The estimates you're referring to I believe go up to 80,000 tonnes.

It's hard to extrapolate the exact number since a lot iron production in the Empire at the time were done by small-scale private operations that was spread all over. I think 50,000 tonnes is probably close to what was actually produced for an economically strong state like the RE with a population of 50 million. We know Roman iron smelters were especially good at their craft, running bloomery furnaces that had nominal yields of 20 kg of processed bar iron per furnace run at the upper end.

Assuming 8 men worth of labour needed for smelting/processing 15 kg of bar iron per furnace run, 100 furnace runs per year with spare days in between for processing the bloom, repairing furnaces, restocking, and rest - to produce 50,000 tonnes of iron a year will require an estimated manpower of ~270,000 men. Which will account for ~0.54 percent of a population of 50 million (or 1 worker per 185 people). A bit high but not an impractical ratio given how important of a commodity iron was. At 30,000 tonnes of iron per year, that ratio goes down to 0.32%, or 1 worker per 312 people. My guess is the actual production at peak was 20,000-50,000 tonnes per annum.