What useful materials can be extracted from Venusian atmosphere?

Question

Consider a cloud-top colony on Venus. What materials needed for the upkeep and expanding of the colony can be taken from Venusian atmosphere, excluding any possibility of mining the surface?

Answer 1

This is a rather broad question, so I'll mostly try to point you in the right direction than directly answer it; First, Venusian atmosphere is highly dynamic and diverse environment both in constitution as well as ambient pressure, temperature and even weather. It forms many distinct layers at different altitudes, and its troposphere extends to about 100 km (I presume there's a typo in Wikipedia article and they meant 65 miles, not 65 km). For easier reference, here's atmospheric pressure chart on Venus from already linked Wikipedia article:

Its composition is mostly carbon dioxide ($\require{mhchem}\ce{CO2}$ 96.5%) and smaller amount of nitrogen ($\ce{N2}$ 3.5%), while other constituents are in trace amounts, but that doesn't really exclude them from the possibility of extracting them from the atmosphere.

For example, in the cloud layers between ~ 50 and 70 km, large concentrations of sulfuric acid ($\ce{H2SO4}$) and smaller concentrations of hydrogen sulfide ($\ce{H2S}$) were detected and it would be possible to extract hydrogen, sulfur and oxygen from it by electrolysis and the use of reducing catalysts. Similar can be done with carbon dioxide to extract oxygen and carbon in a two-step electrolysis of the atmosphere or photosynthesis.

These constituent elements alone already give you any number of molecular compounds of interest, including for breathable air (nitrogen and carbon dioxide as they are, just in different concentrations, oxygen, and water to control ambient humidity), assuming reasonable deuterium to hydrogen concentrations also as potable water, otherwise deuterium and hydrogen atoms can be separated during electrolysis or heavy water ($\ce{D2O}$) from water ($\ce{H2O}$) with additional separation by molecular weight. Nitrogen and hydrogen give you ammonia ($\ce{NH3}$) that can be used as liquid coolant / refrigerant, fertilizer, fuel,...

Carbon and hydrogen also enable production of synthesized or naturally grown carbohydrates and polycarbohydrates as nutrients, carbohydrate chains and aromatic carbohydrates as plastics, e.g. vinyl, polyethylene that you might recognize in many products by having that HDPE - high density polyethylene or PE recycle sign print or embedding and HDPE are even not corroded by sulfuric acid so they could be extensively used in Venusian atmosphere for construction. Additionally, provided you can extract chlorine that is also present just below the cloud layer, you could also make PVC.

Boiling points of some metals and metallic alloys are also below Venusian surface temperature of ~ 462 °C (e.g. cadmium, lead, some magnesium alloys, mercury, phosphorus, potassium, selenium,...) so they could form vapor that would be transported to higher altitudes by thermal winds, where they would condense or recombine into heavier molecules (the latter might be true for molecules containing phosphorus and potassium) with the drop of temperature, and form metallic precipitate deposits. It would be possible to collect some of these metals from lower atmosphere on condensing surface low altitude balloons, or even collect their snow-like precipitates from high mountain surfaces by cable cranes.

But, for any serious colony in Venusian clouds where pressure and temperature are Earth surface like, breathable air serves as lifting gas, and one that wouldn't have to import materials from elsewhere in the Solar system, you'd still require the ability to at least pluck rocks and boulders off the surface with cable cranes or alike, to also provide your colony with silicon, iron, copper, and other useful elements and compounds. E.g. to produce silicon carbide ($\ce{SiC}$) low power electronics, gallium nitride ($\ce{GaN}$) high power transistors, diodes or photovoltaics, or gallium phosphide ($\ce{GaP}$) since all these materials have good heat and radiation tolerances.

For further reference, I suggest searching NASA Technical Report Server (NTRS) for Geoffrey A. Landis' works, perhaps staring with Colonization of Venus (PDF) that was published for 2003 Conference on Human Space Exploration proceedings, and concisely presents possibility of constructing aerostat colonies in Venusian atmosphere and natural resources available to them.

Answer 2

Old topic, but for those just showing up:

1. There are two leading candidates for the "unknown UV absorber" in Venus's atmosphere, and probably the most likely answer is some degree of both. One of these is elemental sulfur. The other? Ferrous chloride. Indeed, one of the Venera probes detected iron during its descent. All evidence points to there being a small amount of iron in the air in Venus.

2. "(e.g. cadmium, lead, some magnesium alloys, mercury, phosphorus, potassium, selenium, ...)"

Just because something can boil off in some form doesn't mean that it actually will in practice (chemical reactions come into play), nor that it could manage to be transported all the way up a whopping 50+ kilometers (on Earth that would be halfway to the Karman line) through an atmosphere which at the base is 90 atm, without precipitating out. On the other hand, the world isn't made of pure elements, there's all sorts of compounds, and many have vastly lower boiling points than their elemental forms. It gets complicated.

The honest fact is, we don't know what minor constituents make up the Venusian cloud decks. Back in the 1960s, it was theorized that the clouds were a wide range of mercury compounds. Now we know that mercury can't be but a trace element in the clouds. Another theorized one that's been fairly well ruled out is aluminum chloride. Some antimony compounds, bromine compounds, and iodine compounds are considered possible if not likely, but only in small quantities.

There are a number of chemicals that are well known to exist in Venus's atmosphere that are commonly not listed in lists of Venus's atmospheric components. For example, the lower haze and possibly a lot of the lower cloud deck are rich in to dominated by phosphoric acid. A wide variety of acidic/corrosive chlorine compounds also exist in Venus's atmosphere (most lists show only HCl), include some that make sulfuric acid seem tame (for example, perchloric acid is believed to make up a small component of the cloud particles). By the way, note that the cloud particles are a fine mist, it's not like a bath of acid... more like a really bad smog/vog that tends to eat away at things over time. There's some evidence, contrary to the oversimplified picture often presented, that there might even be "surface hazes" - there was some dimming experienced by the landers during their last 1-2km that some interpret as hazes. These would be some interesting compounds.

There's pretty good evidence that Venus's surface has exotic frosts or snows, although the composition is still unknown. Venus's surface appears to be made of lavas that on their own tend to be rather rich in interesting minerals (for example, there's good evidence of carbonatites - go check out what sort of economic deposits of minerals they're associated with on Earth). But it's also exposed to some intense chemical weathering processes, which tend to concentrate specific minerals in different environments. So the surface of Venus is probably a mining treasure trove. It's easy to overstate the difficulty of accessing the surface; no, it's no walk in the park, but on the other hand, it's not vastly more difficult than a submarine. Temperature issues only affect the outside; the inside is insulated and relies largely on thermal inertia to maintain itself at a comfortable operating temperature. The Soviets landed functional and capable probes with 1960s technology. The Soviets never lifted off the surface and went back up to the cloud deck, but we know how to do that - it's called a phase change balloon.

No, you don't need to do electrolysis to extract oxygen from H₂SO₄ - you just have to heat it. H₂SO₄ breaks down at high temperatures to H₂O + SO₃, and the SO₃ reduces to SO₂ + O₂. So you get both H₂O and O₂ from a simple process. Of course, the details make it tricky, because you have the other mixed compounds in there, you have to separate the acid gases (many of which are hygroscopic) from the water stream, etc. But on the upside, Venus's atmosphere is really giving one the gift of providing all but one of the major industrial acids (all but nitric) in a relatively easy to acquire form, and nitric is relatively easy to produce. A fun side benefit of Venus is that many major industrial processes (the Haber process, the Sabatier reaction, etc.) require elevated temperatures and pressures for the thermodynamics to work out. On Venus, all that means is "descend". :)

Concerning plastics: there's really no question that the perfect skin material is a PTFE copolymer with IR-reflective additives. PTFE is almost perfectly designed for the Venus environment, in terms of its amazing chemical resistance, heat tolerance, UV stability, relatively simple production process, etc. It of course must be bonded with a ripstop. Normally on Earth we'd use nylon, but it's really not ideal for Venus, the production chains are rather long. UHMWPE (spectra) is probably a much better choice; its monomer is easy to make, it's incredibly high tensile strength (higher than Kevlar), very light (even floats in water), and very abrasion resistant. Also, both UHMWPE and PTFE, while neither of them like to adhere to anything, are both thermoplastics and can thus be thermally bonded.

Note, contrary to what was stated above, HDPE is not long-term stable with concentrated H₂SO₄ (it's about 80% in the middle cloud deck). Although that's for liquids, not mists; it might do better in mists. But the key point is, the PTFE layer is what you have exposed to the clouds.

There's so vastly much more I could write on the topic, but I'll leave it at this for now. :)