Sub-topics Chemical characterization Sorption-Desorption - - PowerPoint PPT Presentation

Sub-topics

• Chemical characterization

Sorption-Desorption Characteristics Determination of kd (The Distribution coefficient)

• Thermal Characterization
• Electrical Characterization

Sorption Absorption Adsorption atoms or molecules move into the bulk of a porous material, e.g. the absorption of water by a sponge Atoms or molecules move from the bulk phase (that is, solid, liquid, or gas) onto a solid or liquid surface.

Incorporation, Assimilation, Inclusion Accumulation of substance on surface

e.g. purification by adsorption where impurities are filtered from liquids or gases by their adsorption onto the surface of a high-surface-area solid such as activated charcoal The adhesion of a thin layer of molecules of some substance to the surface of a solid or liquid

Terms related to Sorption

• Adsorbates - molecules that have been adsorbed onto solid surfaces
• Substrate or Adsorbent - the surface to which adsorbates are adsorbed
• e.g. in case of adsorbed cations tightly held on surfaces of negatively

charged dry clay particles, clay particle is substrate and cations are adorbates. Clay particle

cations

Desorption

• a phenomenon whereby a substance is released from or through a

surface

• process is the opposite of sorption
• ccurs in a system being in the state of sorption equilibrium between

bulk phase (fluid, i.e. gas or liquid solution) and an adsorbing surface (solid or boundary separating two fluids)

• When the concentration (or pressure) of substance in the bulk phase

is lowered, some of the sorbed substance moves to the bulk state

Simple representation of these processes

The cations get fully hydrated, which results in their desorption from clay surface Dry condition (cations strongly sorbed on clay particles)

Clay layers Adsorbed cation

The water molecules wedge into the inter-layer after adding water

Water molecule

• Soil washing
• Soil flushing
• Vitrification
• Solidification
• Immobilization

Important to determine Sorption and Desorption Characteristics of Geomaterial and Immobilizing Agents

SORPTION & DESORPTION CHARACTERISTICS

• f Geomaterials

Strategies for Remediation of Contaminated Soils/Geomaterials (Site cleanup/Site remediation) Excellent philosophy to simulate geomaterial-contaminant interaction Sorption and Desorption are opposite interaction mechanisms

Importance of Sorption and Desorption Characteristics

• Fate and Transport of Reactive Contaminant(s)
• Efficiency of Environmental Cleanup Strategies
• Selection of Suitable Geological Formations and Backfill Materials
• Design of Barrier Layers of Waste Containment System
• Accumulation of Heavy Metals and Pesticides in Subsoil

Challenge Precise Determination of these Characteristics (kd & kdl) in a short duration kd : the coefficient describing sorption process kdl : the coefficient describing desorption process (subscript l corresponds to leaching process)