METALS TREATMENT AND IN SITU PRECIPITATION. Mike Hay September 30, 2016

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1 METALS TREATMENT AND IN SITU PRECIPITATION Mike Hay September 30, 2016

2 Disclaimers and Notices The materials herein are intended to furnish viewers with a summary and overview of general information on matters that they may find to be of interest, and are provided solely for personal, non-commercial, and informational purposes. The materials and information contained herein are subject to continuous change and may not be current, correct, or error free, and should not be construed as professional advice or service. You should consult with an Arcadis or other professional familiar with your particular factual situation for advice concerning specific matters. THE MATERIALS AND INFORMATION HEREIN ARE PROVIDED "AS IS" AND WITH ALL FAULTS AND WITHOUT ANY REPRESENTATION OR WARRANTY, EXPRESS, IMPLIED OR STATUTORY, OF ANY KIND BY ARCADIS, INCLUDING, BUT NOT LIMITED TO, WARRANTIES OF MERCHANTABILITY, NON- INFRINGEMENT, NO ERRORS OR OMISSIONS, COMPLETENESS, ACCURACY, TIMELINESS, OR FITNESS FOR ANY PARTICULAR PURPOSE. ARCADIS DISCLAIMS ALL EQUITABLE INDEMNITIES. ANY RELIANCE ON THE MATERIALS AND INFORMATION HEREIN SHALL BE AT YOUR SOLE RISK. ARCADIS DISCLAIMS ANY DUTY TO UPDATE THE MATERIALS. ARCADIS MAY MAKE ANY OTHER CHANGES TO THE MATERIALS AT ANY TIME WITHOUT NOTICE. The materials are protected under copyright laws and may not be copied, reproduced, transmitted, displayed, performed, distributed, rented, sublicensed, altered, or otherwise used in whole or in part without Arcadis' prior written consent.

3 About the Presenter MICHAEL HAY, PHD Senior Geochemist and the Geochemical Modeling focus area lead within Arcadis o e michael.hay@arcadis.com

4 Learning Objectives After attending this session, participants should be able to: Identify challenges unique to in situ metals treatment Recognize in situ treatment approaches: injection-based vs. barriers Explain the importance of precipitate stability Describe geochemical processes/principles that can be used to yield metals precipitation Explain the importance of long-term precipitate stability and geochemical parameters that may affect stability

5 In Situ Metals Precipitation In situ treatment of metals vs. organics: What is the fundamental difference? Organics can be irreversibly altered, destroyed Reductive Dechlorination Hydrocarbon Bio-Oxidation Carbon source CO 2 O 2 H 2 O e - e - TCE Ethene C 6 H 6 CO 2 Metals cannot ( metals = metals/metalloids/oxoanions, etc ) o Removed from solution via adsorption, precipitation: Reversible processes o Requires long-term alteration/stabilization of geochemical environment

6 Implications of Fixation Metals Plume Organic Plume

7 Implications of Fixation Immobilized Contaminant Mass Original Plume Boundary Metals Plume Organic Plume Mobile Contaminant Mass

8 Implementation Approaches 1) Soluble Injections 2) Permeable Reactive Barriers Aqueous phase delivery of treatment reagents through injection wells Excavation and direct emplacement of solid-phase reagent

9 Injection-Based Approaches Alteration of geochemical environment to yield mineral saturation o Redox environment Reduce/oxidize the metal: U(VI) U(IV) UO 2 (solid) Reduce/oxidize other constituents: SO 4 2- S 2- Ni 2+ + S 2- = NiS (solid) o ph Reduce solubility of the metal: Al 3+ Al(OH) 3 (solid) Pb 2+ Pb(OH) 2 (solid) Reduce solubility of other constituents: Fe 3+ Fe(OH) 3 (solid) HAsO 2-4 o Dissolved ion concentrations Example: Sulfide Addition Pb 2+ + NaHS = PbS (solid) + Na + + H + Example: Phosphate Addition UO PO Ca 2+ = Ca(UO 2 ) 2 (PO 4 ) 2 (solid)

10 Challenges Long-term effectiveness ph rebound? Ability to maintain redox environment? Wash-out of added reagents? Secondary effects Organic Carbon Fe 2+ CO 2 Geochemical alteration Release of other constituents Reagent injectability/radius of influence Balance between reagent distribution and reagent deposition

11 Field Examples 1) Microbial reduction of Cr(VI) Direct-redox effect 2) Arsenic coprecipitation with iron Indirect-redox effect, ph adjustment 3) Uranium Precipitation with Phosphate Precipitation with co-solute addition

12 1) In Situ Treatment of Cr(VI) Organic carbon injection Microbial reduction of Cr(VI) to Cr(III) Iron reduction enhances Cr precipitation

13 In Situ Treatment of Cr(VI) Organic carbon injection Microbial reduction of Cr(VI) to Cr(III) Iron reduction enhances Cr precipitation

14 In Situ Treatment of Cr(VI) Reoxidation of Cr(III) by O 2 Thermodynamically favorable Kinetically limited! In practice, reoxidation by O 2 is not observed Reoxidation of Cr(III) by Mn(III/IV) oxyhydroxides Primary known/environmentally-relevant oxidant of Cr(III) Kinetically limited: Solid-solid interaction Cr(III) extremely stable upon redox rebound 1.0 Eh (volts) ph = n Oxidized O 2 O Reduced H 2 O - NO 3 N 2 MnO 2 Mn 2+ SeO 4 2- UO 2 2+ HSeO HCrO 4 Cr(OH) 3 - HSeO 3 Se UO 2 Fe(OH) 3 Fe HAsO 4 H 3 AsO 3 SO 4 2- HCO 3 - H 2 S CH 4

15 5, In Situ Treatment of Cr(VI) Pilot testing Cr(VI) effectively reduced Reductive dissolution/release of Fe, Mn, As Hexavalent Chromium (ppb) Sulfate (mg/l) 4,000 3,000 2,000 1, ,200 1, Hexavalent Chromium Total Organic Carbon PT-1D Elapsed Time (days) Sulfate Nitrate Total Organic Carbon (mg/l) Nitrate (mg/l) Mar-06 Apr-06 May-06 Jun-06 Jul-06 Aug-06 Sep-06 Date Oct-06 Nov-06 Dec-06 Jan-07 Feb-07 Mar Arsenic (ppb) Dissolved Arsenic Elapsed Time (days)

16 Controlling Byproduct Generation Field-scale predictions: Attenuation of As and Mn before river discharge Chromium Manganese

17 2) Arsenic Removal with Iron Strategy: Addition of iron as soluble Fe(II) Addition of chemical oxidant to achieve: Fe(II) Fe(III) As(III) As(V) Alkaline oxidant (e.g., CaO 2 ) balances acidity Arsenic co-precipitation with iron Arsenic Oxidation Challenges: In situ mixing of soluble iron and oxidant Retardation/consumption of reagents: Fe(II), oxidant Achieving target ROI Iron Oxidation CaO 2 Ca(OH) 2 Sorption, Coprecipitation Ca(OH) 2 CaO 2 As(V) As(III) As(V) Iron oxyhydroxide As(V) Fe(III) Fe(II)

18 Field Pilot Test Groundwater arsenic at a coal ash site View along highway of arsenic hot spot area Well installation Completed well network, with IW-1 in center

19 Field Pilot Test Groundwater arsenic at a coal ash site Reagent tanks Injection well (IW-1) below grade Ferrous sulfate injection, with tube added to provide additional head for gravity injection Fluorescein tracer and ferric iron precipitate in observation well

20 Coal Ash Site Field Pilot Test Specific capacity loss with solid-phase CaO 2 injection Capacity regained with acidic ferrous sulfate injection Specific Capacity (gpm/ft) Ferrous sulfate Calcium peroxide Cumulative Volume Injected (gal)

21 Coal Ash Site Field Pilot Test Iron and calcium largely retained in 10-ft ROI Emplaced reactive zone established GW Flow Reagent and Tracer Recovery 100% 90% OW-3 Calcium - Dissolved Iron - Dissolved Bromide 80% 70% 60% 50% 40% 30% 20% 10% 0% Days Post-injection

22 Coal Ash Site Field Pilot Test Arsenic treatment at injection well OW-3: As treated to 20 ppb, gradual rebound Rebound due to change in flow direction, bypass of narrow treatment zone ph GW-41 IW-1 OW-3 OW Days Post-injection GW Flow Dissolved Arsenic Concentration (µg/l) GW-41 IW-1 OW-3 OW Method and laboratory reporting limit changed Days Post-injection

23 3) Uranium Precipitation with Phosphate Uranium Mill Tailings Site, New Mexico Former Uranium Mine, Colorado

24 Uranium Precipitation with Phosphate U(VI) highly soluble U(VI) U(IV) reduction: Effective, but sensitive to reoxidation U(VI) insoluble in phosphate precipitates MCL Autunite: Ca(UO 2 ) 2 (PO 4 ) 2 3H 2 O Chernikovite: H 3 O(UO 2 )(PO 4 ) 3H 2 O Mehta et al., 2014

25 Uranium Precipitation with Phosphate Injection strategies Direct injection as orthophosphate Injection of polyphosphate, timed release of orthophosphate Tripolyphosphate Orthophosphate P P P P P P

26 Uranium Mine Implementation Underground Mine Workings Waste Rock Piles

27 Underground Mine Workings Implementation Push-Pull Test Results 1800 Phase-2b Pull: Phosphate 80 Phase-2b Pull: Fluorescein Concentration (mg/l) Phosphate (total) Phosphate (dissolved) Mixing Prediction Injectate Average Concentration (mg/l) Pull-Phase Measured Injectate Average Gallons Extracted from P Gallons Extracted from P Phase-2b Pull: Uranium Theoretical concentration based on mixing of injectate and groundwater (calculated using fluorescein tracer) Actual measured concentration Concentration (mg/l) Uranium (dissolved) Uranium (total) Mixing Prediction Injectate Average Actual < Theoretical = REMOVAL P-11 Baseline Gallons Extracted from P-11

28 Waste Rock Dump Implementation Sustained uranium removal observed in downgradient well (~60 ft) RD-01 Injection Well RD-02,03 RD-04 Extraction Wells Monitoring Well GW flow Additional results pending Concentration (mg/l) Uranium (dissolved) RD-01 RD-02 RD-03 RD-04 Injections Acti ve /19/2016 6/29/2016 7/9/2016 7/19/2016 7/29/2016 8/8/2016 8/18/2016 8/28/2016

29 Learning Objectives After attending this session, participants should be able to: Identify challenges unique to in situ metals treatment Recognize in situ treatment approaches: injection-based vs. barriers Explain the importance of precipitate stability Describe geochemical processes/principles that can be used to yield metals precipitation Explain the importance of long-term precipitate stability and geochemical parameters that may affect stability

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