Miho Uchida

New method of treating dilute mineral acids using magnesium–aluminum oxide

Mineral acids, such as H(3)PO(4), H(2)SO(4), HCl, and HNO(3,) were treated with magnesium-aluminum oxide (Mg-Al oxide), which behaved as a neutralizer and fixative of anions. Anion removal increased with increasing Mg-Al oxide quantity, time, Mg/Al molar ratio, and initial acid concentration. Up to 95% removal of anions was achieved in 0.5 N acids using a stoichiometric quantity of Mg(0.80)Al(0.20)O(1.10) for H(3)PO(4), 1.75 stoichiometric quantities for H(2)SO(4), or 2.5 stoichiometric quantities for HCl or HNO(3) at 20 degrees C over a period of 6 h. The final solutions were found to have a pH in the range of 8-12. Selectivity of acid removal was found to follow the following order: H(3)PO(4) > H(2)SO(4) > HCl > HNO(3). The equivalent of acid removal per 1 g of Mg-Al oxide decreased as the Mg/Al molar ratio of Mg-Al oxide increased.

The simultaneous removal of calcium and chloride ions from calcium chloride solution using magnesium-aluminum oxide.

We investigated the removal of Ca(2+) and Cl(-) from CaCl(2) solution at 20-60 degrees C, using magnesium-aluminum oxide, Mg(0.80)Al(0.20)O(1.10), prepared by the thermal decomposition of a hydrotalcite-like compound, Mg(0.80)Al(0.20)(OH)(2)(CO(3))(0.10).0.78 H(2)O. The degree of Ca(2+) and Cl(-) removal from the solution increased with increasing initial CaCl(2) concentration, temperature, and quantity of Mg(0.80)Al(0.20)O(1.10) added. When Mg(0.80)Al(0.20)O(1.10) was added to 0.25 M CaCl(2) solution in a Mg(0.80)Al(0.20)O(1.10)/CaCl(2) molar ratio of 20, the degree of Ca(2+) and Cl(-) removal from the solution at 60 degrees C after 0.5 h was 93.0% and 98.2%, respectively. These results reveal that Mg(0.80)Al(0.20)O(1.10) has the capacity to remove Ca(2+) and Cl(-) simultaneously from aqueous solution.

Synthesis of Hydrotalcite from Seawater and Its Application to Phosphorus Removal

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.

Polymerase chain reaction-denaturing gradient gel electrophoresis analysis of microbial community structure in landfill leachate.

The structures of microbial communities in water samples obtained from a landfill site that had been a source of environmental pollution by emitting hydrogen sulfide were elucidated using polymerase chain reaction-denaturing gradient gel electrophoresis. The microbial communities, which consisted of a limited number of major microorganisms, were stable for several months. Microorganisms capable of degrading such chemical compounds as 2-hydroxybenzothiazole and bisphenol A were observed in landfill leachate. Microorganisms responsible for the production of hydrogen sulfide were not the primary microbes detected, even in water samples obtained from the site of gas emission.

Decomposition of 2-bromophenol in NaOH solution at high temperature

2-Bromophenol was reacted in aqueous sodium hydroxide at 200-250 degrees C. The decomposition rate was remarkably faster at 250 degrees C than at 225 or 200 degrees C, and the percentage debromination reached almost 100% in 1M NaOH at 250 degrees C for 4h. The percentage increased with NaOH concentration over the range 0.1-1M. Aliphatic compounds, such as 2,2-dimethoxypropane and 4-hydroxy-4-methyl-2-pentanone, and aromatic compounds, such as phenol and cresol, were formed as decomposition products. The formation of carboxylic acids, such as formic, acetic, and propionic acids, in the presence of oxygen was also confirmed. Under a nitrogen atmosphere, the oxidation caused by oxygen in solution was suppressed and hydrolysis became the dominant reaction in the decomposition of 2-bromophenol.

Decomposition of nitrate by in situ buff abrasion of lead plate

Abstract A new approach to the decomposition of nitrate ion using Pb metal has been developed. Removal of the oxide layer formed on the surface of Pb plate and the production of Pb powder have been achieved by in situ abrasion of Pb plate in NH 4 NO 3 solution with an abrasive buff. NO 3 − was reduced to NO 2 − at initial concentrations of NH 4 NO 3 in the range 0.01–0.2 M, rotational speed of buff, 100–800 rpm and temperature, 25–80°C. Complete reduction of NO 3 − in 0.05–0.2 M NH 4 NO 3 solution was achieved at 80°C within 4 h. As the temperature increases, the reduction rate of NO 3 − to NO 2 − increases abruptly. The reduction rate increases gradually with rotational speed. The formation of NO 2 − is almost independent of the initial NO 3 − concentration. Reduction of NO 3 − to NO 2 − is related to corrosion of Pb in NH 4 NO 3 solution.

Potentiometric Determination of the First Hydrolysis Constant of Gallium(III) in NaCl Solution to 100°C

The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg−1 NaCl over a range of low pH was measured potentiometrically with a hydrogen ion concentration cell at temperatures from 25 to 100°C at 25°C intervals. Potentials at temperatures above 100°C increased gradually because of further hydrolysis of the gallium(III) ion, followed by precipitation. The results were treated with a nonlinear least-squares computer program to determine the equilibrium constants for gallium(III)–hydroxo complexes using the Debye–Hückel equation. The log K (mol-kg−1) values of the first hydrolysis constant for the reaction, Ga3+ + H2O ⇆ GaOH2+ + H+ were −2.85 ± 0.03 at 25°C, −2.36 ± 0.03 at 50°C, −1.98 ± 0.01 at 75°C, and −1.45 ± 0.02 at 100°C. The computed standard enthalpy and entropy changes for the hydrolysis reaction are presented over the range of experimental temperatures.

Morphology of barium sulfate synthesized with barium(II)–aminocarboxylate chelating precursors

The morphology of barium sulfate (BaSO4), synthesized using the hydrothermal reaction of BaII–aminocarboxylate chelating precursors, was investigated. The precursors ethylenediaminetetraacetic acid (EDTA), bis(2-aminoethyl)ethyleneglycoltetraacetic acid (EGTA) and nitrilotriacetic acid (NTA) were dissolved by heating, resulting in the formation of BaSO4 with rod-like, rhombohedral and spindle-shaped morphologies, respectively. Changing the chelating reagent resulted in the formation of BaSO4 with differing morphologies. There was a correlation between the morphology of BaSO4 and the dissociation constant of the BaII–aminocarboxylic acid complexes. When the dissociation constant was small, BaSO4 formed rhombohedral morphologies, when it was large, spindle-shaped morphologies were formed. N 1s XPS measurements indicated that the aminocarboxylic acid was adsorbed on the surface of the precipitated particles. Comparison of the peak intensity X-ray diffraction patterns of EDTA and EGTA showed growth of the {101} face when EDTA was used.

Solubility of gallium(III) oxyhydroxide in aqueous NaCl solutions at 100°C

The hydrolysis-precipitation equilibrium reaction of aqueous gallium(III) solution was investigated in 0–3 mol-kg-1 NaCl media at low pH at 100°C using a pressure-tight glass vessel. All precipitates were identified as GaOOH. The results were analyzed with a nonlinear least-squares computer program to obtain the solubility product Kso for gallium(III) oxyhydroxide using a single-parameter type of Debye-Hückel equation. The value of log Kso for GaOOH(s) + 3H+ ⇆ Ga3+ + 2H2O was -0.60 at 100°C. The solubility product calculated from thermodynamic data was compared with the experimental result.

Synthesis of Hydrotalcite using Magnesium from Seawater and Dolomite

Abstract Three methods of synthesizing hydrotalcite(HT) have been developed using magnesium from seawater and dolomite(MgCa(CO3)2). In the first process, 1.0M Na2CO3solution was added to calcium ion free artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 2.0∼3.7 until a pH of 10 was obtained. The solution was then continuously stirred for Ih at 60°C. CO3 2--HT was precipitated as a single phase, and the initial Mg/Al molar ratio, which each recovery of Mg2+and Al3+ from the solution was above 98%, was 2.0–2.3. In the second process, a Ca(OH)2 slurry was added to artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 1.0∼5.0 until a pH of 10.5 was obtained, and then was stirred for Ih at 60°C. HT was also precipitated as a single phase with initial Mg/Al molar ratio 2.0∼4.0. The initial Mg/Al molar ratio, which each recovery of Mg2+ and Al3+ from the solution was above 98%, was 2.2∼3.3, but SO4 2- and Cl− were contained in the precipitated HT. When HT was produced using initial Mg/Al molar ratio of 3.0 at 25°C, SO4 2- and Cl−in the HT were ion-exchanged with CO3 2- in a 0.05M Na2CO3solution for 24h at 25°C, and SO4 2- and Cl− content of the HT were decreased to 0.5 and 0.05wt%, respectively. In the third process, dolomite calcined at 1000°C was added to an AlCl3 solution with an initial Mg/Al molar ratio of 1.0∼2.0, and the solution was stirred for 1∼4h at 25∼90°C. HT was precipitated with the smallest amount of MgO and Mg(OH)2 when the initial Mg/Al molar ratio was 1.5 and the solution was stirred for 4h at 90°C.