Utilization of aluminum hydroxide waste generated in fluoride adsorption and coagulation processes for adsorptive removal of cadmium ion

Although Al-based coagulation and adsorption processes have been proved highly efficient for fluoride (F) removal, the two processes both generate large amount of Al(OH)(3) solid waste containing F (Al(OH)(3)-F). This study aimed to investigate the feasibility of utilizing Al(OH)(3)-F generated in Al(OH)(3) adsorption (Al(OH)(3)-F-ads) and coagulation (Al(OH)(3)-F-coag) for the adsorption of cadmium ion (Cd(II)). The adsorption capacity of Al(OH)(3)-F-ads and Al(OH)(3)-F-coag for Cd(II) was similar as that of pristine aluminum hydroxide (Al(OH)(3)), being of 24.39 and 19.90 mg.g(-1), respectively. The adsorption of Cd(II) onto Al(OH)(3)-F-ads and Al(OH)(3)-F-coag was identified to be dominated by ion-exchange with sodium ion (Na+) or hydrogen ion (H+), surface microprecitation, and electrostatic attraction. The maximum concentration of the leached fluoride from Al(OH)(3)-F-ads and Al(OH)(3)-F-coag is below the Chinese Class-I IndustrialWastewater Discharge Standard for fluoride (<10 mg.L-1). This study demonstrates that the Al(OH)(3) solid wastes generated in fluoride removal process could be potentially utilized as a adsorbent for Cd(II) removal.