Caracterización hidroquímica del primer tramo contaminado por AMD del río Odiel (Huelva)

Resum

Odiel River headwaters show a good quality, however suffer a progressive deterioration downstream flowing accross the Iberian Pyrite Belt (IPB) when it receives the acid mine drainage (AMD) from Concepción, San Platón, Esperanza, Poderosa and Riotinto mines. In this reach of the river a sampling was carried out during average discharge conditions with the aim to characterize the hydrochemical behavior of some elements. Despite the acid discharges, the river pH remained close to 7,7 down to the Agrio river confluence. The dissolved concentrations of Fe and Al persisted below the detection limit meanwhile sulfates and other mining-related elements increased progressively. Downstream of the Agrio confluence, the pH decreased to 3,9 and increased notably the concentration of toxic elements. The saturation state for various minerals associated to Fe, Al and sulfates have been predicted by the PHREEQC code. At pH values close to 7,7, the water is supersaturated in ferrihydrite, schwertmannite and gibbsite. Downstream of the Agrio confluence, at a pH value of 3.9, the water is still supersaturated in schwertmannite and close to the K-jarosite equilibrium.