Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux

Type de document

COMMUNICATION AVEC ACTES INTERNATIONAL (ACTI)

Langue

anglais

Auteur

LE ROUZIC ; CHAUSSADENT ; STEFAN ; PLATRET

Résumé / Abstract

Magnesium phosphate cements can be used as an alternative of Portland cements for the stabilization/solidification (S/S) process of specific wastes like mercury, lead, … These cements are based on the reaction between magnesium oxide (MgO) and monopotassium phosphate (KH2PO4) mixed with water which leads to the formation of the solid skeleton of the matrix: MgO + KH2PO4 + 5H2O  MgKPO4.6H2O. The development of k-struvite crystals (MgKPO4.6H2O) leads to the setting of these cements which have interesting properties for the stabilization/solidification (S/S) of nuclear wastes: good chemical stability of the waste form, fast setting, low permeability, rapid compressive strength development. However under certain conditions newberyite (MgHPO4.3H2O), which has low strength and low stability in water, forms instead of k-struvite. In this framework, the influences of pH and of the species in solution on the precipitation of k-struvite are studied. From pH and conductivity measurements of an MgO + KH2PO4 solution, it can be assumed that the k-struvite precipitation involves a precipitation and dissolution of an intermediate product. To determine the pH conditions and the nature of the product formed, precipitations at different pH are conducted. Calculations based on supersaturation conditions confirm the results observed during precipitation tests. First newberyite (MgHPO4.3H2O) is formed, then with the pH increasing, newberyite is dissolved and k-struvite will be able to crystallize. A k-struvite formation mechanism is proposed.