Acid mine drainage (AMD), resulting from the oxidation of iron pyrite (FeS₂) and other sulfide minerals, is a major problem in coal-and metal-mining districts in that such water often has a lower pH and contains high concentrations of heavy metals as well as Fe and SO₄^2-. Preventing the formation or migration of AMD from its source is generally considered to be the preferable option. However, due to the practical operational difficulties in many locations, efforts are directed towards the collection and treatment of the effluent. There are various options available for AMD treatment, and lime neutralization seems to be the most widely-used method in the mining industry. Unlike Fe³⁺, Fe²⁺ is difficult to be precipitated unless pH is elevated to 8.5, thus, from the economic viewpoint, the oxidation of Fe²⁺ to Fe³⁺ prior to neutralization is required during the treatment of the Fe²⁺-rich AMD. Acidithiobacillus ferrooxidans was proved to be efficient for the oxidation of Fe²⁺ under low pH conditions. During the biological iron oxidation, abundant amounts of ferric iron oxyhydrosulfate (mainly jarosite) would precipitate. One of the advantages of the precipitate is the relative easiness of filtra-tion, thereby the problems associated with settling and filtering neutralized iron solutions are avoided. Therefore, the enhancement of the formation of ferric iron oxyhydrosulfate will favor the removal of soluble iron in AMD. Several factors affect the precipitation of ferric iron oxyhydrosulfate, such as temperature, initial pH, retention time, types and concentrations of jarosite-directing cations (K⁺, Na⁺, NH₄⁺, etc.) and the amounts of crystal seed.This paper reported the beneficial role of diatomite, quartz sand and K⁺ in iron oxyhydrosulfate formation in the presence of A. ferrooxidans. It was found that both the rate and extent of the formation of iron oxyhydrosulfate precipitate increased with the increase of the amount of the three materials added to the reaction system. Compared with the control without the addition of diatomite, quartz sand, or K⁺, the treatments with 10 g of diatomite, 10 g of quartz sand and 80 mmol/L of K⁺ increased the removal efficiency of total iron by 8%, 24%, and 20%, respectively, after 72 h of reaction in 160 mmol/L of the initial FeSO₄ biooxidation system. The contents of K and S of the jarosite produced in the K⁺ series increased with the increase of the initial concentration of K⁺ in the liquid media, whereas the content of Fe decreased.