Transport parameters of I− and IO3 − determined in crushed granitic rock columns and groundwater system under dynamic flow conditions

Abstract

Transport of two principal inorganic iodine anions separately in two crushed crystalline granitic rocks, gabbro and tonalite, have been investigated. The rocks were crushed and sieved, and finally a fraction between 0.25 and 0.80 mm was filled in 5 cm3 PET columns (medical syringes) of 5.40 cm length and 1.24 cm in inner diameter. NaI and NaIO3 were dissolved in synthetic groundwater (SGW) in a concentration as low as 10−4 mol/dm3. The SGW was pumped into the columns at a seepage velocity of 0.031 ± 0.001 cm/min using a multi-head peristaltic pump. Iodine concentration in the outflow SGW from the columns was determined by UV–Vis spectrophotometry at 510 nm absorption maximum in CHCl3 using redox reactions. By the use of a dependence of concentration on the number of pore volumes from the outflow and the linear isotherm model, based on erfc-function, breakthrough curves were constructed and the principal transport parameters were calculated. The values of sorption and desorption retardation coefficients of about 1 for both iodide and iodate have been obtained, which show evidence of practically non-sorption behavior of these chemical forms of iodine in the tested granitic rocks. The values of hydrodynamic dispersion coefficients and corresponding Peclet numbers were about 0.0077 ± 0.0006 and 21.6 ± 1.8 cm2/min, respectively, for both anions and rocks under given conditions.