Rare earth elements (REEs) are of great importance to modern society and their reliable supply is a major concern of many industries that utilize them in metal alloys, semiconductors, electrical equipment, and defense equipment. REEs in the coal waste have been revealed to be an alternative resource for REEs production. In this study, the extraction, recovery, and upgrading of the REEs from coal waste has been realized with the bioleaching and precipitation processes. Reliable and sustainable acid and oxidant production from the oxidation of the pyrite with Acidithiobacillus ferrooxidans to generate acid for leaching were realized in this research. The acidified bioleaching solution was used to extract REEs from coal waste, with 13–14% yields for most REE elements (~72 h of leaching). However, recovery for longer duration tests was significant higher (varies from 40–60% for individual REEs). After extraction, precipitation and separation processes were designed with the aid of Visual Minteq calculations and modeling to concentrate the REEs. With the procedures designed in this research, a final REEs precipitate product containing 36.7% REEs was produced.

Many electrochemical processes involve gas evolution and bubble generation on the electrodes. Understanding the behavior of bubbles on the electrode surface and in the electrolyte is crucial to the design and optimization of the electrochemical process. Gas bubbles tend to coalesce and detach from the electrode surface once they are formed and as they grow, but these processes have not been investigated and understood well. The phase-field modeling method is excellent at tracking the interface between different phases, and the simulation results can give a precise prediction of the interaction between phases. In this research, taking advantage of the phase-field method, a gas-liquid two-phase model has been constructed to investigate the bubble coalescence and detachment in the electrochemical system. Sophisticated, tiny gas bubble coalescence on and off electrode and the detachment of bubbles from the electrode surface were predicted by the model. The results are helpful for the understanding of these transient processes in the electrochemically generated bubble-liquid system.

Lithium isotope fractionation, based on the difference of the diffusion coefficients, migration mobility, as well as the electrochemical isotope effect, can be achieved in the appropriate solvents. The Propylene Carbonate-Polyethylene Oxide gel electrolyte was utilized to separate Li isotopes by eliminating the fluid flow mixing and part of the solvation shell around Li ions. A higher Li isotope fractionation (△⁷Li = −4.53‰) was achieved with the effects of both diffusion and electrochemical migration in a long 10-cm cell test. Also, a short 2-cm cell gel electrolyte short duration test yielded a very high separation factor of 1.033, which is a very promising separation factor for Li isotope separation. Similarly, the electrochemical intercalation test into the graphite plate electrode associated with the diffusion and migration assisted separation shows a separation factor of 1.033. Influence of the electrochemical cell length was studied with an electrochemical model, and results show that an appropriate cell length needs to be determined by considering both the separation time and the separation factor.

Zinc electrowinning is by nature complex, involving the electrodeposition of Zn ions on cathode, oxygen evolution on the anode, as well as the hydrogen evolution on the cathode as a side reaction which decreases the current efficiency and increases the energy consumption while improving local mass transport. Because of the capital-intensive features and the low efficiencies of experimental research approaches, modeling and simulation have become a promising way to study the electrowinning processes. The coupling of gas-liquid two-phase flow from gas evolution with the electrochemistry process, however, is challenging to simulate. In this paper, an approach of building a comprehensive Zn electrowinning model based on COMSOL Multiphysics was introduced. Further, the basic model results in velocity field, concentration distribution, gas fractions, and current efficiency were demonstrated and discussed. In addition, validation of the current efficiency predictions from the model was performed through a comparison with experimental test data.