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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - GaLIophore (Selective recovery of gallium from wastewaters of GaAs fabrication industry using siderophore based bisorptive biocomposites)

Teaser

Summary

The projected use of GaAs and CIGS solar panel will lead to 137 tonnes deficit of Ga in 2020. As the Ga can only be economically mined as a by-product of bauxite mining which is not going to increase dramatically in near future, the only way to meet the projected EU requirement is by the recovery of Ga from scraps (LED waste) or GaAs fabrication industry wastewater. However, there is so far no commercially viable technology available.

The objective of this project is to develop a commercially viable green technology for the recovery of Ga from GaAs fabrication industry wastewater. This project exploits the high affinity of siderophores towards Ga(III) to selectively recover a from GaAs fabrication industry wastewater. The biggest challenge in developing siderophores based Ga recovery technology is achieving efficient solid-liquid separation and easy scalability.

This study proposes to anchor, entrap and immobilize selected siderophores on solid surfaces, gels and cellulose filter, respectively, thus easing solid-liquid separation and scalability. Batch adsorption and desorption experiments will be carried out to optimize the experimental conditions for the recovery of Ga from the GaAs fabrication industry wastewater. The interaction of Ga(III) and siderophores will be studied at molecular level.

This understanding will help us to apply the developed technology to different critical metals as well and develop siderophores based bioleaching process and biosensors. The next phase of the project would involve semi-continuous and continuous experiments to scale-up the best possible configuration selected during the batch study. Finally, economic modeling will be carried out to support the commercialization of the developed technology.

This project will train the experienced researcher in developing green technology and soft skills, make host the forte of innovative biotechnology and increase the competitiveness of EU at global scale in critical raw metals.

Work performed

The recovery of gallium (Ga) from its low concentrated wastewater using siderophores was attempted. The project was divided into 4 work packages. The first work package deals with the anchoring/entrapment/immobilization of the siderophores on different carrier material and characterization them. This anchoring/entrapment/immobilization was needed for the efficient solid-liquid separation. The anchoring using one of the hydroxamate group of the siderophores is not possible as it affect the complexing ability of the siderophores. Thus, the immobilization was carried out using free NH3 group of desferrioxamine B (DFOB). The coupling was carried out onto carboxylated beads.

Another method for the separation of Ga-siderophores complex from the wastewater is through reversed-phase chromatography. This was attempted, even when not mentioned in the proposal, as a natural extension. The advantage of this method is it can be applied to any siderophores and not just only those siderophores with a free functional group. This was demonstrated by separating the Ga from low concentrated wastewater in the form of Ga-DFOB complex. Further, desferrioxamine E (DFOE) was used to complex Ga from GaAs wafer fabrication industry wastewater and separated using reversed-phase chromatography.

In the second work package, the complexation of DFOB and DFOE with Ga3+ was investigated in the solution phase. The complexation of Ga3+ with DFOB/E was not affected by presence of anionic/cationic contaminants, pH, arsenite, arsenate or KCl. The DFOE forms stronger complex with Ga when compared to DFOB. These findings was revealed from Density Functional Theory (DFT) calculations. Similar observations were made when Ga3+ was complexed with DFOB immobilized onto polystyrene beads.

The molecular understanding of Ga3+ complexation with DFOB or DFOE was also revealed by means of IR spectroscopy, Nuclear Magnetic Resonance (NMR) and Density Functional Theory (DFT) calculations. The complexation, as expected, was carried out by means of 3 hydroxamate groups.

In the third work package, decomplexation of Ga-DFOB/E complex was successfully carried out using ethylenediaminetetraacetic acid (EDTA). The pH plays a major role in the decomplexation. The acidic pH is required for desorption while desorption at alkaline pH was not successful. 10 cycles of complexation and desorption were carried out using DFOB immobilized polystyrene beads. No loss of the complexation ability of Ga was observed.

In the fourth work package, semi-continuous reactor was operated, however, the attempt was not successful due to the failure to choose the right membrane for the separation of DFOB immobilized polystyrene beads from wastewater. However, there is no reason for the continuous reactor to fail when the correct membrane is chosen. The cost-benefit analysis pointed to a very low operational cost of operating DFOB immobilized polystyrene beads resulting in possible high rate of returns of the technology. In the chromatographic separation method, the operating cost is higher than DFOB immobilized polystyrene beads but still the technology is cost-effective. The major cost inputs is siderophores and if their prices are reduced to 1000 â‚¬ per kg and at least 50 cycles, then the technology is commercially viable.

Final results

The â€œGaLIophoreâ€ technology was undertaken for the recovery of gallium (Ga) from the low Ga containing wastewater generated from the GaAs wafer manufacturing industry. There is no conventional technology available for the recovery of the Ga from these wastewater. The challenge is due to the low concentration of the Ga and presence of other contaminants in the wastewater. This project developed the only technology that can recover Ga from these wastewaters. Further, effect of constituents of real wastewater on the Ga3+ complexing ability of the siderophore was never investigated. The decomplexation of the Ga3+ from Ga-DFOB/Ga-DFOE complex was never investigated. All these experiments were conducted in the GaLIophore project to advance the state-of-art.

This technology is based on siderophores produced by microorganisms, thus support the bio-economy. The recycling of the Ga, which is a critical metal, supports the circular economy and EU commitment to achieve ambitious recycling targets. The technology can also be implemented for indium, germanium and scandium. All these metals are critical elements, as listed by EU, whose supply is not assured in future. This project also support the recycling of these metals. One more important aspect is these metals are required for renewable energy generation and improving energy efficiency, thus this project also secures the availability of these material that can help fight climate change.