Adsorption, kinetic and thermodynamic study of Al, Mn and Fe adsorption with natural attapulgite

摘要

Natural attapulgite was utilized as an adsorbent for the removal of Al, Fe and Mn from a mixed metal effluent. Adsorption experiments were carried out by agitation of a fixed amount of attapulgite with a fixed volume of effluent waste stream in a thermostatic shaker for varying times. Attapulgite showed that it was capable of neutralising the acidic waste stream effluent as pH after 3 hour rose from 2 to 7.46. 4% solid loading of attapulgite could remove 85% Mn(II), 90% Al(III) and 100% Fe(III) The experimental data best fit Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and the adsorption mechanism was physisorption. The adsorption process fitted well the pseudo second order kinetics for all metal ions studied. Thermodynamic data showed that Fe(III) and Mn(II) adsorption was thermodynamically spontaneous whilst Al(III) was not thermodynamically spontaneous. The process is endothermic for all metal ions. An increase in temperature resulted in an increase in spontaneity of the adsorption process. An increase in metal concentration resulted in an increase in amount of metal ion adsorbed per unit weight of attapulgite.