Most scientists agree that iron oxidation kept Oxygen concentrations in Earth's atmosphere low for billions of years. It took that long for the Oxygen released by algae to react with, first, the dissolved iron in the oceans, and then the pure iron in the Earth's crust. Only when those had been rusted out into either ocean sediment or iron ore deposits, was Oxygen able to accumulate in the atmosphere, and allow complex life to form.
Oxygen is consumed in the process of iron oxidation, not released. This would, as a previous answerer suggested, keep the concentration of oxygen in the atmosphere low as oxygen is used by the spontanious reaction between iron rich rocks and the oxygen in the atmosphere.
As a rough guess, I would say that the oxidisation of iron on the primordial earth would have increased the concentration of oxygen present in the atmosphere. As sulphurous, carbonic and ammonia based compounds oxidised iron rich materials, oxygen would be released. Oxygen would be released in favour of far more oxidising caustic compounds. Once the Earth is cool enough and a critical mass of oxygen has been liberated from both volcanic and chemical emissions, the oceans begin to form and even more oxygen is liberated. At a guess
