The Chemical Stability Of Neodymium-Doped Titanate Composite Minerals Waste Form Under THMC

The neodymium-doped titanate composite minerals were synthesized by solid-state reaction method using the natural of zirconite(ZrSiO4), CaCO3, TiO2, Nd2O3,Al2O3as raw materials. The high density neodymium-doped titanate composite minerals waste form were synthesized by hot-pressing sintering at lower temperature. The better formula, the better hot-pressing sintering condition and the chemical stability of the titanate composite minerals waste form were n(XRD), scanning electric microscopy(SEM), back scattering(BSE), energy-dispersive spectroscopy(EDS), inductively coupled plasma (ICP) and inductively coupled plasma mass spectrometry(ICP-MS) etc. The results indicated that the high purity titanate composite minerals solidification could be synthesized at1230℃holding30min; the better formula was adding10%silica for displacement; the better hot-pressing sintering condition of Nd-doped composite minerals was1130℃holding2h under30MPa and its relative density was more than99%.With reference to the MCC-1static leaching test method, using water kettle polyure leaching device to simulate the deep geological disposal of the environment. The neodymium-doped titanate Synroc had a good chemical stability; Neodymium, zirconium, titanium had good chemical stability; calcium, silicon, aluminum had good chemical stability; element chemical stability order in the neodymium-doped titanate Synroc at90℃and pH=7was silicon<calcium<aluminum<titanium<(neodymium, zirconium); the element chemical stability order in the neodymium-doped titanate Synroc at200℃and pH=7was aluminum<(calcium, silicon)<titanium<(neodymium, zirconium); the leaching rate of the42th day of neodymium was less than2.68×10-12m·d-1and the normalized leaching rate was less than1.09×10-5g·m-2·d-1; temperature had little influence on the immobilization for neodymium and the better chemical stability condition was at90℃; the pH values had influence on the immobilization for neodymium, the best chemical stability in weak alkaline solution (pH=9), better in neutral aqueous solution, worse in weak acid aqueous solution; the pH values had no influence on the immobilization for titanium, zirconium, silicon and had little influence on the immobilization for calcium and had much influence on the immobilization for aluminum; temperature had no influence on the immobilization for titanium and had certain influence on the immobilization for zirconium and had much influence on the immobilization for calcium, aluminum, silicon; different solid solution mechanism had little influence on the immobilization.