High-efficiency and low-cost α-Fe2O3 nanoparticles-coated volcanic rock for Cd(II) removal from wastewater

Volcanic rock with the α-Fe2O3 nanoparticles coating was fabricated to be an efficient and low-cost adsorbent for Cd(II) ions in water. ESEM, TEM, XPS and BET characterizations of the coated volcanic rock showed that the α-Fe2O3 nanoparticles were successfully and homogeneously disseminated throughout the rock, including penetration into rock pores. Batch experiments were conducted to examine adsorption performance. The highest adsorption values were observed in a pH range of 4.0-7.0; hence, a pH value of 6.0 was used in this study. The maximum adsorption capacities of Cd(II) ions were found to be 127.23 mg/g, 146.41 mg/g and 158.48 mg/g at 293 K, 303 K and 313 K, respectively. The adsorption kinetic features of Cd(II) ions were found to be fitted best by a pseudo-second-order model, suggesting the presence of chemisorption processes. Intra-particle diffusion model results show that the adsorption processes can be divided into different stages, and the adsorption of the exterior and interior surfaces reached saturation at approximately 40 and 240 min, respectively. The adsorption process was also found to be endothermic and spontaneous. Hence, volcanic rock coated with α-Fe2O3 nanoparticles serves as a high-efficiency and low-cost adsorbent.