Fluoride retardation from quartz sand-packed column tests

inasmuch as both low and high concentrations of f- in groundwater have different detrimental effects on human health (increased dental caries, and mottled enamel or even severe structural bone deformations, respectively), many efforts have focused on the movement of such anion in aqueous systems. it is so because water drinking is the main intake of f- by humans. this paper presents the results of seven dynamic experiments in which solutions of varying [f-], ph, and flow velocities circulated through columns packed with clean quartz sand. the breakthrough data were analyzed by means of a computer code adapted to the estimation of equilibrium and non-equilibrium solute transport parameters from miscible displacement experiments in a steady-state, uniform flow field using a pulse-type or continuous source. it was found that larger retardation factors (r) are associated with low ph, low [f-] in the feed solutions, and larger flow velocities. such results appear to be related to the form of the f species, the rather weak bond between the adsorbate and the quartz sand, and stronger anion repulsion at low pore velocities. the estimated values for r vary between 1,22 and 1,50, whereas the distribution coefficients were in the range of 0,1 to 0,05 l kg-1. it should be said that the breakthrough curves display hysteresis, leading to a desorption behavior that proceeds faster than the adsorption process.