Lead-Zinc Adsorption in Surface Water Christopher Capecchi Geochemistry Geol 628 – North Dakota State University

Overview Source Onion Creek water chemistry Field measurements MINITEQA2 model PHREEQC model Onion Creek [1] Columbia River [2]

Source Van Stone Mine Open pit mine ( ), ( ) Sphalerite (zinc iron sulfide), galena (lead sulfide), chalcopyrite (copper iron sulfide) Zinc, lead, and silver 8.77 million tons combined ore and waste North pit [3] West end pit lake [3]

Source North pit [3] South pit [4] Mine tailing pond barriers breached over time Intense rainfalls likely overflowed ponds The result, moderate contamination of Onion Creek

Water Chemistry - Onion Creek

Water Chemistry Environmental Concerns – Transport of contaminants to Columbia River – Biological uptake by plants and aquatic species Columbia River [6] Carp in lower Onion Creek [7]

MINITEQA2 Modeling Measured samples show decreasing concentrations of lead and zinc downstream Theories proposed: – Enhanced carbonate dissolution (increasing pH) – Sorption to oxides – Change from carbonate to granite

MINITEQA2 Modeling Diffuse double layer model Precipitation-dissolution reactions Ferrihydrite adsorption Hematite, diaspore, calcite, dolomite, barite, and manganite at equilibrium, with SI ~ 0 pH range

MINITEQA2 Results Complete adsorption of Pb 2+ and Zn 2+ to ferrihydrite rather than surface precipitation Pb 2+ and Zn 2+ will remain immobilized unless pH is drastically lowered (pH≥4) Onion Creek not source of contamination for Columbia River Stream sediments major sink for TE’s Model uses enrichment factor vs. flow rate Model dependent upon conductivity, not ORP

PHREEQC Inputs MINITEQA2 results show small differences compared with field measurments PHREEQC Inputs: (1) mixing, (2) sorption, (3) equilibrium phases ORP not considered in MINITEQ2A Upstream Onion Creek E h ~ (-300 mV) [4] Hematite, calcite, dolomite, and manganite at equilibrium, with SI ~ 0 pH variation

Sorption by Hydrous Iron Oxides- Input SURFACE_SPECIES Hfo_sOH + H+ = Hfo_sOH2+ log_k 7.18 Hfo_sOH = Hfo_sO- + H+ log_k Hfo_sOH + Zn+2 = Hfo_sOZn+ + H+ log_k 0.66 Hfo_wOH + H+ = Hfo_wOH2+ log_k 7.18 Hfo_wOH = Hfo_wO- + H+ log_k Hfo_wOH + Zn+2 = Hfo_wOZn+ + H+ log_k -2.32

Mixing Model dependent upon mixing of mine runoff with Onion Creek stream 1 yr rain storm creates 10:1 mix [8] Water chemistry for both solutions taken from field measurements. Upstream_1 pH 7.7 charge temp 11 Pe units ppm Al 12.2 Ca 34.5 C 79 as HCO3 Cl 5 Cu.23 Fe(2) 45 Pb.14 Mg 5.2 N.1 as N03- K.95 Na 1.8 S 16 as S Zn.65 Near Mine Pit_2 pH 8.1 charge temp 12.2 Pe 0 units ppm Al 23.6 Ca 75.3 C 132 as HCO3 Cl 7 Cu.75 Fe(2) 93.5 Pb 18.6 Mg 41.5 N 4.4 as N03- K.95 Na 5.2 S 183 as S Zn 153

Mixing MIX_ Based upon Onion Creek discharge = 125 cfs [8] Rainfall drainage area = 1000 square miles [8] [9]

Results ElementMeasured Downstream (mg/L) MINITEQA2 Model (mg/L) PHREEQC Model (mg/L) Zn1.3≥ Pb0.16~ PHREEQC Calculations Total Zn = 9.945X10 -6 Moles/L = mg/L (Zn = g/mole) Total Pb = 6.758X10 -7 Moles/L = mg/L (Pb = g/mole)

Results Saturation indices Phase SI Al(OH)3(a) 1.25 Alunite 4.59 Anglesite Anhydrite Aragonite Calcite Cerrusite 1.96 CH4(g) CO2(g) Dolomite FeS(ppt) Gibbsite 4.06 Gypsum H2(g) H2O(g) H2S(g) Halite Mackinawite Melanterite N2(g) NH3(g) O2(g) Pb(OH) Pyrite Siderite 2.24 Smithsonite 1.25 Sphalerite Sulfur Zn(OH)2(e) Description of solution pH = Charge balance pe = Specific Conductance (uS/cm, 12 oC) = 793 Density (g/cm3) = Activity of water = Ionic strength = 2.072e-002 Mass of water (kg) = 1.000e+000 Total alkalinity (eq/kg) = 6.663e-003 Total CO2 (mol/kg) = 2.165e-003 Temperature (deg C) = Electrical balance (eq) = e-017 Percent error= Iterations = 11 Total H = e+002 Total O = e+001

Variable pH Original paper suggests that when pH falls below 4 TE’s go back into solution To test this pH was varied in PHREEQ model The results are shown to the right

Errors? Biggest source of uncertainty is mixing ratio Oxidation potentials are approximate Over time, adsorbed Pb, Zn may be released downstream under varying water chemistry

Discussion Some chemicals are being discharged and transported from abandoned mine Maximum contaminant level (MCL) for Pb = 0 ORP potential has high impact on sorption Mixing ratios need to be considered carefully If ambient pH remains neutral or above neutral, TE’s will remain immobilized

References [1] [2] _Gorge [3] INACTIVE AND ABANDONED MINE LANDS—Van Stone mine, Northport Mining District, Stevens County, Washington. Wolff, E.F.; Washington Department of Natural Resources (2005) [4] Washington Department of Ecology (DOE) [5] Routh J., Trace-element geochemistry of Onion Creek near Van Stone lead-zinc mine(Washington, USA) Chemical analysis and geochemical modeling (2006). Chemical Geology, 133 pg [6] [7] [8] [9] [10] &ie=UTF-8&source=og&sa=N&tab=wi&biw=1280&bih=805