Recovery of Gallium from the Bayer Process for Alumina Using Amidoxime Impregnated Fibers.

[NNadir]

I'm very fond of the amidoxime functional group which has been widely investigated for the recovery of uranium from seawater, a process to which appeal is often made to show that uranium, given its high energy density, (especially when converted to plutonium) is inexhaustible.

I came across this paper referencing this functional group, using a similar idea, for the recovery of the strategic metal gallium from alumina production, using the Bayer process, alumina being refined from the mineral bauxite to make aluminum metal as well as certain refractories.

The Bayer Process:



Code of Practice to Reduce Emissions of Fine Particulate Matter (PM2.5) from the Aluminium Sector (Canada)

I don't have a lot of time to spend with this paper, but here it is: Innovative Amidoxime Nanofiber Membranes for Highly Effective Adsorption of Ga(III) from Waste Bayer Solution Zhifeng Qin, Yuyi Liao, Zhenghao Wang, Shenghong Wang, Lei Song, Kui Ma, Dongmei Luo, and Hairong Yue Industrial & Engineering Chemistry Research 2023 62 (28), 11140-11150.

Some rhetoric from the introduction, covering the case:

Gallium, known as the new grain of the semiconductor industry, has been listed as a strategic reserve metal by the United States, Japan, the European Union, and China. (1−3) With the rapid rise of emerging technologies, especially in the cutting-edge science and technology fields such as communications, integrated circuits, and aerospace, the reserve of gallium elements has increasingly become an essential and urgent task owing to its excellent semiconductor properties. (4) The booming electronic information industry further highlights the strategic position of gallium, and gallium has become a strategic emerging mineral resource. (5−8)

Gallium resources are an associated resource and are the byproduct of aluminum extraction from bauxite ores, (probably more 90%) or zinc extraction from zinc ores. (9,10) The waste Bayer solution, obtained from the seed mother liquor in the Bayer process to produce alumina, typically contains roughly 70% gallium, making it the most economical Ga resource with recovery value. (11,12) It has been reported that amidoxime chelating resin was beneficial to extracting gallium from the waste Bayer solution. (13) Zheng et al. studied the adsorption performance of commercial resin AO on gallium with a maximum adsorption effect of 28.26 mg/g. (14) Zhao et al. investigated the mechanism of gallium adsorption by the commercial resin LSC 700 and showed that the oxygen on the amidoxime group of LSC 700 formed a complex with Ga(III). (15) The density functional theory (DFT) can be used to obtain the energy of the binding model between amidoxime resin and Ga(III). (16) In view of the resin synthesis process, which is typically conducted by suspension polymerization using acrylonitrile or styrene as monomers, it usually suffers a lot from the long synthesis times, low resin qualification rates, and low adsorption capacity, limiting its application in gallium adsorption. Therefore, it is urgent to develop efficient, durable, easy scale-up, and low-cost adsorbents for the economic and highly efficient extraction of gallium.

Owing to the excellent material physical chemistry and structural characteristics, such as a large specific surface area, high adsorption capacity, fast exchange rate, and easy regeneration, ionic fibers have been widely applied in environmental protection, analysis, purification of precious metals, waste gas, and wastewater, and recovery of other substances. (17−19) Chen and Gu et al. reviewed the recovery of radioactive elements from solution by covalent organic materials. (20,21) The study showed that the amidoxime group could recover metal ions from the solution effectively. Polyacrylonitrile (PAN) contains wealthy cyano-functional groups, which can undergo a nucleophilic addition reaction with hydroxylamine reagent to obtain compounds with amidoxime groups. (22) It can be divided into PAN fiber direct modification, chemical grafting, and pre-irradiation grafting according to the different ways of introducing the cyanide group. (23) The proposed lysine-covalently grafted polyacrylonitrile fiber method has been applied in removing U(VI) from seawater. (24) The effect of amidoxime degree of polyacrylonitrile fiber has also been investigated on uranium adsorption. (25)

Gallium is a constituent of CIGS type solar cells, and I have sometimes been stalked by a "solar will save us" type moron who wishes to argue that the supply of indium, another constituent of these cells, is inexhaustible. (The moron in question loves to post links in a barely literate fashion to the USGS website.) This of course, seems to be true only because after the expenditure of trillions of dollars and tons of cheering for the last half a century, the solar industry remains a trivial affectation that has proved useless to address climate change, although it's great at converting wilderness into industrial parks at the behest of self-declared "environmentalists" who nonetheless seem to hate wilderness. These people are not environmentalists. They are Ayn Rand type advocates of development.

Nonetheless, gallium (and indium) are important elements in their own right, beyond insipid "solar will save us" ideas and are considered, quite correctly, to be strategic materials, and thus efficiency in processing to recover them is an important task.

Enjoy the holiday weekend.

[niyad]

1. Thank you. Skimmed, but will have to read it more closely.

[eppur_se_muova]

2. Interesting -- I thought Ga was extracted under acidic conditions.

Apparently, GaCl3 is very soluble in some organic solvents. I guess that's old technology now, even though it's been reported with ionic liquids.

Isn't that chart missing a step or two? I thought precipitation of Al2O3 only occurred after acidification with CO2. If so, that "Al2O3.3H2O suspension" is really aluminate solution. I don't see an input for CO2 anywhere.

[NNadir]

3. To be perfectly honest, I just pulled this flow chart off the Canadian...

...equivalent of the EPA's website.

One can, in detail, imagine a number of acids to precipitate the aluminum.

Since the reduction of alumina in the Hall Heroult process generates both CO2 and CF4 from the "green anodes" I would imagine that CO2 is readily available and cheap. The added advantage I suppose would be the bicarbonate buffer, but I haven't looked that deeply into the process details of the "normal" Bayer process. I would imagine that historical "red mud" from the time before gallium demand rise to cover the cost, would constitute a crude gallium ore.