Do hydrogen sulfide and oxygen produce pure sulfur or sulfur dioxide? If both, under which circumstances does each scenario occur? If both of the following hydrogen sulfide and oxygen chemical equations can occur, under what circumstances is the harmless pure sulfur and the toxic sulfur dioxide produced?
$\ce{2H2S + O2 -&gt; 2H2O + 2S}$
$\ce{2H2S + 3O2 -&gt; 2H2O + 2SO2}$
Specifically I have a fresh water aquarium with sand, plants, and small creatures I collected from a creek. I want to prevent hydrogen sulfide building up by oxygenation with an air pump, but I want to make sure the environment does not result in the harmful sulfur dioxide in the tank.
Sulfur dioxide is not a problem ; in an aquarium it will make very dilute sulfurous acid which will likely neutralize with some carbonate mineral/gravel. H2S is lethal , extended exposure at 50 ppm for a day , or short exposure at 500 ppm. On the other hand , what you smell in aquarium sand is less then 1 ppm, the sense of smell is very sensitive to H2S. There are several answers on the internet but I expect most people can smell H2S at 0.1 ppm. An aerator will have no significant affect on H2S in an aquarium. When I clean my pond , which is well aerated ,the smell of H2s is strong from decomposing leaves, etc.
Regarding the first part of your question ; Hundreds of tons a day of elemental sulfur are made ,world wide, every day by burning H2S with limited air at high temperature. By recycling and control of gas compositions the only products are elemental sulfur and water,