page_title: Biomineralization
section_title: Uranium contaminants in groundwater
hierarchical_section_title: Biomineralization / Potential applications / Uranium contaminants in groundwater
caption_attribution_description: English: Autunite Locality: Daybreak Mine (Dahl lease), Mount Kit Carson, Spokane County, Washington, USA (Locality at mindat.org) Very elegant thumbnail of this classic material, probably from the 1950s or 60s! 2.3 x 2 x 1.2 cm Deutsch: Autunit Fundort: Daybreak Mine (Dahl lease), Mount Kit Carson, Spokane County, Washington , Vereinigte Staaten (Fundort bei mindat.org)
context_page_description: Biomineralization, or biomineralisation is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Such tissues are called mineralized tissues. It is an extremely widespread phenomenon; all six taxonomic kingdoms contain members that are able to form minerals, and over 60 different minerals have been identified in organisms. Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates. These minerals often form structural features such as sea shells and the bone in mammals and birds. Organisms have been producing mineralised skeletons for the past 550 million years. Ca carbonates and Ca phosphates are usually crystalline, but silica organisms are always non crystalline minerals. Other examples include copper, iron and gold deposits involving bacteria. Biologically-formed minerals often have special uses such as magnetic sensors in magnetotactic bacteria, gravity sensing devices and iron storage and mobilization.
context_section_description: Biomineralization may be used to remediate groundwater contaminated with uranium. The biomineralization of uranium primarily involves the precipitation of uranium phosphate minerals associated with the release of phosphate by microorganisms. Negatively charged ligands at the surface of the cells attract the positively charged uranyl ion (UO₂²⁺). If the concentrations of phosphate and UO₂²⁺ are sufficiently high, minerals such as autunite (Ca(UO₂)₂(PO₄)₂•10-12H₂O) or polycrystalline HUO₂PO₄ may form thus reducing the mobility of UO₂²⁺.  Compared to the direct addition of inorganic phosphate to contaminated groundwater, biomineralization has the advantage that the ligands produced by microbes will target uranium compounds more specifically rather than react actively with all aqueous metals. Stimulating bacterial phosphatase activity to liberate phosphate under controlled conditions limits the rate of bacterial hydrolysis of organophosphate and the release of phosphate to the system, thus avoiding clogging of the injection location with metal phosphate minerals. The high concentration of ligands near the cell surface also provides nucleation foci for precipitation, which leads to higher efficiency than chemical precipitation.
caption: Autunite crystal.
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