Finding the Seventh Calcium Carbonate in Alkaline Lakes

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K18649
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 17:Earth and planetary science and related fields
• Research Institution: Kanazawa University
• Principal Investigator: Fukushi Keisuke 金沢大学, 環日本海域環境研究センター, 教授 (90444207)
• Co-Investigator(Kenkyū-buntansha): 高橋 嘉夫 東京大学, 大学院理学系研究科(理学部), 教授 (10304396) ; 濱田 麻希 金沢大学, 地球社会基盤学系, 助教 (90635997)
• Project Period (FY): 2021-07-09 – 2024-03-31
• Keywords: カルシウム炭酸塩1/2水和物 / 溶解度 / アルカリ塩湖

Outline of Final Research Achievements

Six calcium carbonates were previously recognized to occur in nature. A new species, Calcium Carbonate Hemihydrate (CCHH), was discovered in 2019 from laboratory synthesis experiments. In order to find CCHH in nature, this study (1) measured the solubility of CCHH, (2) constrained the possible formation site of CCHH by comparing the solubility with lake water data from around the world, and (3) searched for CCHH in nature. From (1) and (2), we found that the possible formation site of CCHH is alkaline lakes in the interior of continents. Next, we conducted a survey of alkaline lakes in southern Mongolia and were found the possible presence of CCHH in samples that were quickly conducted a solid-liquid separation on site. However, we considered that other mineralogical evidences were needed to support the reliable identification of CCHH.

Free Research Field

地球化学

Academic Significance and Societal Importance of the Research Achievements

カルシウム炭酸塩は地球上の普遍的に存在し、炭素循環において重要な役割を果たす。カルシウム炭酸塩はこれまで、古環境復元・バイオミネラリゼーション・二酸化炭素の地層貯留など、幅広い分野で研究されてきている。本研究ではカルシウム炭酸塩の新種であるCalcium Carbonate Hemihydrate (CCHH)の溶解度を世界で初めて測定し、その結果に基づき、アルカリ塩湖にCCHHが存在する可能性を得た。アルカリ塩湖は大気二酸化炭素の吸収源として機能する可能性を持つことが近年指摘されている。CCHHはアルカリ塩湖における二酸化炭素の固定反応に重要な寄与を果たすことが推測される。