Correlation of Sr2 + retention and distribution with properties of different soil types

• Relationships between Sr2 + sorption parameters and soil properties were established.
• Sorption pH edge was correlated with soil pH, whereas maximum capacity with CEC.
• Sr2 + was mainly found in exchangeable fraction of all contaminated soils.
• Major factor reducing Sr2 + mobility is soil pH.
• Huge Sr2 + mobility points toward chemical extraction as a suitable remediation method.

90Sr is a long-lived radionuclide, which enters the environment by accidental release of liquid radioactive waste. In this study, Sr2 + sorption was investigated using eight different soil types. Experiments were conducted by varying different parameters such as: contact time, solution pH and initial Sr2 + concentration, while distribution of Sr2 + in various soil fractions was studied using modified Tessier et al. sequential extraction protocol. The aim of this study is to give a correlation of Sr2 + sorption and distribution with the properties of studied soils. Retention of Sr2 + was generally a fast process. Regardless of soil type, only small fluctuations of sorbed amounts were observed in the investigated time frame (30 min to 30 days). Sr2 + sorption edge, characterized by the narrow pH range in which a large increase of Sr2 + sorption occurs, varied between samples. Thus, equilibrium solution pH values at which 50% of the overall Sr2 + amount was sorbed (pH50) were between 3.6 and 7.7 for different soil types. Maximum sorption capacities of analyzed soils were in the range 0.061–0.125 mmol/g, and decreased in sequence according to soil type: Rendzic Leptosols > Humic Fluvisol > Eutric Cambisol ≥ Leptosol > Fluvisol ≥ Dystric Cambisol > Mollic Leptosol > Stagnosol. According to the results of correlation analysis (CA), positive correlations were found between soil pH and the position of pH50, content of clay and Ca/Sr ion-exchange ratio, and between cation exchange capacity (CEC) and Sr2 + maximum sorption capacity. In undisturbed soils, the total Sr2 + amounts and distribution differed notably, i.e. exchangeable, carbonate or residual fractions were the major reservoirs for Sr2 +. Content of Sr2 + in exchangeable phase was positively correlated with the sum of clay and silt fraction, Sr2 + concentration in carbonate and Fe,Mn-oxide phase was related to soil pH, while Sr2 + amount in organic phase was related to the content of total organic carbon (TOC). Completely different Sr2 + distribution was found in contaminated soil samples, where it was accumulated in exchangeable fraction, regardless of soil type, contamination level and aging time. Soils with higher CEC exhibited less amounts of Sr2 + in water soluble fraction, furthermore, the increase of soil pH provoked redistribution of Sr2 + from exchangeable to carbonate and Fe,Mn-oxide fraction.