Geochemical behavior of an acid drainage system: the case of the Amarillo River, Famatina (La Rioja, Argentina).

LECOMTE K.L.; MAZA, S.N.; COLLO, G.; DEPETRIS P.J.; SARMIENTO AM

ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2017 vol. 24 p. 1630 - 1647

0944-1344

Amarillo River (Famatina range, Argentina, ~29° S and ~67° W) is unusual becauseacid mine drainage (AMD) is superimposed on the previously existing acid rockdrainage (ARD) scenario, as a Holocene paleolake sedimentary sequence shows. In amarkedly oxidizing environment, its water is currently ferrous and of the sulfatemagnesiumtype with high electrical conductivity (>10 mS cm-1 in uppermostcatchments). At the time of sampling, the interaction with the mineralized zone andremnants of mining labors, determined an increase in some elements (e.g., Cu ~3 to~45 mg L-1; As ~0.2 to ~0.5 mg L-1). Dissolved concentrations were controlled by pH,decreasing significantly by precipitation of neoformed solids (jarosite andschwertmannite) and subsequent metal sorption (~700 mg kg-1 As, 320 mg kg-1 Zn);and by dilution (i.e., mixing with circumneutral waters which reduce dissolvedconcentration and also enhance mineral precipitation). Downstream, most metalsexhibited a significant attenuation (As 100%, Fe 100%, Zn 99%). PHREEQCcalculatedsaturation indices (SI) indicated that Fe-bearing minerals, especiallyschwertmannite, were supersaturated throughout the basin. All positive SI increasedthrough the input of circumneutral water. PHREEQC inverse geochemical modelsshowed throughout the upper and middle basin, that about 1.5 mmol L-1 of Fe-bearingminerals were precipitated. The modeling exercise of mixing different waters yieldedresults with a >99% of correlation between observed and modeled data.