Dr David Johnson SS Remediation Consultancy

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Dr David JohnsonS/S Remediation Consultancy

• Radioactive Elements Present in Cementitious
  Grouts

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DONT

• PANIC

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Outline of Presentation

• Cementitious stabilisation of metals
• Potential problems relating to grouts
• Grout components
• Standards relating to composition of components
• Radioactive elements in the components

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Cementitious Grouts

• Cementitious grouts are used to encapsulate
  certain radioactive waste streams
• Metals are immobilised by both physical and
  chemical means

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Chemical Treatment of Contaminants

• Heavy metal salts are converted to low solubility
  forms

• Antimony
• Arsenic
• Barium
• Beryllium
• Cadmium
• Chromium
• Cobalt

• Copper
• Lead
• Mercury
• Nickel
• Selenium
• Zinc

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Decreased Solubility of Metals
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Some Technical Concerns

• Cementitious materials contain heavy metals and
  radioactive elements
• These can add to those already present in the
  waste
• Composition varies with source
• Raw materials used in manufacturing may be
  obtained from outside UK
• There may be scale-up inconsistencies

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Heavy Metals Present in Cement

• PCA (US) data from 97 kilns
• Metals held in glassy matrix of clinker and do
  not leach out

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Effect of Cement Source

• Obtained samples of cement (BS EN 197-1 CEM I
  Class 42.5N) from 8 works across England,
  Scotland and N.Ireland
• Used samples of the local soil to represent made
  ground
• Soil (at constant water content) mixed with 10
  cement
• Compacted and cured for 28 days gt strength
• Cured for 28 days gt leaching

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Effect of Cement Source on 28-Day Strength
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Effect of Cement Source on Leaching of Cr and Cu
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Grout Components

• Cement
• Portland cement (OPC)
• Calcium sulfoaluminate cement (CSA)
• Ground granulated blastfurnace slag (GGBS or BFS)
• Pulverised-fuel ash (PFA)
• Water

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Standardisation of Grout Components

• Composition refers to silica, alumina, chloride
  and sulphate contents

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Raw Materials Used in Manufacturing

• Natural sources are certain to contain
  radioactive elements
• Source of raw materials likely to vary globally

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Composition of Cement

• Major CaO, SiO2, Al2O3 and Fe2O3
• Minor MgO, Na2O, K2O and SO3
• Trace elements Ba, Ni, Co, Cr, Cu, V, As, Zn,
  Pb, Cd, Hg
• Radioactive elements U, Ra, K
• Present as the oxide or incorporated in the
  clinker
• Trace and radioactive elements are obtained from
  natural feedstock, fuels and secondary raw
  materials (wastes)

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Wastes Used in OPC

• Phosphogypsum is employed as set time adjuster
• By-product of fertiliser industry
• Relatively high levels of 238U, 234U, 210Pb and
  210Po
• 222Rd emission also observed
• Content varies with origin of phosphate rock

• Red Mud is used as source of iron oxide or
  alumina
• By-product of bauxite processing
• Contains significant levels of 238U and 232Th

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Hungary (1984)

• 232Th (0.6-199 Bq/kg), 226Ra (0.6-228 Bq/kg) and
  40K (7-709 Bq/kg)
• Within permitted values
• High values due to high activity of additives
  such as fly ash and blastfurnace slag
• In some cases, high radioactivity of clay

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Albanian Clays (2000)

• 52 clay samples examined
• Most contained radioactive elements within
  normal values
• Some were high in Uranium (gt10ppm), Thorium
  (20ppm) and Potassium (gt5)

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Other Countries

• Pakistan (1992), Sudan (2001), Egypt (2004)
• 238U, 232Th, 226Ra, 40K within permitted values
• High Radon exhalation rate using blastfurnace
  slag cement (Egypt 1999) banned from use in
  residential buildings

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CSA Manufacture

• Bauxite ores can contain significant levels of
  238U and 232Th and their respective decay
  products (Australia 2003 Germany 2002)
• Phosphogypsum contains 226Ra, 232Th and 40K
  (Australia 2003 Germany 2002)

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Radioactivity Associated with BFS

• Obtained from production of iron ore
• The ore contains low concentrations of the
  radionuclides associated with the uranium decay
  chain
• Processing leads to radionuclide enrichment in
  the slag, assimilating 98 of all the
  radionuclides from the beginning (Germany 2002)

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Radioactivity of PFA

• US Geological Survey showed presence of U, Th, Ra
  and Rn.
• US(1997) During coal combustion, most of the
  radon is lost in stack emissions the less
  volatile elements (U and Th) and the majority of
  their decay products are retained in the ash

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Radioactivity of Coal (Australia)

• Most coal contains uranium and thorium, as well
  as 40K, 210Pb and 226Ra
• Australia (1984) Some sources of fly ash have
  radioactivity above a safety level, but not
  considered a hazard as the ash is used in small
  proportions in concrete the ash is also
  concentrated in finer particles and can be
  removed prior to use
• Australia exports coal, containing 1.6ppm Uranium
  and 3.5ppm Thorium

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Radioactivity of Coal(The Netherlands)

• Dutch power companies became aware in 2000 of
  presence of 210Pb in the boilers
• The 210Pb originates from the decay of 238U,
  which is present in the coal
• Measured levels of total radioactivity exceeded
  the limit of 100 Bq/g

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Radioactivity of Coal(Hungary Spain)

• Hungarian coal from the Mecsek mountains in the
  South is high in radioactivity due to U, K and Th
  (reports dating back to 1948)
• Coal in the Calaf area, Barcelona, is
  characterised by its U content (1983)

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Conclusions

• Cementitious materials contain relatively low
  levels of heavy metals and radioactive elements
• The levels are usually too low to affect
  performance
• They could affect the chemical composition of the
  solidified radioactive waste streams
• Variation likely between materials obtained from
  different countries

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Dr David JohnsonS/S Remediation Consultancy

• Radioactive Elements Present in Cementitious
  Grouts