Characterization of Mineral Precipitate

The precipitate collected by centrifugation (8000 rpm, 5 min) was first fixed with 2.5% glutaraldehyde fixation solution for 1.5 h. Then, the precipitate collected after centrifugation was formed by the addition of ethanol by 30%, 50%, 70%, 90% and 100% of the gradient to dehydrate for 15–20 min [28 (link)], and the resulting precipitate was dried for 6 h in a lyophilizer (FD-1A-50, Beijing Boyikang Laboratory Instrument Co., Ltd., Beijing, China). An SEM (JSM-6360 LA, Japan Electron Optics Laboratory Co., Ltd, Tokyo, Japan) was used to observe the structural morphology of the mineral precipitate at a stable voltage of 15 kV and EDS (JSM-6360 LA, Japan Electron Optics Laboratory Co., Ltd, Tokyo, Japan) performed a detailed elemental analysis of the mineral precipitation components.