Modeling the Effect of Temperature on Adsorption of Lead(II) and Zinc(II) onto Goethite at Constant pH

Rodda, Darren P.; Johnson, Bruce B.; Wells, John D.

doi:10.1006/jcis.1996.0631

Cited by 81 publications

(69 citation statements)

References 12 publications

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“…Table 3 shows the heats of K/Ca and K/Pb exchange, measured by flow calorimetry in the Oxisol and Ultisol. The adsorption of Ca and Pb was endothermic when replacing exchangeable K, which is consistent with literature for these cations (Deist and Talibudeen, 1967;Elkhatib et al, 1993;Laudelot et al, 1968;Maes and Cre mers, 1977;Parida et al, 1996;Rodda et al, 1996;Scheinost et al, 2001;Udo, 1978). Furthermore, heats for K/Pb exchange were significantly smaller than those for K/Ca exchange in both soils (P Յ 0.1 for Oxisol K/Ca and Ultisol K/Pb) This means that more energy was absorbed from the surroundings when Ca replaced K than when Pb replaced K. This was most likely because Pb has a lower hydration energy and a higher hy drated charge density than Ca, facilitating the re placement of K. Heats of exchange were significantly greater (P Յ 0.1) for the Ultisol than for the Oxisol.…”

Section: Integral Heats Of Adsorptionsupporting

confidence: 90%

HEATS OF K/Ca AND K/Pb EXCHANGE IN TWO TROPICAL SOILS AS MEASURED BY FLOW CALORIMETRY 1

Appel

Rhue²,

Ma³

et al. 2002

Soil Science

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Flow calorimetry can provide useful information about surface chem ical reactions in soils that cannot be obtained readily by other methods. When flow calorimetry is conducted over a range of surface coverages, different sorption heats can be calculated to yield information about how binding energies vary with coverage, i.e., surface heterogeneity. The purpose of this study was to determine heats of exchange for K/Ca and K/Pb systems using flow calorimetry and to evaluate the degree of sur face heterogeneity with respect to cation exchange. Surface horizon sam ples from a Typic Acrorthox and Typic Tropohumult from Puerto Rico were used. Lead was adsorbed specifically in both soils, but no adsorp tion heat was detected for this reaction in either soil. However, heats as sociated with reversible cation exchange between K and Pb were ob served. Heats for K/Ca exchange were greater than those generated for K/Pb exchange in both soils. Heats of exchange were greater in the Ul tisol than in the Oxisol. The differential heats of exchange were inde pendent of exchange composition for both K/Pb and K/Ca exchange in the Oxisol, indicating that all cation exchange sites were similar energet ically. In the Ultisol, the differential heats of exchange increased as ex changeable K decreased, indicating that the exchange sites were not sim ilar energetically. These differences were attributed to the presence of smectite in the Ultisol, which was able, in part, to collapse when satu rated with K. (Soil Science 2002;167:773-781)

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Section: Integral Heats Of Adsorptionsupporting

confidence: 90%

HEATS OF K/Ca AND K/Pb EXCHANGE IN TWO TROPICAL SOILS AS MEASURED BY FLOW CALORIMETRY 1

Appel

Rhue²,

Ma³

et al. 2002

Soil Science

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“…Ademais, a comparação entre os resultados termodinâmicos para reações de adsorção, compilados da literatura, precisa levar em consideração que os valores dependerão do modelo de adsorção selecionado 50 , uma vez que ainda não há um método ideal para aquisição destes parâmetros para sistemas heterogêneos, como o solo 25 .…”

Section: Descrição Do Sistemaunclassified

“…Estudos termodinâmicos da reação de adsorção geralmente contemplam todas as reações envolvidas, o que inclui a hidrólise na solução e a subseqüente adsorção dos produtos desta reação 50 . A descrição completa do sistema culmina com a interação entre a fase sólida e as espécies de boro presentes na fase líquida, que se estabelece pelo fenômeno da adsorção.…”

Section: Descrição Do Sistemaunclassified

“…Variações positivas da entropia implicam que a reação de adsorção requer uma redução da ordem do sistema. Diferenças de solvatação do adsorbato, sejam de suas espécies em solução ou das adsorvidas, assim como o próprio estado da água nas duas situações e a liberação de prótons para a solução 50 , podem ser causas da variação entrópica na adsorção. Dessa forma, parece razoável admitir que, em sistemas de cargas que variam com o pH, os valores de entropia da adsorção de boro devam ser negativos, uma vez que a liberação de prótons para o sistema acarreta a diminuição do pH, restringindo a adsorção de boro.…”

Section: Variação Da Energia Livre Da Adsorção De Boro (δG)unclassified

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Parâmetros termodinâmicos da reação de adsorção de boro em solos tropicais altamente intemperizados

2005

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Recebido em 13/10/04; aceito em 10/3/05; publicado na web em 10/8/05 THERMODYNAMIC PARAMETERS FOR BORON ADSORPTION REACTION ON HIGHLY WEATHERED TROPICAL SOILS. The driving force of boron adsorption on some tropical soils was evaluated by means of thermodynamic parameters. The batch method was employed, and the reaction was monitored at different pH values. The Langmuir equation successfully fitted the experimental results and provided reasonable isotherm parameters. Boron adsorption increased as a function of the pH of the soil solution and the concentration of added boron. The reaction was favorable and proceeded spontaneously, being strongly exoergic, as indicated by a negative free energy (ΔG) and a separation factor (K R ) < 1. The boron adsorption phenomenon and the soilsolution interface were thermodinamically described using a theoretical model. Keywords: tropical soils; boron; adsorption. INTRODUÇÃOO boro é um elemento semi-metálico, considerado um micronutriente que atende aos critérios de essencialidade ao pleno desenvolvimento vegetal 1 . Seu comportamento químico é muito similar ao do silício e relativamente simples quando comparado com o de outros oxiânions 2 . Ao contrário de outros elementos com um número reduzido de elétrons e grande número de orbitais disponíveis para ligação química, aliado ao seu alto potencial de ionização, o boro elementar não é encontrado na natureza, porque está sempre combinado com o oxigênio para a formação de compostos covalentes. Espécies B 2 O 3 normalmente reagem com água para formar o ácido bórico [B(OH) 3 ], que atua como ácido fraco, tendendo a formar íons B(OH) 4 -pela incorporação de uma hidroxila à sua molécula 3 . A reação de formação do hidroxiborato é espontâ-nea, mas em solução aquosa, o boro existe quase que exclusivamente sob a forma não dissociada de ácido bórico, devido à sua pequena constante de dissociação (pK a =9,2) 4 . Em decorrência da neutralidade elétrica de sua forma predominante [B(OH) 3 0 ], o boro é um elemento extremamente móvel no solo e pode ser facilmente lixiviado. Fitotoxicidade por boro pode ocorrer por práticas inadequadas de fertilização, de irrigação e de aplicação de outros insumos agrícolas que contêm boro, tais como herbicidas e inseticidas. Mais recentemente, o descarte de resíduos efluentes de indústrias que empregam o ácido bórico e sais de borato na manufatura de vidros, de esmaltes cerâmicos e de ligas metálicas, tem aumentado o potencial de entrada do boro na cadeia alimentar humana, em concentrações que podem causar sérios riscos à saúde 5 , o que torna importante se conhecer o comportamento químico do boro sob os pontos de vista agronômico e ambiental.Quando o boro é liberado dos minerais do solo, mineralizado da matéria orgânica ou adicionado ao solo por meio de irrigação, fertilização ou descarte de resíduos, parte do elemento permanece na solução do solo e parte é adsorvida pela fase sólida do solo 6 . A mineralogia do adsorvente desempenha uma importante função na intensidade e no mecanismo de adsorção do boro 7,8 , ...

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“…The temperature of the adsorption medium has also been shown to be important where the mechanism of the metal-binding processes is energy dependent (Green-Ruiz, 2009). Changing the temperature may affect the equilibrium adsorption capacity of the adsorbent: for example, the adsorption capacity will decrease with increasing temperature for an exothermic reaction, while it will increase for an endothermic one (Rodda et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

Thiol-functionalised mesoporous silica-coated magnetite nanoparticles for high efficiency removal and recovery of Hg from water

2012

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The preparation and testing of thiol-functionalised silica-coated magnetite nanoparticles (TF-SCMNPs) is described. The characteristics of these particles are assessed at different stages in the production process using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and a magnetometer. The particles were found to be almost spherical with a uniform mesoporous structure with a pore size of ~2.1 nm. The particles were strongly responsive to an external magnetic field making separation from solution possible in less than 1 min. The adsorption characteristics of the particles were quantified in a series of isotherm experiments using Hg(II) solution concentrations between 40 and 1000 μg l -1 at adsorbent concentrations of 4 and 8 mg l -1 . The adsorption capacity was higher than for other commonly used adsorbents with 90% of Hg(II) removed during the first 5 min and equilibrium in less than 15 min. Both the Langmuir and Freundlich isotherm models were applied to the isotherm data and the maximum adsorption capacity was achieved when the ratio of adsorbent to adsorbate was low. temperature and pH had an effect on adsorption but when the TF-SCMNPs were used for removal of Hg(II) from tap water and bottled water, which contained other ions, there appeared to be no interference. Hg(II) could be successfully desorbed using thiourea in a 3M HCl solution; this did not result in the destruction of the nanoparticles and they could subsequently be reused without loss of their activity in repetitive adsorption tests.

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Modeling the Effect of Temperature on Adsorption of Lead(II) and Zinc(II) onto Goethite at Constant pH

Cited by 81 publications

References 12 publications

HEATS OF K/Ca AND K/Pb EXCHANGE IN TWO TROPICAL SOILS AS MEASURED BY FLOW CALORIMETRY 1

HEATS OF K/Ca AND K/Pb EXCHANGE IN TWO TROPICAL SOILS AS MEASURED BY FLOW CALORIMETRY 1

Parâmetros termodinâmicos da reação de adsorção de boro em solos tropicais altamente intemperizados

Thiol-functionalised mesoporous silica-coated magnetite nanoparticles for high efficiency removal and recovery of Hg from water

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