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Fluoride Adsorption by a Saline Sodic Soil Irrigated with a High F Water

Robbins, C.W. (1986) Fluoride Adsorption by a Saline Sodic Soil Irrigated with a High F Water. Irrigation Science. 7:107-112.

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Langmuir isotherm data for F adsorption were obtained from 1 : 10
soil : water extracts of soil samples from a lysimeter study. A sodic silt loam
surface soil with a saline sodic subsoil was irrigated with a high sodium
chloride, high fluoride (0.38 mMF) geothermal well water. A previous study
showed that fluorite (CaF2) was precipitated from solution in the upper portion
of this profile while another mechanism removed F solution in the lower
part of the profile to below 0.02 mMF. The Langmuir isotherm data indicate
that one kind of surfaces or sites remove fluoride from solution over the
0 to 1.1 to 1.2 mMF range. The adsorption capacity for this F removal is about
4.4 to 5.8 mmol F/kg of soil and the equilibrium constant is between 0.54 to
1.00 l/mmol F. Once these surfaces or sites were saturated, a second kind of
sites removed F from solution, and had an adsorption capacity of 9.2 to
11.4 mmol/kg and an equilibrium constant of 0.16 to 0.27 l/mmol. Both data
sets fit the Langmuir equation. At some point before or after this second set of
sites or surfaces was saturated, the fluorite ion activity product was exceeded
and fluoride was then removed from solution via fluorite precipitation. The two
adsorption mechanisms lowered the soil solution F concentration sufficiently to
prevent ground water contamination, but once the adsorption sites were
saturated, fluorite precipitation does not decrease F concentration sufficiently to
meet drinking water standards.

Item Type: Article
NWISRL Publication Number: 0582
Subjects: Soil > Chemistry
Mass Import - autoclassified (may be erroneous)
Depositing User: Dan Stieneke
Date Deposited: 20 Nov 2010 21:52
Last Modified: 13 Jan 2017 20:02
Item ID: 463