Meet the ESRs – Part 1


As the Redmud Project starts to get going across Europe, it's a great time for all 15 of the Early Stage Researchers (ESRs) that make up the European Training Network to introduce ourselves and our research. Coming up today, in no particular order, are the first three - keep posted for the rest of the set!


Name: Rodolfo Marin Rivera

ESR 7: Process intensification for REEs recovery from bauxite residue

Tell us a little about yourself?

My name is Rodolfo and I’m from Chile. Since my childhood I’ve been linked to the mining world, due to fact that I was born in a small town located in the north of Chile next to the biggest copper mining company, Chuquicamata. Therefore, my taste for metal was inevitable: in Music and in Science. At the school, I tried several times to form a heavy metal band in order to fulfil my taste for metal, but it didn’t work. However, I found a most passionate way through science. Thus, at university I fell in love with Metallurgy until I got my Bachelor of Science in Metallurgical Engineering. Nevertheless, I decided to go further with such cosmologic relationship by studying at RWTH Aachen, in Germany, a Master of Science in Metallurgical Engineering with specialization in Process Technology of Metals. Thus, in 2014 I became a “Master of Metal”.

Today, I’m doing my PhD at KU Leuven under the subject of process intensification for rare earth elements recovery from bauxite residue.


How is your PhD going? What is your upcoming research about?

In my eagerness for looking new adventures, I decided to investigate the utilization of ultrasound and carbon dioxide (CO2) as pre-treatment process for recovering later on scandium and rare earth elements (Sc & REEs) from bauxite residue via hydrometallurgical process.

The mixture of CO2 with water leads to the formation of carbonic acid (H2CO3), which dissociates into bicarbonate-ions (HCO3-) and free hydrogen-ions (H+). Sodium is then liberated from its mineral matrix thank to the action of those free hydrogen-ions and, once in solution as sodium-ion (Na+), it will react with HCO3- to form a liquid carbonate according to the following chemical reactions:

CO2 + H2O D H2CO3 D H+ + HCO3-

Na2O + 2H+ D 2Na+ + H2O

2Na+ + HCO3- D Na2CO3 + H+

Therefore, with this carbonation process it will be possible to separate sodium from the red mud and, the result will be a reduction of red mud’s pH thank to the liberation of hydrogen-ions (protons), but why? Why is it necessary to do this before recovering the valuable metals? Red mud is a very fine (particle size <100 µm) and highly alkaline solid material due to its high content of NaOH remaining from the Bayer process (aluminium production), which means that this kind of material has a pH in the range of 10 to 13.

Scandium belongs to group 3 in the periodic table and most of the time can be found with rare earth elements[1]. Therefore, if you are able to find scandium in nature, you have a great possibility to find rare earth elements as well. Within red mud, scandium exists in the so-called traces elements due to their low concentration, and once it is in ionic form, its predominant oxidation state is +3[2] at pH lower than 3. With hydrometallurgical process, it is possible to extract it from the mineral matrix by dissolving the solid material, but to do so, you need a high amount of strong acids in order to decrease the pH from an average value of 12.5 till pH lower than 3. From this point of view, the use of CO2 as a pre-treatment step starts playing a fundamental role in my research. Hence, the consumption of acid can be considerably reduced if sodium can be separated from the matrix of red mud as a carbonate. However, several questions need to be answered, like what is the maximum reduction of pH that can be attained? What is the influence of other chemical elements during the carbonation process? Could a rebound of the pH occur over time? Do the characteristics of the particles change after the carbonation process? How much carbon is it possible to sequester under defined conditions? Could the use of ultrasound improve the efficiency of the process? Is there any limit? Is it feasible the use of this technology at industrial scale?

These questions are being answered during my research at KU Leuven.


What or who motivates and inspires you? Any thoughts and life musings you’d like to share with us?

As a Metallurgist (and “Master of Metal”), I know the fundamentals for extraction, purification and refining of metals, as well as the necessary knowledge to make such a process more sustainable with the environment. However, whatever we do to make a process more environmentally friendly, it is not so easy due to the fact that every chemical, physical and metallurgical process lead to the production of undesired waste materials, which currently are being deposited in dump sites where they produce a significant damage in the ecosystem. I’ve been a witness of this fact. I’ve seen the damage that such waste materials produce in the air, in the aquifers and most important in our life.

I’m conscious of how dependent on metals we are and, for that reason, ever since my first year of college, I have wanted to provide sustainable solutions through innovation and technology development in order to diminish the amount of waste materials produced during those process. Today there is not enough knowledge for processing such of waste materials. However, now I have the chance to provide enough information to develop a technological and sustainable process.


If a chicken had lips, could it whistle?

People have lips, can everybody whistle?