Abstract Details
(2020) Membrane Based Scandium Extraction from Industrial Waste
Hedwig S, Constable EC & Lenz M
https://doi.org/10.46427/gold2020.1007
The author has not provided any additional details.
08r: Plenary Hall, Friday 26th June 07:06 - 07:09
Sebastian Hedwig
View abstracts at 3 conferences in series
Edwin Charles Constable
Markus Lenz View abstracts at 9 conferences in series
Edwin Charles Constable
Markus Lenz View abstracts at 9 conferences in series
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
Submitted by Pieter Bots on Wednesday 24th June 17:04
Thank you for your amazing presentation, it's fascinating to see the extreme selectivity of your membranes for Scandium.. I was wondering if you have any clues why phosphoric acid is so much better at releasing the scandium from the membranes? Has this potentially to do with formation of Sc-phosphate aqueous complexes? Many thanks again.
Thank you very much for the feedback and the interesting question. So far, we did not do any further tests to investigate on the mechanics behind the stripping with Phosphoric acid. However, we assume that 1) since thermodynamically the scandium phosphate is favored above the sulfate or chlorides, it can help shifting the equilibrium ([Sc(DEHPA)3] + 3HA -> Sc3+(aq) + 3A-(aq) + HDEHPA) to the product side at the receiving phase 2) phosphoric acid may weaken the Sc-DEHPA bond by means of hydrogen bonds to the DEHPA itself, thus opening the coordination sphere and giving better access to the central metal for ligand exchange reactions. However, as mentioned these are yet just hypothesis.
Thank you for your amazing presentation, it's fascinating to see the extreme selectivity of your membranes for Scandium.. I was wondering if you have any clues why phosphoric acid is so much better at releasing the scandium from the membranes? Has this potentially to do with formation of Sc-phosphate aqueous complexes? Many thanks again.
Thank you very much for the feedback and the interesting question. So far, we did not do any further tests to investigate on the mechanics behind the stripping with Phosphoric acid. However, we assume that 1) since thermodynamically the scandium phosphate is favored above the sulfate or chlorides, it can help shifting the equilibrium ([Sc(DEHPA)3] + 3HA -> Sc3+(aq) + 3A-(aq) + HDEHPA) to the product side at the receiving phase 2) phosphoric acid may weaken the Sc-DEHPA bond by means of hydrogen bonds to the DEHPA itself, thus opening the coordination sphere and giving better access to the central metal for ligand exchange reactions. However, as mentioned these are yet just hypothesis.
Submitted by Cristina Ruiz Agudo on Thursday 25th June 21:53
1) Which plasticizer did you use for your membrane? 2) Can you estimate the operational life of your membrane (i.e. how many cycles of Sc extraction)? 3) The rise of temperature to increase Sc-recovery, does it affect your membrane?
Thank you very much for the interesting questions. 1) The used plasticizer was NPOE (2-nitrophenyl octyl ether) 2) We did not investigate yet on how many cycles are possible with the membrane. However, we did experiments with at least three feed exchanges, giving similar results for the extraction. 3) We did FTIR measurements of the membrane before and after the tests and could only see little change in the DEHPA signal intensities, speaking for resilience. However, we found a decline of the membrane mass after each experiment (typically 5-10%). This could on one hand show a leaching of the carrier into the aqueous phase. On the other hand, this could also happen due to squeezing DEHPA and plasticizer out of the membrane, when clamping it between the two half cells. Somewhat exaggerated, it could be compared to squeezing a sponge (the membrane has 50% liquid components).
1) Which plasticizer did you use for your membrane? 2) Can you estimate the operational life of your membrane (i.e. how many cycles of Sc extraction)? 3) The rise of temperature to increase Sc-recovery, does it affect your membrane?
Thank you very much for the interesting questions. 1) The used plasticizer was NPOE (2-nitrophenyl octyl ether) 2) We did not investigate yet on how many cycles are possible with the membrane. However, we did experiments with at least three feed exchanges, giving similar results for the extraction. 3) We did FTIR measurements of the membrane before and after the tests and could only see little change in the DEHPA signal intensities, speaking for resilience. However, we found a decline of the membrane mass after each experiment (typically 5-10%). This could on one hand show a leaching of the carrier into the aqueous phase. On the other hand, this could also happen due to squeezing DEHPA and plasticizer out of the membrane, when clamping it between the two half cells. Somewhat exaggerated, it could be compared to squeezing a sponge (the membrane has 50% liquid components).
Submitted by Fulvio Di Lorenzo on Thursday 25th June 22:54
Do you think that the higher extraction observed at high temperatures compensate the cost increase associated with heating? Is there an optimal temperature to maximise the ratio cost(heat) / benefits(extraction) ?
Many thanks for the interesting questions! In fact, heating would cause additional costs and we did so far not investigate on an optimal temperature. However, the production of white pigment causes a lot of waste heat and also a pH adjustment of the acid waste has to be carried out before the extraction, meaning even more available reaction heat. Therefore, the overall process has a great potential to mitigate heating costs. However, an economical benefit can be easily estimated. We can consider 1m3 with 45 mg / L Sc in the pretreated acid waste, heating from 10 °C to 60 °C, a price of 13.35 $/MBtu (0.046 $/kWh) for natural gas, the heat capacity of water with 4.2 kJ/kg (0.0166 kWh/kg), an energy conversion efficiency of 50 % (which is rather low), while neglecting heat loss, a price of Sc2O3 of 4 $/g (USGS) and compare an extraction yield of 30 % vs 60 % in the room temperature vs. the heated case. Thus, it follows, that at least 46.7 kWh/m3 are required, including the conversion efficiency and the price, this means around 4.25 $/m3 cost for the natural gas. In contrast by doubling the extraction yield, the amount of recovered Sc2O3 may rises from 20.7 to 41.4 g/m3 or 83 $ vs 166 $ of value per m3. Hence, the heating seems at least from this point of view economically justified.
Do you think that the higher extraction observed at high temperatures compensate the cost increase associated with heating? Is there an optimal temperature to maximise the ratio cost(heat) / benefits(extraction) ?
Many thanks for the interesting questions! In fact, heating would cause additional costs and we did so far not investigate on an optimal temperature. However, the production of white pigment causes a lot of waste heat and also a pH adjustment of the acid waste has to be carried out before the extraction, meaning even more available reaction heat. Therefore, the overall process has a great potential to mitigate heating costs. However, an economical benefit can be easily estimated. We can consider 1m3 with 45 mg / L Sc in the pretreated acid waste, heating from 10 °C to 60 °C, a price of 13.35 $/MBtu (0.046 $/kWh) for natural gas, the heat capacity of water with 4.2 kJ/kg (0.0166 kWh/kg), an energy conversion efficiency of 50 % (which is rather low), while neglecting heat loss, a price of Sc2O3 of 4 $/g (USGS) and compare an extraction yield of 30 % vs 60 % in the room temperature vs. the heated case. Thus, it follows, that at least 46.7 kWh/m3 are required, including the conversion efficiency and the price, this means around 4.25 $/m3 cost for the natural gas. In contrast by doubling the extraction yield, the amount of recovered Sc2O3 may rises from 20.7 to 41.4 g/m3 or 83 $ vs 166 $ of value per m3. Hence, the heating seems at least from this point of view economically justified.
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