It is a well-known fact that many inorganic species that may be present as a component of a complex aqueous waste can have an adverse effect upon the set of cements and subsequent properties of a final waste form product. Chemical species such as sulfates, aluminates, borates, phosphates, and zinc, to namea few, especially when present in combination, can result in false sets, flash sets, and expansive mineral phases along with many other unwanted changes in physical properties.
Generally, the approach is to adjust the type of additives present in a waste form formulation to compensate or sometimes to rely upon raw waste dilution to minimize or mitigate potential problems. Another approach which is discussed in this paper, in addition to a comprehensive literature review, is based upon an understanding of the chemistry of the waste solution and its components: that is, we rely upon pretreatment of the waste solution to prevent interactions during or after solidification. Various types of precipitation options are available for the removal of certain waste species, or we may simply alter them to a stable, more insoluble form. Undesirable reactions in the cementitious solid phase, as well as some of the various waste pretreatment options which are available, are discussed.