In the last decade, interest in deep-sea mining (DSM) has surged. The expansion of the global economy, advancement of technologies and the transition to more renewable energy solutions have caused an increased demand for metals like lithium and cobalt and rare earth elements. With land resources diminishing, there is a growing interest in the vast deposits that the deep sea holds in enriched mineral deposits. To evaluate the effect of DSM operations on sea life, it is important to study the dynamics of resettling sediment plumes and their effect on the ocean environment. A convenient method to do that is by studying the settling of suspended sediment material in small-scale lab setups. When discharging a suspension drop into a water tank, settling velocities can be several times higher than normal (Stokes) settling velocities, leading to an error in the estimation of particle properties. To make these experiments more useful and effective, it is thus important to study for what conditions settling velocities of suspension drops are sufficiently close to the Stokes velocity.

With the enormous growth of portable electronics and the market expansion of electric vehicles, the demand for lithium-ion batteries is increasing enormously. To meet this demand, efficient recovery of battery components becomes crucial. Graphite, the material of choice for lithium-ion battery anodes, faces significant supply risks as current recycling technologies primarily focus on recovering economically valuable metal components like cobalt and nickel. Therefore, the effective separation of graphite from lithium-ion batteries is essential for recycling and reusing anode materials. The key to the direct recycling of graphite is the separation of the finest material fractions of Li-ion batteries: the anode and cathode. This work tests a circular battery manufacturing principle based on the idea that the an ode and cathode could be designed to have a difference in particle size to allow easy separation by centrifugation.
We analysed the particle sizes of anode and cathode material obtained from a spent Li-ion battery. A shift in particle size distributions is observed by grinding the materials, significantly reducing the particle sizes. We calculated the velocity distributions using Stokes’ formula for the settling velocity of spherical particles in dilute suspensions from these size distributions. Combining the velocity distributions for the anode andcathode showed the overlap of the velocities. A combination of milled and unmilled material shows the smallest overlap between the velocity distributions and, therefore, the largest difference in sedimentation velocity and the highest theoretical separation.
We measured the sedimentation of anode and cathode particles in water optically using a light source. A camera tracks the moving front of the dilute suspensions over time. Experiments of different milled samples for various concentrations show insights into the anode and cathode sedimentation behaviour. Results show that increasing concentration significantly reduces sedimentation velocities for the anode material. Theseresults deviate from what would be expected from the hindered settling of dilute suspension. A significant velocity reduction is measured for the milled anode and cathode, therefore showing the potential for separation if the materials have a marked difference in size.
In this thesis, a novel method is developed for characterising the sediment structure of the mixed active materials. By freezing sedimented suspensions, sample layers are horizontally cut off to look for the spreading of the different material components through the sediment. A combination of characterisation methods offers information about the anode and cathode fractions through the sediment layers. Significant differences between the sediment’s top and bottom layers regarding morphology, elemental components and thermal stability are observed.
The results show the potential for circular batteries in the future, where centrifugation can play a vital role in separating the electrode materials if they have a marked size difference.

The demand of the lithium ion battery (LIB) is increasing exponentially, as it is the state-of-the-art solu tion to achieve electrification of the mobility sector and to ensure the stability of the electricity grid. The anode and cathode of these batteries consist of graphite and a lithium transition metal oxide (LTMO), respectively, which have both been designated as critical raw materials and face serious supply risks. At present, only a small amount of cathode material can be recovered through chemical separation processes, which are expensive and energy-intensive and produce a lot of waste. Direct physical re cycling of these materials is a far more efficient approach, but no scalable direct recycling routes are currently available. Sink-float separation using dense media had been successfully performed, indi cating that density is a suitable differentiating property. However, dense media are associated with serious drawbacks due to their high viscosity, toxicity and cost, making them unsuitable for large-scale application. Therefore, the objective of this research is to evaluate whether magnetic density separa tion (MDS), which applies a magnetic liquid subjected to a magnetic field to create an artificial density gradient within the liquid, can be applied in practice for the separation between anode and cathode ma terials from spent LIBs. This is achieved through magnetic field simulations, developing and executing a method for measuring the magnetic susceptibility, and Magnetic Levitation (MagLev) experiments. Following from the magnetic field simulations, an array of permanent disc magnets, stacked into one larger cylindrical magnet, was selected as the optimal magnetic configuration. Further, samples of para magnetic MnCl2 solutions were prepared at different concentrations, up to the saturation concentration. Their densities and magnetic susceptibilities had to be determined in order to be able to estimate the achievable apparent densities. From the literature it became clear that the magnetic susceptibility is a property that cannot be easily measured and a very wide range of values was used by different sources. Because of this, a new method was developed to measure the magnetic susceptibility of a liquid: the magnetic pendant drop method. The deformation of the drop was studied as it was brought into prox imity of the magnets. The results from this experiment were of the same order of magnitude as the reported magnetic susceptibilities found from the literature, which were quite dispersed. Finally, MagLev experiments were performed with anode and cathode materials. The cathode mate rial sunk to the bottom for each concentration. On the other hand, MagLev of anode material was achieved in samples of high MnCl2 concentration. From their levitation heights, the magnetic suscep tibility was once again calculated, and was even closer to the value reported in one of the sources. The equilibrium height at which the anode material levitated was at approximately 6 mm above the magnet’s surface. This means that careful design considerations will need to be taken in the design of a continuous process, and possibly a different option of magnets and paramagnetic medium should be selected. Nonetheless, the fact that levitation of graphite can be achieved, offers a positive prospect for separation by MDS on lab-scale.

The demand of the lithium ion battery (LIB) is increasing exponentially, as it is the state-of-the-art solution to achieve electrification of the mobility sector and to ensure the stability of the electricity grid. The anode and cathode of these batteries consist of graphite and a lithium transition metal oxide (LTMO), respectively, which have both been designated as critical raw materials and face serious supply risks. At present, only a small amount of cathode material can be recovered through chemical separation processes, which are expensive and energy-intensive and produce a lot of waste. Direct physical recycling of these materials is a far more efficient approach, but no scalable direct recycling routes are currently available. Sink-float separation using dense media had been successfully performed, indicating that density is a suitable differentiating property. However, dense media are associated with serious drawbacks due to their high viscosity, toxicity and cost, making them unsuitable for large-scale application. Therefore, the objective of this research is to evaluate whether magnetic density separation (MDS), which applies a magnetic liquid subjected to a magnetic field to create an artificial density gradient within the liquid, can be applied in practice for the separation between anode and cathode materials from spent LIBs. This is achieved through magnetic field simulations, developing and executing a method for measuring the magnetic susceptibility, and Magnetic Levitation (MagLev) experiments.

Following from the magnetic field simulations, an array of permanent disc magnets, stacked into one larger cylindrical magnet, was selected as the optimal magnetic configuration. Further, samples of paramagnetic MnCl2 solutions were prepared at different concentrations, up to the saturation concentration. Their densities and magnetic susceptibilities had to be determined in order to be able to estimate the achievable apparent densities. From the literature it became clear that the magnetic susceptibility is a property that cannot be easily measured and a very wide range of values was used by different sources. Because of this, a new method was developed to measure the magnetic susceptibility of a liquid: the magnetic pendant drop method. The deformation of the drop was studied as it was brought into proximity of the magnets. The results from this experiment were of the same order of magnitude as the reported magnetic susceptibilities found from the literature, which were quite dispersed.

Finally, MagLev experiments were performed with anode and cathode materials. The cathode material sunk to the bottom for each concentration. On the other hand, MagLev of anode material was achieved in samples of high MnCl2 concentration. From their levitation heights, the magnetic susceptibility was once again calculated, and was even closer to the value reported in one of the sources. The equilibrium height at which the anode material levitated was at approximately 6 mm above the magnet’s surface. This means that careful design considerations will need to be taken in the design of a continuous process, and possibly a different option of magnets and paramagnetic medium should be selected. Nonetheless, the fact that levitation of graphite can be achieved, offers a positive prospect for separation by MDS on lab-scale.

Graphene, a 2D nanomaterial made of carbon, has gained interest in the scientific community since its discovery in 2004. Among other properties, graphene has excellent tensile strength, electrical and thermal conductivity and can be used as catalyst. Graphene has no shortage of applications, but large scale production methods are yet to be developed. LPE is a promising method, in which the layers that make up graphite are separated to produce graphene in a liquid medium. However, the flakes that are produced are polydispersed in size and thickness, which leads to the need for size selection. Current studies have achieved size selection with centrifugation. However, centrifugation has thus far been a trial and-error procedure, without understanding the underlying physics and statistics. This research focuses on creating a rational basis by combining experiments with simulations based on fluid dynamics and statistics. By combining results from simulations and experiments we are able to arrive at the size distributions of initial stock dispersion of graphene that was made from LPE. The simulations entail plate particle settling in a tube, where randomly generated polydisperse particles are randomly distributed in a tube. Stokes settling velocity is assumed for each particle. In parallel to this, we perform sedimentation experiments of stock dispersion at fixed relative centrifugal force (RCF) for different times. From the experiments we know the mass transfer from the supernatant to the sediment and the average thickness of the plates in the supernatant. Both these experimental results allow us to narrow the initial particle size distributions we assumed in the simulations. Thus we have developed a technique based on simple experiments and simulations that gives great insight into particle size distribution without having to perform tedious characterization such as AFM or TEM. Once the particle size distribution is known for a specific LPE protocol, it will allow the likes of both industry and academia to standardize graphene quality.

Biochar for horticultural and agricultural applications using high temperature torrefaction technology Pradeep Ravi Supervisors: Prof Dr. D.J.E.M Roekaerts, ir.Bart de Vries, Dr. Luis Cutz, Dr.Lorenzo Botto & Dr.Ralph Lindeboom Biomass currently accounts for less than 10 percentage of the world’s renewable energy production. Currently the major global sustainability issue stems from the sourcing of virgin wood chips from dense forests for pellet production. An alternative is to use residual biomass from agriculture or forestry, which is produced in large volumes, to produce different products that range from biofuels to chemicals via thermochemical conversion technologies. Among thermochemical technologies, torrefaction is a promising route to produce solid biofuel known as biochar. With an increasing potential for biomass production coupled with an increased scrutiny on the use of biomass as a green fuel, the need for alternative clean applications for the biochar is critical. The aim of this study is to investigate new and novel agricultural residues or other waste streams to produce biochar using high temperature (350 °C) torrefaction technology. The obtained biochar is evaluated experimentally to determine the best feedstocks out of the ones that are selected from a performance and cost point of view for horticultural applications. . This research aims to provide a clear and useful analytical tool which will benefit the scientific community to select suitable biomass materials based on material properties and end applications. The efficacy for the various torrefied biomass feedstocks on the soil and its stability are tested. Overall, about 50 different biomass feedstocks were identified and evaluated based on past performances from literature. The top 10 best performing feedstocks were sourced and subjected to various physical and chemical characterization tests with a specific focus on soil remediation. The selected materials were torrefied in a fixed bed pilot reactor Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET) and pH measurements. Ultimately the feedstocks were scored and ranked from best to worst performing biochar for soil remediation and sequestration-based applications. The results of this project indicate potential for biochar production from woody, grassy and other processed materials that could help to remove the dependence on evergreen forests and wood chips. The system proposed in this work could also yield negative emissions since the feedstocks are residual flows and the biochar is going to be used in the soil.

Water electrolysis is a popular energy storage technique used in tandem with many renewable sources to convert the generated energy into storeable hydrogen. The efficiency of water electrolyzers is greatly affected by overpotential losses. Bubble evolution is a unique characteristic of flows in water electrolysis. The evolution of bubbles alter electrokinetics close to the electrodes and vary ionic mass transport. The localized flow features close to a bubble are often attributed to the variation in the current density and subsequently, the electrolyzer efficiency. For the purpose of modelling flows close to a bubble better, a Lagrangian method for the simulation of passive tracers is developed and programmed to be coupled to the flow field of Bluebottle, an open-source particulate multiphase flow solver that uses the Physalis algorithm.
The dynamics of the tracers are modelled using a simplified Langevin equation. In the present work, the migration flux is omitted and priority is given to convection and diffusion with the objective of establishing a foundation for the simulation of ionic mass transport. Brownian motion is described using a random displacement term. The coupling with the flow field is achieved using trilinear interpolation. The domain boundaries in regards to tracer dynamics are modelled as either a rigid wall pair or as a periodic boundary pair. Specular reflection is programmed for the former ensuring elastic collision of a tracer with the domain boundary. For the latter, the tracer position is altered so as to place the tracer in the opposite side of the domain in the axis of intrusion. Particles are assumed to be non-penetrative and hence, specular reflection is implemented at the surface of each particle. Since the tracer module is coupled one-way with the flow field and executed after a Bluebottle time-step, a subroutine is developed to push the tracers out of a particle radially if a tracer is located inside a particle after a Bluebottle time-step. To ensure particle interaction is ensured across periodic boundaries, a subroutine is developed that places the particle in an apparent location that enables particle-tracer interaction. 
The module execution time is found to be linearly proportional to the number of particles and the number of tracers and consumes roughly 10% of a Bluebottle iteration execution time in nominal tests. The module is tested to ensure the Brownian displacement term obeys diffusion statistics and also to ensure that the trilinear interpolation works as intended. The numerically enforced no-penetration boundary at particle surfaces is also tested and observed to prevent intrusion of tracers. 
The tracer module is then used to stochastically simulate mass transport across a particulate suspension in a stagnant and a sheared flow field. The Sherwood number Sh determined from the tracer module is found to agree well with the expected experimental and numerical results of Wang et al. (2009). The tracer module is also compared to a scalar field solver of Bluebottle. The tracer module is observed to capture features of the flow field quite well. However, the transient tracer positions upon conversion to a transient continuous concentration field exhibits noise due to the discrete nature of the tracers. Hence, transient comparisons with a continuous field in terms of absolute magnitude requires a large number of tracers.
Recommendations for improvement of the code is provided. The present work is intended to be followed up with the addition of migration flux to the equations of motion for the tracers through the solution of an additional equation for velocity of the tracer using a force equivalence of Coulomb's law and Stokes' drag law. Future challenges that will be encountered in the development of an accurate ionic mass transport solver is briefly discussed.