Eggshell can help recover rare earth elements, make process sustainable
Researchers have discovered that the commonly found eggshell waste can help recover rare earth elements (REEs) from water.
The discovery offers a new and environment-friendly method for REEs’ extraction.
The research team included members from Trinity College Dublin’s School of Natural Sciences and iCRAG, the Ireland Research Centre in Applied Geosciences.
REEs are needed in high volumes for the transition to green energy, as they are essential for the permanent magnets used in electric cars and wind turbines.
However, the REEs’ extraction process is chemical-intensive and is generally quite damaging to the environment. This means that the extraction process adds to the pollution and is a setback to the whole green transition process.
Therefore, the researchers set about to find a sustainable way to extract them from the environment.
The discovery using eggshells
The team discovered that the calcium carbonate present in eggshells is a valuable addition to the process as it can absorb and separate the REEs from water with surprising efficiency.
The process which comes into play here is diffusion. The same was tested by the researchers over a three month period.
They put eggshells in solutions containing REEs at varying temperatures – ranging from 77° Fahrenheit (25° Celsius) to 401° Fahrenheit (205° Celsius) – for different time periods to a maximum of up to three months.
The experiment yielded several remarkable findings. First, REEs had entered the eggshell through diffusion along calcite boundaries. Second, at higher temperatures, REEs formed new minerals on the eggshell surface.
With the eggshells, kozoite was detected in minute quantities at 194° Fahrenheit (90 °C) after one day, amounting to a few weight percent after two weeks and close to 100 percent after 80 days.
At 329° Fahrenheit (165 °C), calcite was gradually replaced by kozoite, and after two days, only kozoite remained.
Further conclusions drawn from the study
The same replacement pattern was observed at the scorching temperature of 401° Fahrenheit (205 °C); additionally, there was an emergence, followed by a slow but gradual increase, of hydroxylbastnäsite.
Bastnäsite is a stable rare earth carbonate mineral that is used across the globe to extract REEs for technology applications.
The unique characteristic of eggshell calcite makes it a potential sustainable sorbent for REE, the researchers say.
Additionally, the study shows that at higher temperatures, eggshell calcite also has the potential to be used as a precipitant.
Besides, the research indicated that eggshells are seemingly more powerful than inorganic calcite crystals in aiding the process.
“The dissolution–precipitation reaction also generates minor grain-scale REE partitioning, which, if magnified, could be exploited as an environmentally friendly technique for REE separation,” the study says.
Source: Interesting Engineering
Eggshell can help recover rare earth elements, make process sustainable