Selective and Efficient Removal of Anionic Dyes from Solution by Zirconium(IV) Hydroxide-Coated Magnetic Materials

An effective adsorbent, a zirconium hydroxide coating on the surface of magnetic materials (Zr–Fe 3 O 4 ), was successfully synthesized by a precipitation method to selectively adsorb Alizarin red (AR) from solution in batch mode. The characterizations of Zr–Fe 3 O 4 were achieved by XRF, XRD, SEM, and XPS. Adsorption conditions of AR on Zr–Fe 3 O 4, including the pH, contact time, concentration of the dye, and ionic strength of the aqueous solution, were optimized, and the maximum adsorption capacity from experiments was 83.7 mg·g –1 at 313 K. Common salts existing in solution were beneficial to AR adsorption. The analysis of adsorption isotherm data showed that the Redlich–Peterson model could better describe the adsorption procedure of AR on the magnetic adsorbent. The kinetic data could be fitted well by the Elovich equation. The adsorption process was spontaneous, endothermic, and entropy-produced according to the thermodynamic results. XPS analysis showed that there was interaction between Zr from the adsorbent and O from AR. In addition, adsorption in a single system was compared to competitive adsorption in the binary system between AR and acid chrome blue K (AK). It was concluded that the complexation was the main force between Zr–Fe 3 O 4 and AR, while there was selective adsorption of AR from solution. Zr–Fe 3 O 4 was selective and effective in the removal of AR from solution.