Sediment plumes and financial modeling in the context of deep-sea polymetallic nodule mining
Deep-sea polymetallic nodule mining commercial operations are close to becoming a reality. In recent years, research activity in the field has substantially increased, but there are yet many technical, environmental and financial challenges to be addressed. This work tackles three critical topics es...
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Massachusetts Institute of Technology
2022
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| Online Access: | https://hdl.handle.net/1721.1/140142 https://orcid.org/0000-0002-2181-0577 |
| Summary: | Deep-sea polymetallic nodule mining commercial operations are close to becoming a reality. In recent years, research activity in the field has substantially increased, but there are yet many technical, environmental and financial challenges to be addressed. This work tackles three critical topics essential to advance the knowledge and understanding in the field, namely, (i) nodule collector and (ii) return water sediment plumes discharged to the ocean during nodule mining operations, and (iii) the financial modeling of a nodule mining operation and the analysis of royalty payment systems for the International Seabed Authority.
A nodule collector vehicle will operate on the seabed to pick up polymetallic nodules and, inevitably, also certain amount of seabed sediment. Most of the unwanted sediment will be discharged directly at the rear of the collector vehicle, creating the so-called collector plume, which will then be transported away from the mining area with the consequent environmental impact. DSM21, a dedicated collector plume field study with a prototype nodule collector vehicle, was designed and conducted for the first time at 4500 m of depth in the Clarion Clipperton Fracture Zone in the Pacific ocean to monitor the collector sediment plume. Field observations confirm that the sediment discharge initially behaves as a turbidity current, shifting the currently established modeling paradigm for such plumes towards a multi-scale approach. The turbidity current sets the initial conditions of the subsequent ambient plume that is then transported by ocean currents, and subjected to the ocean turbulence in the bottom boundary layer and the sediment settling. The observations from the field studies also suggest that the design of the collector vehicle may have a direct influence on the initial height reached by the sediment, which, in turn, is critical to set the impact time and length-scales.
A fraction of the unwanted sediment will be lifted up to a mining vessel together with the nodules. There, the sediment and water will be separated and discharged back to the ocean at depth. First, a Monte Carlo analysis is conducted to define the parameter space of the discharge characteristics and its dynamic regime. Then, a multi-scale modeling approach based on well-established fluid dynamic principles is developed to model the discharge in the midwater column and close to the seabed. PLUMEX, a large scale field study, was designed and conducted for the first time in the Pacific ocean aboard R/V Sally Ride to discharge and monitor six plumes in the midwater column. Field observations served as a validation of the near field modeling approach, and showed that sediment aggregation is not relevant for this type of discharge.
The International Seabed Authority is currently developing the regulations for the commercial exploitation of polymetallic nodules in international waters. Nodules are common heritage of mankind and, as such, their exploitation for commercial purposes is to be financially compensated via a royalty payment, as established in the current version of the draft regulations. However, the singularities of nodule mining in international waters, the available number of alternative royalty systems and their implications make it challenging to determine which system is best for this application. As requested by the International Seabed Authority, a financial model of a nodule mining operation in international waters was developed incorporating feedback from stakeholders. The model was then used to analyze and compare a number of royalty systems, concluding that the characteristics, flexibility and risk profile of a variable ad valorem system are most suitable for this application. |
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