Meet the 2018 Beijing Scholars
Kevin Jin, North Carolina School of Science and Mathematics
Hometown: Charlotte, NC
Project: Selective Recovery of Rare Earth Elements Utilizing Novel Liquid Membrane Processes
Abstract: Disposal of coal ash, also called coal combustion residue (CCR) which is a by‐product of incineration of coal and municipal solid wastes, is becoming an increasing economic and environmental burden, due to its abundance and its potential to leach toxic metals at disposal sites. Given coal’s role in heat generation, solving this problem is important. Thus, there’s a growing interest in looking for avenues where coal ash can be used as a potential resource for preparation of value‐added products.
Although CCR can be utilized in cementitious products like highway road bases, the rate of production of coal ash far exceeds the rate of consumption. CCR has another potential use as a source for rare earth elements (REEs). REEs consist of the yttrium, scandium, and the lanthanide series; they’re not found in nature as pure metals and must be isolated from host minerals and are very valuable. REEs are useful because they are critical in automotive, energy, electronics, and defense industries, especially in new technological developments. With the recent instabilities in the REE global market, it is important to establish the potential for alternative sources of REEs. Sourcing, or recovering, REEs from CCRs has advantages when compared to traditional recovery methods of REE ores. CCRs are a readily available waste product, require money to safely dispose of otherwise, and do not require extensive, environmentally‐destructive excavation. Additionally, CCR is a fine powder which is ideal for chemical processing compared to costly ore processing steps of REE ores. There is also a lot of potential value in the REE content of coal ash. The value of the REEs present in CCRs is very high, particularly with scandium. This total value of REEs is estimated to be around 4 billion dollars in the USA. The beneficial outcome for recovering metals from CCRs is promising; this necessitates the development of methods for greater utilization and production of high-value compounds from this waste.
The classical method to extract metals from CCR solids includes acid digestion. After the acid digest, the solid residue is filtered and washed, which can achieve low concentrations of trace elements. However, the effectiveness of this method is low, as certain compounds are less affected by acid treatment, but this method also extracts all the metal ions present in the residue, while only REEs are desired.
I designed two phases to overcome this disadvantage and then demonstrate the feasibility in the selected recovery of rare earth elements. This design was based on previous liquid membranes that have recovered ions from a solution. Liquid emulsion membranes (LEM) and supported liquid membranes (SLM) are liquid membrane methods that have been used to recover metal cations from aqueous mixtures.
Phase 1 studies the kinetics of the REE leaching from coal ash to determine key parameters that are efficient and effective to reach an equilibrium of REE extraction, which is ideal for the following selected recovery.
Phase 2 designs and tests selective recovery methods to optimally recover REEs from CCRs utilizing hydro metallurgical-based methods of liquid membrane processes.