FRP Tanks for Mining: Leaching & Electrowinning (SX-EW)

Few services punish materials the way a solvent extraction–electrowinning (SX-EW) circuit does. The process moves dilute sulfuric acid solutions through leaching, extraction, and electrowinning while carrying suspended solids, dissolved metals, and—depending on the orebody—chlorides and other aggressive ions. As manufacturers, we do not design a tank that simply "holds liquid"; we design equipment that survives years of acid, heat, and abrasion without leaks, without contaminating the process, and without causing unplanned shutdowns. Fiberglass reinforced plastic (FRP) has become the natural choice for PLS ponds and tanks, raffinate tanks, electrolyte storage, and a range of process vessels—but only when it is built to the correct standard.

This article explains, from the inside, what makes SX-EW service so demanding, how we build FRP for that duty, and what we verify in the shop before a tank ever sees acid.

Why SX-EW Is So Demanding

SX-EW combines three deterioration mechanisms that rarely appear together at this intensity:

1. Sustained acid exposure. PLS, raffinate, and electrolyte streams are sulfuric-acid based and run continuously, not in batches. The material is wetted around the clock.
2. Elevated temperature. Leaching and electrowinning streams often run warm, and temperature accelerates nearly every corrosion mechanism. A material that resists acid cold can fail quickly with the same acid hot.
3. Abrasion and entrained solids. Leach circuits carry fine particulates that, over time, thin the barrier and expose the structural laminate to chemical attack.

On top of this, many sites are remote and high-altitude, where a failed metal tank means long lead times, costly cranes, and lost production. Getting the material wrong is paid in downtime, not just replacement steel.

How We Build FRP for This Duty

FRP is not a single material; it is a system. A properly built corrosion-service tank has two functional zones. The inner corrosion barrier—a resin-rich layer reinforced with surfacing veil and chopped strand—is what actually contacts the acid and does the chemical work. Behind it, the structural laminate carries the mechanical loads. When we build a tank for SX-EW, the first thing we define is the resin chemistry of that barrier and the integrity of the laminate behind it.

For sulfuric acid service, corrosion-grade vinyl ester resins are the workhorse. As a practical design figure, standard vinyl ester FRP suits continuous service in the range of roughly 82–93°C (180–200°F), which covers the great majority of SX-EW streams. Where a process runs hotter or combines acid, oxidizers, or chlorides unusually, we reinforce the barrier with a thermoplastic fluoropolymer liner. These liners extend the temperature window substantially—ECTFE, for example, works to about 160°C (320°F) and PVDF to about 140°C (284°F)—and add a dense, low-permeation barrier against the most severe chemistries.

Resin Selection Decides Everything

The most important line in any specification is the resin. Two tanks that look identical can behave oppositely because of the resin in their corrosion barrier. Here we apply ASTM C581: the standard practice for evaluating the chemical resistance of a thermosetting resin in the specific environment it will see. Rather than accept a generic "chemical resistant" label, we tie the resin to the actual stream—acid concentration, temperature, and contaminants—within the C581 framework.

1. We define the chemistry, temperature, and solids loading of each stream. "Sulfuric acid" alone is not a specification.
2. We build a corrosion barrier suited to the service, with a liner defined where temperature or chemistry demand it.
3. We recommend a fluoropolymer liner only on the hottest or most aggressive vessels, rather than over-building every tank.

Fabrication Method and Quality Control

How the tank is built matters as much as the resin. Two ASTM standards govern corrosion-resistant FRP tanks, and the right one depends on geometry and loads:

1. ASTM D3299 covers filament-wound tanks, where continuous glass is wound under controlled tension. It delivers high, predictable structural strength, ideal for large vertical tanks.
2. ASTM D4097 covers contact-molded (hand lay-up) tanks, with flexibility for complex shapes, fittings, and project-specific geometry.

For aggressive acid service, hardness is a simple, inexpensive quality check. ASTM D2583 measures Barcol hardness, which confirms the resin has fully cured. An under-cured laminate will not deliver the chemical resistance the resin is capable of, so a Barcol reading on the finished part validates build quality before the tank sees acid.

Design Considerations We Apply in the Shop

To deliver a tank built for SX-EW rather than a generic vessel, on every project we define:

1. Service definition: stream type (PLS, raffinate, electrolyte), chemistry, maximum operating temperature, and solids content.
2. Corrosion barrier: resin tied to ASTM C581 evaluation, with a fluoropolymer liner where temperature or chemistry require it.
3. Fabrication standard: ASTM D3299 (filament-wound) or ASTM D4097 (contact-molded), matched to geometry and loads.
4. Quality verification: Barcol hardness per ASTM D2583, plus visual and dimensional acceptance criteria.
5. Details: nozzle and manway locations, anchoring and seismic loads, venting, and abrasion provisions for solids-laden streams.

Applicable ASTM Standards

SX-EW tanks are atmospheric process and storage vessels, so the governing standards are the FRP tank specifications—ASTM D3299 and ASTM D4097—supported by ASTM C581 for resin chemical resistance and ASTM D2583 for cure verification. Pressure-vessel codes do not apply to these atmospheric tanks.

Our Experience

We have spent more than 40 years building exclusively in FRP, across more than 2,600 projects, with a heavy concentration in mining, chemical processing, and water treatment. We have built tanks and process vessels for sulfuric acid circuits where the combination of acid, heat, and abrasion leaves no margin for a generic build. For the hottest and most aggressive duties, we have applied thermoplastic fluoropolymer liners for over 20 years, matching the liner to the stream rather than over-building every vessel. That experience is what turns a material specification into a tank that runs for years.

Conclusion

FRP earns its place in SX-EW because it resists sulfuric acid, tolerates the temperatures of most leaching and electrowinning streams, and—when lined—handles the hot, aggressive exceptions, all without the corrosion liabilities of metals. The difference between a tank that lasts and one that fails is in the specification: the resin in the barrier, the fabrication standard, and verified cure. At Plastimarmol we build to these standards on every project. Tell us your circuit chemistry, temperature, and solids loading, and we will match the barrier, liner, and fabrication method to your service. Request a quote.

References

ASTM International. (2020). Standard practice for determining chemical resistance of thermosetting resins used in glass-fiber-reinforced structures intended for liquid service (ASTM C581-20). ASTM International.

ASTM International. (2021). Standard test method for indentation hardness of rigid plastics by means of a Barcol impressor (ASTM D2583-13a(2021)). ASTM International.

ASTM International. (2020). Standard specification for filament-wound glass-fiber-reinforced thermoset resin corrosion-resistant tanks (ASTM D3299-10(2020)). ASTM International.

ASTM International. (2019). Standard specification for contact-molded glass-fiber-reinforced thermoset resin chemical-resistant tanks (ASTM D4097-19). ASTM International.