Effect of Fe2O3 on the Immobilization of High-Level Waste with Magnesium Potassium Phosphate Ceramic

Abstract

For the proposed novel procedure of immobilizing HLW with magnesium potassium phosphate cement (MKPC), Fe2O3 was added as a modifying agent to verify its effect on the solidification form and the immobilization of the radioactive nuclide. The results show that Fe2O3 is inert during the hydration reaction. It slows down the hydration reaction and lowers the heat release rate of the MKPC system, leading to a 3°C-5°C drop in the mixture temperature during hydration. Early comprehensive strength of Fe2O3 containing samples decreased slightly while the long-term strength remained unchanged. For the sintering process, Fe2O3 played a positive role, lowering the melting point and aiding the formation of ceramic structure. CsFe(PO4)2, or CsFePO4, was generated by sintering at 900°C. These products together with the ceramic structure and absorption benefit the immobilization of Cs+. The optimal sintering temperature for heat treatment is 900°C; it makes the solidification form a fired ceramic-like structure.

Leaching pattern of phosphate glass fertilizers with different compositions under Soxhlet distillation conditions

“…It is well known the water durability of phosphate glasses is improved by adding of one or more of intermediate divalent metal oxides (MO, M= Zn and/or others) [33][34][35][36] or intermediate trivalent metal oxides (M* 2 O 3 , M*= Fe and/ or others) [37][38][39][40] to P 2 O 5 network, which results in the formation of M-O-P or M*-O-P bonds leading to increase the degree of condensation of the phosphate network. Fe 2 O 3 has special features, i.e., mechanically iron ions, Fe 3+ , can enter into the phosphate network structure replacing P 5+ because of its stronger electropositivity, thus forming a Fe-O-P bond which strengthens the cross-bonding between the polyphosphate chains, which has better water resistance [37][38][39][40][41][42]. Furthermore, due to the smaller radius, the iron ion (Fe 3+ /Fe 2+ ) can hinder the larger water molecule from passing through the glass structure, therefore, significantly improving the chemical durability of the glass matrix.…”

Preparation and Properties of Magnesium Phosphate Cement-Based Fire Retardant Coating for Steel

“…When the temperature was between 800 and 900 • C the residual strength was lowest, but more than 30% of the original [23]. When the temperature was above 900 • C, the residual strength increased, and even the strength was higher than the original strength when the temperature was above 1000 • C due to some ceramic formation in the coating [32]. During the fire test, the mineral compositions of the hardened MPC coating changed not only with the time fired, but also with the position.…”

Preparation of Magnesium Oxide and Potassium Magnesium Phosphate Cement From Lithium-Extracting Magnesium Slag

“…Compared with other cement materials, MKPC has the advantages of a short hardening time [2], high early strength [3], good cohesion [4][5], and low drying shrinkage [6]. MKPC has been widely used in engineering for rapid repairs [7], reinforcement, refractory material applications, curing of harmful substances [8] and bio-adhesives [9], and national defence engineering construction. However, due to the high energy consumption and cost of dead-burned magnesia powder, the uneven distribution of magnesite resources [10], and rapid acid-base reaction rate with the phosphate solution, the addition of expensive retarders to slow down the process is necessary owing to the rapid solidification rate of the slurry [11].…”