Equilibrium and kinetics of cadmium adsorption from aqueous solutions using untreated Pinus halepensis sawdust

Untreated Pinus halepensis sawdust has been investigated as an adsorbent for the removal of cadmium from aqueous solutions. Batch experiments were carried out to investigate the effect of pH, adsorbent dose, contact time, and metal concentration on sorption efficiency. The favorable pH for maximum cadmium adsorption was at 9.0. For the investigated cadmium concentrations (1-50 mg/L), maximum adsorption rates were achieved almost in the 10-20 min of contact. An adsorbent dose of 10 g/L was optimum for almost complete cadmium removal within 30 min from a 5 mg/L cadmium solution. For all contact times, an increase in cadmium concentration resulted in decrease in the percent cadmium removal (100-87%), and an increase in adsorption capacity (0.11-5.36 mg/g). The equilibrium adsorption data were best fitted with the Freundlich isotherm (R2 = 0.960). The kinetics of cadmium adsorption was very well described by the pseudo-second-order kinetic model (R2 > 0.999).