BY DR. JOSE PALU-AY DACUDAO
(Why Chernobyl mammalian wildlife survive)
THERE are other tree plantations in other parts of the globe that act as carbon sinks.
A prime example is the eucalyptus tree plantations of Brazil. There are more than 7.5 million hectares of them. From planting to harvest, it also takes about seven years.
The final products made from these eucalyptus trees are mostly paper and, peculiar to Brazil, charcoal. Massive quantities of Brazil’s commercial eucalyptus trees are converted into charcoal in huge iron retorts. The charcoal is used for smelting iron oxides. Brazil is one of the world’s a leading producer of iron, behind China and India. Most iron-producing countries use coal as the reducing agent to smelt iron oxides, but Brazil lacks substantial coal deposits, while being rich in minable iron oxides, hence the use of charcoal as the reducing agent to smelt iron oxides.
It has been mentioned in previous articles that strictly speaking, using charcoal to smelt iron oxide, and other metal oxides is merely carbon-neutral and does not result in a net carbon dioxide sequestration. Recall the following processes:
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, strictly speaking, 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.
However, it is important to note that massive amounts of charcoal are wasted in the process, from leftovers in the place where charring occurs to the place where smelting occurs. Recall the following processes:
Photosynthesis:
6 CO2 (carbon dioxide) + 6 H2O (water) → C6H12O6 (organic substance) + 6 O2 (oxygen)
Charring:
C6H12O6 (organic substance) → 6 C (elemental carbon) + 6 H2O (water)
Overall summary of the two above processes:
6 CO2 → 6 C (elemental carbon) + 6 O2 (oxygen)
Thus, when elemental carbon in the form of charcoal gets inevitably left behind or wasted, there is a net sequestration of carbon dioxide away from the atmosphere.
The same is true for charcoal made for cooking purposes. It must be noted that tropical countries char wood in massive quantities to produce charcoal used in cooking. Charcoal is always wasted in the process, from leftovers in the place where charring occurs to the place where cooking takes place. (To be continued)/PN
