[M-IS07] Aqua planetology

[MIS07-P05] Experimental study of phosphorus dissolution from hydroxyapatite in liquid CO₂

*Kaito Seo^1,2,3, Takazo Shibuya³, Fujishima Kosuke⁴, Ken Takai³, Masaru Tomita^1,2 (1.Graduate School of Media & Governance, Keio Univ., 2.Inst. Adv. Biosci., Keio Univ., 3.X-Star, JAMSTEC, 4.ELSI, Tokyo Tech)

Keywords:origin of life, P, phosphorus mineral, liquid CO2, apatite

Phosphorus (P) is known as one of the essential elements for life. It is incorporated in various macromolecules like DNA and RNA, phospholipids that forms cell membrane, as well as the energy currency and cofactors including but not limited to ATP, Acetyl-CoA and NADPH [1]. In the biogeochemical P cycle, oceanic content is far less than that on land, due to low solubility of phosphate minerals in seawater [2]. On Earth, major mineral that contains P is apatite [Ca₅(PO₄)_3-(F,Cl,OH)] in which, over 95% of P in the crust is included [3]. Few studies suggest additional supply sources of P through meteorites or other terrestrial minerals but their contribution to early chemical evolution is still under debate[4]. Under the ocean floor near hydrothermal vent sites, pool of liquid carbon dioxide (CO₂) was found [5,6]. Liquid CO₂ has unique property as a solvent, which can dissolve various hydrophobic chemical compounds including alcohols, carboxylic acids, phenol, esters, amides, etc., that are in many cases insoluble in water [7,8]. It is plausible that such liquid CO₂ reservoirs likely existed on hadean Earth, due to higher CO₂ concentration in the atmosphere [9] and deeper ocean compared to today. Apatite is known for their insoluble nature in seawater, however it has been shown to dissolve in CO₂ rich brines [10]. Hence, in this study, we performed dissolution of P from the powder of hydroxyapatite in liquid CO₂ saturated system with aqueous solution and analyzed the P concentration in both liquids.

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