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Koniambo S.a.S is one of the largest nickel-producing complexes in New Caledonia, with a plant that produces 60,000 tons of nickel at full operation.

The challenge

The industrial wastewater treatment system covers an area of 7500 m2 and treats different industrial waste streams produced at the “Vavouto” site. A flow rate of 150 m3/h of the treated effluent is available for reuse for dust suppression and potentially for other applications, such as make-up to the ferronickel shotting system and as service water inside the wastewater treatment plant. Excess treated effluent is discharged to the marine environment.

The effluent produced from the complex is rich in solids and heavy metals such as iron, zinc, aluminum, nickel, manganese, and chromium, while the latter is very hard to remove.

The project

Our team studied a dedicated process for removing solids and metals besides chromium (VI) reduction. Wastewater is collected from the equalization plant for coagulation to reduce the presence of solids and metals. It then moves on to flocculation treatment with the dosing of ferrous chlorine, caustic soda, and flocculant (polymer). Caustic soda allows the precipitation of heavy metals by increasing the pH and hence promoting metal hydroxide formation and precipitation. The presence of ferrous chlorine in the coagulation tanks enhances the aggregates (flocs) formation.

Flocculation is the second step, as the flocs increase by adding polymer. Effluent, before discharge, passes through sand filtration. The plant design puts great attention to sludge treatment and dewatering so that Koniambo can recover metals from it using proprietary technology.

Thanks to our consolidated approach, we proposed some changes to the basic tender specification to optimize chemical consumption, choosing the best process for chromium reduction and guaranteeing very high performance.

The supplied solution

The solution that our team provided consists of three different parts.
The equalization section collects all the different inlet industrial streams and internal recycling within the package.

The PH adjustment/coagulation/flocculation section doses the correct chemicals to promote precipitation of heavy metals, such as hydroxides and salts. It enlarges suspended solids in flocs to be retained in the successive clarification and sand filtration sections.

Finally, the sludge thickening section uses a thickener and filter press to concentrate all retained suspended solids and reduce the obtained sludge volume to be discharged.
The package treats an overall flow rate of 155 m3/h.