Zn-biominerals: a perspective for environmental technologies to treat mine waters

Since life flourishing, biological processes have been producing a profound impact on the Earth’s environment (Hazen et al. 2008). Often, biomineralization processes respond to processes of life adaptation to extreme environments. Science and technology have advanced to the point where their relationship can now be explored in interdisciplinary studies. Thus, Nature offers many examples of sustainable materials that can be used in environmental and material science technologies. An extracellular Zn-biomineralization seasonally occurs in Naraculi river in the mine area of Ingurtosu (Sardinia, Italy). This biomineralization is made of hydrozincite and has relevant environmental implication for the abatement of Zn transported by river water. The cyanobacteria Scytonema sp. is responsible for the hydrozincite biomineralization. Several different factors affect the Naracauli biologically controlled mineralization, and bioremediation technology should be calibrated to optmize many of these factors. However, the Naracauli biomineralization occurs extracellularly, thus it is intrinsically a good candidate to be synthesized from Zn adsorption and nanocrystal nucleation onto a template. In this work, biomineral hydrozincite is investigated in order to assess molecular mechanism ruling nucleation and growth. Wanty et al. (2013) found that Zn is adsorbed onto organic filaments, and hydrozincite nanocrystals there nucleate and aggregate to form (100) flattened mesocrystals. Biologically produced hydrozincite was sampled and then analyzed by various techniques. Focusing Ion Beam was used to cut oriented thin slices comprising both organic filaments and hydrozincite mesocrystals. The thin slices were then investigated by HR-TEM imaging finding that the organic filaments are substantially made of an amorphous phase. Then, organic molecules were extracted from the biomineralization material and analysed by H-NMR finding the lipidic composition. Actually, the ongoing research is aimed to fully characterize the Scytonema sp. produced template, and then nucleate hydrozincite from adsorption of Zn onto a corresponding synthetic template