636 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Results of the Reverse Osmosis Process
The pilot plant RO process operated steadily with a recov-
ery of 70% without observing saturation of membranes
by gypsum scale or any other type of fouling. The wash-
ings of the membranes were carried out only for preventive
maintenance purposes after every 15 days of operation. The
addition of antiscalant reagents was not required to prevent
gypsum scaling, nor is it possible to add this or any other
product with a pH greater than 3. A pH of 3 or higher in
the RO feed during the operation will cause iron precipita-
tion and therefore premature fouling of the membranes.
The washing reagents used for membrane cleanings are
those commonly used in industry and include acid washing
with citric acid, hydrochloric acid (pH 2.0) and basic wash-
ing (pH 11.0) with caustic soda.
It was observed that even in an acidic environment,
calcium and sulfates in the combined feed solution could
cause fouling of the membranes. A chart with a safe operat-
ing zone was developed for the RO feed solution shown in
Figure 9. Depending on the concentrations of calcium and
sulfates in the feed solution, the RO recovery is adjusted
accordingly using this chart (Figure 8). For the case of
this study, calcium had concentrations in the range of 75
to 150 mg/L and the average sulfate concentration was
2,400 mg/L with peaks of up to 3,000 mg/L. With this
feed chemistry the RO recovery ranges between [70–75]%.
In one of the tests we operated at 80% recovery without
major problems. These high recoveries support the concept
that the use of RO to treat acidic waters is possible, exceed-
ing typical recoveries between [60–70]% which is common
in conventional applications for alkaline solutions with the
presence of gypsum.
Results of the Ultrafiltration Process
Ultrafiltration is the stage prior to reverse osmosis where the
solid/liquid separation is performed. The processed acidic
water contained concentrations of iron (Fe) in a range of
100 to 500 mg/L, and a pH of 2.5 was maintained at
all times in the UF feed solution. This feed pH was main-
tained in order to keep the iron in solution and prevent it
from precipitating in the membranes (Figure 11). Sulfuric
acid was used to adjust the pH when necessary.
When the different feed sources were mixed in the UF
feed tank, an increase in suspended solids was observed and
Figure 8. Safe working zone of reverse osmosis in acid conditions, the recovery varies depending
on calcium and sulphates concentrations
Results of the Reverse Osmosis Process
The pilot plant RO process operated steadily with a recov-
ery of 70% without observing saturation of membranes
by gypsum scale or any other type of fouling. The wash-
ings of the membranes were carried out only for preventive
maintenance purposes after every 15 days of operation. The
addition of antiscalant reagents was not required to prevent
gypsum scaling, nor is it possible to add this or any other
product with a pH greater than 3. A pH of 3 or higher in
the RO feed during the operation will cause iron precipita-
tion and therefore premature fouling of the membranes.
The washing reagents used for membrane cleanings are
those commonly used in industry and include acid washing
with citric acid, hydrochloric acid (pH 2.0) and basic wash-
ing (pH 11.0) with caustic soda.
It was observed that even in an acidic environment,
calcium and sulfates in the combined feed solution could
cause fouling of the membranes. A chart with a safe operat-
ing zone was developed for the RO feed solution shown in
Figure 9. Depending on the concentrations of calcium and
sulfates in the feed solution, the RO recovery is adjusted
accordingly using this chart (Figure 8). For the case of
this study, calcium had concentrations in the range of 75
to 150 mg/L and the average sulfate concentration was
2,400 mg/L with peaks of up to 3,000 mg/L. With this
feed chemistry the RO recovery ranges between [70–75]%.
In one of the tests we operated at 80% recovery without
major problems. These high recoveries support the concept
that the use of RO to treat acidic waters is possible, exceed-
ing typical recoveries between [60–70]% which is common
in conventional applications for alkaline solutions with the
presence of gypsum.
Results of the Ultrafiltration Process
Ultrafiltration is the stage prior to reverse osmosis where the
solid/liquid separation is performed. The processed acidic
water contained concentrations of iron (Fe) in a range of
100 to 500 mg/L, and a pH of 2.5 was maintained at
all times in the UF feed solution. This feed pH was main-
tained in order to keep the iron in solution and prevent it
from precipitating in the membranes (Figure 11). Sulfuric
acid was used to adjust the pH when necessary.
When the different feed sources were mixed in the UF
feed tank, an increase in suspended solids was observed and
Figure 8. Safe working zone of reverse osmosis in acid conditions, the recovery varies depending
on calcium and sulphates concentrations