Context
METALKOL operates a cobalt-copper mine in Lualaba province using a hydrometallurgical process. The retention lake contains acidic effluents (pH 2–3.5) requiring permanent floating platforms for pump maintenance work.
Technical constraints
Stability under variable loads (200–800 kg pumps), chemical resistance to dilute sulphuric acid over 15 years, UV durability, and repositioning with site equipment.
Material selection
Testing of HDPE, hot-dip galvanised steel and 316 stainless steel in actual lake water samples over 30 days. Stainless steel showed pitting at week 3. HDPE and galvanised steel remained intact.
Design
12 × 4 m pontoons, S355 steel hot-dip galvanised (92–118 µm zinc), electro-forged grating surface. Buoyancy by 8 HDPE modules per pontoon, mechanically fixed with A4 stainless fittings. 40% buoyancy reserve above nominal load. Metacentric height GM = 0.59 m (ISO 12217 minimum: 0.20 m).
Fabrication and testing
Kinshasa workshop: MIG welding, Sa 2.5 blast, hot-dip galvanising. Flotation basin tests: draught at void 152 mm, at full load 398 mm, freeboard 252 mm. Inclination test at 400 kg offset load: 3.2° (spec ≤ 5°).
Results after 2 years
No stability incident, no chemical degradation, 30% reduction in maintenance intervention time vs inflatable craft. Zero acid immersion accidents.
