Patent Number: 043292488
Section: abstract

A process for immobilizing high level waste (HLW) sludge containing aluminium and/or iron compounds which comprises the steps of:. (1) mixing the sludge with a mixture of oxides, the oxides in said mixture and the relative proportions thereof being selected so as to form a mixture when heated at temperatures between 800.degree. and 1400.degree. C. crystallizes to produce a mineral assemblage containing (i) crystals capable of providing lattice sites in which the fission product and actinide elements of said HLW sludge are securely bound, and (ii) crystals of at least one inert phase containing excess aluminium and/or iron, said crystals belonging to or possessing crystal structures closely related to crystals belonging to mineral classes which are resistant to leaching and alteration in appropriate geologic environments; and PA0 (2) heating and then cooling said mixture under reducing conditions so as to cause crystallization of the mixture to a mineral assemblage having the fission product and actinide elements of said HLW sludge incorporated as solid solutions within the crystals thereof, and the excess aluminium and/or iron crystallized in at least one inert phase.. A mineral assemblage containing immobilized HLW sludge containing aluminium and/or iron compounds incorporated within the crystals thereof is also disclosed.