Reducing carbon dioxide emissions in the smelting of metals in General, Ores of Oxides and Sulfides, 1

BY JOSE PALU-AY DACUDAO

THE MOST commonly used structural metals that we utilize in their elemental forms (alone or admixed in alloys with other elemental metals such as ferrochrome and ferromanganese) are iron, aluminum, magnesium, chromium, copper, manganese, and zinc.

All these come from mineral metal oxides except copper and zinc, which we obtain from their mineral sulfides. These are the most abundantly used metals because they are the main structural metals that human world civilization utilizes.

All mineral oxides are fundamentally derivations from the metal oxide. The most common examples are: Iron oxides (hematite Fe₂O₃ or magnetite Fe₃O₄); Aluminum oxide (alumina Al₂O₃); Magnesium oxide (magnesia MgO). As previously discussed, obtaining the elemental metal from its oxide mineral is usually done by chemical reduction – “stealing” the oxygen from the oxide leaving being the pure metal. The stolen oxygen is attached to elemental carbon, forming CO₂.

2 MeO (metal oxide) + C (elemental carbon) → 2 Me (elemental metal) + CO₂ (carbon dioxide)

Thus, almost all smelting processes that involves metal oxides as the source material for the elemental metal intrinsically produces CO_2.

As previously discussed, using charcoal as the source of elemental carbon eliminates a net CO₂ output from the fundamental smelting process. The formula is:

2 MeO (metal oxide) + C (charcoal elemental carbon, fixed by photosynthetic plants from atmospheric CO₂ in a geological instant) → 2 Me (elemental metal) + CO₂ (carbon dioxide released back to the atmosphere in a geological instant in the smelting procedure)

What about sulfide ores, from which copper and zinc are obtained?

The process usually involves oxidizing the copper and zinc sulfides into their oxides and sulfur dioxide CO₂. The oxide is them chemically reduced (as in other oxides above) by elemental carbon (leaving behind carbon dioxide), hydrogen (leaving behind water), or electrolyzed (leaving behind oxygen).

In brief, the basic over-all formula for smelting sulfides (the source of copper and zinc) is:

MeS (metal sulfide) + O₂ → Me (elemental metal, for example elemental copper or zinc or cobalt or nickel) + SO₂ (sulfur dioxide)

Next question: Is sulfur dioxide SO₂ a greenhouse gas?

No, it’s not. The main issue about SO₂ is that in large amounts, it can get oxidized in the atmosphere into sulfuric acid H₂SO₄. Sulfuric acid is a cause of acid rain.

But what if it gets produced only in small amounts? That is not enough to cause acid rain.

The strange answer is that it can actually benefit plants.

The leaves of land plants have the ability to take in sulfur dioxide through their stomata. The SO₂ gets dissolved in water inside the plants’ leaves, and eventually gets reduced by the plant and incorporated into its proteins. Sulfur is a component of the two proteinogenic amino acids cysteine and methionine, which all plants and other living organisms that have proteins need. We humans are about 0.2% sulfur by mass, and plants have even more sulfur. Sulfur is a macronutrient. (To be continued)/PN