The present invention relates to a method of immobilizing aqueous waste, including low level nuclear waste, by converting the waste to a solid. Solidification is accomplished with the addition of a compound having the formula Me(II)O or Me(II)(OH).sub.2 in combination with compounds of the general formula Me(II)O.R.sub.2O.sub.3, R.sub.2O.sub.3, R(OH).sub.3 or ROOH, where Me is a cation selected from the group consisting of Ca, Ba, Sr, Mn, and Zn, and R is selected from the group consisting of Al...