The removal of Cr(VI) ions from aqueous solutions with wet pomace treated with laponite was investigated. A direct comparison with untreated biomass revealed an increase in both the rate of adsorption and the amount adsorbed. A cooperative interaction between the laponite platelets and biomass surface making more adsorption sites accessible was suggested. In this process, a key role is played by intraparticle diffusion. The experimental results indicate that intraparticle diffusion plays an important role in the adsorption process. A simple diffusion-binding model is presented to discuss the experimental results. The diffusion lifetime is linearly related to the adsorbent mass. The model combined with experimental results allowed us to estimate the average free path of a Cr(VI) molecule. Particularly, it was obtained that, in 1 dm3 of solution, the diffusion path increased by nearly 1 cm per gram of adsorbent. However, this did not imply that the amount of Cr(VI) removed decreased because the total number of adsorption sites also increased.
Understanding the sedimentation behaviour and chemical–physical properties of clay sediments is crucial in planning their storage in geotubes. Analysis of the sedimentation curves of the solids taken from the artificial reservoir of the Camastra reveal that a two-parameter curve identifies all the sedimentation profiles. One parameter depends on the type of settling material, and the other is the lifetime of the process. Using the solid concentration per unit area, the lifetime is converted into a true kinetic constant. These parameters uniquely identify the sedimentation profile to be used in the management of dredging using geotubes. Furthermore, the resulting particles after the decantation of the coarse-grained solids are dispersed according to a log-normal distribution with an average diameter between 250 and 500 nm. The low ζ-potential of the particles dispersed in the supernatant indicates that they can either aggregate or adsorb to the geotube tissue, slowing or blocking the dredging operations.
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