Optimization of Hg(II) adsorption on bio-apatite based materials using CCD-RSM design: characterization and mechanism...

Bio-apatite based materials were prepared from bovine bone wastes (BBW) by thermal treatments using a direct flame (BBS) and annealing at 500-1,100 °C (BB500-BB1100). These low-crystalline materials were characterized by means of SEM, XRD, FTIR, TG, and pH_PZC and were used for the adsorption of Hg(II) ions. A CCD-RSM design was used to optimize and analyze independent variables consisting of initial mercury concentration (10-100 mg L^-1), pH (2-9), adsorbent mass (0.1-0.5 g), temperature (20-60 °C), and contact time (15-120 min). The results indicated that the order of the mercury uptakes for bio-apatite based adsorbents was BB500 > BB600 > BB800 > BB1100 > BBS > BBW. The dissolution-precipitation and ion-exchange reaction are the two dominant mechanisms for the removal of Hg(II) ions at low and high pH values, respectively. The CCD-RSM predicted maximum mercury adsorption of 99.99% under the optimal conditions of 51.31 mg L^-1, 0.44 g, 6.5, 67.5 min, and 50 °C for initial mercury concentration, adsorbent mass, pH, contact time, and temperature, respectively. The findings of the present study revealed that the bio-apatite based materials, particularly BB500, are suitable and versatile adsorbents for the treatment of mercury-containing wastewater.