title: Nutrient-substituted hydroxyapatites: synthesis and characterization.
abstract: Incorporation of Mg, S, and plant-essential micronutrients into the structure of synthetic hydroxyapatite (HA) may be advantageous for closed-loop systems, such as will be required on Lunar and Martian outposts, because these apatites can be used as slow-release fertilizers. Our objective was to synthesize HA with Ca, P, Mg, S, Fe, Cu, Mn, Zn, Mo, B, and Cl incorporated into the structure, i.e., nutrient-substituted apatites. Hydroxyapatite, carbonate hydroxyapatite (CHA), nutrient-substituted hydroxyapatite (NHA), and nutrient-substituted carbonate hydroxyapatite (NCHA) were synthesized by precipitating from solution. Chemical and mineralogical analysis of precipitated samples indicated a considerable fraction of the added cations were incorporated into HA, without mineral impurities. Particle size of the HA was in the 1 to 40 nm range, and decreased with increased substitution of nutrient elements. The particle shape of HA was elongated in the c-direction in unsubstituted HA and NHA but more spherical in CHA and NCHA. The substitution of cations and anions in the HA structure was confirmed by the decrease of the d[002] spacing of HA with substitution of ions with an ionic radius less than that of Ca or P. The DTPA-extractable Cu ranged from 8 to 8429 mg kg-1, Zn ranged from 57 to 1279 mg kg-1, Fe from 211 to 2573 mg kg-1, and Mn from 190 to 1719 mg kg-1, depending on the substitution level of each element in HA. Nutrient-substituted HA has the potential to be used as a slow-release fertilizer to supply micronutrients, S, and Mg in addition to Ca and P.
authors.affiliation: Lockheed-Martin Corp., Houston, TX 77258-8561, USA. d.c.golden1@jsc.nasa.gov
authors.forename: D C
authors.initials: DC
authors.lastname: Golden
authors.forename: D W
authors.initials: DW
authors.lastname: Ming
mesh_terms: D002254:Carbonates / Q000032:analysis / Q000138:chemical synthesis*; D019343:Citric Acid / Q000737:chemistry; D018504:Ecological Systems, Closed; D005308:Fertilizers / Q000032:analysis*; D018527:Hydroponics; D006882:Hydroxyapatites / Q000032:analysis / Q000138:chemical synthesis*; D008021:Life Support Systems; D018977:Micronutrients; D008854:Microscopy, Electron; D008903:Minerals / Q000032:analysis; D012987:Soil / Q000032:analysis; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D002254:Carbonates; D005308:Fertilizers; D006882:Hydroxyapatites; D018977:Micronutrients; D008903:Minerals; D012987:Soil; D012996:Solutions; D019343:Citric Acid