1274 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
operation. As is frequently the case when developing new
processes and integrating technology into existing complex
systems, several technical challenges were encountered with
the unique system, necessitating a complete rebuild of the
RDA and extensive testing to define specific operating win-
dows based on feed variability to the circuit. Mitigations
to most of the key operating challenges have been identi-
fied and demonstrated at a laboratory scale, and additional
opportunities for improvement have been engineered to a
pre-feasibility level. Project outcomes indicate the restart of
the Re plant could be technically feasible with additional
investment.
Additionally, over this period, there has been consid-
erable development in new processes and technologies for
the recovery and production of critical minerals, several of
which may be applicable to Re. At present, Rio Tinto is
also evaluating several new and emerging technologies as
potential alternative approaches to produce Re which could
provide improved technoeconomic outcomes.
Bismuth
The U.S. ceased production of primary refined bismuth
(Bi) in 1997 and is highly reliant on imports to meet its
Bi demand. Recycled Bi makes up less than 10% of U.S.
consumption (U.S. Geological Survey 2022 and 2023).
Bismuth has a variety of applications including use in
pharmaceuticals, medical equipment, alloys, production of
synthetic fibers and rubber. The U.S. does not have any
domestic primary Bi production and relies entirely on
imports, primarily from China, which accounts for 67% of
U.S. imports (U.S. Geological Survey 2022). Therefore, Bi
is considered a critical material with strategic importance
for the U.S. due to its essential roles in advanced technolo-
gies and industries (U.S. Geological Survey 2023).
We have explored the recovery of Bi from different
waste streams because of its strategic value and adequate
availability at Rio Tinto’s Kennecott location. Figure 7
shows that concentrations in upstream circuits are insignifi-
cant until Bi reaches the refinery where it separates from the
copper anodes during the electrorefining process. During
this process, Bi becomes part of the insoluble solid precip-
itates (“slimes”) by reacting with arsenic dissolved in the
electrolyte. Later, as the slimes move further downstream
to the precious metal plant, only a small fraction of the
original concentration remains in the downstream solids.
As shown in Figure 8, Bi is a by-product of the precious
metals recovery and refining processes, and it accumulates
in the raffinate solution from the gold solvent extraction,
which is an acidic waste stream. This waste stream has the
highest level of Bi in solution, usually between 6,000 and
12,000 mg/L Bi. Along with other smelter acid wastes, this
stream is then processed at the smelter’s hydrometallurgical
plant. Here, Bi and other metals are removed from solution
during the acid neutralization process, using limestone to
produce a mixed gypsum-Bi filter cake. Currently, this filter
cake is disposed of in the tailings disposal facility (TDF).
The disposal of Bi as a waste currently incurs more reagent
and operating costs and increases the volume needed for
Figure 7. RTK downstream evaluation of bismuth concentration in solids
operation. As is frequently the case when developing new
processes and integrating technology into existing complex
systems, several technical challenges were encountered with
the unique system, necessitating a complete rebuild of the
RDA and extensive testing to define specific operating win-
dows based on feed variability to the circuit. Mitigations
to most of the key operating challenges have been identi-
fied and demonstrated at a laboratory scale, and additional
opportunities for improvement have been engineered to a
pre-feasibility level. Project outcomes indicate the restart of
the Re plant could be technically feasible with additional
investment.
Additionally, over this period, there has been consid-
erable development in new processes and technologies for
the recovery and production of critical minerals, several of
which may be applicable to Re. At present, Rio Tinto is
also evaluating several new and emerging technologies as
potential alternative approaches to produce Re which could
provide improved technoeconomic outcomes.
Bismuth
The U.S. ceased production of primary refined bismuth
(Bi) in 1997 and is highly reliant on imports to meet its
Bi demand. Recycled Bi makes up less than 10% of U.S.
consumption (U.S. Geological Survey 2022 and 2023).
Bismuth has a variety of applications including use in
pharmaceuticals, medical equipment, alloys, production of
synthetic fibers and rubber. The U.S. does not have any
domestic primary Bi production and relies entirely on
imports, primarily from China, which accounts for 67% of
U.S. imports (U.S. Geological Survey 2022). Therefore, Bi
is considered a critical material with strategic importance
for the U.S. due to its essential roles in advanced technolo-
gies and industries (U.S. Geological Survey 2023).
We have explored the recovery of Bi from different
waste streams because of its strategic value and adequate
availability at Rio Tinto’s Kennecott location. Figure 7
shows that concentrations in upstream circuits are insignifi-
cant until Bi reaches the refinery where it separates from the
copper anodes during the electrorefining process. During
this process, Bi becomes part of the insoluble solid precip-
itates (“slimes”) by reacting with arsenic dissolved in the
electrolyte. Later, as the slimes move further downstream
to the precious metal plant, only a small fraction of the
original concentration remains in the downstream solids.
As shown in Figure 8, Bi is a by-product of the precious
metals recovery and refining processes, and it accumulates
in the raffinate solution from the gold solvent extraction,
which is an acidic waste stream. This waste stream has the
highest level of Bi in solution, usually between 6,000 and
12,000 mg/L Bi. Along with other smelter acid wastes, this
stream is then processed at the smelter’s hydrometallurgical
plant. Here, Bi and other metals are removed from solution
during the acid neutralization process, using limestone to
produce a mixed gypsum-Bi filter cake. Currently, this filter
cake is disposed of in the tailings disposal facility (TDF).
The disposal of Bi as a waste currently incurs more reagent
and operating costs and increases the volume needed for
Figure 7. RTK downstream evaluation of bismuth concentration in solids