Evaluation of the Control of Reactivity and Longevity of Nano Scale
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Nanoscale Iron Particle 200 – 600 nm Evaluation of the Control of Reactivity and Longevity of Nano Scale Colloids by the Method of Colloid Manufacture Nanotechnology for Hazardous Waste Site Remediation Technical Workshop Washington DC October 20-21, 2005 David Vance 1 Current Practical Manufacturing Methods Bottom Up – Precipitation – Dominant Known Technology is Sodium Borohydride Reduction – Others ? Bottom Down – Attrition via Ball Milling Bottom Down Iron Oxides then Hydrothermal Reduction 2 What Defines a Practical Manufacturing Technology Cost Capacity to be produced in ton lots Capacity to be produced in relatively short time frames 3 Top Down Nano-Scale Fe Colloids 4 Bottom Up Nano Scale Fe Colloids (ARCADIS) 5 Another Bottom Up Iron 120 nm 10 µm 6 Key Performance Issues Transport and Delivery – Size – the balance between gravitational settling and attractive forces – 200 to 600 nm ideal Colloid Longevity – Passivation by dissolved inorganics in Water – Unproductive hydrogen generation – Kinetic Response 7 Delivery 8 Nanoscale Iron Particle Size Comparison Size Ranges of Zero Valent Iron Compared to Pore Slot Size Particles Subject to Sedimentation Injection Methods Particle Strongly Adsorptive 7μ 0.1 μ Aperture of Fractures in Natural Pore Throat Sizes 25,000 μ 200 μ 254 μ Typical Monitoring Well Screen Opening Gravel 7000 μ Coarse-Fine Silts Sands 720 μ 240 μ 24 μ 7μ 0.7 μ Hydrogen Reduced Iron ARS Powder Material 0.3 μ 0.05 μ 70 μ - 40 μ Particle Size Vapor Deposition Iron 0.02 μ 0.002 μ Ground (Ball Milled) 30 μ Zhang Precipitated 0.03 μ Conventional Iron Filling 0.1 μ 2000 μ LARGE 100000 10000 1000 1μ 100 100 10 1 0.001 μ Typical Colloidal Size Material 0.001 μ 0.1 0.01 0.001 SMALL 0.0001 Size, μ 9 Point of Zero Charge - pHpznpc Binding or Dissociation of Protons α-Al2O3 α-Al(OH)3 γ-AlOOH CuO α-Fe3O4 α-FeOOH Fe2O3 Fe(OH)3 (amorph) MgO 9.1 5.0 8.2 9.5 6.5 7.8 8.5 8.5 12.4 δ-MnO2 β-MnO2 SiO2 ZrSiO4 Feldspars Kaolinite Montmorillonite Albite Chrysotile 2.8 7.2 2.0 5 2-2.4 4.6 2.5 2.0 >10 10 Stokes Settling Velocity Vs. Fe Colloid Diameter 140 V e l o c i ty c m / D a y 120 100 80 60 40 20 0 100 1000 Diameter in Nano Meters 10000 11 Colloid Velocity Due to Brownian Motion Colloid Velocity Due to Brownian Motion 0.00E+00 200 to 400 nm 2.00E-04 4.00E-04 6.00E-04 8.00E-04 18000 17000 16000 15000 14000 13000 12000 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 1.00E-03 Microns/Second 20 to 40 nm Colloid Diameter in mm 12 Colloid Reactivity and Longevity 13 Environmental Impacts on ZVI Longevity Effect of high TDS – Sulfate and Soluble Carbonates Effect of water dissociation Effect of CVOC reactions 14 Intrinsic Controls on Colloid Longevity Colloid structure – Particle morphology – shape, pits – Particle crystal structure – size of crystal domains, kinks, amorphous zones Control composition - Secondary constituents in colloids – Catalysts – Manufacturing byproducts Modification of the colloid surface – Catalysts – Inorganic inhibitors – Polymers 15 Kinetics Batch Test Results (higher values indicate short half-lives) Experimental Data and Data from Literature 3.000 2.500 0 (1) = Data obtained from batch studies done with Fe only 0 (2) = Data obtained from column studies done with Fe0 only (3) = Data obtained from column studies done with Fe /Pd 2.000 1.500 Kobs (hr-1) 1.000 0.500 0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.001 0.000 1 2 3 5 6 8 9 10 12 13a 13b 14a 15a 15b 15c 15d (1) (2) (3) Kinetics Test # Red Bars are Vendor C Ball Milled Green Bar is Vendor A Precipitated Blue Bars are Vendor B Precipitated 16 Reactivity of Top Down Vs. Bottom Up Colloids 14 12 T C E C o n c e n t ra t io n , m g /L <100 nm Precipitated 10 400 nm Top Dow n 8 6 4 2 0 0 1 2 3 4 Elapsed time, hour 17 BNI TCE Dechlorination Kinetics Stability of Ball Milled Stability ofColloids Ball Milled Colloids TCE Concentration, (mg/L) 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 Elapsed Time (Hours) 7/10/02 BNI Batch 10/17/02 BNI Batch 18 Three Classes of Colloid Reaction Three Two One 19 What Causes Type Three Behavior? Oxidation during shipment or handling, surface coatings – Acid treatment does not remove effect The presence of by products from the manufacturing process that interfere with electron transfer – Borohydride leaves % concentrations of boron in the colloid Structural changes – Annealing or Ostwald Ripening Palladization restores reactivity 20 Percent of Atoms on Surface Versus Diameter 60% 50% 40% 30% 20% 10% 0% 1 10 Nanometers 100 1,000 21 Variations in Iron Colloid Response Class One – Typical response from all early product runs Class Two – Effect due to size and chemical make up or structure – colloids from 100 nm to 2 Microns – Becomes class one with palladization Class Three – Acid pretreatment has no effect – Repeated testing by independent labs as well – Becomes class one with palladization 22 The Good News Type One and Type Two Each Have a Valuable Niche Type one colloids are of value for treatment of DNAPL or high concentrations of adsorbed CVOC – Think of reductive version of chemical oxidation – The “Champaign effect” is observed with the most extreme examples Type two colloids are of value for use in reactive walls for the long term treatment dissolved CVOCs under natural flow conditions 23 A New Technology with Unique Potential Problems We understand how to manipulate isolated molecular systems, chemical oxidation for example Efficient bacterial enzymatic pathways have been developed over several billion years Nano scale colloids are large assemblages of molecules subject to atomic forces with complex structure and a behavior that is in the process of definition 24 Total Number of Atoms in Colloid 1E+11 1E+10 Num ber of Atom s 1E+09 1E+08 1E+07 100000 0 100000 10000 1000 100 10 1 0 100 200 300 400 500 600 700 800 900 1,000 Diameter in Nanometers 25 “Reality is that which, when you stop believing in it, does not go away” The Bottom Line Make Assumptions at Your Own Risk 26
