How realistic are the required fluorine mining quantities for terraforming Mars compared to the real mining practices on Earth?

Question

Energy balance calculations in the JGR article Radiative-convective model of warming Mars with artificial greenhouse gases suggest that the addition of 0.2 Pa of the best greenhouse gases mixture (15% $C_2F_6$, 62.5% $C_3F_8$, and 22.5% $SF_6$ ) to Mars' atmosphere would shift the equilibrium to the extent that $CO_2$ would no longer be stable at the Martian poles and a runaway greenhouse effect would result, that would nearly double the atmospheric pressure on Mars throughout the year.

To get the 0.2 Pa of the best mixture I calculated that 43275 kg fluorine per km² would be needed.
If that amount of fluorine could be mined every day, then after 396000 years that 0.2 Pa of greenhouse gases would have been reached for the whole surface area of Mars.
How does the mining of 43725 kg fluorine each day on Mars compare with the mining practices on Earth and could the production become ten-fold for instance, so that the job could be done in 39600 years instead ?

Answer 1

As stated in the comment by @JG, Wikipedia confirms that 17 kt of fluorine is produced annually. The reference used by both Wikipedia and The Essential Chemical Industry website is Ullmann's Encyclopaedia of Industrial Chemistry. Wikipedia expands further, stating that figure is for 11 companies, all from G7 countries.

The predominant mineral used in producing fluorine is fluorite, also known as fluorspar (CaF₂). The Statista website lists the total global production of fluorite, in 2021, as 8.353 Mt, the vast majority of it being mined in China (5.4 Mt). Mexico and Mongolia are the next largest producers at 990 kt and 800 kt respectively.

Now, 48.67% of fluorite is fluorine. However, only high grade fluorite, known as acidspar which contains 97% CaF₂ is used to make fluorine. Metspar, which contains 60% to 80% fluorine is used in steel production. Apparently 49% of fluorite mined is acidspar. A question that could be asked is, on Mars would metspar be used to produce fluorine or would it be dumped onto a stockpile? My speculation is, on Mars one would try to utilize as much of the available fluorite as possible.

Your calculations require 43 725 kg fluorine each day, which amounts to 16 kt of fluorine per Earth year. Only 42% of acidspar is used to produce fluorocarbons. Even if all Martian production of fluorine minerals were used to produce fluorocarbon gases the amount required would be magnitudes more than what is currently mined on Earth.

Regarding the capability to mine ten times what you calculated comes down to:

• The quantity of fluorine minerals on Mars
• How large are the deposits: lateral dimensions, depth and tonnes?
• What would be the grade of the deposits – percentage of CaF₂?
• What is the shape and orientation of the deposits: steeply dipping or near horizontal, tabular or like a pipe.
• What is the geographical distribution of the deposits
• Would all the deposits be able to be mined by open pit methods and if so how deep would be the deepest pit? This would incorporate depth of mineralization and geomechanical properties of the rocks in the walls of the pits and geological structures affecting pit wall stability.
• Would underground mining be required?
• Are all the other resources required to make fluorine compounds available and can they be utilized?
• Would it be possible to get the amount of equipment required on Mars to mine at such a rate of production and also the stationary processing plant required?

Some example of open pit fluorspar mines are:

Okorusu Fluorspar Mine, Namibia. An open pit operation that mines 100 kt of acid grade (high grade) fluorspar/fluorite per annum. The resource (not to be confused with reserve) is 9 Mt @ 30% CaF₂.

Sepfluor in South Africa, have a few mines. They mine 600 kt/a to produce between 130 kt and 185 kt of acid grade fluorite. They have total reserves of 12 Mt @ 26.6% CaF₂ for 3.2 Mt of CaF₂.

In the US, the Las Cuevas Fluorspar Mine is a small underground operation that is 120 m deep. The orebody is narrow. In 1993, the resources were 15Mt @ 84.5% CaF₂.

In terms of geology, fluorine tends to be concentrated in residual magma leading to a concentration of fluorine in some igneous rocks and in hydrothermal deposits associated with such rocks.

Most deposits mined for fluorine are hydrothermal, however, and consist of fluorine minerals that precipitated from hot water.

Fluorite has low solubility in a common range of hydrothermal temperatures, particularly from about 160 degrees Celsius (°C) down to 60 °C. The increasing fluorite solubility below 60 °C partly explains why some water with exceptionally high levels of dissolved fluorine are found even at ambient temperatures in evaporitic lake basins in some East African Rift valleys in Kenya and Tanzania.

Fluorite

is often associated with lead and silver ores; it also occurs in cavities, in sedimentary rocks, in pegmatites, and in hot-spring areas.

Fluorine occurs in many different styles of geology that have had an association with molten rock and hot ground waters. The massive copper, uranium, gold, rare earth and iron deposit Olympic Dam, in South Australia also contains 2.5 weight percent of of fluorite,amounting to approximately 106 Mt of fluorite/fluorspar, but it is thrown out as waste due to it being uneconomic to process.

Answer 2

There is little I can add to this superb answer, so please vote it up!

I wanted to add a slightly different perspective, which hopefully will contribute to the discussion.

To me the answer can be broken into three questions:

1) If we want to accelerate the process described in the previous answer, how much fluorite mining is required?

0.2 Pa of $CF_4$ is of the order of 7.2 billion tonnes of $CF_4$, which is close to 6.2 billion tonnes of elemental fluorine (7.2x76/88 - I'm using molecular weight ratios) requiring 12.7 billion tonnes of pure $CaF_2$ ore (6.2x78/38). Zubrin envisions a 50-year fluorocarbon production period to warm Mars. It's hard to see how a much longer period would be tolerated.

(Note my calculation of 6.2 billion tonnes of fluorine agrees with the 43275 kg fluorine per km^2 in the question, since Mars' surface area is ~144 million km^2.)

So a reasonable mining rate would be 250 Mt $CaF_2$ as acidspar per year, nearly 15 times Earth's annual mine production.

This is not in itself a massive undertaking. About 2,500 Mt of iron ore are mined globally each year along with 8,000 Mt of coal. With appropriate demand and resources, 250 Mt ore a year is not insurmountable, especially if large scale automated mining processes and high purity ore are available.

2) Is this quantity of fluorite available on Mars?

Martian regolith contains between 0.8% and 2.2% fluorine by weight, mostly as fluorite ($CaF_2$), much higher than the concentration in Earth's crust of 600-800 ppm. There is at least 10 times as much fluorine on Mars compared with Earth.

3) Is this fluorite readily available as high grade "acidspar" (>97% $CaF_2$) on Mars?

The answer to this question is (necessarily?) long, so strap yourself in. There's inorganic chemistry coming...

As explained in the previous answer, this depends on the geology of fluorite ores, and particular the mechanisms of their formation.

High grade fluorspar (acidspar) is almost exclusively formed hydrothermally. Fortunately ancient Mars appears to have had hydrothermal activity in abundance.

Sodium fluoride ($NaF$) and potassium fluoride ($KF$), and many other fluoride salts, are highly soluble in water. In contrast, calcium fluoride or fluorite ($CaF_2$) is very insoluble. If fluoride ions in solution (say from dissolved $NaF$ for example) mix with dissolved calcium ions, $CaF_2$ will crystalise at high purity. That's acidspar.

Calcium carbonate ($CaCO_3$) or calcite is a common source of calcium ions in solution. On first appearance, calcium carbonate appears no more soluble in water than calcium fluoride. However in the presence of dissolved CO2 or in acids, calcium carbonate can be quite soluble.

Such coupled reactions can result in the precipitation or crystallisation of one compound at the expense of the dissolution of another. Calcium ions will be precipitated from solution in the presence of fluoride, driving further dissolution of calcium carbonate to replace the calcium ions in solution. This can result in massive formations of high purity fluorspar (i.e. acidspar).

Mars has abundant calcite deposits. It's likely much of Mars original $CO_2$ is sequestered as calcite in beneath the surface of Mars. Far more calcite likely originated from ancient hydrothermal/volcanic activity.

However the presence of acidspar grade fluorite can only be determined by detailed prospecting, exploration, and feasibility studies. The thickness of any deposits and mining viability can't be determined by remote sensing or surface analysis alone.

In conclusion: Mars has much higher surface concentrations of the fluorite required for production of fluorocarbons than Earth. High purity fluorite (acidspar) forms as a result of hydrothermal processes involving mixing of soluble fluorides with dissolved calcium, such as occur in calcite deposits under appropriate conditions. Rich calcite deposits occur on Mars as a result of its early wet history.

There are good reasons to suspect large high-purity fluorite deposits exists on Mars, possibly on the scale required to produce vast quantities of fluorocarbons. However, only detailed geological surveys can determine this with confidence.