Effect of different thermal activation on hydroxyapatite to eliminate mercury from aqueous solutions in continuous adsorption system

ABSTRACT

The present study evaluated the performance of modified hydroxyapatite by thermal activation in mercury removal from aqueous solution in a continuous adsorption system. The bone waste (BW), bone soot (BS), bone heated at 500, 600, 800, and 1100°C were specified using Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric and pH_PZC. Heat treatment led to removing all of the organic components of the bone and appearance of pores in the hydroxyapatite surfaces. Comparison between the adsorbents confirmed the absorbency of bone heated at 500°C, so this adsorbent was selected to study the effective parameters on mercury elimination in a continuous adsorption system, including flow rate (0.5–1.5 mL/min), bed height (3, 6 and 9 cm), initial mercury concentration (20–80 mg/L) and solution pH (2–9). Reduction in initial mercury concentration and flow rate, enhancement in bed height and pH led to delaying in breakthrough time and consequently increased the mercury adsorption. Results revealed that the optimum sorption of mercury(II) occurred at pH 7, mercury initial concentration 80 mg/L, bed height 6 cm and a flow rate of 0.5 mL/min. Among the models used in packed-bed assessment, the bed depth service time, Yoon–Nelson, and Thomas models are proper to describe the packed-bed adsorption. Generally, the modified bones indicated a remarkable capability to remove mercury ions in a dynamic system.

KEYWORDS:

• Adsorption
• fixed-bed column
• hydroxyapatite
• mercury
• thermal activation

Acknowledgments

The authors would like to thank water quality laboratory of Fasa University for providing the facilities to perform this research.

Disclosure statement

No potential conflict of interest was reported by the authors.