Published: Oct 1999
Pages: 394 - 404
Abstract: The Fe ochre precipitates from three mine districts of Slovakia (Smolnik, Banska Stiavnica and Pezinok) were studied. The X-ray diffraction, electron microscopic methods (TEM, SEM) with elemental X-ray analyses and the selective dissolution method were used to make mineralogical phase characteristics of Fe-ochre precipitates. Many fresh precipitates are X-ray amorphous, but in the extremely fine-grained material it is possible to identify some Fe-mineral phases like schwertmannite and ferrihydrite. In the strongly acid degraded and artificial soils mainly amorphous ferric oxyhydroxide is found. Unstable oxyhydroxides, oxyhydroxysulphate and amorphous Fe-phases were dissolved by acid ammonium oxalate solution (pH 3) and by 1M HCl. All free iron (Al, Mn) compounds of the samples were extracted by dithionite-citrate-bicarbonate solution. The extracts were analyzed for Al, Fe, Zn, Pb, Cu, As, Cd, Mn by the AAS, AES-ICP methods. Samples with different contents of Fe-phases (10–99 wt. % of samples) and formed over a wide pH range (2 to 7) were analyzed. The ochres formed under strongly acid conditions contain mainly high concentrations of Al. The ochres formed in slightly acidic or neutral conditions are enriched in Cu, Pb, Zn, Mn and As. Such conditions were found in the drainage of inactive tailing impoundments. The element attenuation by Fe-ochres are controlled to a great extent by pH and by sulphate concentrations. The comparison of oxalate and HCl extracts concentration show that analyzed elements are attenuated by the active or poorly crystalline Fe-phases to a great extent.
Keywords: Acid mine drainage precipitate, aluminium, Fe/oxyhydroxide, mine acid water, mine waste pollution, microelements, pH-dependence, poorly crystalline phases, selective dissolutionDownload PDF document