632 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
than 250 mg/L (ECA 1-A1) for waters that are able to be
purified with conventional treatment for drinking water.
(Decreto Supremo N° 004‑2017-MINAM).
Pyrite (FeS2) is the ore mainly associated with sulfates
generation and acidity in water.
The process commonly adopted in mining to reduce sul-
fates is the chemical precipitation of sulfates with hydrated
lime Ca(OH)2 which produces gypsum. This established
type treatment is denominated as “Conventional Treatment”
in this article. Gypsum has a high potential for scaling for-
mation when it precipitates, and easily forms a hard layer
of scaling in pipes and equipment. Conventional treatment
produces a treated water with high sulfates concentration,
typically in a range of 1,800 to 2,400 mg/L. These con-
centrations are much higher than the required discharge
limits [250 – 1,000] mg/ L. Solutions after conventional
treatment requires additional treatment through reverse
osmosis membranes, which produces a permeate stream
with low sulfates concentrations of less than 100 mg/L. The
concentrated stream produced in the RO process requires
additional treatment. The main problem with processing
solutions containing gypsum through an RO is the gypsum
scale that is generated. This gypsum scale decreases the pro-
duction efficiency of RO permeate and increases operating
costs since it requires the addition of antiscalant reagent.
Gypsum scale in RO systems also requires more frequent
chemical washing of the membranes and high frequency
of membrane replacement. Once gypsum is precipitated in
the membranes surface, it can be removed using aggressive
cleaning techniques, however, the RO membranes perfor-
mance is permanently compromised.
The Newmont Technical Services department carried
out initial tests 10 years ago which focused on directly
treating acidic mine waters through RO membranes. This
test work showed that treating acid mine effluents before
the addition of lime does not produce gypsum scale. Thus,
in 2021, the operation of a 2 m3/h pilot plant located in the
Newmont Yanacocha mining unit began operation in order
to verify that the process is indeed viable. The operation of
this pilot plant lasted two years.
Other existing sulfate reduction processes such as ion
exchange, ettringite and bacterial reduction, were evalu-
ated, though only at the theoretical and benchmarking
level. These other treatment options have high operational
complexities and associated costs for use at Newmont’s
operations, and for these reasons, they were not considered
for further evaluation.
OBJECTIVES
Demonstrate that acidic mining effluents can be treated
directly through Reverse Osmosis (RO) membranes while
maintaining an efficient, stable and reliable operation of the
Table 1. Newmont’s operations around the world
Region Operation Country
North America Eleonore
Musselwhite
Porcupine
Brucejack
Red Chris
Cripple Creek &
Victor
Peñasquito
Canada
Canada
Canada
Canada
Canada
USA
Mexico
South
America
Cerro Negro
Merian
Yanacocha
Argentina
Suriname
Peru
Africa Ahafo South
Akyem
Ghana
Ghana
Oceania Boddington
Tanami
Telfer
Cadia
Lihir
Australia
Australia
Australia
Australia
Papua New
Guinea
Source: Bryan Moravec 1995.
Figure 1. Chemical formulas for sulfate generation and pyrite acidity
than 250 mg/L (ECA 1-A1) for waters that are able to be
purified with conventional treatment for drinking water.
(Decreto Supremo N° 004‑2017-MINAM).
Pyrite (FeS2) is the ore mainly associated with sulfates
generation and acidity in water.
The process commonly adopted in mining to reduce sul-
fates is the chemical precipitation of sulfates with hydrated
lime Ca(OH)2 which produces gypsum. This established
type treatment is denominated as “Conventional Treatment”
in this article. Gypsum has a high potential for scaling for-
mation when it precipitates, and easily forms a hard layer
of scaling in pipes and equipment. Conventional treatment
produces a treated water with high sulfates concentration,
typically in a range of 1,800 to 2,400 mg/L. These con-
centrations are much higher than the required discharge
limits [250 – 1,000] mg/ L. Solutions after conventional
treatment requires additional treatment through reverse
osmosis membranes, which produces a permeate stream
with low sulfates concentrations of less than 100 mg/L. The
concentrated stream produced in the RO process requires
additional treatment. The main problem with processing
solutions containing gypsum through an RO is the gypsum
scale that is generated. This gypsum scale decreases the pro-
duction efficiency of RO permeate and increases operating
costs since it requires the addition of antiscalant reagent.
Gypsum scale in RO systems also requires more frequent
chemical washing of the membranes and high frequency
of membrane replacement. Once gypsum is precipitated in
the membranes surface, it can be removed using aggressive
cleaning techniques, however, the RO membranes perfor-
mance is permanently compromised.
The Newmont Technical Services department carried
out initial tests 10 years ago which focused on directly
treating acidic mine waters through RO membranes. This
test work showed that treating acid mine effluents before
the addition of lime does not produce gypsum scale. Thus,
in 2021, the operation of a 2 m3/h pilot plant located in the
Newmont Yanacocha mining unit began operation in order
to verify that the process is indeed viable. The operation of
this pilot plant lasted two years.
Other existing sulfate reduction processes such as ion
exchange, ettringite and bacterial reduction, were evalu-
ated, though only at the theoretical and benchmarking
level. These other treatment options have high operational
complexities and associated costs for use at Newmont’s
operations, and for these reasons, they were not considered
for further evaluation.
OBJECTIVES
Demonstrate that acidic mining effluents can be treated
directly through Reverse Osmosis (RO) membranes while
maintaining an efficient, stable and reliable operation of the
Table 1. Newmont’s operations around the world
Region Operation Country
North America Eleonore
Musselwhite
Porcupine
Brucejack
Red Chris
Cripple Creek &
Victor
Peñasquito
Canada
Canada
Canada
Canada
Canada
USA
Mexico
South
America
Cerro Negro
Merian
Yanacocha
Argentina
Suriname
Peru
Africa Ahafo South
Akyem
Ghana
Ghana
Oceania Boddington
Tanami
Telfer
Cadia
Lihir
Australia
Australia
Australia
Australia
Papua New
Guinea
Source: Bryan Moravec 1995.
Figure 1. Chemical formulas for sulfate generation and pyrite acidity