I’m Nor Kamariah, ESR7 of the European H2020 MSCA-ETN SULTAN project. This is my first post on this blog. I hope I can write something interesting for you on my debut post.
Alright, I will start with a short introduction about the research I’m working on right now. As part of SULTAN team, my project aims to develop an advanced leaching using microwave heating to extract valuable metals from sulfidic tailings. As complicated as it might sound, it offers me so many things to dig up and learn about. Let me share with you (hopefully) useful information about them: What is leaching? And what methods are available for us to extract metals?
(If you want to know more about tailings, please read a nice post by ESR6 (Ana Luiza) here)
What is leaching?
Leaching, also considered as solid-liquid extraction, is a process to extract valuable metals from ore . Chemically, metals bound to the mineral are converted into metal ions and then are released to the leaching solution. The metal rich solution will later be subsequently processed for metal recovery .
Though probably it’s a bit hard to imagine the definition above, we witness easily this leaching phenomenon in our daily life. Most of us are familiar with making a cup of coffee, right? We proceed it by taking ground coffee and adding hot water. When we mix them, hot water will dissolve different tastes and flavors from the coffee. There we go, we already perform coffee extraction.
Similarly, when minerals (solid materials) come into contact with leaching agents (lixiviants), metal ions are extracted from the minerals to the solution, also known as Pregnant Leach Solution (PLS).
Figure 1. Coffee Brewing 
Metal extraction methods
Generally, pyrometallurgy and hydrometallurgy are the most common methods in metal extraction.
Pyrometallurgy involves the process at high temperatures (300 – 1600 °C ) to extract valuable metal from ores. This method is suitable to treat high grade ores – ores contain large enough profitable mineral and low impurities – due to maximum thermal efficiency of the furnace during heat exchange operation . However, the high energy requirement makes pyrometallurgy not suitable to extract metals from low grade ores. In this case, hydrometallurgy becomes a better option.
Hydrometallurgy employs aqueous solutions and reactions at lower temperatures (< 200 °C ). When I mentioned ‘solution’, of course you still remember about leaching. Yes, leaching that we previously talked about, is a primary process in hydrometallurgy which involves metal dissolution to the aqueous solution. The most common used leaching agents are acids, for instance dilute sulfuric acid.
Figure 2. Processing of Copper Ores via hydrometallurgy 
The ability of strong acids to leach various metals can be a benefit and drawback at the same time. We know that the extraction of metal values is our goal, but what if metal impurities had been extracted as well, or worse that the metal values were extracted less than the impurities? This drawback leads many studies to investigate more selective methods and leaching agents that are capable of extracting valuable metals with improved efficiency and selectivity.
Biohydrometallurgy and solvometallurgy are ones of those recent developments that can serve as an alternative to more conventional hydrometallurgical method for low grade ores and secondary resources, including tailings. Bioleaching is a process in biohydrometallurgy that extracts valuable metals using bacterial microorganisms . That’s the topic that my colleagues, ESR9 (Belsonia) and partially ESR8 (Tamara) are working on.
Meanwhile, differ from aqueous leaching in hydrometallurgy, leaching in solvometallurgy – also called solvoleaching – makes use of non-aqueous solvents, without (minimum) addition of water, to extract valuable metals.
Figure 3. Solvometallurgical process of copper extraction using Ethylene glycol-FeCl3 as lixiviant 
Solvent selection plays an important role in solvometallurgy . To make solvometallurgical process sustainable, not only does it look at solvent performance (e.g. to achieve selective leaching), it considers the safety and environmental impacts of the selected solvents too. Alcohols and ionic liquids are some examples of potential green solvent for solvometallurgy. My PhD project will study on this topic: the development of advanced leaching, particularly based on solvometallurgical process, in a combination with microwave heating to extract valuable metals from tailings. Please wish me luck :).
I hope I will be able to update you with interesting findings in the upcoming blog post. Lastly, thanks for reading and have a good summer!!
- J. Evans and L. D. Jonghe, “The Production and Processing of Inorganic Materials,” Springer Nature, 2016, doi:10.1007/978-3-319-48163-0.
Link to full paper: X. Li, W. Monnens, Z. Li, J. Fransaer, and K. Binnemans, “Solvometallurgical process for extraction of copper from chalcopyrite and other sulfidic ore minerals,” Green Chem., vol. 22, no. 2, pp. 417–426, 2020, doi: 10.1039/c9gc02983d.
- K. Binnemans and P. T. Jones, “Solvometallurgy: An Emerging Branch of Extractive Metallurgy,” J. Sustain. Metall., vol. 3, no. 3, pp. 570–600, 2017, doi: 10.1007/s40831-017-0128-2.