Abstract

Dissolution of gypsum has great influence on water flow and solute transport occurring in
gypsiferous-calcareous soils. Many models based on convection and diffusion processes have
been developed to describe transport in soil. Constraints of estimation of transport parameters in
gypsiferous-calcareous soils are mainly due to gypsum influence .The objectives of this study,
were to i: modeling the transport of solute (36Cl) in gypsiferous-calcareous soil treated with fuel
of FO on dissolution of gypsum associated with calcium carbonate content. Radiotracer of
chloride as carrier free of 36Cl was applied to surfaces of saturated soil columns that have 20, 250
and 500 g kg-1 gypsum treated with 0, 1, 2, and 4% of fuel oil and leached with water until
complete displacement of chloride. During leaching, samples of effluent were collected and
measured for Cl36 . The application of 1 to 2% FO improved the transport properties due to
modification in soil structure. The applied models gave good fit between measured and predicted
breakthrough curves of 36Cl with significant linear correlation coefficient (r) that ranged between
0.972 and 0.999. They gave a calculated dispersion coefficient (D) ranging from 2.1 to 79.2 cm2
day-1, and retardation factor (R) ranging from 0.92 to 1.58. It was found that D was also linearly
related to pore water velocity (v). Also, the results indicate the possibility of predicting the
distribution of chloride in gypsiferous-calcareous soil for different time periods using correct
boundary conditions. Experimental results show that gypsum dissolution in the soil columns is
mainly determined by the flow velocity, soil saturation and then partially coating with FO. The
role of lime was not well explained in reducing gypsum dissolution because the co-existence of
gypsum and lime is not clear enough.