Comparison of the adsorption of maize root mucilage and polygalacturonic acid on montmorillonite homoionic to divalent lead and cadmium |
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| Authors: | J L Morel F Andreux L Habib A Guckert |
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| Institution: | (1) Ecole Nationale Supérieure d'Agronomie et des Industries Alimentaires, 2, avenue de la Forêt de Haye, BP 172, F-54500 Vandoeuvre les Nancy, France;(2) Centre de Pédologie Biologique, CNRS, BP 5, F-54501 Vandoeuvre les Nancy, Cedex, France |
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| Abstract: | Summary Root mucilage material (RM) was isolated from maize plants grown in the field, and its affinity to montmorillonite (M) homoionic to Pb2+ and Cd2+ was compared with that of a commercial polygalacturonic acid (PGA). Adsorption isotherms of the commercial and natural materials on the two clay systems were compared in unbuffered systems at pH 3 and pH 6. Adsorption of PGA occurred only at pH 3, and was higher on M-Pb than on M-Cd. In contrast, the adsorption of RM was higher on M-Cd than on M-Pb. Total amounts of RM adsorbed at pH 3 were about 3 times lower on M-Cd and 20 times lower on M-Pb than the respective amounts of PGA adsorbed at the same pH. Polygalacturonic acid had a high content of relatively well dissociated (pKa = 3.5) carboxylic groups, and adsorbed on the clay surface at pH values lower than its pKa. At pH 6, the dissociation of the acid groups favoured its solubility, and the metal cations were then probably displaced by ion exchange. The lower affinity of RM to the clay materials was related to its average molecular weight, which was lower than that of PGA, and to its water solubility, which was higher than that of PGA. The low pH dependence of the adsorption of RM was related to its lower carboxylic acidity and higher content in hydroxyl and amino groups. |
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| Keywords: | Maize root mucilage Polygalacturonic acid Montmorillonite Lead Cadmium Adsorption isotherms Zea mays |
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