Prony Resources New Caledonia is a forward-thinking company committed to the sustainable development of New Caledonia’s nickel and cobalt resources to the highest industrial and environmental standards. The company is one of only three in the world that produces nickel hydroxide cake (NHC), which is used in the manufacture of lithium-ion/nickel batteries for electric vehicles.
Case Studies
Challenge
The hydro-metallurgical process of extracting nickel and cobalt produces a neutralized wet residue composed of iron oxides and gypsum. This wet residue is stored in a tailings dam that Prony Resources continuously monitors and regularly inspects to ensure structural stability and integrity.
However, with the tailings dam reaching maximum authorized capacity, Prony Resources began researching a more sustainable solution to the wet storage of its tailings, a solution that would have the minimum impact on the surrounding environment. Prony Resources New Caledonia is located in a pristine natural environment, bordering a UNESCO World Heritage site, a Ramsar wetlands zone and several provincial reserves.
“We’re in a very unique environment,” said Jacques Montserrat, Operations Readiness Manager at Prony Resources New Caledonia. “We have a park all around the plant, and we need to take care of this vegetation to have the minimum impact. We know that we cannot have zero impact, but we need to really minimize this impact.”
Prony Resources’ tailings management options included extending the dam or going in a different direction completely and “dry stacking” the residue. After numerous different studies, Prony Resources decided to go with the dry stack option due to the environmental concerns and costs associated with constructing a new dam.
“Operating a dry stack, it’s new and it’s completely different because in the past, we were more used to a big dam with liquid mud and with all the risk around breaching a dam and damaging the downstream area,” Montserrat explained. “If we compare to the dry stack, it’s really the opposite. We don’t have any more dam; we have only a dry storage, and this dry storage is self-supporting, so we don’t need to have an extra dam to contain this cake.
“And this makes a difference,” continued Montserrat. “You create a mountain of dry residue compared to storing in a wet area.”
Solution
To implement the dry stacking solution, Prony Resources New Caledonia turned to tailings management equipment, which included two 38m High-Rate Thickeners from McLanahan. The McLanahan Thickeners concentrate the neutralized wet residue from the hydro-met plant in preparation for further dewatering by filter presses, which are used to produce the solid cakes for the dry stack.
The Thickeners needed to be designed to process 530 tph of dry solids and maintain an underflow density of approximately 35% solids. McLanahan performed bench-scale testing on the wet residue, including on-site dynamic settling tests to confirm the size and design parameters of the Thickeners.
During this testing phase, the team observed foam was forming on the surface of the pilot Thickener. McLanahan proposed a new design for the overflow launder to avoid the entrainment of air downstream.
Once the Thickener design was confirmed, the challenge then became how to get the large tanks to Prony Resources’ site. To avoid incurring hefty installation fees because of limited site labor, McLanahan recommended the Thickeners be shipped in segments, resembling pie pieces, and assembled on site. For these reasons, the segments were also designed to be bolted together rather than welded together due to New Caledonia’s tropical rains making site welding difficult.
“The bolting and all the installation went well,” said Monserrat. “We didn’t have any leaks, so the bolting was a good solution.”
Throughout the assembly and installation phase, McLanahan personnel were on hand to ensure the process went smoothly and that Prony Resources New Caledonia was trained to operate the Thickeners optimally after commissioning.
Results
Dubbed the Lucy Project, Prony Resources New Caledonia’s innovative technological process to dewater the wet residue aims to optimize the capacity of its current tailings storage dam. The Lucy Project will significantly reduce land clearing to better preserve biodiversity and allow Prony Resources better control of water management. The McLanahan Thickeners play a major role in the success of this project.
“The performance of the Thickener is really a key point that we are monitoring,” Monserrat said. “We have been quite happy with the results that we get.”
He explained that the McLanahan Thickeners are hitting Prony Resources New Caledonia’s target underflow density of 35% solids, as well as exceeding its design flow at 550 tph of dry solids.
In addition to being pleased with the operational results from the Thickeners, Prony Resources New Caledonia has also been happy with the support they’ve received from McLanahan throughout the project.
“We have been satisfied with the design, with the support and with the equipment at the end,” shared Monserrat. “We have been able to run the Thickeners alone at PRNC, but we know that we have still the opportunity to have some support in case of need from McLanahan.
“But the good thing is, today, we are not asking for this support because our Thickeners are working fine.”
