Abstract
The purpose of this study was to elucidate the characteristics and mechanisms of adsorption and desorption for heavy metals by micro and nano-sized biogenic CaCO(3) induced by Bacillus subtilis, and the pH effect on adsorption was investigated. The results showed that the adsorption characteristics of Cd(2+) and Pb(2+) are well described by the Langmuir adsorption isothermal equation, and the maximum adsorption amounts for Cd(2+) and Pb(2+) were 94.340 and 416.667 mg/g, respectively. The maximum removal efficiencies were 97% for Cd(2+), 100% for Pb(2+), and the desorption rate was smaller than 3%. Further experiments revealed that the biogenic CaCO(3) could maintain its high adsorption capability for heavy metals within wide pH ranges (3-8). The FTIR and XRD results showed that, after the biogenic CaCO(3) adsorbed Cd(2+) or Pb(2+), it did not produce a new phase, which indicated that biogenic CaCO(3) and heavy metal ions were governed by a physical adsorption process, and the high adsorptive capacity of biogenic CaCO(3) for Cd(2+) and Pb(2+) were mainly attributed to its large total specific surface area. The findings could improve the state of knowledge about biogenic CaCO(3) formation in the environment and its potential roles in the biogeochemical cycles of heavy metals.