Abstract: This invention relates to the treatment of contaminated materials including soils and solids to stabilize and reduce the mobility of heavy metal contaminated materials. Compositions and processes are disclosed for encapsulating and/or complexing certain heavy metals to render waste non-hazardous. Preferred treatment compositions include mixtures of monoammonium phosphate and bed ash which includes among other components, lime. The bed ash typically comprises lime, silicon dioxide, aluminum oxide, sulfur, and may comprise additional components such as, for example, magnesium oxide, and iron oxide. Processes are disclosed for using the treatment compositions at various application amounts, including relatively low application amounts, such as an amount of 5% by weight, to treat waste such as heavy metal contaminated soil to reduce the levels of certain heavy metals, and, in particular barium, to acceptable limits.