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 PROTECTING THE ENVIRONMENT

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hogwarts201
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PostSubject: PROTECTING THE ENVIRONMENT   Sun Dec 26, 2010 1:46 pm



Is there a safe chemical way to remove CO2 from air?

Alkali metal hydroxides (column I and II metal hydroxides) can be used to absorb carbon dioxide (CO2) in an enclosed atmosphere, like in a space craft or submarine. However, they're corrosive and absorb water vapor. (1) Is there any commonly-available material that is not toxic/dangerous that will absorb CO2? (2) What is used in underwater rebreathers/CO2-scrubbers?

Plants absorb CO2, of course, but they take up a lot of room and are slow, inefficient CO2 absorbers.
Most industrial CO2 scrubbers use chemicals that don't meet your criteria. Monoethanolamine (MEA) is used to scrub carbon dioxide from gas streams, but it's corrosive and toxic in very small amounts. Ascarite II is a very efficient CO2 absorbent, but it's basically nonfibrous asbestos covered with sodium hydroxide.
Potassium superoxide is an interesting possibility for spacecraft and submarine CO2 scrubbing, since it regenerates oxygen as it reacts with carbon dioxide:

4 KO2(s) + 2 CO2(g) = 2 K2CO3(s) + 3 O2(g)

But it isn't common, and it is quite toxic.

Calcium hydroxide (mixed with a small amount of sodium and potassium hydroxides) is used in most underwater rebreathers. The reaction between the hydroxides and CO2 is exothermic, and divers can tell from the warmth of the scrubber canister that the absorption reaction is working. Failure of the canister lid can give the diver a mouthful of hydroxides- called a "caustic cocktail" in diving circles. It's apparently a memorable experience.
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hogwarts201
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PostSubject: Re: PROTECTING THE ENVIRONMENT   Sun Dec 26, 2010 1:48 pm




How is SO2 waste recycled to make wallboard?

Steam locomotives in the 1950s burned coal containing sulphur which released sulphur dioxide into the atmosphere. Scrubbers could have removed SO2 from flue gases by reaction with calcium carbonate, CaCO3. What is this reaction?

SO2 is usually removed by spraying the hot exhaust gases with a slurry of limestone, dolomite, or (less frequently) lime. The process is called 'wet scrubbing', and it involves many separate dissolution, oxidation, and neutralization processes. For wet scrubbing with CaCO3 slurry, the most important reactions can be summarized by

SO2(g) + H2O(l) SO2•H2O(aq)
SO2•H2O(aq) + CaCO3(s) CaSO3(s) + H2O(l) + CO2(g)
CaSO3(s) + 2 H2O(l) + 1/2 O2(g) CaSO4•2 H2O

The final reaction produces gypsum, which has economic value. In fact, some power plants earn additional income by selling the gypsum to industry for use in plaster, wallboard, and Portland cement.

It's interesting to note that although wet scrubbing has been used since the 1920's and 1930's in Great Britain's coal-fired power plants, scrubbing didn't catch on in the United States until the Clean Air Act Amendments of 1970 and 1977, for economic reasons.
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hogwarts201
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PostSubject: Re: PROTECTING THE ENVIRONMENT   Sun Dec 26, 2010 1:50 pm



What are soda cans made of? What environmental problems do they cause?
What chemical substances are contained in a pop can and what environmental problems can be caused by pop cans. Are there any solutions to those problems?

Soda cans are almost entirely (99%+) aluminum.

Aluminum is a very reactive metal, but it forms an oxide coating which is highly resistant to corrosion. The body of the can is usually alloyed with a small amount of manganese to improve its strength and workability.

The cans take up a lot of landfill space, and energy is required to make (and collect and recycle) them. The aluminum is refined from bauxite, and bauxite mining also has an impact on the environment.

Refillable containers may be one solution to the problem.
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