Clays Mineralogy and Applications
The Big Picture Small-scale chemistry Large-scale natural processes
Outline What are clays? Clay properties: Chemistry and structure Clays and slope failure: landslides and mudflows Clay and contaminants: Hazardous waste and dkitty litter?
What is a clay? Clay: Particle with size < 2 m Clay Mineral: A type of phyllosilicate (layer structured)
Clays are secondary minerals Not present in the original rock Created from the weathering of other minerals 2KAlSi +2K + +2OH - 3 O 8 + 11H 2 O Al 2 Si 2 O 5 (OH) 4 +4HSiO 4 4 K-feldspar + water kaolinite + free ions + Si-acid p (soluble silica)
The Building Blocks Tetrahedra Octahedra Silicon (Si) with Aluminum (Al) or Oxygen (O) Magnesium (Mg) with Oxygen (O) and Hydrogen (H)
Building block #1 Tetrahedra of SiO -4 4 O -2 Si +4 O -2 O -2 O -2
Building block #1 Tetrahedra of SiO -4 4 O -2 Si +4 O -2 O -2 O -2
Tetrahedra link together O -2 O -2 Si +4 Si +4 O -2 O -2 O -2 O -2 O -2
Tetrahedra form layers
Building Block #2 Octahedra Al(OH) -3 6 or Mg(OH) -4 6 H + O -2 O -2 O -2 Al +3 or Mg +2 O -2 O -2 O -2
Building Block #2 Octahedra Al(OH) -3 6 or Mg(OH) -2 6 H + O -2 O -2 O -2 O Al +3 or Mg +2 O -2 O -2 O -2
Octahedra form layers
Tetrahedral and octahedral layers combined to form clay minerals Si-Tetrahedra Al-Octahedra 1:1 (T-O) Clays: Kaolinite
2:1 (T-O-T) Clays are also common Si-Tetrahedra Tt hd Octahedra Si-Tetrahedra
2:1 (TOT) Layer Clays 1:1 (TO) Layer Clays T O T T O T Interlayer T O T O Smectite (bentonite), illite, micas Kaolinite
21L 2:1 Layer Cookies 11L 1:1 Layer Cookies
Surfaces are charged; layers glued together by ions of opposite charge T O T T O T 2:1 Layer Clays Interlayer Negative charge Charge balancing cations Balance negative surfaces glue layers together
Why are the layers charged? Edges want more bonds Ions are in the wrong gp place (isomorphic substitution) Accidentally getting Al +3 where Si +4 belongs (or Mg +2 for Al +3 ) Can occur in either tetrahedra and octahedra So clays are electrically active
Charge (where, how much) controls the interspace layer preference Illite Smectite (bentonite) 1 nm K + M + or H 2 O 1-2 nm K 0.5-0.75 Al 2 (Si,Al) 4 O 10 (OH) 2 M + 0.7(Al +3,Mg +2 ) 4-6 (Si,Al) 8 O 20 (OH) 4. nh 2 O Structure is fixed Limited swelling Structure (layer charge) is Variable, Clay swells
from Environmental Geochemistry Eby
Clays swell when water pushes the layers apart Water Bentonite Swelling Clays Expansive Soils Initial clay level l
Clays and contaminants Clays limit contaminant transport: Natural barriers to flow (impermeable) Electrically active points attract and hold contaminants
Uses of Clays American Colloid Company big supplier http://www.colloid.com/isg/applications.aspx Sorptive Minerals Institute Represents absorbant clay industry http://www.sorptive.org/applications.html
Clays and Contaminants Dry Bentonite
Clays and Contaminants Wet Bentonite
Clays and Contaminants Bentonite Sand
Pinewood South Carolina Opaline claystone Formed in a lagoon behind a barrier island about 58 million years ago Mostly illite/smectite clays cemented with opal Adsorbs twice its volume in water Quarried for kitty litter starting early 1970 s
The quarry ygradually switched from a quarry to a landfill Switched to waste oil disposal in mid-1970s Permitted as a hazardous waste landfill When RCRA began regulating hazardous wastes (1976) Designed landfills finished i in the mid 1980s
Designed Waste-containment System of the 1980s from Chapelle, 2000, The Hidden Sea
Pinewood geology generalized From Chapelle, The Hidden Sea
Did clay work as a barrier? Contaminants were found in ground water and surface water mid 1980s. Heavy metals chromium, lead, mercury Volatile organic compounds (VOCs) Tetrachloroethene trichloroethene Benzene-toluene-ethylbenzene-xylene
So why didn t the clay work?? Clay thickness inconsistent across site thinner in the west (near Lake Marion) Clay breached during construction
Possible Effects of Contamination Pinewood Landfill
Pinewood, South Carolina Charleston Fort Sumter National Monument
History of Environmental Regulations Resource Conservation and Recovery Act (RCRA) passed by U.S. Congress in 1976 regulates waste disposal, including LUST at existing and active facilities revised 1980 and 1984 Pinewood is a RCRA site (!?) Comprehensive Environmental Response, Compensation and Liability Act (Superfund or CERCLA) passed by U.S. Congress, Dec. 1980, amended 1986 regulates closed and abandoned hazardous waste sites tries to find a responsible party to pay for clean-up
Pinewood Landfill September 2000 Landfill was closed October 2002 The S.C. Department of Health and Environmental Control and Safety-Kleen reached an agreement that would provide funding for closure and maintenance of the site (Safety-Kleen paid ~$27.5 million into trust fund)
Clays and contaminants Clay is a barrier to contaminant transport Impermeable Sorbs contaminants But it only works if the layer doesn t have any holes or cracks!
Possible Effects of Contamination Pinewood Landfill
Congaree National Park South Carolina Pinewood
Hazardous Waste Landfills University vesyof Arizona oasuperfund udresearch eseac Program oga http://superfund.pharmacy.arizona.edu/content/ourprogram Environmental Health & Safety On-line http://www.ehso.com/cssepa/tsdflandfills.php US Ecology operates facilities for Western states t http://www.americanecology.com/services.htm EPA Hazardous Wastes Site http://www.epa.gov/epawaste/hazard/index.htm