Quantitative evaluation and leaching behavior of cobalt immobilized in sulfur polymer concrete composites based on lignite fly ash, slag and phosphogypsum

Combined method coupling problematic industrial waste utilization with immobilization of hazardous radioactive waste is proposed. Nine different sulfur polymer composites (SPC) containing radioactive Co-60 were prepared by hot mixing and pressing in order to determine possibility of radioactive cobalt immobilization in SPC matrix. For matrix preparation three different industrial wastes fillers were used: phosphogypsum (PG), lignite slag (SL) and lignite fly ash (FA) and three different compositions of sulfur modified with styrene, dicyclopentadiene and decene. Formulations of SPC were tested against Co-60 immobilization efficiency according to the slightly modified ANSI/ANS 16.1 leaching test. Results indicate for very good immobilization efficiency for SL and FA based SPC formulations, and worse parameters regarding phosphogypsum based matrices. Effective diffusion coefficients determined for slag and fly ash based composites were determined to be within the range of 1.41.10(-10)-1.85.10(10) cm(2) s(-1) and 1.37.10(-11)-4.33.10(-11) cm(2) S-1, whereas for phosphogypsum based samples between 6.22.10(-8)-1.60.10(-7) cm(2) s(-1). Measured leaching rates from SPC after 28 days were determined to be between 1.28.10(-4)-2.61.10(-4) g cm(-2).d(-1) (PG), 5.84.10(-6)-7.65.10(-6) g cm(-2)-d(-1) (SL) and 2.53.10(-6)-4.50.10(-6) g cm(-2).d(-1) (FA). Immobilization, as well as release mechanisms for Co-60 radionuclide in sulfur polymer composite matrices were proposed to be physical adsorption-dissolution for phosphogypsum based composites, and silicate/aluminate binding-dissolution-re-immobilization in case of fly ash based matrices. (C) 2019 Elsevier Ltd. All rights reserved.