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In this study, we confirmed that the characteristics of anion intercalation into the interlayer of a hydrotalcite-like compound (HT) during synthesis are similar to those of the anion-exchange reaction of HTs as well as the reconstruction reaction of HTs from Mg-Al oxide. We demonstrated that (i) Cl-, which has a higher charge density than NO3-, more easily reacted with Mg and Al species to form HT structure, resulting in greater intercalation of Cl- into the HT interlayer; and (ii) for HTs with lower Mg : Al molar ratios, OH-, which has a higher charge density than Cl- and NO3-, was more likely to interact with Mg and Al species to form HT structure, blocking the intercalation of Cl- and NO3-. Furthermore, we showed that high concentrations of Cl- and NO3- in solution regulated their intercalation into the HT interlayer. The high activity of Cl- and NO3- in solution would facilitate the anions' reactions with Mg and Al species to form HTs, resulting in a high degree of anion intercalation into the interlayer of HTs. [ABSTRACT FROM AUTHOR]

Magnesium—aluminum oxide (Mg—Al oxide), which was prepared by the thermal decomposition of a hydrotal-cite-like compound, was found to take up fluoride and borate ions in low concentrations in aqueous solution. The degree of fluoride and borate removal increased with the quantity of Mg—Al oxide and temperature. When Mg—Al oxide with a Mg/Al molar ratio of 4.0 was added to 1 mM NaF or H3BO3 solution at five times the stoichiometric amount, the degree of fluoride and borate removal at 60 °C for 1 h reached 92.8 and 95.7%, respectively. The fluoride and borate concentrations decreased from 20 and 10 mg L-1 to 1.4 and 0.5 mg L-1, respectively. Borate was thought to be removed from the solution via combination of the Mg—Al oxide and orthoborate ion, i.e., H2BO3- produced with increasing pH. The fluoride and borate removal reactions could be described as first-order for the fluoride and borate concentrations. The apparent activation energies for the fluoride and borate removal were 33.8 and 51.2 kJ mol-1, respectively, indicating that the reaction proceeded under chemical reaction control. The apparent activation energy for borate removal was higher than that for fluoride removal, indicating that the combination of H2BO3- with Mg—Al oxide was more difficult than that of the fluoride ion. This was attributable to the lower charge density of H2BO3- compared to the fluoride ion. [ABSTRACT FROM AUTHOR]

To reduce the generation of hydrogen sulfide gas from sulfate ions, we synthesized a layered double hydroxide hydrotalcite-like compound intercalated with chloride ions in the interlayer (HT-Cl) using a coprecipitation reaction. The resultant HT-Cl material had a Mg/Al molar ratio of approximately 2, and the molar fraction of the chloride ions on the intercalated anion layer of the HT was 0.90. A higher molar fraction of chloride ions can be inserted into the interlayers of the HT by increasing the initial concentration ratio of chloride ions to aluminum ions [Cl−]0/[Al3+]0 in the solution. Approximately 98% of the sulfate ions in the solution were removed within 10min after adding 1.12 times the stoichiometric quantity of synthesized HT-Cl, which contained a Mg/Al molar ratio of 2 equal to a solution containing a 12mM calcium sulfate solution. [Copyright &y& Elsevier]

A new method of supplying radical species to aqueous solutions using a hydrogen-oxygen flame is investigated. When a hydrogen-oxygen flame is directed on the surface of an aqueous solution, hydroxyl radicals (•OH) produced in the flame are extracted into the aqueous phase. The presence of •OH in the aqueous solution was confirmed by electron paramagnetic resonance with spin trapping using 5,5-dimethyl-1 -pyrroline-N-oxide. The extraction of •OH into the aqueous solution was monitored using a quantitative analysis of hydrogen peroxide (H2O2). The effects of the hydrogen and oxygen gas flow rates, hydrogen/oxygen ratio, and atmosphere on H2O2 formation were studied. When the hydrogen-oxygen flame blew on a phosphate buffer solution (pH 6.7) under an Ar atmosphere, the concentration of H2O2 increased with the blowing time of the flame and the flow rate of hydrogen gas. Under air, nitrate and nitrite ions were formed in the aqueous phase in addition to H2O2, and the H2O2 concentration was lower than that under argon. The application of this new method to an aqueous solution of Cu(II)-ethylenediaminetetraacetic acid (EDTA) caused a remarkable decrease in the concentration of Cu(II)-EDTA and total organic carbon. [ABSTRACT FROM AUTHOR]

10.0 wt% milk of lime was added to seawater containing AlCl 3 at Mg/Al molar ratio of 3.0 until pH 10.5 with stirring, and kept at 25°C for 1 h. Hydrotalcite (HT) was precipitated as a single phase, and Mg 2+ and Al 3+ were quantitatively precipitated. The chemical composition was [Mg 0.75 Al 0.25 (OH) 2 ][(SO 4 ) 0.06 (Cl) 0.02 (OH) 0.11 *]·0.27H 2 O* (*Balance). A 100 mg-P/L Na 2 HPO 4 solution and the HT were shaken at 25°C. Phosphate removal increased with increasing time and the HT quantity, and was the highest at pH 7-9. Phosphate ion could be quantitatively removed, adding 8 times the stoichiometric quantity of the HT at pH 8.7 for 6 h. [ABSTRACT FROM AUTHOR]

Magnesium–aluminum oxide (Mg–Al oxide) prepared by the thermal decomposition of a hydrotalcite-like compound was found to have potential for treating NaBF4 wastewater. The Mg–Al oxide removed the and F− and H3BO3 from the NaBF4 solution. With increasing Mg–Al oxide quantity and time, the concentration decreased and the degree of , F−, and boron removal increased. The decrease in the concentration resulted from uptake by the Mg–Al oxide and not hydrolysis. The Mg–Al oxide took up F− from the solution preferentially. The Mg–Al oxide also converted the H3BO3 in the aqueous solution into , which it took up. [Copyright &y& Elsevier]

Abstract: Our results demonstrate that magnesium–aluminum oxide (Mg–Al oxide) can be advantageous in treating hydrochloric acid waste at temperatures between 10 and 30°C, by acting as both a neutralizer and fixative for Cl−. The Mg–Al oxide was prepared by the thermal decomposition of a hydrotalcite-like compound. The extent of Cl− removal by Mg–Al oxide increased with increases of temperature, oxide quantity and Mg/Al molar ratio. The initial pH had little effect on Cl− removal; the pH increased rapidly from the start of the reaction and attained a nearly constant value. The reaction involved in Cl− removal from HCl by Mg–Al oxide proceeded under surface chemical reaction control, with apparent activation energy of 65.6kJmol−1. [Copyright &y& Elsevier]