Microbially induced calcium carbonate precipitation (MICP) is a bio-geochemical process involving calcium carbonate precipitation and possible co-precipitation of other metals. The study investigated the extent to which a urease-positive bacterium, Sporosarcina pasteurii, can tolerate a range of metals (e.g., Cu, Zn, Pb, Cd, and Sr), and analyzed the role of calcium carbonate bioprecipitation in eliminating these divalent toxicants from aqueous solutions. The experiments using S. pasteurii were performed aerobically in growth media including urea, CaCl2 (30 mM) and different metals such Cu, Zn, Pb, and Cd (0.01 ∼ 1 mM), and Sr (1 ∼ 30 mM). Microbial growth and urea degradation led to an increase in pH and OD600, facilitating the precipitation of calcium carbonate. The metal types and concentrations contributed to the mineralogy of various calcium carbonates precipitated and differences in metal removal rates. Pb and Sr showed more than 99% removal efficiency, whereas Cu, Zn, and Cd showed a low removal efficiency of 30∼60% at a low concentration of 0.05 mM or less. Thus the removal efficiency of metal ions during MICP varied with the types and concentrations of divalent cations. The MICP in the presence of divalent metals also affected the mineralogical properties such as carbonate mineralogy, shape, and crystallinity.
Opaline mudstone (OM) composed of opal-CT (SiO2·nH2O) has high potential use as a cesium (Cs) adsorbent, due to its high specific surface area (SSA). The objective of this study was to investigate the Cs adsorption capacity of chemically activated OM and the adsorption mechanism based on its physico-chemical properties. We used acid- and base-activation methods for the surface modification of OM. Both acid- and base- activations highly increased the specific surface area (SSA) of OM, however, the base-activation decreased the zeta potential value more (− 16.67 mV), compared to the effects of acid-activation (− 6.60 mV) or non-activation method (− 6.66 mV). Base-activated OM showed higher Cs adsorption capacity (32.14 mg/g) than the others (acid: 12.22 mg/g, non: 15.47 mg/g). These results indicate that base-activation generates pH-dependent negative charge, which facilitates Cs adsorption via electrostatic attraction. In terms of the dynamic atomic behavior, Cs cation adsorbed on the OM mainly exist in the form of inner-sphere complexes (IS) containing minor amounts of water molecules. Consequently, the OM can be used as an effective Cs adsorbent via base-activation as an economical and simple modification method.
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