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The present work focuses on the study of several aspects concerned with acid mine drainage which affects the Balan mining area (Romania). The study is supported by the geochemical and mineralogical characterisation of certain solid products resulted after the processes of acid mine drainage, and by the description of the chemical composition of the waters in the researched area (mine waters, surface waters). The methods used for the mineralogical and geochemical investigation are the X-ray diffraction (PHILLIPS X'PERT ADP-PW 1830 diffractometer) and the atomic absorption spectrometry (AAS Vario 6 FL atomic absorption spectrometer); the pH and Eh values were obtained by using a Corning M555 pH/Ion Meter.
The mineralization is made up of stratoid bodies, 200-300m long and maximum 35m wide. The solid products generated by the processes of acid mine drainage were seen in the Wetter quarry under the form of efflorescences on the surface of epimetamorphic slate blocks, mainly in the crevices that affect those rocks. The colour of these products is either yellow-brown (for rock blocks where the pyrite has been identified), or greenish-blue (in case of blocks with larger amounts of chalcopyrite).
The efflorescences produced by the acid drainage have an argillaceous aspect, if they are hydrated, and respectively a powdery aspect, if they suffer from dehydration. Irrespective of their colour, the efflorescences are extremely soluble in distilled water; the solutions resulted after their solubilisation, have an acid character, with pH values between 3.0 and 3.5.
X-ray diffraction established the fact that the mineralogy of the efflorescences is dominated by the minerals of the group of the hydrated sulphates of Al, Fe3+, Fe2+, Mn, Mg. Thus, in most analysed samples, the following mineralogical terms have been identified: alunogene, magnesia alum, iron alum, kalinite; to these we add, quantitatively subordinate, apjohnite, jarosite and plaster.
The fraction of the solid products that is insoluble in distilled water is represented either by sericite and chlorite - resulted from the host-rock of the mineralization, or illite, vermiculite and interstratified terms of the chlorite-vermiculite type. The samples taken from the area of the deposit fall into two categories: mine waters, and surface waters from the area of the Wetter quarry.
The medium pH value of the water samples varies between 3.1 and 3.6 for mine waters and 4.1 and 4.8 for surface waters. The data concerning the pH, together with the ones regarding the Eh, indicate the presence of Fe2+ in the solution; in some mine water samples the Eh/pH ratio indicate the presence of Fe3+ (s). The content determinations for Zn, Pb and Cd indicate medium participations higher in mine waters as compared to the ones in the quarry area.
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