The casting of magnesium and potassium phosphate (KMgPO4•6H2O; K-struvite) cements becomes possible after the aqueous reaction between magnesium oxide and potassium dihydrogen phosphate. This reaction is quite exothermic and allows the resulting paste setting in just few minutes. Those cements, when are cast with magnesium oxides of high purity, are used to retain and encapsulate special residues and as repairing concrete mortar, as it is described in the bibliography. However, it is also possible formulate those cements using low grade magnesium oxides, which cost are nearly 10 or 15 times cheaper than those of high grade. The aim of this work is to evaluate the possibility of using low grade magnesium oxides (˜70% MgO), obtained from the calcinations process of natural magnesites, for KMgPO4•6H2O cement casting. The research and selection of the best formulation for obtaining that cement will be done also from the point of view of their mechanical properties as for their setting time.