Tween 80 and Triton X-100 effects on morphological evolvement and stability of schwertmannite during bacterial reproduction

Nonionic surfactants with ideal surface properties and lower ecotoxicities have been highly attended in metal bioleaching and pollutant bio-treatment in environmental science field. In this study, both Acidithiobacillus ferrooxidans HX3 and Tween 80 (or Triton X-100) presence in cultures, bio-production and development of schwertmannite as a potential metal scavenger were investigated. To explore their correlations, the resulting ferric oxyhydroxides under various surfactant levels (lower/optimal/higher ones for Gp I/II/III treatments) were identified by many characterization methods. Result showed that after 48 h of normally bacterial reproduction, surfactant-rich cultures with Tween 80 more than 50 mg/L (25 mg/L for Triton X-100) could only achieve down 80% of ferrous oxidation percent and 10 cells/mL of cell numbers, while those with lower surfactant level were ahead 12 h. Culture pH values decreased to about 2.4 (or 2.0) from initially 2.8. All initial ferric oxyhydroxides were only pincushion-schwertmannite spheres. When cells sequentially reproduced within 36 h–48 h, presence of surfactants (except for Triton X-100 at 75 mg/L) could induce schwertmannite-pincushion assembling on developed spherical particles with a little of diamond-jarosite. And then during bacterial stability state (48 h–72 h), the pincushion assemblages on developed schwertmannite-spheres would disappear, following occurrence of more jarosite amount. Obviously, schwertmannite stability and morphological evolvement were affected by type and level of the added surfactants. These results will give a convincing proof for understanding biomineralization principles of iron minerals in natural environments with nonionic surfactants.