<p> Cerium oxide (CeO<sub>2</sub>) nanoparticles (NPs) were used for the removal of cadmium (II), lead (II) and chromium (VI) ions in single aqueous solutions and in solutions with mixtures of the three metals. The adsorption studies were carried out at pH 5 and 7 using a systematic factorial experimental design that considered the metal concentration from 1 mg l<sup>-1</sup> to 10 mg l<sup>-1</sup> and NP concentration from 0.064 g l<sup>-1</sup> to 0.640 g l<sup>-1</sup>. The highest adsorption capacity was obtained in the removal of lead (II) (128.1 mg g<sup>-1</sup>), followed by cadmium (II) (93.4</p>
<div>
<p>mg g<sup>-1</sup>) and finally chromium (VI) (34.4 mg g<sup>-1</sup>). Data were fitted to a polynomial function obtaining the best reduced models. The type of system (single, multi-component) did not affect sorption capacity, whilst pH affected the sorption of Cd and Cr, but not that of lead. CeO<sub>2</sub> nanoparticles proved to be effective adsorbents in removing all three heavy metals in multi-component systems, which opens a new window for their use as sorbent materials in complex waters contaminated with mixtures of heavy metals. </p>
</div>
<p> </p>
Cr (VI) removal from aqueous solutions by fly ash and fly ash composite filter material: Factorial experimental design
