Metal-organic frameworks for the recovery of critical metals for batteries

Lithium mining is a much sought after metal that is essential in many green technologies, especially battery technology. With the rising pressure on the planet’s climate a shift to greener alternatives is growing and with it demand for lithium. The current mining of lithium is however inefficient and resource intensive in regards to water and land areal. To address this challenge a new method for extracting lithium utilising adsorbents is being explored. A shortcoming of many adsorbents used in the treatment of water is low porosity (and lack of selectivity). Prospects in regards to adsorption will likely involve synthetic crystalline materials called metal-organic frameworks (MOFs). MOFs combine inorganic and organic building units, metal ions/clusters and linkers respectively. These materials have been shown to possess much greater porosity and inner surface area. So far most research activities have focused on gas adsorption using MOFs as most are unstable in water. Water stability has been a challenge, fortunately, a large number of MOF structures have been discovered, and, opportunely from the University of Oslo in Norway a series of water-stable zirconium-based MOFs have been reported [7]. This thesis work will use the opportune Zr-cluster based MOFs with carboxylate functional groups that could be sites of ion exchange interaction. In particular two MOFs with 1,2,4-Benzenetricarboxylic acid (BDC-COOH) and 1,2,4,5-Benezenetetracarboxylic acid (BDC-(COOH)2) are explored in this thesis. MOF characteristics have been determined using powder x-ray diffraction, thermogravimetric analysis, nitrogen adsorption, scanning electron microscope with energy dispersive x-ray spectrometry, and infrared spectroscopy. Furthermore, MOF samples synthesised are used to carry out batch adsorption experiments to find whether they are applicative for metal ion uptake in water solution. Two studies were set up, where five vials of different metal ion concentration, one with lithium chloride and the other with magnesium chloride, had MOF samples added to them and were left to adsorb overnight. UiO-66-BDC-COOH and Zr-BDC-(COOH)2 were both successfully synthesised and employed in metal adsorption studies. Samples JA01 and JA04 were chosen as adsorbents since they showed the strongest results after characterisation analysis. JA01 and JA04 syntheses were upscaled (JA09 and JA10 respectively) to have enough quantity for batch adsorption. JA09 proved not to be chemically stable in water. JA10 did not show any sign of significant metal ion uptake. Likely the problem was the low pH value. Solutions after adsorption experiment turned out to be much more acidic, and showed greater conducitivity than before adsorption