The large-scale production of sulfuric acid via the oxidation and hydration of pyrite (iron disulfide) is a well-established industrial and geochemical process for which formal academic citation is not required.
The claim describes a standard chemical and industrial process (burning pyrite to generate sulfur dioxide, oxidizing it to sulfur trioxide, and hydrating it to form sulfuric acid). None of the retrieved papers directly test or challenge this basic chemical fact; papers discussing sulfuric acid production or sulfur metabolism merely touch on related contexts. Therefore, the claim is common knowledge requiring no citation.