In the Purex process, a solvent extraction method of nuclear fuel reprocessing, a stable emulsion called crud forms at the interface between the oil and water phases. Crud is an emulsion stabilized by finely dispersed solids. Insoluble residues and precipitates of zirconium and radiation-degraded products of tributyl phosphate (TBP) are key materials in crud formation. Cruds formed by precipitates of zirconium and TBP degradation products, such as di-n-butyl phosphate (HDBP), mono-n-butyl phosphate (H2MBP), and phosphoric acid (H3PO4) are studied. Experimental results show that the precipitate of zirconium and HDBP is not effective in stabilizing emulsions. However, the refractory complex of zirconium and H3PO4 is an important material for stabilizing an oil-in-water emulsion in a solution with or without uranium. Moreover, it is shown that the complex of zirconium and H2MBP has a significant role in stabilizing a water-in-oil emulsion, especially when uranium is also present.