This paper presents a review on adsorption of organic chemicals on soils sediments and their constituents. The first part of this review deals with adsorption from gas and liquid phases and gives a discussion on the physical meaning of the shape of adsorption isotherms. Results show that no general rules can be proposed to describe univocally the relation between the shape of isotherms and the nature of adsorbate-adsorbent system. Kinetics of adsorption is discussed through the description of various models. Theoretical developments exist both for the thermodynamics and the kinetics of adsorption, but there is a strong need for experimental results. Possible adsorption mechanisms are ion exchange, interaction with metallic cations, hydrogen bonds, charge transfers, and London-van der Waals dispersion forces/hydrophobic effect. However, direct proofs of a given mechanism are rare. Several factors influence adsorption behavior. Electronic structure of adsorbed molecules, properties of adsorbents, and characteristics of the liquid phase are discussed in relation to adsorption. Such properties as water solubility, organic carbon content of adsorbing materials, and the composition of the liquid phase are particularly important. Evaluation of adsorption can be obtained through either laboratory measurements or use of several correlations. Adsorption measurements must be interpreted, taking into account treatment of adsorbent materials, experimental conditions, and secondary phenomena such as degradations. Correlations between adsorption coefficients and water-octanol partition coefficient or water solubility are numerous. They may be useful tools for prediction purposes. Relations with transport, bioavailability, and degradation are described.

Abstract-The migration of small cations into the empty octahedral sites of dioctahedral clays allows one to study the local effects in the trioctahedral structure and the consequences of the exchange capacity decrease on the solvation properties. The results concern essentially the montmorillonite saturated by lithium. Computations based on a point charge model shows the necessity for the OH groups to undergo a reorientation when the lithium ions are within the octahedral sites. This change of orientation was studied by i.r. spectroscopy which permits one to estimate the amounts of lithium present in the structure. By analogy with i.r. results obtained for the Li, Mg, Ca and K montmorillonites, one can say that the non-exchangeable lithium which is not within the octahedral sites must be in the bottom of the hexagonal cavities. Moreover, it is shown that the solvation properties of the clay depend on the number of exchangeable cations and on the nature of the solvent. The clay does not swell with water when the amount of exchangeable cation is lower than 50 per cent of the exchange capacity. This limit is 30 per cent with glycerol, and 20 per cent with ethylene glycol.INTRODUCTION THE THERMAL treatment of a montmorillonite saturated by cations of small radius (less than 0-7 A) results in marked decrease of its exchange capacity. This was first shown for lithium (Hoffman and Klemen, 1950) and then for Mg 2+ and AP + (Greene-Kelly, 1955;Glaeser and Meting, 1967).Hoffman and Klemen have suggested that lithium ions migrate from the interlayer positions to the vacant octahedral sites. While Greene-Kelly and Glaeser and Meting agree with this hypothesis, Tettenhorst does not (Tettenhorst, 1962).If lithium ions are really in vacant octahedral sites two consequences can be predicted:(1) The existence of local trioctahedral configurations which would result in some special spectroscopic properties.(2) A decrease of exchangeability of interlamellar cations which would certainly lead to changes in the solvation properties.

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Dissolved organic matter (DOM) from several sources influenced the adsorption and the desorption by soil of three herbicides: dimefuron {4‐[2‐chloro‐4‐(3,3‐dimethylureido) phenyl]‐2‐t‐butyl‐1,3,4‐oxadiazolin‐5‐one},atrazine (2‐chloro‐4‐ethylamino‐6‐isopropyl‐amino‐striazine), and carbetamide [D‐N‐ethyl‐2‐(phenyl‐carbamoyloxy)propioamide)]. The DOM was endogenous (water soluble and humic compounds directly extracted from soil) or exogenous (water soluble organic matter from compounds applied to soils through agricultural practices: sewage sludge, fermented straw, and farmyard slurry; and two model compounds—tannic acid and an anionic surface active agent). Experiments were conducted to quantify the importance of herbicide sorption in three separate systems: DOM‐soil, DOM‐herbicide in solution, and DOM‐adsorbed herbicide. Herbicide adsorption strongly increased in the presence of water soluble materials from fermented straw, which explained the lowest desorption obtained with this DOM. On the other hand, the water soluble extracts of liquid or solid sludge favored herbicide desorption. Generally, adsorption of the less soluble herbicides (dimefuron and atrazine) was favored when soil was pretreated with DOM, and their adsorption generally decreased when DOM was preincubated with herbicides before soil contact. Opposite effects were generally noted for the most soluble herbicide (carbetamide). A new empirical, two‐compartment model provided a good description of desorption isotherms. The first compartment (a linear desorption) was similar for most DOM types. The differences in desorption isotherms were mainly related to the different behavior of the second compartment (an exponential desorption), in which the molecules were more strongly adsorbed.

This paper presents a review on adsorption of organic chemicals on soils sediments and their constituents. The first part of this review deals with adsorption from gas and liquid phases and gives a discussion on the physical meaning of the shape of adsorption isotherms. Results show that no general rules can be proposed to describe univocally the relation between the shape of isotherms and the nature of adsorbateadsorbent system. Kinetics of adsorption is discussed through the description of various models.Theoretical developments exist both for the thermodynamics and the kinetics of adsorption, but there is a strong need for experimental results. Possible adsorption mechanisms are ion exchange, interaction with metallic cations, hydrogen bonds, charge transfers, and London-van der Waals dispersion forces/ hydrophobic effect. However, direct proofs of a given mechanism are rare. Several factors influence adsorption behavior. Electronic structure of adsorbed molecules, properties of adsorbents, and characteristics of the liquid phase are discussed in relation to adsorption. Such properties as water solubility, organic carbon content of adsorbing materials, and the composition of the liquid phase are particularly important. Evaluation of adsorption can be obtained through either laboratory measurements or use of several correlations. Adsorption measurements must be interpreted, taking into account treatment of adsorbent materials, experimental conditions, and secondary phenomena such as degradations. Correlations between adsorption coefficients and water-octanol partition coefficient or water solubility are numerous. They may be useful tools for prediction purposes. Relations with transport, bioavailability, and degradation are described.

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The sorption-desorption properties of three organic pollutants, 4-chlorophenol(4-CP), 2,4-dichlorophenol (2,4-DCP) and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on soil organic matter (SOM) were studied using kinetic and equilibrium measurements in aqueous suspensions. Chestnut wood, wheat straw, &aft lignin, composted straw and a soil humic acid were chosen as sorbents to model different states of humification. Physico-chemical characterization using chemical fractionation, potentiometric titration and IR spectroscopy was done on all sorbents. The microbial biomass, sizes of total bacterial and fungal microflora and phenoloxidases activities were determined for the plant materials. The irreversibility of sorption was revealed by the desorption isotherms. Only a small proportion of 2,4-D, which has little affinity for the fresh organic materials, was desorbed. Sorption of 2.4-DCP was strong on straw but was reversible to a large extent, indicating weaker interactions. By comparison, the sorption of 4-CP was significantly less reversible. Thus, the nature of SOM and the properties of the chemicals strongly influenced the extent of sorption and the type of interactions, and it controlled subsequent desorption and possible transformation of the sorbed species.Influence de la nature de la matibe organique du sol sur la sorption et la desorption du 4-chlorophenol, 2,4-dichlorophenol et de l'herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) RCsumCLes propriCtts de sorption et de dCsorption de la matibre organique du sol (MOS) vis h vis de trois polluants organiques, 4-chlorophCnol(4-CP), 2,4-dichlorophCnol (2,4-DCP), et acide 2,4-dichlorophCnoxyacCtique (2,4-D) ont Ct C CtudiCes en suspensions aqueuses lors d'expCrimentations cinttiques et a I'Cquilibre. Plusieurs matitres organiques ont Ct C choisies comme adsorbants pour modCliser diffkrents Ctats d'humification: bois de chgtaignier, paille de blb, lignine, paille de blC compostCe et acide humique extrait d'un sol. Les propriCtCs physicochimiques des diffkrents adsorbants ont Ct C caract6risCes en utilisant des techniques de fractionnement chimique, titration potentiomCtrique et spectroscopie IR. Une caractCrisation biologique des rCsidus vCgCtaux a Ct C menCe en effectuant des mesures de biomasse microbienne, de la taille des populations bacttrienne et fongique ainsi que d'activitks exoenzymatiques (phenoloxydases). Pour la plupart des associations polluant-matitre organique adsorbante, les cinCtiques d'adsorption ont une allure identique, montrant un Cquilibre d'adsorption atteint aprts les premikres heures de contact. Cependant, les cinCtiques d'adsorption des chlorophCnols sur la paille compostke suggtrent que des transformations microbiennes ou exoenzymatiques peuvent modifier la retention lorsque une activitd microbienne importante est associCe aux matibres organiques en cours de d6composition. Certains constituants vCgCtaux comme les lignines ou les composes phknoliques solubles influencent les proprittks de sorption et de dksorption. Les plus grande...

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