Effects of seawater mixing on the mobility of trace elements in acid phosphogypsum leachates

This work was supported by the Regional Government of Andalusia through the research project FOREVER (P12-RNM-2260) and the Spanish Ministry of Economic and Competitiveness through the research project CAPOTE (CGL2017-86050-R). The authors are very grateful to the funding support for the Committee of Experts on “The environmental diagnosis and the proposal of measures of restoration of the phosphogypsum stacks of Huelva”, appointed by the City Hall of Huelva. Dr. A Parviainen acknowledges the ‘Juan de la Cierva – Formación’ (FJCI-2014-19582) Fellowship and Dr. C. Marchesi the “Ramón y Cajal” (RYC-2012-11314) Fellowship financed by the Spanish Ministry of Economy and Competitiveness.

This research reports the effects of pH increase on contaminant mobility in phosphogypsum leachates by seawater mixing, as occurs with dumpings on marine environments. Acid leachates from a phosphogypsum stack located in the Estuary of Huelva (Spain) were mixed with seawater to achieve gradually pH 7. Concentrations of Al, Fe, Cr, Pb and U in mixed solutions significantly decreased with increasing pH by sorption and/or precipitation processes. Nevertheless, this study provides insight into the high contribution of the phosphogypsum stack to the release of other toxic elements (Co, Ni, Cu, Zn, As, Cd and Sb) to the coastal areas, as 80–100% of their initial concentrations behaved conservatively in mixing solutions with no participation in sorption processes. Stable isotopes ruled out connexion between different phosphogypsum-related wastewaters and unveiled possible weathering inputs of estuarine waters to the stack. The urgency of adopting effective restoration measures in the study area is also stressed.

Regional Government of Andalusia FOREVER (P12-RNM-2260)

Spanish Ministry of Economy and Competitiveness CAPOTE (CGL2017-86050-R), (FJCI-2014-19582), (RYC-2012-11314)

Committee of Experts, City Hall of Huelva