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• W2025814101 abstract "Dried activated sludge (DS) and thermally modified samples (MDS) [1] were used as adsorbents of Cu(II) from water at zero and 0.1 ionic strength. Three mechanisms are essentially implied at the solid-liquid interface: 1. ion exchange of free metals and hydroxo-complexes with surface protons 2. adsorption and hydrolysis at the surface 3. hydrolysis followed by an adsorption reaction The use of activated sludge as adsorbent is also justified by its bacterial nature [2]. Experimental Two kinds of adsorbent were prepared: the samples obtained from a pilot plant were thickened and dried at 100 °C in air, powdered and sieved in the 42–200 mesh range (DS), and heated at 110 °C in air for 24 h (MDS). The BET surface evaluation resulted in 2±0.1 m 2 /g for DS and 0.5±0.1 m 2 /g for MDS; this may be interpreted assuming that grain agglomeration takes place. The calometric experiments were carried out using a SETARAM rotating C.R.M.T. calorimeter [3], with a cell we constructed because of the impossibility of any handling from outside after introduction of the sample. The method has already been described in detail [4]. Results and Discussion In Fig. 1 we have reported the enthalpies of displacement, -H12 (J/g), as a function of the specific quantities of Cu(II) adsorbed, n 2s (mg/g). Heat changes measured are actually heats of displacement, the water being gradually replaced by the solute [3]. The trend of the enthalpies of displacement in Fig. 1 considering influence of the thermal treatment shows that the MDS exhibit at every surface coverage a higher enthalpy of displacement; this fact is interpreted by supposing that the thermal treatment favours the exhibition at the surface of chemical and polar groups capable of strong interaction with the Cu(II) ions. This fact could be interpreted as due to an increase in the electrical potential of the Stern Gouy diffuse layer [5] with a consequent more difficult diffusion of Cu(II) ions toward the polar surface: analogous results have been obtained on an oxide surface [6]. From the analysis of calometric peaks, relative to DS and MDS samples, we can deduce that the thermokinetic trend is somewhat different, the MDS showing an apparently smaller reaction rate. Starting from the hypothesis that the rate determining step is the diffusion of the solute, we have tried to apply a semiempirical treatment assuming a time dependence of the diffusion equation [8]. In Fig.2 we have reported the function: F(t) = log P + 3 2 log t where P ≅KW is the instantaneous deviation of the calorimeter vs . the reciprocal of time. The linearity of the curves in Fig. 2 is satisfactory enough both for DS and MDS samples. The MDS samples show a greater slope, that means a smaller diffusion coefficient; that would correspond to a more dense Gouy layer; in other words, the MDS sample that exhibits a greater number of polar and ionic groups would have a higher repulsive potential field in the diffuse layer. We may conclude that kinetic [1] and thermokinetic studies are in agreement and show that the initial uptake rate is smaller on MDS than DS; but the limiting adsorption quantities are higher for the former. This situation could be interpreted by assuming that the determining step is the diffusion of the ions through the double layer which should be characterized by a higher electrical potential in the case of MDS." @default.
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• W2025814101 date "1983-01-01" @default.
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• W2025814101 title "Energetics of the adsorption of Cu(II) on activated sludge" @default.
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• W2025814101 doi "https://doi.org/10.1016/s0020-1693(00)95275-7" @default.
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