The Colloid Chemistry of Acid Rock Drainage Solution from an Abandoned Zn-Pb-Ag Mine

Acid rock drainage (ARD) solution from an abandoned ore mine (pH 2.7, sulfate concentration 411 mMol/L, Fe concentration 93.5 mMol/L) was investigated by photon correlation spectroscopy, centrifugation, filtration, ultrafiltration, scanning electron microscopy, ICP-MS, AAS, ion chromatography, TOC analysis and X-ray absorption fine structure (EXAFS) spectroscopy. A colloid concentration of $ 1 g/L was found. The prevailing particle size was < 5 nm. The most probable mineralogical composition of the colloidal particles is a mixture of hydronium jarosite and schwertmannite. Conclusions as to the type of binding of arsenic onto the particles are drawn.