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Abstract:

Si-enriched coatings form on the surface of silicate minerals under acidic conditions. Although they are often only a few nanometers thick, their large specific surface area may control the interaction between silicate minerals in acidic soils, aquifers, and mine tailings. Micrometer thick, hydrous-silica coatings occur on the surface of a granite outcrop in contact with acidic pond water at the Coppercliff mine-tailings area in the Greater City of Sudbury, Ontario, and are ideal to study the concentration and speciation of metals and metalloids inside Si-enriched coatings. These coatings have higher average concentrations of Cr, Mn, Co, Ni, Cu, Zn, and Pb than coatings composed of schwertmannite, Fe8O8(OH)4.4(SO4)1.8(H2O)8.4. Microscopic and spectroscopic examination of the hydroussilica coating indicates the occurrence of Fe- and Cu-Zn-oxyhydroxide particles, tetrahedrally coordinated Fe3+and a high proportion of M-O-Si bonds (M = metal). These observations suggest that metals occur either finely distributed in the hydrous-silica matrix or in oxy-hydroxide particles. The latter particles are products of the diffusion of metals into the hydrous silica and the subsequent nucleation of oxyhydroxide phases. 2009 American Chemical Society.

Notes:

Compilation and indexing terms, Copyright 2018 Elsevier Inc.<br/>20095212579054<br/>Acidic conditions<br/>Average concentration<br/>Environmental significance<br/>Hydrous silica<br/>Large specific surface areas<br/>Metals and metalloids<br/>Schwertmannite<br/>Spectroscopic examination