Foundry sands as low-cost adsorbent material for Cr (VI) removal

The potential of foundry sands, industrial waste from the iron foundry industry, was evaluated for the removal of Cr (VI) using discontinuous assays. Chemical foundry sands are composed of fine silica sand, furanic resins as binder, chemical catalyst and residual iron particles. The influence of pH, agitation rate and metal concentration on the removal process was investigated. Kinetic and equilibrium tests were conducted to determine Cr (VI) removal from aqueous solutions at a temperature range of 25-55 degrees C. Cr (VI) removal of 40-100% for a range of pH 6-1.6 was obtained. This removal was attributed to the presence of a large number of protonated silanol and aluminol groups. Cr (VI) adsorption in foundry sands follows a pseudo-second-order kinetic reaction (Ho model, r(2)>0.999) reaching kinetic constants of 0.341, 0.551, 0.775 and 0.920g/mgh at 25, 35, 45 and 55 degrees C, respectively. The adsorption data were fitted to the Langmuir adsorption isotherm model (r(2)>0.99) obtaining adsorption capacities (q(max)) of 1.99, 2.40, 2.50, and 3.14mg Cr (VI)/g sand at 25, 35, 45 and 55 degrees C, respectively. Calculated Gibbs free energy change ( G(0)), adsorption energy (E) and activation energy (E-a) values indicate that a physisorption mechanism governs Cr (VI) adsorption process in foundry sands.