Influence of silica fume on radioactive fluoride concentrate liquid waste solidified by magnesium potassium phosphate ce
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Influence of silica fume on radioactive fluoride concentrate liquid waste solidified by magnesium potassium phosphate cement Zheng‑hua Qian1 · Bo‑wen Yu1 · Shun Zhou1 · Yan‑bo Qiao1 · Xue‑yang Liu1 · Shuai Wang1 · Qiang Qin1 · Ji‑fei Ma1 · Xiao‑ling Wu1 Received: 2 December 2019 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract This paper investigated the influence of silica fume on radioactive fluoride concentrate liquid waste cementation with magnesium potassium phosphate cement (MKPC). The results showed that when the silica fume mass fraction increased from 0 to 20%, the setting time and fluidity of the MKPC slurry decreased, while the 28-day compressive strength of the solidified form increased. The main hydration products were MgKPO4·6H2O and magnesium silicate hydrate (M–S–H). Silica fume had good physical adsorption of cesium, whose 42-day cumulative leaching fraction decreased from 0.083 ± 0.003 to 0.044 ± 0.002 cm. The formation of magnesium fluosilicate and its hydrate led to a decrease of fluorine leaching. Keywords MKPC · Radioactive fluoride concentrate liquid waste · Silica fume · Solidified form · M–S–H
Introduction Radioactive fluoride concentrate liquid waste is a type of radioactive waste specific to molten salt reactors. The treatment and disposal of this radioactive waste are the biggest problems in managing radioactive waste from molten salt reactors [1, 2]. The results of our experiments show that there are some inevitable problems in the cementation of radioactive fluoride concentrate liquid waste with traditional Portland cement. Magnesium potassium phosphate cement (MKPC) is a new kind of chemically bonded cementitious material. Potassium dihydrogen phosphate when dissolved in water gives a pH of about 3.7, the reaction between magnesium oxide and potassium dihydrogen phosphate is acid–base and occurs in an aqueous medium [3–5]. The reactions were as follows:
MgO + KH2 PO4 + 5H2 O → MgKPO4 ⋅ 6H2 O MKPC is a material friendly to the environment and has many advantages, such as good volume stability, high compressive strength, and high nuclide encapsulation rate [6, 7]. * Yan‑bo Qiao [email protected] 1
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
MKPC is attractive for its applications in the cementation of radioactive waste [8–12], and it provides a feasible solution for the treatment of radioactive fluoride concentrate liquid waste. Although MKPC has many advantages over traditional materials, its shortcoming is that its poor chemical stability in water affects its application in practical engineering projects [13, 14]. A common method to improve the chemical stability of MKPC solidified forms in water is to improve their pore structure and make the cementation as compact as possible. Silica fume is usually added as a mixture into MKPC because of its economic applicability and effective performance [15, 16]. In addition to being a porous filler, silica fume is also a reactive complementary cementitious material for potassium dih
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