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Fri Sep 16, 2016, 01:29 PM

Fun with Chemistry: Recovering the rare element gallium from dead solar cells.

Last edited Fri Sep 16, 2016, 09:15 PM - Edit history (1)

Last night I was reading several papers in the literature concerned with what the badly screwed future generations might do with all the solar cells we've been manufacturing in recent years, despite the fact that they have failed to do a damned thing to address the accelerating rate of climate change.

The solar industry is tiny and clearly useless despite soaking up trillions of dollars, and there are many rote assumptions that claim they are "green" (as in environmentally benign) and "sustainable" (they can be used indefinitely).

As is the case with many rote assumptions, they are wrong.

The paper to which I will refer here is this one: Separating and Recycling Plastic, Glass, and Gallium from Waste Solar Cell Modules by Nitrogen Pyrolysis and Vacuum Decomposition (Lingen Zhang and Zhenming Xu, Environ. Sci. Technol., 2016, 50 (17), pp 9242–9250)

Some text from the paper:

The first solar cell was invented at Bell Laboratories in 1954. After the energy crisis of the 1970s, the products of solar cells started to be used in civilian fields. Converting the energy of sunlight into an easily usable form is one of the most attractive solutions to the shortage of fossil energy.(1) Photovoltaic energy has been known as the cleanest energy in the 21st century. With the rapidly expanding of photovoltaic market, the output of solar cells is growing by about 28.14% a year in China.(2) The solar cells have been widely used in transportation, communications, space, and other fields. Crystalline silicon has become an important and dominant semiconductor material in most of solar cells.(3) Apart from Si wafer-based module, gallium arsenide (GaAs) which is a compound semiconductor has been used for decades to make ultrahigh-efficiency solar cells because of its advantages, including their high photoelectric conversion efficiency and excellent antiradiation performance.(4, 5)...

...Gallium, as an important strategic resource, has been categorized as one of 14 mineral resources by the European Commission in extreme shortage.(11) The world reserve of gallium has been estimated to be 18 000 tones, which is merely one tenth of gold.(12) In nature, gallium has no ores of its own at all; rather it occurs in trace and minor amounts in various associated minerals types, such as bauxite, zinc, tin, and tungsten ores.(13, 14) Hence, it has led to strong interest for recovery of gallium from wastes. At present, various researches have been developed to recycle gallium. Technologies include acid leaching,(15) organic solvent,(16, 17) chemical precipitation, electrochemistry,(18, 19) and supercritical extraction(20) etc. I.M. Ahmed(21) proposed extracting method by Cyanex 923 (a mixture of four trialkylphosphine oxides) and Cyanex 925 (bis(2,4,4-trimethylpentyl) octylphosphine oxide) in kerosene from hydrochloric acid medium to recycle Ga(III). Although these studies have focused on recycling gallium resource, environmental improvement are still challenging due to limitations on using large volume of acid/alkali/organic reagent with high concentration.

The bold is mine. That bolded remark doesn't sound all that "renewable" to me.

The authors propose nitrogen pyrolysis and vacuum decomposition which is (they say) cleaner. Here's some of their investigation of the "clean" process.

The effect of temperature on the organic conversion rate was investigated in the range from 573 to 1073 K at 0.5 L/min N2 flow rate lasting 30 min. It could be seen from Figure 6(a) that the organic conversion rate was low when temperature was 573 and 623 K, which was 19.61% and 36.02%, respectively. But when temperature reached 673 K, the organic conversion rate sharply increased and exceeded 98%. With the temperature over 773 K, the organic conversion rate reached approximately 100%. It indicated that the pyrolysis temperature of plastic components was 773 K. We analyzed the organic components of oil products from 773 to 1073 K. The results were summarized graphically in Figure 7(a). We found that the organic components of oil and gas products had obvious changes with the increasing of temperature. When the temperature reached 773 K, alkanes and olefins were main organic components in the oil products. But, some naphthenes, acetophenone, and methyl naphthalene, etc. began to be detected in pyrolysis oil products with the temperature rising to 873 K. When the temperature arrived 973 and 1073 K, anthracene, phenanthrene, and homologues of benzene were main components of pyrolysis oil products. For pyrolysis gas products from panel materials (as shown in Figure 7(b)), benzene rapidly increased with increasing of temperature. But, components of gas products were not change. Therefore, the temperature of pyrolysis should be controlled under the condition of 773 K.

Um...benzene. I'm sure they'll be absolutely safe, since all recycling facilities for electronic waste are absolutely safe.

The arsenic is recovered as diatomic arsenic gas which distills away.

The process is in no way quantitative.

he effect of temperature on the recovery efficiency of gallium was investigated in the range from 973 to 1273 K, maintaining system pressure of 1 Pa and reaction time of 40 min. As shown in Figure 9(a), the recovery efficiency of gallium increased sharply with an increase of temperature from 973 to 1023 K. The recovery efficiency reached 60.9% when the temperature was 1023 K, and then its rise began to slow. The recovery efficiency of gallium increased to 76.4% with the temperatures reached 1273 K. Figure 9(b) showed the theoretical and experimental evaporation rate of Ga particles. In theory, the evaporation rate of gallium should be increased with the increase of temperature, according to Langmuir-Knudsen eq (eq 3). However, the evaporation rate has not changed in our experiment. The experimental evaporation rate of Ga presented nearly linear relationship with temperature, which was range from 5.64 × 10–5 to 2.12 × 10–4. Its explanation may be that on the one hand, first, the decomposition reaction of GaAs is happened, which needed a high temperature and then metallic gallium can volatilize.

Well, whatever gallium and arsenic remains, we can always take it to a "green landfill."

It's amazing how much handwaving and how many ill thought out beliefs, dogmatic beliefs, get attached to the solar industry, since for many decades it was all theory and no practice.

The practice is quite different. Trillion dollar quantities of resources have been thrown at this industry in the last ten years, with the result that the annual increases in the dangerous fossil fuel waste carbon dioxide is the highest ever observed.

It is expected that in about twenty years, about two million tons of used and dysfunctional solar cells will need disposal on this planet. cf (Sustainable System for Raw-Metal Recovery from Crystalline Silicon Solar Panels: From Noble-Metal Extraction to Lead Removal (Byungjo Jung†, Jongsung Park‡, Donghwan Seo†, and Nochang Park*, ACS Sustainable Chem. Eng., 2016, 4 (8), pp 4079–4083)

Enjoy the coming weekend.

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Reply Fun with Chemistry: Recovering the rare element gallium from dead solar cells. (Original post)
NNadir Sep 2016 OP
kristopher Sep 2016 #1

Response to NNadir (Original post)

Fri Sep 16, 2016, 02:47 PM

1. Fun with reality

Gallium nds its greatest application in electronic circuitry, laser diodes, and light emitting diodes (LEDs) (Kelly and Matos, 2006; Matos, 2006). Photovoltaic cells that incorporate gallium arsenide are mostly used for generating electricity for satellites and space exploration. Although gallium arsenide is well suited to photovoltaic cells, its application for consumer use is greatly limited by the high cost of producing gallium arsenide crystals, a necessary component of the cell. Lowering the cost of production will likely be key to commericialization of the technology.

US Geological Survey,
Sources and Supplies of Commodities Used in Photovoltaic Cells, Page 5

Domestic Production and Use: No domestic primary (low-grade, unrefined) gallium has been recovered since 1987. Globally, primary gallium is recovered as a byproduct of processing bauxite and zinc ores. One company in Utah recovered and refined high-purity gallium from imported low-grade primary gallium metal and new scrap. Imports of gallium were valued at about $9 million. Gallium arsenide (GaAs) and gallium nitride (GaN) wafers used in integrated circuits (ICs) and optoelectronic devices accounted for approximately 75% of domestic gallium consumption. Production of trimethyl gallium and triethyl gallium, metalorganic sources of gallium used in the epitaxial layering process for the production of light-emitting diodes (LEDs), accounted for most of the remainder. About 57% of the gallium consumed was used in ICs. Optoelectronic devices, which include laser diodes, LEDs, photodetectors, and solar cells, accounted for nearly all of the remaining gallium consumption. Optoelectronic devices were used in aerospace applications, consumer goods, industrial equipment, medical equipment, and telecommunications equipment. Uses of ICs included defense applications, high-performance computers, and telecommunications equipment.

U.S. Geological Survey,
Mineral Commodity Summaries, January 2016, Page 64

Poor Nnadir, I have some really, really bad news for you regarding your effort to put lipstick on the nuclear pig by misrepresenting renewable energy.

They've just confirmed that cancers caused by ionizing radiation have a distinct genetic signature that is different from all other causes of cancer.
Ionizing radiation is a potent carcinogen, inducing cancer through DNA damage. The signatures of mutations arising in human tissues following in vivo exposure to ionizing radiation have not been documented. Here, we searched for signatures of ionizing radiation in 12 radiation-associated second malignancies of different tumour types. Two signatures of somatic mutation characterize ionizing radiation exposure irrespective of tumour type. Compared with 319 radiation-naive tumours, radiation-associated tumours carry a median extra 201 deletions genome-wide, sized 1–100 base pairs often with microhomology at the junction. Unlike deletions of radiation-naive tumours, these show no variation in density across the genome or correlation with sequence context, replication timing or chromatin structure. Furthermore, we observe a significant increase in balanced inversions in radiation-associated tumours. Both small deletions and inversions generate driver mutations. Thus, ionizing radiation generates distinctive mutational signatures that explain its carcinogenic potential.

Mutational signatures of ionizing radiation in second malignancies
Sam Behjati, Gunes GundemPeter J. Campbell
Nature Communications 7, Article number: 12605 (2016)
Open Access http://www.nature.com/articles/ncomms12605


How long do you think it is going to take to start getting a handle on the real consequences of nuclear power now that they will no longer be able to hide behind the lack of proof regarding cause and effect?

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