Effects of heat and humidity gradients on MX-80 bentonite geochemistry and mineralogy

Roberto Gómez-Espina, María Victoria Villar

Resultado de la investigación: Article

7 Citas (Scopus)

Resumen

To simulate the conditions of a sealing material in a nuclear waste repository a 20-cm long column of MX-80 bentonite compacted at a nominal dry density of 1.7g/cm3 with a water content of 17% was tested in a thermo-hydraulic cell. On top of the column a hydration surface simulated the groundwater coming from the host rock and at the bottom a heater simulated the waste canister. The test comprised two phases: a heating phase (lasting 324days) and a 'heating+hydration' phase (1510days). The temperatures at the ends of the column were set during the last phase to 30°C and 140°C. The thermo-hydraulic treatment resulted in major changes related to the location of the bentonite along the column. These changes led to important gradients along the column with respect to the physical state (water content, dry density) and geochemistry of the bentonite. Due to the dissolution of low-solubility species and to the loss of exchangeable positions in the smectite, the content of soluble salts in the pore water increased with respect to the original one. The solubilised ions were transported; sodium, calcium, magnesium and sulphate having a similar mobility, which was in turn lower than that of potassium and chloride. The cationic exchange complex was also modified. Smectite dissolution processes (probably colloidal) occurred, particularly in the more hydrated areas. Consequently, an overall decrease of the smectite content with respect to the initial value took place, especially in the most hydrated areas, where the percentage of interestratified illite also increased. On the other hand, the content of cristobalite and calcite increased.

Idioma originalEnglish
Páginas (desde-hasta)39-48
Número de páginas10
PublicaciónApplied Clay Science
Volumen109-110
DOI
EstadoPublished - 1 jun 2015

Huella dactilar

Bentonite
Geochemistry
Mineralogy
bentonite
Atmospheric humidity
humidity
mineralogy
geochemistry
Hydration
Water content
smectite
Dissolution
Hydraulics
dry density
Radioactive Waste
Heating
Magnesium Sulfate
hydration
Potassium Chloride
Calcium Carbonate

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geology

Citar esto

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abstract = "To simulate the conditions of a sealing material in a nuclear waste repository a 20-cm long column of MX-80 bentonite compacted at a nominal dry density of 1.7g/cm3 with a water content of 17{\%} was tested in a thermo-hydraulic cell. On top of the column a hydration surface simulated the groundwater coming from the host rock and at the bottom a heater simulated the waste canister. The test comprised two phases: a heating phase (lasting 324days) and a 'heating+hydration' phase (1510days). The temperatures at the ends of the column were set during the last phase to 30°C and 140°C. The thermo-hydraulic treatment resulted in major changes related to the location of the bentonite along the column. These changes led to important gradients along the column with respect to the physical state (water content, dry density) and geochemistry of the bentonite. Due to the dissolution of low-solubility species and to the loss of exchangeable positions in the smectite, the content of soluble salts in the pore water increased with respect to the original one. The solubilised ions were transported; sodium, calcium, magnesium and sulphate having a similar mobility, which was in turn lower than that of potassium and chloride. The cationic exchange complex was also modified. Smectite dissolution processes (probably colloidal) occurred, particularly in the more hydrated areas. Consequently, an overall decrease of the smectite content with respect to the initial value took place, especially in the most hydrated areas, where the percentage of interestratified illite also increased. On the other hand, the content of cristobalite and calcite increased.",
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Effects of heat and humidity gradients on MX-80 bentonite geochemistry and mineralogy. / Gómez-Espina, Roberto; Villar, María Victoria.

En: Applied Clay Science, Vol. 109-110, 01.06.2015, p. 39-48.

Resultado de la investigación: Article

TY - JOUR

T1 - Effects of heat and humidity gradients on MX-80 bentonite geochemistry and mineralogy

AU - Gómez-Espina, Roberto

AU - Villar, María Victoria

PY - 2015/6/1

Y1 - 2015/6/1

N2 - To simulate the conditions of a sealing material in a nuclear waste repository a 20-cm long column of MX-80 bentonite compacted at a nominal dry density of 1.7g/cm3 with a water content of 17% was tested in a thermo-hydraulic cell. On top of the column a hydration surface simulated the groundwater coming from the host rock and at the bottom a heater simulated the waste canister. The test comprised two phases: a heating phase (lasting 324days) and a 'heating+hydration' phase (1510days). The temperatures at the ends of the column were set during the last phase to 30°C and 140°C. The thermo-hydraulic treatment resulted in major changes related to the location of the bentonite along the column. These changes led to important gradients along the column with respect to the physical state (water content, dry density) and geochemistry of the bentonite. Due to the dissolution of low-solubility species and to the loss of exchangeable positions in the smectite, the content of soluble salts in the pore water increased with respect to the original one. The solubilised ions were transported; sodium, calcium, magnesium and sulphate having a similar mobility, which was in turn lower than that of potassium and chloride. The cationic exchange complex was also modified. Smectite dissolution processes (probably colloidal) occurred, particularly in the more hydrated areas. Consequently, an overall decrease of the smectite content with respect to the initial value took place, especially in the most hydrated areas, where the percentage of interestratified illite also increased. On the other hand, the content of cristobalite and calcite increased.

AB - To simulate the conditions of a sealing material in a nuclear waste repository a 20-cm long column of MX-80 bentonite compacted at a nominal dry density of 1.7g/cm3 with a water content of 17% was tested in a thermo-hydraulic cell. On top of the column a hydration surface simulated the groundwater coming from the host rock and at the bottom a heater simulated the waste canister. The test comprised two phases: a heating phase (lasting 324days) and a 'heating+hydration' phase (1510days). The temperatures at the ends of the column were set during the last phase to 30°C and 140°C. The thermo-hydraulic treatment resulted in major changes related to the location of the bentonite along the column. These changes led to important gradients along the column with respect to the physical state (water content, dry density) and geochemistry of the bentonite. Due to the dissolution of low-solubility species and to the loss of exchangeable positions in the smectite, the content of soluble salts in the pore water increased with respect to the original one. The solubilised ions were transported; sodium, calcium, magnesium and sulphate having a similar mobility, which was in turn lower than that of potassium and chloride. The cationic exchange complex was also modified. Smectite dissolution processes (probably colloidal) occurred, particularly in the more hydrated areas. Consequently, an overall decrease of the smectite content with respect to the initial value took place, especially in the most hydrated areas, where the percentage of interestratified illite also increased. On the other hand, the content of cristobalite and calcite increased.

KW - Bentonite

KW - Engineered barriers

KW - Nuclear waste

KW - Pore water

KW - Thermo-hydraulic treatment

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U2 - 10.1016/j.clay.2015.03.012

DO - 10.1016/j.clay.2015.03.012

M3 - Article

AN - SCOPUS:84925857102

VL - 109-110

SP - 39

EP - 48

JO - Applied Clay Science

JF - Applied Clay Science

SN - 0169-1317

ER -