The dissolution–precipitation mechanism has been suggested for the immobilization of aqueous lead cation with calcium hydroxyapatite (Ca10(PO4)6(OH)2; CaHAp). Here Na2HPO4, K2HPO4, MgHPO4 and CaHPO4 were employed for CaHAp. These hydrogenphosphates could favorably remove Pb2+, Cd2+, Co2+ and Cu2+ from aqueous solution for 0.5 h at 293 K. The removability of those hydrogenphosphates was evidently greater than that of CaHAp and seemed to be dependent on solubility of those hydrogenphosphates and the hydration enthalpy of those heavy metal cations. The structures of phosphates recovered after immobilization of Pb2+, Cd2+, and Co2+ were strongly influenced by the pH in the aqueous solution, while the structures after immobilization of Cu2+ for 0.5 and 12 h were amorphous compound and Cu2(PO4)(OH), respectively. The employment of solid state 31P MAS NMR and XRD revealed that the amorphous compound was also Cu2(PO4)(OH). The removability found with those hydrogenphosphates was also observed in the immobilization of Pb2+ with MgSO4 and CaSO4.
羟基磷灰石钙(Ca10(PO4)6(OH)2;CaHAp)固定
水溶液中
铅阳离子的溶解沉淀机制已被提出。这里的 CaHAp 使用了 Na2HPO4、K2HPO4、MgHPO4 和 CaHPO4。这些氢
磷酸盐在 293 K 下 0.5 小时可从
水溶液中去除 Pb2+、Cd2+、Co2+ 和 Cu2+。这些氢
磷酸盐的去除率明显高于 CaHAp,而且似乎取决于这些氢
磷酸盐的溶解度和这些重
金属阳离子的
水合焓。固定 Pb2+、Cd2+ 和 Co2+ 后回收的
磷酸盐结构受
水溶液 pH 值的影响很大,而固定 Cu2+ 0.5 和 12 h 后的结构分别为无定形化合物和 Cu2(PO4)(OH)。固态 31P MAS NMR 和 XRD 显示,无定形化合物也是 Cu2(PO4)(OH)。在用 MgSO4 和 CaSO4 固定 Pb2+ 时,也观察到了这些
磷酸盐的可去除性。