Abstract:

Schwertmannites are secondary minerals widespread in acid mine drainages, and their development and transformations are controlled by environmental factors such as temperature, pH, and coexisting ions. In this study, the effects of temperature and ion concentration on the stability and transformation of biogenic and Ascontaining schwertmannites were investigated. The results showed that the increase of aging temperature favored mineral phase transformations (MPT): for schwertmannites with and without As incubated for 15 weeks, MPT did not take place at 4 ℃, but partially occurred at 40 ℃. In addition, the change of potassium ion concentration resulted in different aging products of schwertmannites: for the biogenic schwertmannites incubated  for 15 weeks, the major aging products were goethite and jarosite/goethite at potassium ion concentrations of 0.01 mM and 100 mM, respectively; for the As(Ⅲ)containing schwertmannites incubated for 15 weeks, MPT did not occur when potassium ion concentration was 0.01 mM, whereas partial MPT took place and jarosite was the major aging products. Moreover, when exposed to temperature or pH fluctuation, As(Ⅲ)containing schwertmannite appeared to be more stable than pure schwertmannite.

Key words:  biomineralization, schwertmannite, arsenite, phase transformation, goethite, jarosite