Effect of Modified Eggshell on Adsorption Capacity of Chromium(VI) from Aqueous Solution

The aim of this work is to investigate the use of eggshell for adsorption of Cr(VI) from aqueoussolution and the effect of thermal treatment as well as coating with Fe2O3 of eggshell on the extractionpercent of Cr(VI). The XRD, FTIR and SEM techniques proved that the eggshell mainly composed ofcalcite rhombohedral structure in addition to a trace of quartz silica residual protein fibers. Heating at550 ºC does not decompose eggshell but decomposes the residual protein. The effect of pH, weight ofeggshell adsorbent, contact time, and initial concentration of Cr(VI) ions on the adsorption of Cr(VI)on eggshell sorbents were determined under static conditions by the batch equilibrium technique. Thesorption kinetic as well as mechanistic isotherm parameters of Cr(VI) on the eggshell sorbent, wereanalyzed. It was concluded that the adsorption of Cr(VI) on eggshell increases as pH increases in therange 3-7, then, with decreases at higher pH. The extraction percent of Cr(VI) increases with anincrease in the dosage of eggshell sorbents. The optimum dosage of eggshell adsorbents was found tobe 5 g after which the extraction percent of Cr(VI) did not marked increase. The extraction percent ofCr(VI) by eggshell sorbents rapidly increases within 60 min followed by a slower extraction after thatwhen maximum adsorption was reported. The adsorption capacity of Cr(VI) ions is slightly reducedin case of heated eggshell due to the change that occurs in the pore size distribution and structure ofeggshell during heating. Hence, the thermal treatment and coating with Fe2O3 do not affect the chemicalstructure of eggshell sorbents. The adsorption kinetics data were best fitted with the pseudo-second-orderequation and the adsorption isotherms were best fitted with the Langmuir isotherm model.