Study of Co-crystallization of Neodymium and Strontium Sulfates in the Absence of Potassium Ions

Co-crystallization of neodymium and strontium sulfates was studied using powder X-ray diffraction, energy dispersive X-ray spectroscopy, and microscopy. High absorption activity of crystalline matrices, trigonal SrSO₄∙0.5H₂O and dehydrated monoclinic SrSO₄, towards the isomorphic heterovalent inclusion of Nd³⁺ ions to give solid solutions stable in the absence of water was established for the first time. The unit cell parameters and the structural similarity of the solid solutions were determined. In a moist environment, solid solutions degrade within 6–10 h to give stable poorly soluble single compounds Nd₂(SO₄)₃∙8H₂O and orthorhombic SrSO₄.