Today I saw the 3rd episode of Stargate Univers on German TV. I was looking forward to it, especially because of the geologist's character. The problem was to find a substance to filter CO2 from the air. They travel to a desert planet to search for limestone (CaCO3) to act as an air filter. But one thing at a time.
Upon arrivel the geologist looks down and takes some grains of sand into her hand. She attests it to be Gypsum (CaSO4+2*H20). The next sentence she utters ruins my evening. She says that is good because Gypsum is 36% Calciumcarbonate (CaCO3). I am shocked. Numbers aside, there is no carbonate whatsoever in Gypsum!
She says Gypsum is Calcium-Sulfide...ehem...Sulfate is the word!
Next she explains they need to find limestone. They use a funny red liquid that has to turn clear, they do not explain what it is, to show that the sand is limestone. Sounds complicated - bad geologist: Don't they have any weak acid? 5% or 10% HCl would be a much quicker and water (one drop instead of half a liter) saving method to determine limestone. Even without any acid a good geologists should be able to identify Calcite - especially in contrast to Gypsum.
Then we learn that they need to find a salt lake to discover limestone. I am confused. Although there are terrestrial and sabhka carbonate deposits, looking for those in the middle of a Gypsum desert seems not very promising. Salt lakes have a higher potential for finding evaporites or brines to use. The brines of a number of salts could theoretically be used to absorb CO2. Apparently the Stargate Univers geologists is completely unaware of that potential and fixed on limestone.
The geologist and some other guy rebell and go to some other planet through the gate. I assume they get stranded there for eternity. A good punishment!
Also, even with a couple of cubic meters of limestone they will first need to exert a lot of their precious energy to remove the CO2 from it to gain CaO which they need to dissolve in water (also rare on the spaceship). It would be much more practical to get a some of the natural brines from the salt lake. There seems to be an underground brine source even. They would no longer require massive amounts of energy or processing.
And then - if there is so much energy as to burn lime why not use the waste heat to drive the crystal water from the gypsum? Wouldn't it be an ingenious method to also replenish the small water supplies?!
Oh well - I shouldn't have paid attention to the geologist there. Sigh.