20
This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications
with Umicore’s Hoboken plant in Belgium. As with data on production, information on refinery
technology and processing methodology is generally difficult to obtain, because processes are
proprietary and a large part of the production is in China. Figure 9 summarizes the process
described in Fthenakis et al. (2007), which is in turn based on Ullmann’s encyclopedia and other
information from manufacturers’ reports.
As described in Section 3.5.3, after roasting the zinc oxides undergo leaching and purification,
which precipitates indium in a solution pregnant with other minerals such as zinc, arsenic, and
cadmium. As detailed in Figure 9, the precipitates formed in zinc refining undergo a series of
leaching steps, followed by cementation. The cements are then washed and pressed to form
briquettes that are refined in a furnace and poured into ingots (Fthenakis et al. 2009 and
de Souza 2010).
Precipitates of: Cd, sludge, Ge, In,
Ga, Pb & Zn.
30%Zn, 30%Pb, 3.5%As, 3%Cd,
0.4%In (Fthenakis et al., 2007)
Pre-leaching in
dilute H
2
SO
4
Leaching in dilute
HCl
50-65%, Pb, 1% Zn,
0.15%In
, 0.2-0.3%
As
6%Zn, 50%Pb,
0.68%In
Neutralization
(pH 1)
20% As, 5-10% Sn,
5%Sb,
0.2% In
3g/L In, 15g/L As,
20-40g/L Zn, 6g/L Cd
Precipitation of In
Filtrate: 40g/L Zn,
6g/L Cd, 1g/L As,
10-50mg/L In
NaOH Leaching
10% As, 8%Zn,
10%In, 0.6%Cd
10g/L As, 4g/L Zn,
0.2g/L Sn, 60g/L
NaOH
20%In, 1.5%-3%As,
6%Zn, 0.5-2% Cd
Leaching in dilute
HCL
Cementation of Cu
with Fe
Fe
Cu-As cement
Cementation of Sn
and Pb with In
In
Cementation of In
with Al
Al
Indium cement
Firing in furnace
with chloride
Indium ingots
Losses
Inputs
Intermediate products
Legend
Figure 9. Advanced refining of indium from the precipitates of zinc smelting
Note: % refers to the weight % (i.e., concentration) of the output. Sources: Fthenakis et al. (2009) and de Souza
(2011)
The product is normally at least 99.99% pure; however, at least 97% purity can also be achieved
if the impurities are high; purities kept in check may have a final indium purity higher than
99.995%. The total recovery of refining is ~80% (Alfantazi 2003; de Souza 2011).
21
This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications
3.5.5 Costs of Refining
Although the price structures for indium sponge and other forms of indium are negotiated with
refineries on a case-by-case basis, sales contracts generally feature: (1) price discounts used in
long-term off-take contract agreements; (2) refining charges for upgrading 95% to 99% indium
products to 4N8 (99.998%) grade indium metal; and (3) terms will reflect refining yields
(Thibault et al. 2010).
Based on a recent feasibility study for a mine in Canada, a toll treatment charge of approximately
CAD 66/kg of 4N8 indium produced from 95% pure indium sponge received is approximately
representative of current refining costs and efficiencies (Table 7).
Table 7. Indium Refining Terms for Indium Sponge Revenue Calculations Used in
NI 43-10118 Report for Mount Pleasant Property
Parameter
Units
Value
Notes
Price discount factor for
indium sponge
%
87.5%
Typical discount used for pricing indium
sponge relative to 4N grade indium
Recovery of indium in
refining process
19
Wt%
93.0%
No payment is received for indium lost
during refining process
Total refining and penalty
charge
CAD/kg
4N8
indium
20
$66
Charge based on refining 95% (by wt.)
indium sponge to 4N8 grade indium
Source: Thibault et al. (2010)
By comparison, when shipping concentrates for toll processing by refiners, one can expect to
obtain 53% and 15% of the final market price of zinc and indium, respectively, because of
deductions. (Exact figures will vary depending on the unique characteristics of the concentrate.)
When shipping indium sponge, one would expect to achieve 71% credit of the final market price
(Thibault et al. 2010).
3.5.6 Overall Recovery Efficiency
Principally because of its low economic contribution to zinc and other base metal producers and
the complexity of metallurgical extraction, the overall recovery of primary indium over its value
chain is poor. Typically, less than 20% of the indium content in concentrates is extracted to yield
indium metal, but higher indium prices and technological developments can make it
economically viable for mines, smelters, and refineries to invest to increase yields and capacities.
A study undertaken by Indium Corp. shows that only approximately 30% of the total indium
mined annually becomes refined indium metal (Mikolajczak 2009). Our calculations put the
overall recovery closer to 15%–20% and, as depicted in Figure 10, the major causes of the low
overall recovery rate follow:
18
NI 43-101 (or National Instrument 43-101) represents the Canadian standard for reporting economic and mineral resource
information for companies traded on Canadian stock exchanges.
19
One would expect the latest estimates of recovery efficiency to exceed industry averages (~80%, Alfantazi
and
Moskalyk
2003 and de Souza 2011) as new or planned facilities would use the latest technologies.
20
As of April 27, 2012, 1 CAD = 0.98 USD.