Abstract
Pyrometallurgical nickel industry in New Caledonia produces several tons of slag per year, which is stocked on site. There is no valorization today, except for a small transformation into sand. Pyrometallurgy highly consumes fossil-fuel energy and electricity for ore pre-treatment and nickel extraction inside electrical furnaces, which produces significant CO2 emissions. A new valorization approach is suggested to use these two local productions (slag and CO2) to mineralize slag and produce silico-magnesian cement for the construction sector. In order to ensure suitable environmental performances, many questions arise about the target valorized product: where and how to capture CO2 and produce cement, what constraints should be targeted for the mineralization process, can products be exported and where? Moreover, New Caledonia aims to develop renewable energies for electricity grid, which would mitigate local industries impacts in the future. A prospective Life Cycle Assessment (LCA) is used to define constraints on future product development. Two hundred scenarios are defined and compared as well as electricity grid evolution, using Brightway software. Thirteen scenarios can compete with traditional Portland cement for 12 of the 16 impacts of the ILCD midpoint method. The evolution of electricity grid slightly affects the performance of the scenarios by a mean of less than+/−25%, bringing a small difference on the number of acceptable scenarios. The main constraint requires improving the mineralization process by considerably reducing electricity consumption of the attrition-leaching operation. To be in line with scenarios concerning carbon neutrality of the cement industry by 2050, a sensitivity analysis provides the maximum energy consumption target for the mineralization process that is 0.9100 kWh/kg of carbonated slag, representing a 70% reduction of the current energy measured at lab scale. Valorization of nickel slag and CO2 should turn to carbon capture and utilization technology, which allows for the production of supplementary cementitious materials, another product for the construction sector. It will be the topic of a next prospective study.
Highlights
Carbon Capture and Utilization (CCU) is a promising field to reduce upcoming climate change
A few scenarios enable nickel slag cement to be advantageous on freshwater and terrestrial acidification, freshwater ecotoxicity and especially ozone layer depletion, as only the lowest part of the boxplots passes under the Portland cement line
This study shows how Life Cycle Assessment (LCA) can help to design circular economy projects at early stage of development, given a territorial context
Summary
Carbon Capture and Utilization (CCU) is a promising field to reduce upcoming climate change. Several capture technologies exist and various applications have been studied over the past 2 decades (Cuéllar-Franca and Azapagic 2015). Mineral carbonation allows the capture of CO2 inside rocks, such as serpentinite, or waste such as steel making slags and platinum tailings (Khool et al, 2011; Nduagu et al, 2012; Giannoulakis et al, 2014; Xiao et al, 2014; Ostovari et al, 2020). CCU is interesting for industrial solid waste, allowing a double advantage by capturing carbon dioxide and offering waste valorization, despite high energy issues (Liu et al, 2021). As studied by (Di Maria et al, 2020; Pedraza et al, 2021) to manufacture construction products with CCU of industrial solid waste, some technology and energy scenarios can be evaluated with LCA. Other characteristics of construction products can be compared with LCA, such as chemical properties, which leads to investigate a wider set of scenarios, e.g. several dozens for (Shahmansouri et al, 2021)
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