BY DR. JOSE PALU-AY DACUDAO
ANOTHER hypothesis is that most waste plastic simply sink into the anoxic sea bottom. Their ultimate fate will be to transform back into fossil fuels.
Both of the above hypotheses may be true.
In conclusion, if we want plastics to act as a carbon sink, then we should find a way to make them from recently harvested organic material. As of now, being made from petroleum, plastic is not a carbon sink.
How about smelting iron oxides, aluminum oxides, and other metal oxides?
The essential chemical process in the reduction of the metal oxide (MeO) is:
2 MeO (metal oxide) + C (elemental carbon) → 2 Me (elemental metal) + CO2 (carbon dioxide)
If the elemental carbon is taken from coal, whose carbon was fixed from the atmosphere millions of years ago by now fossilized ancient plants, then we are outputting a net amount of carbon dioxide into the atmosphere.
But what about taking the elemental carbon from charcoal? In this case, carbon was fixed from the atmosphere less than a few decades ago by today’s plants, then we are essentially taking CO2 from the atmosphere and releasing it back again with no net input or output in a geological instant.
Equation for photosynthesis:
6 CO2 (carbon dioxide taken from the atmosphere in a geological instant of a few decades or less) + 6 H2O (water) → C6H12O6 (organic substance) + 6 O2 (oxygen)
Equation for charring/ carbonization/ pyrolysis (charcoal production):
C6H12O6 (organic substance) → 6 H2O (water) + 6 C (charcoal elemental carbon)
The equation for the chemical reduction of the metal oxide is essentially:
2 MeO (metal oxide) + C (charcoal elemental carbon) → 2 Me (elemental metal) + CO2 (carbon dioxide released back to the atmosphere in a geological instant in the smelting procedure)
Thus, if charcoal is used as the reducing agent, the over-all process of smelting metal oxides, upon cancelling the appropriate terms on either side of the equations, is:
2 MeO (metal oxide) → 2 Me (elemental metal – iron, aluminum, magnesium, chromium, and so on) + O2 (oxygen released to the atmosphere in a geological instant)
Therefore, smelting metal oxides is not a carbon sink. If coal is used as the reducing agent, then there will even be a net emission of carbon dioxide. If charcoal is used, smelting metal oxides will be carbon neutral.
(Notice that charcoal production or charring from organic matter in all of the above examples results in a net oxygen emission into the atmosphere. So does lignin production if the lignin is not burned or decomposed. But certainly no one will complain about net oxygen emissions.)
In conclusion, as far as I can discern, there are only three processes done by humans in a massive scale that result in a net carbon dioxide sequestration away from the atmosphere. First is responsible forestry. Second is charring plant remains after a harvest and plowing the char into the soil. Third is charcoal production (also by charring)./PN
