Characteristics and mechanisms of molybdenum(VI) adsorption by drinking water treatment residue

Molybdenum (Mo) is an important pollutant in surface water. Removal of Mo from aqueous solutions by adsorption using low-cost and environmental friendly adsorbents has gained wide acceptance. Drinking water treatment residue (DWTR) is an inevitable by-product during potable water production that has the high capability of adsorption of heavy metals. However, the characteristics and mechanisms of Mo adsorption by DWTR still remain unclear. In this study, we showed that Mo(VI) adsorption by DWTR followed the pseudo-second-order rate. The adsorption isotherms for Mo(VI) were best described by the Langmuir model. Thermodynamic parameters indicated that the adsorption process was endothermal, entropy increasing, and spontaneous. Electrostatic interaction and surface complexation were found to be major adsorption mechanisms. The adsorption rate of Mo(VI) by DWTR was dependent on pH values and lineally increased as pH decreased from 10 to 4. The estimated maximum adsorption capacity was 31.06 mg/g at 318 K at pH 2.0. Desorption experiments were also performed to evaluate the potential of DWTR regeneration. These results suggested that DWTR was a green, efficient, and recyclable adsorbent for Mo(VI) and could be used for removal and recovery of Mo from polluted environments.