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      KINETICS OF MOLYBDATE AND PHOSPHATE SORPTION BY SOME CHILEAN ANDISOLS Translated title: Cinética de adsorción de molibdato y fosfato en algunos Andisoles chilenos

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          Abstract

          The kinetics for the sorption of molybdate and phosphate by four Chilean Andisols have been determined. About 55%o of the molybdate and 61% of the phosphate was sorbed in the first 0.5 h, after which sorption slowly increased, reaching 90%o for molybdate and 97% for phosphate after 72 h. At the same time, OH¯ ions were released into the external solution, raising its pH by 0.85 units for molybdate and by 0.65 units in the case of phosphate. These observations indicated that both anions were sorpbed by a ligand exchange mechanims. Among the five kinetic models examined (),Table, 2 the Elovich equation gave the best fit of the experimental data (R² = 0.93 to 0.97, standard error = 0.35 to 0.94). The sorption rate constant (α) for both anions was related to the organic matter (OM) content of the soils, especially the content of Al- and Fe-humus complexes. The α values for molybdate were 2.24x10(15) mmol kg-1 h-1 for the Vilcun soil (15% OM), 2.49 x10(12) mmol kg-1 h-1 for the Pemehue soil (16% OM), 8.76x10(10) mmol kg- h-1 for the Osorno soil (20% OM), and 3.11x10(7) mmol kg-1 h-1 for the Piedras Negras soil (24% OM). The corresponding values for phosphate were 3.89x10(7), 5.21x10¹ , 3.11 x10(12) and 1.08x10(16) mmol kg-1 h-1. The desorption rate constant (β) for the four soils (in the above order) ranged from 0.47 to 0.28 for molybdate, and 0.22 to 0.39 mmol kg-1 h-1 for phosphate. The results suggest that the mineralogical composition and organic matter content of the Andisols control the kinetics for the sorption of both molybdate and phosphate. Molybdate appeared to have a high affinity for Fe- and Al-oxides, while phosphate was largely sorbed to Fe-and Al-humus complexes.

          Translated abstract

          Se determinaron las cinéticas de adsorción de molibdato y fosfato en cuatro Andisoles Chilenos. Cerca del 55% del molibdato y 61% del fosfato fueron adsorbidos en las primeras 0,5 h; después la adsorción aumentó lentamente, donde se adsorbió aproximadamente el 90% del molibdato y el 97% del fosfato después de 72 h. Al mismo tiempo, aumentó la concentración de iones OH¯ en la solución de suelo, aumentando el pH en 0,85 unidades para molibdato y en 0,65 unidades en el caso de fosfato. Estas observaciones indican que ambos aniones son adsorbidos por el mecanismo de intercambio de ligandos. Entre los cinco modelos cinéticos examinados (Tabla 2), la ecuación de Elovich mostró los mejores ajustes de los datos experimentales (R² = 0,93 a 0,97; SE = 0,35 a 0,94). La velocidad de adsorción (α), para ambos aniones, se relacionó con el contenido de materia orgánica (MO) de los suelos, especialmente con los contenidos de los complejos humus-Al y humus-Fe. Los valores de α para molibdato fueron 2,24x10(15) mmol kg- h-1 en el suelo Vilcún (15% MO); 2,49 x10(12) mmol kg-1 h-1 en el suelo Pemehue Í16% MO); 8,76x10(10) mmol kg-1 h-1 en el suelo Osorno (20% MO), y 3,11x10(7) mmol kg- h-1 en el suelo Piedras Negras (24% MO). Los valores correspondientes para fosfato fueron 3,89x10(7); 5,21x10(10); 3,11x10(12); y l,08x10(16) mmol kg-1 h-1. La velocidad de desorción (β) en los cuatro suelos (en el orden anterior) fluctuó en el rango de 0,47 a 0,28 para molibdato, y 0,22 a 0,39 mmol kg-1 h-1 para fosfato. Los resultados sugieren que la composición mineralógica y el contenido de materia orgánica de estos Andisoles controlan la cinética de adsorción de molibdato y fosfato. Molibdato parece tener mayor afinidad por los óxidos-Fe y óxidos-Al, mientras que fosfato es mayormente adsorbido por los complejos humus-Fe y humus-Al.

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          Most cited references 45

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          A modified single solution method for the determination of phosphate in natural waters

           J. Murphy,  J.P. Riley (1962)
          Analytica Chimica Acta, 27, 31-36
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            Application of Elovich Equation to the Kinetics of Phosphate Release and Sorption in Soils1

             S. Chien,  W. Clayton (1980)
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              Estimation of forms of Fe and Al - a review, and analysis of contrasting soils by dissolution and Mossbauer methods

                RL Parfitt,   Childs (1988)
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                Author and article information

                Journal
                rcsuelo
                Revista de la ciencia del suelo y nutrición vegetal
                R.C. Suelo Nutr. Veg.
                Sociedad Chilena de la Ciencia del Suelo (Temuco, , Chile )
                0718-2791
                2009
                : 9
                : 1
                : 55-68
                Affiliations
                orgnameLandcare Research orgdiv1Manawatu Mail Centre New Zealand
                Temuco orgnameUniversidad de la Frontera orgdiv1Facultad de Ingeniería, Ciencias y Administración orgdiv2departamento de Ciencias Químicas Chile mariluz@ 123456ufro.cl
                Osorno orgnameNational Institute for Agricultural Research (INIA )Remehe orgdiv1Research Centre Chile
                orgnameUniversity of South Australia orgdiv1Centre for Environmental Risk Assessment Australia
                Article
                S0718-27912009000100005 S0718-2791(09)00900105
                10.4067/S0718-27912009000100005

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 33, Pages: 14
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