Mechanism of Ni mobilization in a groundwater well field; case study from Racibórz, Poland

Mechanism of Ni mobilization in a groundwater well field; case study from Racibórz, Poland Konrad Miotliński, Andrzej Kowalczyk University of Silesia, Faculty of Earth Sciences, Sosnowiec, PL Lisbon, 31 October 2008

Purpose of the study Characteristics of factors and identification into the processes that control mobilization of Ni to groundwater in the biggest groundwater well field in Racibórz

RACIBÓRZ • 60 thousand inhabitants • 100% supplied by groundwater • Oder River • Ulga Channel

BURIED VALLEY • Main source of water provision • Pleistocene • Lenght: 10 km • Width: 2 km • Thickness of Q deposits: up to 60 m • Axis of the valley – 2 km to the W of the modern river valley A B

Hydrogeological cross-section A B Sitek i in., 2007

Well S-I Kations, meq/L Start of increase of Ni concentration Anions, meq/L

WellS-II Kations, meq/L Start of increase of Ni concentration Anions, meq/L

Water table elevation s = 20m s = 10m

1-D Reactive transport modelling(Phreeqc) S-II Fe+Mn+Ni Fe Ni*100 Concentration, mmol/L Mn*10

Ni concentration in the depth profile Content of Ni in sediment, ppm Concentration of Ni in groundwater, mmol/L Water table 94% Ni bound to oxides 6% bound to pyrite All Ni bound to pyrite Maximal admissible concentration: 0,02 mgNi/L =0,339 molNi/L

Contents of Ni in pyrite • Racibórz (Poland): • 16-54*10-5 molNi/molFeS2 (This contribution) • Aarhus (Denmark): • 40-140*10-5 molNi/molFeS2(Larsen&Postma, 1997) • Contemporary marine sediments: • 2*10-5-6*10-2 molNi/molFeS2(Huerta-Diaz&Morse, 1992)

a) b) Ni/Mn Ni/Fe Concentration Mn, mmol/L Concentration Fe, mmol/L c) Data: August 2005 Ni/pH 6,7 pH Correlations

Sorption of Ni in siliceous environment Dzombak & Morel, 1990 (synthetic Fe(OH)3(a)) Kjøller et al., 2004 Amount of adsorbed Ni, % pH range of studied water Christensen et al., 1996 pH of water Solid line – syntethetic Fe(OH)3(a); Dotted lines – natural sediment

Conceptual model of Ni mobilization Before groundwater exploitation

Conceptual model of Ni mobilization Start of exploitation (Fe(1-x), Nix)S2 + 7/2O2 + H2O → (1-x)Fe2+ + xNi2+ + 2SO42- +2H+ 5(Fe(1-x), Nix)S2 + 14NO3 + 4H+→ 7N2 + 5(1-x)Fe2+ + 5xNi2+ + 10SO42- +2H2O

Conceptual model of Ni mobilization During extensive exploitation Fe2+ + ¼ O 2 + H+→ Fe 3+ + ½H2O Fe 3+ + 3H2O → Fe(OH)3+3H+ Mn2+ + 2O2 +4H+→ MnO2+2H2O Surface complexation of Ni: SOH + Ni2+ = SONi+ +H+

Conceptual model of Ni mobilization Groundwater recovery (since 1994) • Flooding of Mn and Fe-oxides

Conceptual model of Ni mobilization At present 2Fe2+ + MnO2 + 4 H2O → 2Fe(OH)3 + Mn2++ 2H+ (wtórna mobilizacja Ni)

1-D Reactive transport modelling(Phreeqc) S-II Fe+Mn+Ni Fe Ni*100 Concentration, mmol/L Mn*10

Reduction of Mn-oxides Århus, Dania (Larsen i Postma, 1997) 20 10 m a.s.l. 0 -10

Conclusions • Pyrite – primary source of Ni • Pyrite oxidation – Ni mobilization • Sorption of Ni on solid phase – Mn- and Fe-oxidese • Flooding of Mn-oxides causes the reaction of oxides with ferrous iron, their reduction and Ni re-mobilization.

Thank you for you attention

Mechanism of Ni mobilization in a groundwater well field; case study from Racibórz, Poland