An electrowinning tankhouse at a copper SX/EW plant operates at roughly 2 volts per cell — but with thousands of cells in series, the bus voltage can exceed 400 volts DC. The platforms that operators walk on to inspect cells, check electrolyte levels, and harvest cathodes are surrounded by energized copper busbars and acidic electrolyte mist. If the platform conducts electricity, it becomes a hazard. If it corrodes in the acid mist, it becomes a maintenance burden. FRP platforms address both conditions simultaneously, which explains their widespread adoption in hydrometallurgical processing.
The mining platform environment: acid, electricity, and abrasion
Hydrometallurgical mining — primarily copper, nickel, and zinc extraction — uses sulfuric acid as the leaching agent and electrolyte. The entire solvent extraction and electrowinning area operates under conditions that combine multiple material degradation mechanisms:
- Acid mist: Electrowinning cells generate a fine sulfuric acid aerosol that settles on every surface in the tankhouse. The acid concentration in the mist is low (typically 150–200 g/L H₂SO₄ in the electrolyte, diluted in the mist), but it's continuous. Steel structures in a tankhouse environment require protective coating systems that typically need repair within 3–5 years.
- Stray electrical currents: In an operating tankhouse, electrolyte leaks and conductive paths can create stray currents that accelerate the corrosion of metallic structures through electrolytic corrosion. FRP is non-conductive — it can't participate in a stray-current corrosion cell.
- Operator safety near energized cells: The platform that an operator stands on while inspecting cells at 400+ volts DC potential must not become part of an electrical path to ground. FRP platforms provide inherent electrical isolation without requiring insulating mats or coatings that can be damaged or misplaced.
- Mechanical loading from cathode handling: Harvested copper cathodes weigh 50–80 kg each. Platforms in the harvesting area see impact loads from cathode handling equipment and foot traffic from crews in safety boots. The FRP platform must be designed for these loads — the material handles them, but the design must account for FRP's different stiffness characteristics.
Platform locations in a mining operation
- Electrowinning cell top platforms: Walkways between cell rows, providing access for electrolyte level checks, cathode inspection, and anode cleaning. These platforms are continuously exposed to acid mist and are adjacent to energized busbars.
- Solvent extraction (SX) mixer-settler platforms: Access platforms around the mixer-settler units where organic extractant (kerosene-based) and acidic aqueous solution are mixed and separated. The organic phase can attack certain polymer systems — vinyl ester resin is specified for chemical resistance to both the organic and aqueous phases.
- Tank access platforms: Operating levels around raffinate, pregnant leach solution, and electrolyte storage tanks. These platforms are exposed to the same chemical environment as the tank contents, plus outdoor weather conditions at many mine sites.
- Leach pad solution distribution walkways: Access along leach pad irrigation lines, exposed to sulfuric acid solution, UV radiation, and sometimes high-altitude conditions at Andean or high-desert mine locations.
Typical mining platform configuration
| Parameter | Mining Typical | Rationale |
|---|---|---|
| Grating type | Molded FRP, 38 mm, vinyl ester resin | Vinyl ester for sulfuric acid resistance and organic solvent tolerance |
| Deck load | 4.8 kN/m² (100 psf) standard; 7.2 kN/m² (150 psf) in cathode handling zones | Heavier loading where cathode bundles are temporarily placed |
| Support structure | Pultruded FRP I-beams, 203–305 mm depth | Spans of 1.2–1.8 m typical for tankhouse walkways |
| Electrical isolation | Full FRP structure — no metallic fasteners or supports | FRP bolts and nuts throughout; no bonding or grounding conductors |
| Chemical resistance | Vinyl ester resin throughout grating and structure | Resistance to H₂SO₄ up to 50% concentration at ambient temperature |
| Handrail | FRP pultruded, non-conductive | No metal components that could become energized |
| Slip resistance | Grit-top surface, concave meniscus available | Wet conditions from electrolyte drips and washdown |
| UV resistance | UV-stabilized for outdoor installations (leach pads, tank farms) | Many SX/EW plants are open-air or under simple canopies |
| Fire performance | ASTM E84 Class 1 (flame spread ≤ 25) where building code requires | Tankhouse buildings often classified as industrial occupancy |
"The steel platforms between electrowinning cells were showing severe corrosion within 3 years, and the insulating mats required constant inspection and replacement. The FRP replacement platforms eliminated both the corrosion and the electrical isolation concerns in a single material change."
This page describes where FRP platforms are used in mining operations. For the broader platform systems overview, see FRP Platform Systems — Industrial Applications. For corrosion strategies in aggressive chemical environments, see Corrosion Prevention Solutions.