Kinetics of Heavy Metal Desorption from Three Soils Using Citric Acid, Tartaric Acid, and EDTA

By Wasay, S. A.; Barrington, S. et al. | Journal of Environmental Engineering and Science, November 2007 | Go to article overview

Kinetics of Heavy Metal Desorption from Three Soils Using Citric Acid, Tartaric Acid, and EDTA


Wasay, S. A., Barrington, S., Tokunagal, S., Prasher, S., Journal of Environmental Engineering and Science


Abstract: Organic acids are relatively new soil heavy metal leaching agents requiring the development of desorption kinetics before being applied. The objective was to determine the heavy metal desorption rates for three heavily contaminated soils (clay loam, loam, and sandy clay loam), treated under optimum conditions with either citric acid, tartaric acid, or EDTA for comparison. A two-rate reaction (fast and slow) model was defined to describe desorption kinetics, where both first order rates were assumed irreversible and reversible, respectively. Experimental data were collected by initially subjecting the three soils to batch experiments at optimum leaching agent level, for up to 36 h. The results indicated that citric acid was a more consistent leaching agent compared to tartaric acid and EDTA, which were efficient mainly in treating the clay loam and the sandy clay loam, respectively. The two-rate reaction model fitted the data but its empirical coefficients need to be defined for each individual soil to be treated. For Pb common to all three experimental soils, [k.sub.1], representing the fast desorption rate, increased with the ratio of metal equivalence fraction: soil CEC. The coefficients [k.sub.2] and [[alpha].sub.0], representing the slower rate of desorption and the proportion of Pb involved in this slow rate, respectively, increased with the mass of Pb held by the oxide and organic matter fractions. The coefficient [m.sub.1], related to the relative rate of the backward reaction from the slow to the fast, varied according to the mass of Pb held by the exchangeable site. Despite the empirical values associated with the kinetics coefficients, their correspondence with individual processes indicate that organic acid remediation can be modeled using the two rate kinetic equation proposed in this project.

Key words: heavy metals (Cr, Mn, Hg, Pb, Cd, Cu, Zn), citric acid, tartaric acid, EDTA, two reaction kinetics model.

Resume : Les acides organiques sont des agents relativement nouveaux utilises pour la lixiviation des metaux lourds dans les sols; ils doivent cependant developper une cinetique de desorption avant de pouvoir etre appliques. L'objectif etait de determiner les vitesses de desorption des metaux lourds dans trois sols fortement contamines (loam argileux, loam et loam sablo-argileux), traites sous des conditions optimales avec soit de l'acide citrique, de l'acide tartrique ou de l'EDTA a des fins de comparaison. Un modele de reaction a deux vitesses (rapide et lente) a ete defini pour decrire la cinetique de desorption, ou les deux vitesses du premier ordre ont ete presumees respectivement irreversibles et reversibles. Les donnees experimentales ont ete colligees en soumettant initialement les trois sols a des experiences par lot a un niveau optimal d'agent de lixiviation, pour une duree allant jusqu'a 36 heures. Les resultats indiquent que l'acide citrique etait un agent de lixiviation plus constant que l'acide tartrique et l'EDTA, lesquels etaient principalement efficaces pour le traitement du loam argileux et du loam sablo-argileux respectivement. Le modele de reaction a deux vitesses correspondait bien aux donnees mais les coefficients empiriques doivent etre definis pour chaque sol individuel a etre traite. Quant au Pb, present dans les trois echantillons de sol, [k.sub.1], representant la vitesse elevee de desorption, augmentait avec le rapport de la fraction equivalent metal : la CEC du sol. Les coefficients [k.sub.2] et [[alpha].sub.0], representant respectivement la vitesse de desorption plus lente et la proportion de Pb impliquee dans cette vitesse lente, ont augmente avec la masse de Pb retenue par les fractions d'oxydes et de matieres organiques. Le coefficient [m.sub.1], lie a la vitesse relative de la reaction inverse de lente a rapide, a varie selon la masse de Pb retenu par le site d'echange. Malgre des valeurs empiriques associees aux coefficients cinetiques, leur correspondance aux procedes individuels indique que le retrait de l'acide organique peut etre modelise en utilisant l'equation cinetique a deux vitesses proposee pour dans projet. …

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