The Use of MgO Obtained from Serpentinite in the Synthesis of a Magnesium Potassium Phosphate Matrix for Radioactive Waste Immobilization  
[PERSON]  
1 Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin st., 119991 Moscow, Russia; vinokurov,[EMAIL_ADDRESS] (S.E.V. ); [EMAIL_ADDRESS] (R.K.K. ); [EMAIL_ADDRESS] (K.K.B. ); [EMAIL_ADDRESS] (R.K.D. ); [EMAIL_ADDRESS] (B.F.M.) 2  
[PERSON]  
1 Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin st., 119991 Moscow, Russia; vinokurov,[EMAIL_ADDRESS] (S.E.V. ); [EMAIL_ADDRESS] (R.K.K. ); [EMAIL_ADDRESS] (R.K.D. ); [EMAIL_ADDRESS] (B.F.M.) 2  
[PERSON]  
1 Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin st., 119991 Moscow, Russia; vinokurov,[EMAIL_ADDRESS] (S.E.V. ); [EMAIL_ADDRESS] (R.K.K. ); [EMAIL_ADDRESS] (R.K.D. ); [EMAIL_ADDRESS] (B.F.M.) 2  
[PERSON]  
2  
[PERSON]  
1 Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin st., 119991 Moscow, Russia; vinokurov,[EMAIL_ADDRESS] (S.E.V. ); [EMAIL_ADDRESS] (R.K.K. ); [EMAIL_ADDRESS] (R.K.D. ); [EMAIL_ADDRESS] (B.F.M.) 2  
Footnote 2: email: k.k. 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. Therefore, solving the problem of RW management in order to ensure their reliable isolation from the human environment is key for the further development of nuclear energy and industry. For controlled storage and/or final disposal of RW, it should be converted to a stable solidified form using stable matrices. Earlier, we showed in [1; 2; 3; 4; 5] that magnesium potassium phosphate (MPP) matrix MgKPO\({}_{4}\)\(\times\) 6H\({}_{2}\)O 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. Therefore, MPP matrix was investigated for solidification of liquid intermediate level waste (ILW) [1], high level waste (HLW) [2; 3], and also RW containing radiocarbon \({}^{14}\)C [4] and spent electrolyte [5], obtained as a result of pyrochemical reprocessing of mixed nitride uranium-plutonium SNF. This matrix is obtained by the acid-base reaction (1) of magnesium oxide (MgO) with potassium dihydrogen phosphate (KH\({}_{2}\)PO\({}_{4}\)) in an aqueous solution at room temperature, and it is an analog of the natural mineral K-struvite [6]. \[\text{MgO}+\text{KH}_{2}\text{PO}_{4}+\text{5H}_{2}\text{O}\rightarrow\text{ MgKPO}_{4}\times\text{6H}_{2}\text{O} \tag{1}\]  
Magnesium oxide is a necessary binding agent for reaction (1) for the synthesis of MPP matrix; it is usually produced by calcination of carbonate minerals--magnesite (MgCO\({}_{3}\)) [7] and dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)) [8]. It is widely used to obtain the refractories in the production of steel and cement (70-80% of world consumption) in electrical engineering, agriculture, for wastewater treatment, and gas absorption. Magnesium oxide on the market with a purity of at least 99 wt% has a high cost--up to $5000 per ton. At the same time, it is obvious that for the competitiveness of the technology of RW solidification using the MPP matrix, cheaper raw materials should be used; for example, so that the cost of MgO is at the level of the cost of Portland cement ($300-400 per ton). For this reason, the aim of the study was to find a cost-effective approach to synthesizing the MPP matrix through the use of MgO with low production cost. In this regard, a natural mineral, serpentinite (Mg\({}_{3}\)Si\({}_{2}\)O\({}_{5}\)(OH)\({}_{4}\)), which contains 32-38% of MgO [9], is of special interest.