• Resources Recycling
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• v.30 no.6
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• pp.3-11
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• 2021

In this study, the effect of the solubility of ammonium metavanadate and the decomposition ratio of ammonium ions on a precipitation reaction-the precipitation of ammonium metavanadate by adding ammonium chloride to a sodium vanadate solution-was investigated. As the precipitation temperature and pH increased, the decomposition ratio of ammonium ions increased, and the decomposition ratio was greater than 81% at 45 ℃ and pH 9.3. This was approximately four times higher than that at pH 8. The result of the precipitation reaction, in view of these two factors that significantly influence the precipitation reaction, was that the precipitation yield increased as the temperature increased. However, the effect of temperature was not significant above 35 ℃. A kinetic study of the precipitation reaction revealed that the activation energy of the reaction was 42.3 kJ/mol. Therefore, considering the solubility of ammonium metavanadate, the lower the temperature, the better the vanadium recovery yield. Additionally, considering the decomposition of ammonium ions, the lower the pH of the aqueous solution, the more advantageous. However, at pH 8 or less, sodium polyvanadate is precipitated and the purity of vanadium oxide may reduce.

• Resources Recycling
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• v.29 no.5
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• pp.28-37
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• 2020

In this study, the effect of precipitation temperature, ammonium chloride amount and addition method, vanadium and sodium hydroxide content of the solution on the precipitation of ammonium metavanadate were examined by using the sodium vanadate(NaVO₃) solution in alkali region as a starting material. As the pH of solution decreased, the addition amount of ammonium chloride and the vanadium content of the solution increased, the precipitation rate of ammonium metavanadate increased. In this research condition, the basic conditions for obtaining more than 90% of precipitation yield were 10,000mg/L of vanadium content, 2equivalents of ammonium chloride addition, room temperature, and 2 hours of precipitation time. The size of precipitated particles decreased with increasing precipitation rate. Especially when liquid ammonium chloride was injected into the solution, the precipitation rate was the slowest and the particle size of the precipitate was the largest. After the primary precipitation by adding ammonium chloride as a solid, the secondary precipitation was carried out by adding new reactants. At this time, the precipitation with added ammonium chloride solid was not affected by the precipitates present in the solution. However, when liquid ammonium chloride was added, new precipitate was deposited on the surface of the precipitate present in the solution, increasing its size. Due to the difference in ammonium metavanadate solubility to temperature, the precipitation temperature at the vanadium content of 10,000mg/L in the solution affected the precipitation rate of ammonium metavanadate and the precipitation temperature did not affect the precipitation rate at a high concentration of more than 30,000mg/L vanadium content in the solution.

• Journal of the Korean Chemical Society
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• v.46 no.1
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• pp.7-13
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• 2002

Although it has been known that the magnetized water shows different physicochemical properties, the exact nature of the magnetized water is not clearly elucidated yet. We have explored the effect of magnetized water in the precipitation of salts, i.e., $BaSO_4,\;BaCO_3,\;CaCO_3$, and in the hydration hardening of gypsum plaster. The amount of salt precipitation was measured by salt filter assay in water bath, $25^{\circ}C$ and also the hydration hardening speed of gypsum plaster was measured by the Gillmore needle method at room temperature. When the salt ions were interacted with each other in 0.1 M concentration, the precipitation reactions of $BaSO_4,\;BaCO_3$, and $CaCO_3$ increased more in the magnetized water, about 3.6%, 3.8%, and 4.4%, respectively, than in the control water. And the hydration hardening speed of gypsum plaster increased more in the magnetized water than in the control water. These data suggest that the magnetized water, which is supposed to be organized by forming numerous nano/micro clusters, induces the increase of salt precipitation and also accelerates the hydration hardening speed of gypsum plaster.

• Resources Recycling
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• v.25 no.3
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• pp.63-73
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• 2016

With the purpose of concentrating the magnesium from seawater, in this study, we have conducted experiments to precipitate the magnesium using three precipitants (NaOH, cement kiln dust, and paper sludge ash), and then extract it using sulfuric acid. Results show that the precipitation and extraction performance does not depend so significantly on the kind of precipitant: for all the precipitants used, the precipitation efficiency is measured almost 100% and the extraction efficiency is in the short range of 77 - 89%. The magnesium concentration in the extract is measured 4975 - 5775 mg/L, implying that the magnesium in seawater should be 3.8 - 4.4 times concentrated through the precipitation and extraction reactions. The reaction efficiency of the industrial by-product used as a precipitant in this study is almost 100% similar to those of the other existing expensive precipitants.

• Resources Recycling
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• v.29 no.5
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• pp.48-54
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• 2020

Sulphuric acid (H₂SO₄) leaching and hydrolysis were experimented for the recovery of titanum dioxide (TiO₂) from the water-leached residue followed by soda-roasting spent SCR catalysts. Sulphuric acid leaching of Ti was carried out with leachate concentration (4~8 M) and the others were fixed (temp.: 70 ℃, leaching time: 3 hrs, slurry density: 100 g/L, stirring speed: 500 rpm). For recovering of Ti from the leaching solution, hydrolysis precipitation was conducted at 100 ℃ for 2 hours in various mixing ratio (leached solution:distilled water) of 1:9 to 5:5. The maximum leachability was reached to 95.2 % in 6 M H₂SO₄ leachate. on the other hand, the leachability of Si decreased dramatically 91.7 to 3.0 % with an increase of H₂SO₄ concentration. Hydrolysis precipitation of Ti was proceeded with leaching solution of 8 M H₂SO₄ with the lowest content of Si. The yield of precipitation increased proportionally with a dilution ratio of leaching solution. Moreover, it increased generally by adding 0.2 g TiO₂ as a precipitation seed to the diluted leaching solution. Ultimately, 99.8 % of TiO₂ can be recovered with the purity of 99.46 % from the 1:9 diluted solution.

• Korean Journal of Environmental Agriculture
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• v.12 no.1
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• pp.51-57
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• 1993

Objective of this research was to assess the influence of reaction time on the heavy metal-organic ligand complexation by employing kinetic models. Aqueous solutions of humic (HA) or fulvic acid (FA) were reacted with metal solutions with 1:1 ratio to form complexes. Efficiency of organic ligand on metal removal was determined by separating the precipitates from solution using $0.45\;{\mu}m$ filter paper. Complexation between Cu or Pb and HA or FA followed the first- or multiple first order kinetics, largely depending on metal concentration and kind of organic ligand. Amounts of precipitates were increased proportionally with reaction time but reached to quasiequilibrium where rate of precipitate formation was not varied with time. Copper-ligand complexation was, irrespective of ligand, fitted to the single first order kinetics at Cu concentrations lower than $300{\mu}M$, but this was fitted to the multiple first order kinetics at Cu concentrations higher than $300{\mu}M$. As increasing Cu concentrations, the precipitates formed more readily, judging from the increased rate constants (${\kappa}$). In the multiple first order kinetics, ${\kappa}$ was decreased as reaction steps proceeded. Most of Cu-ligand precipitates were formed within 15 min. FA precipitated Cu more rapidly than HA did. ${\kappa}$ for Pb-HA complexation was decreased but that for Pb-FA reaction was increased, as increasing Pb concentration. Most of Pb-organic ligand complexation occurred within 30 min. Afterwards, ${\kappa}$ values were relatively small and not affected much by time. Pb was precipitated by humic acid more readily than Cu when metal concnetrations were $200{\sim}300{\mu}M$. However, when metal concentrations were in the ranges of $400{\sim}500{\mu}M$, a reversed tendency was observed.

• Journal of the Korean Chemical Society
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• v.42 no.2
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• pp.220-227
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• 1998

Homogeneous precipitation of $Y^{3+}$ with urea has been studied in order to investigate the effect of urea concentration on the preparation of monodispersed colloidal "Yttrium Hydroxycarbonate $(Y(OH)CO_3 \cdot nH_2O)$". As the initial concentration of urea increased, the mean size of colloidal precipitates decreased, and the rate of precipitation of $Y^{3+}$ increased. When the initial concentration of urea was higher than $4.0 \sim 7.0 M$, precipitates obtained were no more monodispersed colloidal particles, but coagulated big particles; and, although the initial concentration of urea increased over 4.0 M, the rate of precipitation did not increased. It is important to decide the proper initial concentration of urea, because excessive urea can cause the environmental problems such as water pollution.

• Korean Journal of Materials Research
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• v.6 no.3
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• pp.275-281
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• 1996

YIG 전구체 분말은 요소의 열분해반응을 이용한 균일침전법에 의해서 질산염으로부터 제조하였다. 침전은 철이온이 먼저 침전한 후 이트륨이온이 침전하는 과정으로 이루어졌다. YGI전구체 분말은 철산화물과 비정질로 구성되어 있으며 그 분말의 대략적인 화학식은 2.5Fe2O3.Y3(OH)9-2x(CO3)x.nH2O로 되어있다. YIG 전구체 분말의 열분해과정은 dehydration, 철산화물의 recrystallization, yttrium carbonate 및 yttrium oxide의 형성과 고상반응등 여러단계로 구성되어 있다. 열처리온도가 증가함에 따라 Y2O3와 Fe2O3의 고상반응에 의해 YFeO3 intermediate을 경유해서 YIG상이 형성됨을 확인하였다. 단일상의 YIG는 120$0^{\circ}C$에서 6시간 공기중에서 소성함에 의해서 얻을 수 있었다.

• Applied Chemistry for Engineering
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• v.2 no.2
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• pp.119-126
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• 1991

This investigation was undertaken to study the synthesis of Boehmite by the hydrothermal homogeneous precipitation reaction of alum with urea. The reactions were carried out at a temperature of 100 to $250^{\circ}C$, 1 : 2 to 1 : 5 in a mole ratio of alum to urea and a reaction time of 0.5 to 20 hrs. The reaction precipitates were examined by X-ray diffraction analysis, scanning electron microscope, and chemical analysis. Under the condition of mole ratio 1 : 4 of alum to urea, the spherical and monodispersed amorphous aluminum sulfate hydrate was formed at $100^{\circ}C$, the mixture of spherical amorphous aluminum sulfate hydrate and Boehmite was formed at $150^{\circ}C$, Boehmite was formed at above $200^{\circ}C$, respectively. The reaction precipitates were dense, superior precipitable and filterable particle of average $2-4{\mu}m$.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.233-236
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• 2002

다양한 산업활동에 의하여 발생하는 6가 크롬 (Cr(Ⅵ))은 대표적인 토양 및 지하수 오염물질이다. Cr(Ⅵ)은 3가크롬(Cr(III))로의 환원에 의한 침전반응으로 이동성이 저하된다고 알려져 있다. 본 연구에서는 기존의 고형화/안정화 공정에 환원.분해 반응을 추가한 2가철 기반 분해성 고형화/안정화(Degradative Solidification/Stabilization)공정에 의한 Cr(Ⅵ) 처리 특성을 고찰하였다. 회분식 실험결과 cemen/Fe(II) system내에 Cr(Ⅵ)은 환원반응 뿐만 아니라 cement에 의한 침전에 의해서도 제거됨이 밝혀졌다. Cr(Ⅵ)의 제거속도는 Fe(II)의 반응당량에 비례하는 것으로 보여진 반면, cement/solution ratio에 따른 Cr(Ⅵ) 제거동역학의 차이는 그다지 크지 않았다