Abstract
The Metals Company (TMC) has commissioned Benchmark Minerals Intelligence (Benchmark) to model the environmental performance of
producing critical minerals from polymetallic nodules found on the seafloor of the Clarion-Clipperton Zone (CCZ), in the Pacific Ocean.
This is a three-part study:
- Part 1: full Life Cycle Assessment (LCA) on TMC processes.
- Part 2: comparison of Part 1 to land-based routes.
- Part 3: waste stream analysis (note that this part has not been third party verified).
This attributional LCA is third party verified and ISO compliant under ISO standards 14040 & 14044. This executive summary provides an overview of the LCA: methodology, key results, and recommendations. It also provides an overview of the TMC’s developing process and technology.
Full LCA: Goal and Scope
The goal is to 1) inform The Metals Company (henceforth TMC) and their stakeholders of the potential environmental impacts
of producing manganese silicate, Ni/Cu/Co matte, nickel sulphate, cobalt sulphate and copper cathode material from polymetallic nodules (PMN) found in NORI-D, and to 2) compare it to the dominant terrestrial mining
This system is a ‘cradle-to-gate’ analysis: the ‘cradle’ starts at raw material extraction and ending with the ‘gate’ – finished product, before packaging is added, with a system expansion approach to multifunctionality of the system. Life Cycle Inventory (LCI) and Life Cycle Impact Assessment (LCIA) Metallurgical demand was adopted when applicable. When this was not available, mass and economic allocation were applied. LCI uses primary data from TCM’s estimated yearly production and secondary data from Ecoinvent (version 3.8). The midpoint and endpoint categories from ReCiPe 2016 methodology were calculated and calibrated in SimaPro (version 9.4.0.2).
Developing process and technology
Once collected, deep-sea polymetallic nodules are on tidewater and can be transported by ship to an onshore processing site. The study analysed Texas, out of three potential locations: Texas, India and Malaysia, where pyrometallurgical steps can be taken to generate Nickel, Copper and Cobalt (Ni/Cu/Co) matte and Manganese silicate slag. The matte can be further processed via a hydrometallurgical process to obtain refined metals in sulphate form.
Results
The combustion, production and distribution of bituminous coal were the biggest drivers behind most impact category results for all five of TMC’s NORI-D project’s products, as shown through the input contribution analysis. The combustion of bituminous coal alone contributed to 63-65% of the Global Warming Potential (GWP) of all products, therefore direct emissions are the major source of GHG emission, making the pyrometallurgical stage the most environmentally impactful stage.
Following ISO, allocation is avoided whenever possible through the identification of sub-processes. The sensitivity analysis shows that the results can be interpreted differently if other allocation methodologies were to be applied. Sensitivity analysis indicates that the results are sensitive to economic allocation and environmental credits, but not to the location of onshore production and variations in metal price.
TMC NORI-D model of all five products resulted in a better environmental performance than analysed traditional land processing routes in the majority of the impact categories, within the mixed allocation methodology applied. For instance, the GWP of TMC NORI-D model are 54-70% lower than the other routes on average. The GWP and water consumption for cobalt sulphate production via the RLE route are the only exceptions. Some explanations for these lower emissions may be due to the absence of blasting and sulphidic tailings in TMC’s NORI-D nodule collection processes.
Other reasons for a lower environmental burden include differences in TMC NORI-D’s engineered onshore processes which encompass lower energy demand (distributed between co-products), renewable electricity in Texas, high-revenue and high-volume co-products, and high metal recovery rates. According to the Waste Stream analysis, TMC NORI-D’s processes could potentially have less hazardous impact on soil. The mobilised sediment represents the highest volume of material displaced in TMC’s NORI-D polymetallic project. However, in comparison to land-based processes, TMC NORI-D would generate less waste overall.
Recommendations
- In order to reduce overall emissions, it is most impactful to focus on finding a replacement for metallurgical coal as a reductant.
- Alternatives such as biomass pellets should be considered. Natural gas used for heat is also a significant source of GHG emissions.
- Ammonia and sulphuric acid should be sourced from suppliers with less emissions attached to the production or strategically engineered to be used in a more efficient fashion.
- At the time of study, due to time constrains, Benchmark was unable to assess sediment composition. Furthermore, SimaPro is not be equipped to fully capture this impact.
- ▪ LCAs only assess environmental impacts covered in the scope and goals of the study. Therefore, not all environmental issues affected by the product system are covered.