Lead-Zinc Adsorption in Surface Water

Christopher CapecchiGeochemistry Geol 628 – 11.30.2010

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 (1952-1970),

(1991-1993)• 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 7.8-8.4

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 Eh ~ (-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 -8.82

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 -8.82

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_1pH 7.7 chargetemp 11Pe -4.69units ppmAl 12.2Ca 34.5C 79 as HCO3Cl 5Cu .23Fe(2) 45Pb .14Mg 5.2N .1 as N03-K .95Na 1.8S 16 as SZn .65

Near Mine Pit_2 pH 8.1 charge

temp 12.2Pe 0units ppmAl 23.6Ca 75.3C 132 as HCO3Cl 7Cu .75Fe(2) 93.5Pb 18.6Mg 41.5N 4.4 as N03-K .95Na 5.2S 183 as SZn 153

Mixing• MIX_1 1 10 2 1• Based upon Onion Creek discharge = 125 cfs [8]

• Rainfall drainage area = 1000 square miles [8]

[9] [9]

ResultsElement Measured

Downstream (mg/L)

MINITEQA2 Model(mg/L)

PHREEQC Model (mg/L)

Zn 1.3 ≥ 0.1 0.650

Pb 0.16 ~ 0 0.140

PHREEQC CalculationsTotal Zn = 9.945X10-6 Moles/L = 0.650 mg/L (Zn = 65.38 g/mole)Total Pb = 6.758X10-7 Moles/L = 0.140 mg/L (Pb = 207.2 g/mole)

Results------------------------------Saturation indices-------------------------------

Phase SI Al(OH)3(a) 1.25 Alunite 4.59 Anglesite -0.63 Anhydrite -1.32 Aragonite -0.23 Calcite -0.08 Cerrusite 1.96 CH4(g) -39.80 CO2(g) -3.27 Dolomite -0.25 FeS(ppt) -30.33 Gibbsite 4.06 Gypsum -1.07 H2(g) -16.04 H2O(g) -1.86 H2S(g) -39.18 Halite -9.03 Mackinawite -29.60 Melanterite -3.35 N2(g) -1.06 NH3(g) -21.33 O2(g) -55.65 Pb(OH)2 1.53 Pyrite -46.52 Siderite 2.24 Smithsonite 1.25 Sphalerite -22.39 Sulfur -29.19 Zn(OH)2(e) 1.37

----------Description of solution----------

pH = 8.019 Charge balance pe = 0.000

Specific Conductance (uS/cm, 12 oC) = 793 Density (g/cm3) = 1.00053

Activity of water = 1.000 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) = 12.200 Electrical balance (eq) = -1.970e-017

Percent error= -0.00 Iterations = 11

Total H = 1.110175e+002 Total O = 5.553927e+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

pH Pb, M Zn, M Pb, mg/L Zn, mg/L2 0.000052 0.000529 10.76 34.593 0.000050 0.000519 10.35 33.934 0.000020 0.000498 4.10 32.565 0.000006 0.000099 1.23 6.466 0.000001 0.000030 0.23 1.957 0.000001 0.000013 0.19 0.848 0.000001 0.000011 0.17 0.719 0.000001 0.000010 0.14 0.6510 0.000001 0.000010 0.14 0.6511 0.000001 0.000010 0.14 0.6512 0.000001 0.000010 0.14 0.65

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]http://www.google.com/images?hl=en&q=Onion+Creek&rlz=1B3GGGL• [2]http://www.google.com/imgres?imgurl=http://craigwolf.com/news/uploaded_images/

Columbia_River_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. 211-224.• [6] http://67pics.com/pictures-columbia-river-gorge.html• [7] http://www.google.com/imgres?imgurl=http://CR.Carp• [8]www.usgs.gov/precipitation/database.3993.html• [9] http://www.tripadvisor.com/LocationPhotos-g54225-html#16911511• [10]http://www.google.com/images?

hl=en&q=stevens+county+wa&rlz=1B3GGGL_enUS212US212&um=1&ie=UTF-8&source=og&sa=N&tab=wi&biw=1280&bih=805