Temperature effects on nickel sorption kinetics at the mineral-water interface

In recent years, innovative studies have shown that sorption of metals onto natural materials results in the formation of new mineral-like precipitate phases that increase in stability with aging time. While these findings ha ve demonstrated the usefulness of current state-of-the-art molecular-scale methods for confirming macroscopic data and elucidating mechanisms, basic k inetic and thermodynamic parameters for the formation of the metal precipit ates have not been examined. This study examined Ni-sorption kinetics on py rophyllite, talc, gibbsite, amorphous silica, and a mixture of gibbsite and amorphous silica over a temperature range of 9 to 35 degreesC. Using the A rrhenius and Eyring equations, we calculated the energy of activation (E-a) and enthalpy (DeltaH(double dagger)), entropy (DeltaS(double dagger)), and free energy of activation (DeltaG(double dagger)), related to the formatio n of the Ni precipitates. Based on values of E-a (93.05 to 123.71 kJ mol(-1 )) and DeltaS(double dagger) (-27.51 to -38.70 J mol(-1)), Ni sorption on t hese sorbents was surface-controlled and an associative mechanism, The Delt aH(double dagger) values (90.60 to 121.26 kJ mol(-1)) suggest, as indicated by E-a values, that an energy barrier was present for the system to overco me in order for the reaction to occur, Additionally, the large, positive De ltaG(double dagger) values suggest there is an energy barrier for product f ormation. Although metal precipitation reactions often occur in the natural environment, this study shows that the rate of these reactions depends str ongly on temperature.