Structural properties and dissolution of iron, manganese and copper containing synthetic hydroxyapatite.

摘要

The National Aeronautics and Space Administration's Advanced Life Support (ALS) program is developing a slow-release fertilizer for growing crops in closed-loop, life-support systems for Lunar and Martian outposts. Crops will provide food and recycle air (photosynthesis) and water (transpiration). This slow-release fertilizer contains synthetic hydroxyapatite (SHA), which has micronutrients incorporated into the SHA structure. Due to the low solubility of SHA, slow-nutrient release from micronutrient-containing SHA at rates suitable for plant growth is expected. This would be ideal for missions expected to last over a year.; The objectives of this research were to (i) synthesize SHA (Pure-SHA) and SHA materials each separately containing one of the plant essential micronutrients iron (Fe), manganese (Mn) and copper (Cu), (ii) characterize the Pure-, Fe-, Mn- and Cu-SHA structures, (iii) examine the dissolution characteristics of Pure-, Fe-, Mn- and Cu-SHA and (iv) utilize the results of this research to assess the potential of the Fe-, Mn- and Cu-SHA to supply adequate levels of calcium (Ca), phosphorus (P), Fe, Mn, and Cu to plants.; X-ray diffraction indicated that hydroxyapatite was produced in all cases. Electron microprobe, nuclear magnetic resonance spectroscopy, electron paramagnetic resonance spectroscopy, infrared spectrometry and Rietveld analyses indicated that Fe3+, Mn2+, and Cu2+ substituted for Ca2+ in their respective SHA structures. Other detected phases included poorly-crystalline (PC) Fe-, Mn- and Cu-phases, bassinite [Ca2(SO4)2·H2O] and Fe- and Mn-phosphates.; Stir-cell dissolution experiments demonstrated that the Fe-, Mn- and Cu-SHA materials released Ca and P at concentrations comparable to Pure-SHA. Iron, Mn and Cu release were initially controlled by the PC transition metal phases. Once the PC phases were removed, Fe, Mn and Cu release were controlled by SHA dissolution. The P, Fe, and Cu release concentrations from SHA were sufficient for plant growth while Ca and Mn concentrations were limiting. Had equilibrium conditions been allowed in the stir-cell experiments, Ca and Mn concentrations may have occurred at levels sufficient for normal plant growth. The low solubility of SHA and the potential to supply sufficient Ca, P, Fe, Mn and Cu to plants indicate that micronutrient containing SHA will satisfy the requirements of the ALS cropping systems.