°C, 500 mV, P80=250 µm # pyrolusite as oxidant
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