Basaluminite Structure and its Environmental Implications

Basaluminite is a nanocrystalline aluminum oxyhydrosulfate of important environmental implications. It is present in areas affected by acid mine drainage and acid sulfate soils, where potential toxic elements present in solution, such as Cu and As, can be retained by co-precipitation or adsorption onto it. Basaluminite has been described as a nanomineral variety of felsöbányaite. In the present study, high-energy X-ray diffraction (HEXD) and extended X-ray adsorption fine structure (EXAFS) experiments were performed to determine the local order of basaluminite nanoparticles. Pair distribution function (PDF) analyses showed that both synthetic and natural basaluminite have identical short-range order, with 1 nm coherent domain size. PDFs also show strong similarities between the local order of basaluminite and felsobanyaite. On the other hand, S K-edge EXAFS showed different structural coordination between natural and synthetic basaluminite, where sulfate in the natural phase were coordinated in outer-sphere positions whereas inner-sphere sulfate was observed in the synthetic samples. Preliminary results indicated that basaluminite is a highly defective felsobanyaite mineral nanoparticle. This nanocrystalline character has therefore important implication in terms of stability in natural condition and contaminant mobility in stream affected by acid sulfate water.