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This study revealed the importance of SO_4^ 2− ions during biogenic scorodite crystallization via a two-stage As-removal process, using a combination of liquid and solid analyses (chemical digestion, FT-IR, SEM, TG-DTA, particle distribution). The first-stage As-removal was induced by microbial oxidation of Fe^2+ and As(III), precipitating SO_4^ 2− -bearing amorphous precursors composed of basic ferric sulfate (MFe_x(SO_4)_y(OH)_z) and ferric arsenate (FeAsO_4·(2+n)H_2O). This was followed by an induction period (a period of constant concentration), where dissolution-recrystallization of unstable amorphous precursors proceeded: Re-dissolved metal ions became locally concentrated on the surface of precursors, which gave the driving force for the second-stage As-removal as secondary layers of crystalline biogenic scorodite (Fe(AsO_4)_0.94(SO4)_0.08·1.69H_2O) out of even more dilute and seeded solution. This phase transformation process was also accompanied by continuous dehydration. This two-stage As-removal via SO_4^ 2- -mediated phase transformation was shown to be key to promote biogenic scorodite formation with greater final As-removal from dilute As(III)-bearing solutions.

The ablation threshold fluence and crater morphology of amorphous and crystalline SiO2 glass were analyzed in the regime of an extreme ultraviolet femtosecond pulse. Despite the difference between the densities (or optical penetration depths) of amorphous and crystalline SiO2 glass, the ablation threshold fluences and crater morphologies were found to be comparable. In addition, we compared our experimental results at a 10.3 nm wavelength with those in a previous work at a 13.5 nm wavelength. We conclude that the impact of the difference in density or optical penetration depth of several tens of percent on the ablation process is limited.