• 상하수도학회지
• /
• 제25권3호
• /
• pp.359-366
• /
• 2011

The feasibility of using volcanic ash for lead ion removal from wastewater was evaluated. The adsorption experiments were carried out in batch tests using volcanic ash that was treated with either NaOH or HCl prior to the use. Volcanic ash dose, temperature and initial Pb(II) concentration were chosen as 3 operational variables for a $2^3$ factorial design. Ash dose and concentration were found to be significant factors affecting Pb(II) adsorption. The removal of Pb(II) was enhanced with increasing volcanic ash dose and with decreasing the initial Pb(II) concentration. Pb(II) adsorption on the volcanic ash surface was spontaneous reaction and favored at high temperatures. Calculation of Gibb's free energy indicated that the adsorption was endothermic reaction. The equilibrium parameters were determined by fitting the Langmuir and Freundlich isotherms, and Langmuir model better fitted to the data than Freundlich model. BTV(base-treated volcanic ash) showed the maximum adsorption capacity($Q_{max}$) of 47.39mg/g. A pseudo second-order kinetic model was fitted to the data and the calculated $q_e$ values from the kinetic model were found close to the values obtained from the equilibrium experiments. The results of this study provided useful information about the adsorption characteristics of volcanic ash for Pb(II) removal from aqueous solution.

• Korean Chemical Engineering Research
• /
• 제55권4호
• /
• pp.514-519
• /
• 2017

활성탄을 사용하여 흡착제의 양, pH, 초기농도, 접촉시간과 온도를 흡착변수로 acid green 27 염료의 흡착특성을 조사하였다. 흡착평형자료는 Freundlich와 Langmuir 등온식을 사용하여 해석하였는데, Freundlich 식이 더 좋은 일치도를 나타냈다. 평가된 Freundlich 분리계수(1/n=0.293~0.387)로부터 활성탄에 의한 acid green 27의 흡착조작이 효과적인 처리방법이 될 수 있음을 알았다. 흡착속도실험 결과는 유사이차 반응속도식에 잘 맞았으며, 유사이차속도상수($k_2$)값은 acid green 27 초기농도가 증가할수록 감소하였다. 활성화에너지값(10.457 kJ/mol)과 표준엔탈피변화값(76.946 kJ/mol)으로 흡착공정이 물리흡착이고 흡열반응임을 알았다. 298~318 K 범위에서 Gibbs 자유에너지값은 온도가 올라갈수록 감소하였기 때문에 흡착반응은 온도가 올라갈수록 더 자발적으로 일어났다.

• 대한화학회지
• /
• 제22권5호
• /
• pp.281-288
• /
• 1978

1-염화 및 2-염화나프탈렌술포닐과 아닐린과의 반응에서 그 반응의 유사 일차 반응속도상수($k_{obs}$)를 구하고 또한 2차 반응속도 상수 $k_2$및 3차반응 촉매속도상수 $k_3$도 $k_{obs}$로 부터 구하였다. 1-염화나프탈렌술포닐과의 반응에서는 Peri-hydrogen 효과가 관측되었다. 또한 Brensted 그림표에서는 큰 값의 ${\beta}$와 Hammett 그림표의 기울기로부터 크 음의 ${\rho}$값을 얻었다. 따라서 이 반응의 메카니즘은 매우 낮은 활성화파라미터의 값을 갖는 결과로$S_AN$반응메카니즘과 잘 일치되지만 associative$S_N2$메카니즘으로도 동일하게 잘 설명될 수 있었다.

• 폴리머
• /
• 제24권1호
• /
• pp.16-22
• /
• 2000

폴리부틸렌테레프탈레이트 (poly(butylene terephthalate), PBT)와 파라아세톡시벤조산 (p-acetoxybenzoic acid, ABA)을 용융 에스테르 교환반응시킴으로써 주쇄 고분자에 강직한 벤젠고리가 도입된 poly(butylene terephthalate-co-oxybenzoate) (PBOT)를 합성하였다. PBT와 ABA를 다양한 조성비에서 중합하는 과정의 속도론적 고찰을 통해 ABA의 단독중합 속도상수와 PBT에의 공중합 속도상수 및 그 비를 구하였으며 각각의 활성화에너지를 구하였다. PBT와 ABA의 조성비를 4/6, 5/5, 6/4로 하고 온도를 각각 250, 260, 27$0^{\circ}C$로 하여 실험한 결과 공중합반응은 ABA함량이 낮고 또 그 전환율이 크지 않을 경우 의사 2차반응으로 볼 수 있었다. 이때의 공중합 속도에 대한 단독중합 속도의 비는 1.08에서 3.17사이의 값을 가졌으며, ABA함량과 온도가 높을수록 큰 값을 가졌다. 이로써 PBT/ABA계의 공중합은 반응온도가 높고 ABA의 조성비가 클수록 ABA의 블록성이 강해지는 경향을 나타내었다.

• Bulletin of the Korean Chemical Society
• /
• 제33권9호
• /
• pp.2971-2975
• /
• 2012

Second-order rate constants $k_N$ have been measured spectrophotometrically for nucleophilic substitution reactions of t-butyl 4-pyridyl carbonate 8 with a series of alicyclic secondary amines in $H_2O$ at $25.0{\pm}0.1^{\circ}C$. The Br${\emptyset}$nsted-type plot for the reactions of 8 is linear with ${\beta}_{nuc}$ = 0.84. The ${\beta}_{nuc}$ value obtained for the reactions of 8 is much larger than that reported for the corresponding reactions of t-butyl 2-pyridyl carbonate 6 (i.e., ${\beta}_{nuc}$ = 0.44), which was proposed to proceed through a forced concerted mechanism. Thus, the aminolysis of 8 has been concluded to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate $T^{\pm}$, in which expulsion of the leaving-group from $T^{\pm}$ occurs at the rate-determining step (RDS). In contrast, aminolysis of benzyl 4-pyridyl carbonate 7 has been reported to proceed through two intermediates, $T^{\pm}$ and its deprotonated form $T^-$ on the basis of the fact that the plots of pseudo-first-order rate constant $k_{obsd}$ vs. amine concentration curve upward. The current study has demonstrated convincingly that the nature of the leaving and nonleaving groups governs the reaction mechanism. The contrasting reaction mechanisms have been rationalized in terms of an intramolecular H-bonding interaction, steric acceleration, and steric inhibition.

• Bulletin of the Korean Chemical Society
• /
• 제35권1호
• /
• pp.225-230
• /
• 2014

A kinetic study on nucleophilic substitution reactions of 4-nitrophenyl X-substituted-benzoates (7a-i) with EtOK in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$ is reported. The plots of pseudo-first-order rate constants ($k_{obsd}$) vs. [EtOK] curve upward. Dissection of $k_{obsd}$ into the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOK (i.e., $k_{EtO^-}$ and $k_{EtOK}$, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated $EtO^-$. Hammett plots for the reactions of 7a-i with the dissociated $EtO^-$ and ion-paired EtOK exhibit excellent linear correlations with ${\rho}_X$ = 3.00 and 2.47, respectively. The reactions have been suggested to proceed through a stepwise mechanism in which departure of the leaving-group occurs after the RDS. The correlation of the $k_{EtOK}/k_{EtO^-}$ ratio with the ${\sigma}_X$ constants exhibits excellent linearity with a slope of -0.53. It is concluded that the ion-paired EtOK catalyzes the reaction by increasing the electrophilicity of the reaction center rather than by enhancing the nucleofugality of the leaving group.

• 자원리싸이클링
• /
• 제29권5호
• /
• pp.38-47
• /
• 2020

본 연구에서는 SCR 탈질 폐촉매의 소다배소-수침출 공정을 통해 얻은 침출액으로부터 강염기성 음이온교환수지인 Lewatit monoplus MP 600을 사용하여, V과 W의 분리/회수를 위한 흡착반응에 영향을 미치는 인자들에 대하여 알아보고, 이를 통하여 흡착 메커니즘을 조사하였다. V과 W 혼합용액의 경우 pH 2-6에서는 두 이온 모두 높은 흡착률을 보였지만, pH 8에서 W의 흡착은 크게 저하되었다. 흡착등온실험에서 V과 W 모두 Langmuir 흡착등온식에 적합하였고, 반응속도론적 고찰 결과 pseudo-second-order에 적합하였다. 침출액에서 V과 W의 흡착을 저해하는 Si를 제거하기 위하여 H₂SO₄로 pH를 조절하여 흡착실험을 수행한 결과, pH 8.5에서 가장 낮은 W 흡착률을 보였다. W의 탈착은 강산성 용액에서 거의 이루어지지 않았으며 V은 강산성 용액과 강염기성 용액 모두에서 탈착이 잘 이루어졌다.

• Environmental Engineering Research
• /
• 제19권1호
• /
• pp.15-22
• /
• 2014

In this study, the performances of various adsorbents-red mud, zeolite, limestone, and oyster shell-were investigated for the adsorption of multi-metal ions ($Cr^{3+}$, $Ni^{2+}$, $Cu^{2+}$, $Zn^{2+}$, $As^{3+}$, $Cd^{2+}$, and $Pb^{2+}$) from aqueous solutions. The result of scanning electron microscopy analyses indicated that the some metal ions were adsorbed onto the surface of the media. Moreover, Fourier transform infrared spectroscopy analysis showed that the Si(Al)-O bond (red mud and zeolite) and C-O bond (limestone and oyster shell) might be involved in heavy metal adsorption. The changes in the pH of the aqueous solutions upon applying adsorbents were investigated and the adsorption kinetics of the metal ions on different adsorbents were simulated by pseudo-first-order and pseudo-second-order models. The sorption process was relatively fast and equilibrium was reached after about 60 min of contact (except for $As^{3+}$). From the maximum capacity of the adsorption kinetic model, the removal of $Pb^{2+}$ and $Cu^{2+}$ were higher than for the other metal ions. Meanwhile, the reaction rate constants ($k_{1,2}$) indicated the slowest sorption in $As^{3+}$. The adsorption mechanisms of heavy metal ions were not only surface adsorption and ion exchange, but also surface precipitation. Based on the metal ions' adsorption efficiencies, red mud was found to be the most efficient of all the tested adsorbents. In addition, impurities in seawater did not lead to a significant decrease in the adsorption performance. It is concluded that red mud is a more economic high-performance alternative than the other tested adsorption materials for applying a removal of multi-metal in seawater.

• Membrane and Water Treatment
• /
• 제9권2호
• /
• pp.95-104
• /
• 2018

Copper pollution around the world has caused serious public health problems recently. The heavy metal adsorption on traditional membranes from wastewater is limited by material properties. Different adsorptive materials are embedded in the membrane matrix and act as the adsorbent for the heavy metal. The carbonized leaf powder has been proven as an effective adsorbent material in removing aqueous Cu(II) because of its relative high specific surface area and inherent beneficial groups such as amine, carboxyl and phosphate after carbonization process. Factors affecting the adsorption of Cu(II) include: adsorbent dosage, initial Cu(II) concentration, solution pH, temperature and duration. The kinetics data fit well with the pseudo-first order kinetics and the pseudo-second order kinetics model. The thermodynamic behavior reveals the endothermic and spontaneous nature of the adsorption. The adsorption isotherm curve fits Sips model well, and the adsorption capacity was determined at 61.77 mg/g. Based on D-R model, the adsorption was predominated by the form of physical adsorption under lower temperatures, while the increased temperature motivated the form of chemical adsorption such as ion-exchange reaction. According to the analysis towards the mechanism, the chemical adsorption process occurs mainly among amine, carbonate, phosphate and copper ions or other surface adsorption. This hypothesis is confirmed by FT-IR test and XRD spectra as well as the predicted parameters calculated based on D-R model.

• 상하수도학회지
• /
• 제35권6호
• /
• pp.455-463
• /
• 2021

The adsorption process using GAC is one of the most secured methods to remove of phosphate from solution. This study was conducted by impregnating Cu(II) to GAC(GAC-Cu) to enhance phosphate adsorption for GAC. In the preparation of GAC-Cu, increasing the concentration of Cu(II) increased the phosphate uptake, confirming the effect of Cu(II) on phosphate uptake. A pH experiment was conducted at pH 4-8 to investigate the effect of the solution pH. Decrease of phosphate removal efficiency was found with increase of pH for both adsorbents, but the reduction rate of GAC-Cu slowed, indicating electrostatic interaction and coordinating bonding were simultaneously involved in phosphate removal. The adsorption was analyzed by Langmuir and Freundlich isotherm to determine the maximum phosphate uptake(q_m) and adsorption mechanism. According to correlation of determination(R²), Freundlich isotherm model showed a better fit than Langmuir isotherm model. Based on the negative values of q_m, Langmuir adsorption constant(b), and the value of 1/n, phosphate adsorption was shown to be unfavorable and favorable for GAC and GAC-Cu, respectively. The attempt of the linearization of each isotherm obtained very poor R². Batch kinetic tests verified that ~30% and ~90 phosphate adsorptions were completed within 1h and 24 h, respectively. Pseudo second order(PSO) model showed more suitable than pseudo first order(PFO) because of higher R². Regardless of type of kinetic model, GAC-Cu obtained higher constant of reaction(K) than GAC.