The Use of MgO Obtained from Serpentinite in the Synthesis of a Magnesium Potassium Phosphate Matrix for Radioactive Waste Immobilization

Svetlana A Kulikova,Kseniya Y Belova,Magomet A Konov,Rustam K Dzhenloda,Boris F Myasoedov,Ruslan K Khamizov,Natal’Ya S Vlasovskikh,Sergey E Vinokurov

doi:10.3390/app11010220

Abstract

Magnesium oxide is a necessary binding agent for the synthesis of a magnesium potassium phosphate (MPP) matrix based on MgKPO4 × 6H2O, which is promising for the solidification of radioactive waste (RW) on an industrial scale. The performed research is devoted to finding a cost-effective approach to the synthesis of MPP matrix by using MgO with an optimal ratio of the quality of the binding agent and the cost of its production. A method for obtaining MgO from the widely available natural mineral serpentinite was proposed. The phase composition, particle morphology, and granulometric composition of MgO were studied. It was found that the obtained MgO sample, in addition to the target periclase phase, also contains impurities of brucite and hydromagnesite; however, after calcining at 1300 °C for 3 h, MgO transforms into a monophase state with a periclase structure with an average crystallite size of 62 nm. The aggregate size of the calcined MgO powder in an aqueous medium was about 55 μm (about 30 μm after ultrasonic dispersion), and the specific surface area was 5.4 m2/g. This powder was used to prepare samples of the MPP matrix, the compressive strength of which was about 6 MPa. The high hydrolytic stability of the MPP matrix was shown: the differential leaching rate of magnesium, potassium, and phosphorus from the sample on the 91st day of its contact with water does not exceed 1.6 × 10−5, 4.7 × 10−4 и 8.9 × 10−5 g/(cm2·day), respectively. Thus, it was confirmed that the obtained MPP matrix possesses the necessary quality indicators for RW immobilization.

Highlights

Industrial activities associated with the production and use of materials containing radioactive substances inevitably lead to the generation of radioactive waste (RW) of various activity levels
We showed in [1,2,3,4,5] that magnesium potassium phosphate (MPP) matrix MgKPO4 × 6H2O is an effective and multipurpose mineral-like material for immobilization of different RW, and it possesses the number of benefits over cement and glass-like compounds
In contrast to the complex chemical formulas used in this work, we introduced simplifications that make it possible to better understand the discussed cyclic process

Summary

Introduction

Industrial activities associated with the production and use of materials containing radioactive substances inevitably lead to the generation of radioactive waste (RW) of various activity levels. The largest amount of RW is generated during the operation of nuclear fuel cycle enterprises and exploitation of nuclear power reactors of various purposes. In some countries, including the USA, Sweden, and Finland, spent nuclear fuel (SNF) of nuclear power reactors is classified as RW and is stored without reprocessing. In other countries, including Russia, France, and Japan, SNF is subject to reprocessing for the purpose of extraction of uranium and plutonium for reuse, as well as a number of valuable components from fission products and actinides, and the residue part is considered to be RW. In case of uncontrolled spread of radioactive substances, they have a negative impact on humans and environmental objects. For controlled storage and/or final disposal of RW, it should be converted to a stable solidified form using stable matrices

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