Clays and Clay Minerals II

Transcription

1 The clay cycle Clays and Clay Minerals II Formation bentonites Diagenetic alteration of pyroclastics Hydrothermal alteration of volcanic glass Formation of smectiterich sediments in salt lakes and sabkha environment (dissolution of detrital smectites) Smectite-Group Saponite Subgroup (trioctahedral) Montmorillonite Subgroup (dioctahedral) Use of bentonite Some historical facts Prior to 400 BC: Bentonite from Kimolos was used in the Mediterranean to clean wool and as a component of soap for bathing (described by Aristophanes 405 BC) Bentonite from the same deposit is still mined today for use in detergents. Native Americans used bentonite to clean hides American settlers used bentonite to clean clothing and as axle grease for wagons Montmorillonite (Al,Mg) 2 [(OH) 2 /Si 4 O 10 ] (Na,Ca) x (H 2 O) n Until the end of 19th century, bentonite was used in small quantities only: for cleansing and for medical purposes Bentonite Bentonite in modern life USA 2006: Bentonite production statistics by end use What makes smectites unique? Small grain size (compared to other clay mineral) large surface area top: smectite bottom: chlorite 1

2 Na-bentonite: More unique properties of smetites (from economical point of view) Each type has his own unique applications Large surface area (up to 800 m 2 /g) Negative layer charge (120 meq/g) Exchangeable surface cations Hydration energy of exchangable cations make a strong affinity for water Results in strong interparticle forces significant for bulk physical properties including: Swelling Sealing Adhesive characteristics Two primary types of smectites (from economical point of view) Each type has his own unique applications Absorb large amount of waters Form viscous, thixotropic suspensions Low layer charge Ca-bentonite: Lower swelling properties Does not stay suspended Low water absorption High layer charge Pet litters Drilling Fluid Prior to 1980s most pet litter products were composed of sand or non-clumping clays Mud flow in borehole Pumped down the drill string Raises in the annulus In the late 1980s Nasmectite was discovered to be ideal for making clumping cat litter Cooling of the drill bit Carries the cuttings to the surface Prevents from blocking the string (thixotropy) Drilling Fluid Thixotropy Fluid forms gelled structure when not subject to shearing and liquefies when agitated Necessary for fast drilling (cooling) Efficient lifting of cuttings Support cuttings when mud flow stoppes 2

3 Thixotropy Metal Casting Adding bentonite to paint prevents the pigments from settling Cast-iron products are made in foundry moulds Increases workability Prevents from smearing Green sand moulding contains bentonite as bonding agent (mixed with sand, coal and small amount of water) Mould material is recycled Na- and Cabentonites are used Iron Ore Pelletizing Allows use of abundant low grade iron ore for steel making Ore is finely ground to liberate the iron oxide Fineness of powdered iron ore creates problems during shipping and handling Use of natural Nabentonite as a binding agent for making pellets and briquettes Bleaching and Clarifying Ca-smectite (especially after acid treatment) is used to decolorize and clarify animal, vegetable and mineral oil from impurities Na-smectite is used as a fining agent for wine; absorption of positively charged proteins; removal though flocculation Civil Engineering Applied Geology Na-bentonite is used for low-permeability insitu barriers; slurry walls, slurry trenches A real situation for a consulting geologist: multiple aquifers have to be monitored Tunnel excavation in unconsolidated soil below ground water level: bentonite slurry is used for stabilizing the excavation face, to lubricate and to seal the tail of the TBM Drilling of cluster boreholes 3

4 Applied Geology A real situation for a consulting geologist: multiple aquifers have to be monitored or Drilling of a single borehole and installation of a multiple-screen piezometer Bentonite based barrier systems Construction of new disposal sites with compacted clay liners (CCL) or geosythetic clay liners (low permeable composite material with 10-mm layer of Na-bentonite) Nuclear waste disposal Nuclear waste disposal Opalinus clay (name from: Leioceras Opalimum) Tagesanzeiger February 19, 2011 Illite/Smectite ML 6-12% Illite 16-22% Kaolinite 26-32% Chlorite 5-9% Quartz 14% Calcite 11% Accessories ca. 5% Samples from Mont Terri Nuclear waste entombement Bentonite is part of a multi-barrier system Barriers: Spent fuel is solidified and encased in corrosion resistant in canisters Canisters are placed in boreholes or galleries in geologically stable formations Canisters are enbedded in bentonite Nuclear waste entombment Lifetime of bentonite as engineered barrier/buffer 3 phases: 1. phase: (0 to ca. 100 years): hydration, swelling and compression of barrier; subject to strong radiation and physico-chemical processes at temperatures up to 220 C 2. phase: ( ca. 100 to 1000 years): exposure to continued but moderating thermal gradient while barrier continues to consolidate Bentonite = tertiary engineered buffer - limit entry of water into the waste - contribute to retension of radionuclides - assist in dissipation of heat from radioactive decay - provide cushoning of canisters against mechanical shock and compression 3. phase: (1000 to years): thermal gradients are no concern but unknown geological, hydrological and climatic changes 4

5 Excavation of a tunnel drift (diameter 2.3 m) Host rock : Grimsel Granodiorite Hydraulic characterization of water conducting zones intersecting the tunnel Filling the tunnel with bentonite blocks (around a central steel liner to facilitate installation and recovery of the canister ) 2 heaters with the dimension and weight of waste canisters were installed Heater inside the bentonite barrier Dismantling of the bentonite liner after 5 years of heating To be noted: the gaps between the bentonite blocks are closed as a result of swelling 5

6 SELFRAC SELFRAC Mont Terri URL Mont Terri URL Simulation of swelling pressure and it s effect on the EDZ A plate loading apparatus is used to apply a load onto the tunnel wall SELFRAC Mont Terri URL Displacement represents a closure of fractures around the tunnel (EDZ) SELFRAC Mont Terri URL Increasing load resulted in decreasing hydraulic conductivity Decrease of a factor 60 between zero load and the maximum load of 4.8 MPa Transmissivity (m 2 /s) Test 10 Test 11 Test 16 Test 12 Test 13 Test 17 Left scale: Calculated transmissivity in m 2 Test 18 /s Right scale: Load in MPa (red line) 3 Bottom: Time axes date and days after first saturation of boreholes (Test 10 = Selfhealing Experiment Test 11 to 18 = Selfrac Experiment) Δt (d): time since 1. saturation Load Pressure (MPa) Clay as raw material for bricks Clay as raw material for bricks Clay is one of the most abundant mineral materials on earth. Sun-dried bricks made from clay, sand and gravel Building made from sun-dried bricks. 6

7 Clay as raw material for bricks Great Mosque of Djenné (Mali) Sieving of the raw material Largest mud brick building in the world UNESCO World Heritage Site oldest fired objects are mostly figures and pottery (Jomon culture, Japan, B.C.) Clay as raw material for bricks History of fired bricks earliest fired bricks found in Knossos (scattered findings); ca B.C. more abundant fired bricks from Mesopotamia; ca B.C. city of Mohenjo-Daro (Indus valley) was built from fired bricks; B.C. To be noted that this was an exception as most buildings were made from sun-dried clay bricks example Morocco advent of construction with bricks in Roman times; but almost complete stop of brick manufacturing until 11 th century; then new advent of brick and tile manufacturing as urban centers start to grow Brick and tile manufacturing in Switzerland 1992: 34 manufacturing places with 7 producing roof tiles Year Manufacturing places Handicraft Mech. Production ca ca. 25 Today in Switzerland: domestic industry meets the demand for bricks and roof tiles Raw material for brick and tile manufacturing Raw material for brick manufacturing in Switzerland 7

8 Requirements for minable deposits Quality of raw material mineralogical composition of raw material Quantity of raw material / reserves high investment costs material for years of production Economical aspect short transports geological situation Quality of raw material Mineralogical composition Clay minerals Illite Chlorite Montmorillonite Kaolinite Other essential minerals (opening materials) Quartz Feldpar Mica Carbonates (active) Environmental aspects Accessory minerals Limonite, Goethite (+) Pyrite, Markasite (-); (sulfur emission) Gypsum (-) Organic material (-/+) (Fletton clay, 7% lignite) Quality of raw material Quality of raw material Mining and mixing Products Preparation and homogenization Storage and pugging Masonry bricks Facing masonry bricks Forming and cutting Clay roof tiles Drying h Coating, coloring Firing: ca C, h Soaking time: 8 h 8

9 Processing Processing Extrusion of clay blocks Extrusion through a die to form bricks with voids and surface texture Processing Changes occurring during firing Change in color Change in size shrinkage Monitoring of mineral reaction during firing X-ray diffraction with a heating attachment Monitoring of mineral reaction during firing X-ray diffraction with a heating attachment New minerals formed Mean values from 10 carbonate rich clays Raw % by wt. Fired % by wt. Quartz 25.0 (18..29) Quartz 19.0 (7..30) Calcite 15.3 (6..25) Plagioklase 18.0 (12..24) Dolomite 3.4 (2..5) Wollastonite 7.1 (4..11) Feldspar 7.5 (3..12) Diopside 15.4 (5..23) Illite 27.4 (21..35) Gehlenite 5.6 (2..13) Montmor. 6.2 (0..16) Sanidine 3.5 (0..7) Chlorite 6.7 (3..12) Hematite 2.6 (0..6) Kaol. +ML 8.3 (0..22) Amorphous 28.8 (20-40) Gehlenite (Melilite-group): Ca 2 Al(AlSi)O 7 Wollastonite: CaSiO 3 Diopside (Clino-pyroxene): CaMgSi 2 O 6 9

10 New minerals formed SEM images: Glassy mass of ceramic body (left); 800 x Volcanic glass from the island of Lipari (right); 445 x Municipal landfill Excerpt from the Swiss regulation on disposal sites Die geologische Barriere weist im Ablagerungsbereich der Deponie eine maximale Gebiets- bzw. Gebirgsdurchlässigkeit von 1.0 x 10-7 m/s und eine minimale Mächtigkeit von 7 m auf Disposal site Koelliken Disposal site Koelliken Former clay pit Disposal of waste from the chemical industries Slurry wall to prevent from seepage Several attempts to encapsulate the waste Finally decision was taken to remove the waste and incinerate it in a special kiln Disposal site Koelliken Disposal site Koelliken A roof prevents from release of toxic gases Low pressure atmosphere inside the enclosed area Disposed waste is recovered and separated 10