In general, the amount of radiocesium sorbed by the five sorbents with 0.01 mol·dm–3 NaCl was in order zeolite > NiFeCN–SiO2 > montmorillonite > aerogel > silica gel. Addition of humic acid solution to the sorbents depressed the sorption of cesium by all sorbents, except for NiFeCN–SiO2 was not seen, with the greatest effect showing to the aerogel. The presence of humic acid resulted in an enhanced desorption of cesium from zeolite, NiFeCN–SiO2 and to a lesser extent from montmorillonite and silica gel. The order of cesium retention following desorption for both sorbent and sorbent/humic-acid mixtures was zeolit > NiFeCN–SiO2 > montmorillonite > silica gel. The presence of humic acid resulted in decreasing of distribution coefficient values for both sorption and desorption processes.
The effect of humic acid addition on the capacity of inorganic sorbents to sorb radioactive cesium and strontium was studied
on montmorillonites in a calcium and potassium form. The Sips isotherm for humic acid sorption and multisite distribution
model of ion sorption was found to suit well for the description of mobility of ions as a function of equilibrium humic acid
concentration as a single variable at given pH and type of silicate. Complexation of the ions was of minor importance at the
conditions investigated. Influence of humic acid on the specific radiocesium interception potential (SRIP) was also evaluated.
A standard analytical technique for determination of the partial ion exchange capacity of mineral or soil for selective uptake
of cesium, the specific radiocesium interception potential (SRIP) is formulated and theoretically discussed. The method is
based on the determination of a retained, leached or sorbed fraction of carrier-free cesium-137 in soil contacted with 0.01M
KNO3-0.01M Ag thiourea complex solution at the phase ratio solution:sorbent 10 ml:0.1 g. Reliability of the method is discussed
in connection of radiocesium carrier and humic substances presence.
A kinetic study of thermal and photoaccelerated U(IV)-U(VI) isotope exchange has been carried out in oxalate solutions at 11–40°C. The rate and quantum yield were determined as a function of U(IV), U(VI) and oxalate concentration, wavelength of incident light, temperature and absorbed dose of -radiation. The kinetic equations for thermal and photoaccelerated exchange have been obtained. It was assumed that the mechanism of exchange involves formation of U(V) as an intermediate, followed by slow exchange between U(V) and U(IV). The isokinetic dependence confirms the identity of limiting stages for thermal and photostimulated exchange. The upper component of photoexcited T1 level of uranyl is supposed to be the most reactive in the process of U(V) generation. It was observed that the small doses of -radiation evoke the acceleration of isotope exchange, however, at D>100 krad the rate of exchange is reduced to the level of thermal exchange.
Authors:P. Rajec, P. Gerhart, F. Macášek, I. Shaban, and P. Bartoš
The high-performance size-exclusion chromatography (HPSEC) and radiochromatography (HPSERC) was used for the identification
of radiocesium and radiostrontium interaction with humic acid. It was found that the behavior of humic acid on size-exclusion
chromatography is sensitive to the salt concentration and pH of the mobile phase. At lower ionic strength and in acidic region
of pH, the Aldrich humic acid exhibited three main fraction within the ranges >760 kDa, 25–100 kDa and <5 kDa. Radiocesium
was found in the low-molecular fractions (<1 kDa) of humic acids but radiostrontium interacts preferably with the fractions
of humic acid of molecular weight within the range 2–5 kDa.