Competitive adsorption of toxic metals on bentonite and use of chitosan as flocculent coagulant to speed up the settling of generated clay suspensions

Evaluation of modified Algerian clay as mineral adsorbent was done for its adsorbing capacity on copper (Cu) and Zinc (Zn) cations. The results obtained show a rapid kinetic adsorption for both metals (less than 2 h) following the pseudo-second order model with high elimination rates of 67.2 and 61.8% for Cu and Zn respectively. The adsorption isotherms analyzed with Langmuir model revealed a correlation with the experimental values. While the use of obtained chitosan at room temperature, as flocculent coagulant, accelerates the decantation of the colloidal particles in suspension generated after adsorption process.

Reactivity of nanostructured MnO(2) in alkaline medium studied with a micro-cavity electrode: effect of synthesizing temperature

The influence of synthesizing temperature of manganese dioxide (MnO(2)) powders on their electrochemical reactivity in 1 M KOH was investigated. These powders were prepared chemically by the hydrothermal method by oxidation of Mn(2+) by ammonium peroxodisulphate. The observations by scanning electronic microscopy, energy-dispersive X-ray analyses, and transmission electron microscopy techniques on MnO(2) obtained at different temperatures show the formation of many nanometre scale sticks lumped together to form a spherical particle of several micrometers. The results obtained by BET and BJH methods reveal mesoporous texture, and the MnO(2) synthesized at 90 degrees C presents the largest expanded surface area. The electrochemical reactivity of these powders in 1 M KOH was characterized with microcavity electrode by cyclic voltammetry and electrochemical impedance spectroscopy. The results illustrate that the nanostructured MnO(2) powder synthesized at 90 degrees C shows the highest electrochemical reactivity in agreement with BET data. The X-ray powder diffraction identified the gamma-MnO(2), known as the most reactive species.