Practical part Flashcards
Miscible displacement
Chemicals that mix well with water during the transport through the soil column are known as miscible solutes, and the transport process is known as miscible displacement. Examples: leaching of salts through the soil profile and movement of fertilizers and pesticides through the soil.
Immiscible displacement
When a solute does not mix with water or a liquid in the soil, it is known as immiscible solute, and the transport process is known as immiscible displacement. Examples: movement of water containing oil and transport of contaminants like dense or light non aqueous phase liquids (DNAPLs or LNAPLs).
Conservative/non-adsorbing solutes
Solutes remaining physically and chemically unchanged and not undergoing irreversible reactions are known as conservative solutes. These solutes are not adsorbed on the soil particle surfaces or are only weakly adsorbed. Examples:
Some examples of conservative solutes are chloride, bromide, nitrate, and sulfate, among others.
Non conservative/adsorbing solutes
Solutes undergoing irreversible reactions with changing physical and chemical makeup are known as non-conservative solutes. Examples: Some examples of non-conservative solutes are phosphates, pesticides, herbicides, heavy metals, mercury, and arsenic, among others.
Fluid
A solute or solution flowing through the porous media is also termed as fluid and is defined as a liquid of a definite physical and chemical makeup, for example, water containing nitrate ions.
Effluent
The solution collected at the exit or outflow end of a soil column or soil matrix is known as the effluent.
Displacing solute
The fluid that is added to the soil matrix or soil column during solute transport experiments that mixes with and displaces the already existing solution in the soil is known as the displacing solute.
Displacing fluid
The fluid that is removed from the soil volume in the soil matrix or soil column is known as displaced fluid.
Pore water velocity
The velocity at which the solute travels through the porous media is known as pore water velocity. It is also known as Darcy’s velocity. The pore water velocity (v) is defined as the ratio of the volumetric flow rate per unit cross-sectional area (Darcy flux; q) and the volumetric water content of soil (θ):
V=q (JW)/ θ JW= -KS ΔH/L
Darcy’s law
According to Darcy’s law, the rate at which water flows through the soil profile is equal to the hydraulic conductivity of soil when the hydraulic gradient causing flow is unity.
Tortuosity
In reality, the flow paths are not straight but are tortuous or irregular, and the property is known as tortuosity T.
ξ = θ10/3
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Convection/mass transfer
The solute transport through the porous media could be due to the mass flow or convection of solutes through the soil pores. The flow is also known as Darcian flow. Jm=qC where Jm is the convective flux q is the volumetric liquid flux density C is the volume-averaged dissolved solute concentration.
Diffusion
When movement of solutes takes place due to the movement of ions in a solution as a result of random motion, the process is known as diffusion. This process commonly occurs within the gaseous and liquid phases in the soil due to the random thermal motion also called Brownian movement. Jdif =- θ Dm ∂ C / ∂x where θ is the volumetric water content Dm is the molecular diffusion coefficient, x is the distance.
Dispersion
The process that mixes and eventually evens out the concentration gradients is known as dispersion. Dispersion is a dynamic process because liquids and solutes both move during the transport; therefore, it is also known as hydrodynamic dispersion. Jdis =- θ Dh ∂ C/ ∂x where Dh is the mechanical dispersion coefficient.
Dispersivity
λ is the dispersivity (cm) and is defined as the property of porous media that combines with the pore water velocity to provide the dispersion characteristic of the porous median and is a constant usually equal to one.
