Nickel slag recovery in New-Caledonia: Study of an innovative process with CO2 mineral carbonation using prospective life cycle assessment

Main Presenter:    Eva Quéheille 

Co-Authors:   Michel Dauvergne     Lauredan Le Guen      Anne Ventura                                    

New-Caledonia is one of the world’s largest suppliers of nickel. However, in producing nickel, the pyrometallurgical industries also produce million tons of nickel slag per year. Currently, only a small quantity is recovered as sand for concrete production, and the cumulated stock of slag on the island has reached several tens of million tons, causing pollution risks for the local population and environment.

An innovative process is developed to recover nickel slag [1]. The heart of the process is the mineral carbonation of CO2 inside slag. Carbonated slag can then be transformed into silico-magnesian cement or supplementary cement materials to partially replace clinker into cement. The process should bring a further environmental benefit by carbonating CO2 from local industries. Indeed, pyrometallurgical industries emit million tons of CO2 per year by consuming fossil fuels and electricity for ore pre-treatment and nickel extraction. But the process is currently at laboratory scale, which means a low Technology Readiness Level (TRL), 3-4 out of 9. The question is how to assess the environmental performance of this recovery process while it is at laboratory scale. How would it be settled at industrial scale in New-Caledonia? How can materials from nickel slag recovery have less environmental impact than conventional materials? Should the process be optimized, e.g. in terms of energy
consumption?

In order to explore the potential of this innovative recovery, a prospective Life Cycle Assessment (LCA) is conducted. Future scenarios for the settlement of the recovery industry in New-Caledonia are created. They tend to assess several decisions such as where to capture CO2, which energy source to use, where to sell the products… The two products (silico-magnesian cement and supplementary cement materials) are initially tested separately [2], but the ultimate objective is to identify if whether co-production is feasible and how this industry would be. The mineral carbonation process is also studied. Sensitivity analyses are conducted specifically on two parameters: the carbonation rate of nickel slag and the electricity consumption. The work is achieved with the Brightway framework [3] and the Premise tool [4].

With this prospective LCA study, the scenarios which would bring environmental benefits are identified. Local stakeholders in New-Caledonia can then use these scenarios to finally prepare the territory for efficient industrial recovery of nickel slag. Eventually, the results also provide a better understanding of the mineral carbonation process and gives useful indications for the team in charge to continue its development.

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