Sayo Moriyama

Uptake of Sr 2+ and Co 2+ into biogenic hydroxyapatite: implications for biomineral ion exchange synthesis

Biomineral hydroxyapatite (Bio-HAp) produced by Serratia sp. has the potential to be a suitable material for the remediation of metal contaminated waters and as a radionuclide waste storage material. Varying the Bio-HAp manufacturing method was found to influence hydroxyapatite (HAp) properties and consequently the uptake of Sr(2+) and Co(2+). All the Bio-HAp tested in this study were more efficient than the commercially available hydroxyapatite (Com-HAp) for Sr(2+) and Co(2+) uptake. For Bio-HAp the uptake for Sr(2+) and Co(2+) ranged from 24 to 39 and 29 to 78 mmol per 100 g, respectively. Whereas, the uptake of Sr(2+) and Co(2+) by Com-HAp ranged from 3 to 11 and 4 to 18 mmol per 100 g, respectively. Properties that increased metal uptake were smaller crystallite size (<40 nm) and higher surface area (>70 m(2) g(-1)). Organic content which influences the structure (e.g., crystallite arrangement, size and surface area) and composition of Bio-HAp was also found to be important in Sr(2+) and Co(2+) uptake. Overall, Bio-HAp shows promise for the remediation of aqueous metal waste especially since Bio-HAp can be synthesized for optimal metal uptake properties.

Sorption characteristics of fluoride on to magnesium oxide-rich phases calcined at different temperatures.

The effect of calcination temperature during production of magnesium oxide-rich phases from MgCO(3) on the sorption of F(-) ions in the aqueous phase has been investigated. Magnesium oxide-rich phases were formed by calcination at over 873 K for 1h. Higher calcination temperatures produced more crystalline MgO with smaller specific surface area and provided larger values of the total basicity per unit surface area. The higher calcination temperatures lead to slower F(-) removal rate, and lower equilibrium F(-) concentrations, when the equilibrium F(-) concentrations are less than 1 mmol dm(-3). Larger total basicity per unit surface area made the reactivity with F(-) ions in aqueous phase more feasible, resulting in a greater degree of F(-) sorption. For equilibrium F(-) concentrations more than 1 mmol dm(-3), lower calcination temperatures favored the co-precipitation of F(-) with Mg(OH)(2), probably leading to the formation of Mg(OH)(2-x)F(x), and the achievement of larger sorption density. This is the first paper which describes the relationship between the solid base characteristics obtained by CO(2)-TPD for MgO with different calcination temperatures as a function of the reactivity of F(-) sorption in the aqueous phase.

Effect of calcination temperature on Mg–Al bimetallic oxides as sorbents for the removal of F− in aqueous solutions

Bimetallic oxides were synthesized from hydrotalcite using increasing calcination temperatures (873, 1073, 1273 K). These bimetallic oxides were fully characterized and the sorption density of F(-) was investigated. X-ray diffraction patterns for the produced bimetallic oxides showed that MgO was the primary phase within the range of investigated calcination temperatures, but MgO crystallinity increased with calcination temperature and an additional MgAl2O4 phase was formed. In the process of F(-) sorption, the bimetallic oxides were primarily transformed into hydrotalcite with intercalation of F(-). The Higher calcination temperature increased the MgAl2O4 phase, which did not contribute to the immobilization of F(-). These findings show that optimizing the calcination temperature can be used to maximize the sorption density of this material for F(-) removal.

Effect of saw dust on borate removal from groundwater in bench-scale simulation of permeable reactive barriers including magnesium oxide

Effective immobilization of boron in groundwater is a major challenge. Permeable reactive barrier (PRB) column tests for removal of borate have been investigated using MgO agglomerates as the primary reactive material over 40 weeks. Additionally, saw dust was also blended with MgO agglomerates to facilitate for borate removal in this system. Boron accumulation was more than 1.6 times greater in the presence of saw dust, although MgO alone performed well. Increased boron accumulation in the presence of saw dust was primarily due to higher porosity of the PRB column, decreasing the impact of secondary Mg(OH)(2) passivating layers and leaving more reactive sites on MgO agglomerates. In addition, Mg(2+) ions released from MgO agglomerates are complexed with carboxylic acids leached from saw dusts. This sequestration prevents the formation of bulky Mg(OH)(2) which is an ineffective sorbent for borate and covers the surfaces and passivating reactive sites on the MgO agglomerates. The morphologies of Mg(OH)(2) precipitated in the PRB column were also significantly affected by the presence of saw dust, with crystallization of needle-like particles of Mg(OH)(2) was prevented by Mg(2+) ions-organic ligand complexation.