Synthesis, structural and leaching studies of phospho-silicates: Bi1/3M1/6Zr2(PO4)8/3(SiO4)1/3; M = Cd2+, Pb2+

Phospho-silicates compounds of zirconium, bismuth and lead or cadmium were prepared according to a sol-gel process. Lead compound crystallizes in a Nasicon type structure where bismuth and lead only occupy every second M1 site, i.e. the 3b site of R 3 space group. A leaching study at room temperature was performed in acid or basic medium. The maximum value of metal concentration is low even at low pH, and this concentration decreases rapidly when the pH increases. A surface process involving the release of metal and phosphate ions is proposed.