Study On The Effect Of Main Ions In High-level Liquid Waste On The Solidification Properties Of Magnesium Phosphate Cement

Magnesium potassium phosphate cement?MKPC?,also known as chemically bonded phosphate ceramic,is a new type of fast-hardening and high-strength composite cementitious material prepared by MgO,phosphate and retarder in a particular proportion.MKPC has the advantages of fast hardening,high early strength,wide molding temperature range and excellent high-temperature resistance,so it has made good progress in the field of solidification high-level radioactive liquid wastes and aroused the research interest of the majority of scholars,but the solidification mechanism of high-level radioactive liquid waste is not evident.Moreover,there are many ions in the high-level radioactive liquid wastes,such as NO₃^-,K⁺,Na⁺,Ni²⁺,Al³⁺,Fe³⁺,Cs⁺and Sr²⁺,the effects of these ions on the hydration process and hydration products of MKPC are not clear;to clarify the impact of a single ion in the high-level radioactive liquid wastes on the solidification performance of MKPC,which is very important to realize the solidification of MKPC in high-level radioactive liquid wastes.Therefore,this study takes MKPC as the research object,adding NO₃^-,K⁺,Na⁺,Ni²⁺,Al³⁺,Fe³⁺,Cs^+,and Sr²⁺inorganic ions respectively,through the analysis and test of compressive strength,pH value,setting time,phase composition?XRD?,microstructure?SEM?,micro-zone element composition?EDS?,hydration product amount?TG?and ion leaching experiment.The effects of main ions in high-level radioactive liquid wastes on the hydration process and hydration products of MKPC were studied to provide a theoretical basis for solidifying high-level radioactive liquid wastes with MKPC.The results show that different ions will participate in the hydration process of MKPC,but the influence is different.The main hydration products of MKPC containing with Sr²⁺,Cs⁺,Fe³⁺,Ni²⁺,Al³⁺,?NO₃^-,K⁺,Na⁺?ions are still K-struvite and unreacted magnesium oxide.The addition of cations will reduce the amount of K-struvite,the hydration product of MKPC.Sr²⁺,Cs⁺,Fe³⁺,Ni²⁺,Al³⁺,?NO₃^-,K⁺,Na⁺?ions also reduce the crystallinity of microstructure of MKPC.The addition of various ions will also increase the porosity of MKPC,which has a more obvious effect on the samples with larger M/P.Simulated high-level radioactive liquid wastes can reduce the compressive strength and increase the porosity of MKPC,but the main hydration products are still K-struvite and magnesia.With the increase of the content of high-level radioactive liquid wastes,the overall strength of MKPC decreased.The addition of borax is not conducive to the compressive strength of the matrix and increases the porosity of the solidified form,which is not conducive to the solidification performance of the solidified form.Although the leaching concentration of each ion will increase with the increase of ion content and sample M/P,compared with the ion content,the ion leaching concentration is very low.Therefore,MKPC has a good solidification effect on the above ions.In summary,when using MKPC to solidify high-level radioactive liquid wastes,the effects of various ions on the hydration and hardening of MKPC must be comprehensively considered,so as to adjust the raw materials ratio and process to achieve the goal of emergency solidification of high-level radioactive liquid wastes.