TY - JOUR

T1 - Influence of calcium and aluminum on crystallization of vivianite, Fe3(PO4)2·8H2O

AU - Madsen, Hans Erik Lundager

PY - 2019

Y1 - 2019

N2 - The iron(II) phosphate vivianite, Fe3(PO4)2·8H2O, has been precipitated at 37 °C from solution of ammonium iron(II) sulfate (Mohr's salt) and ammonium phosphate, to which a small amount of calcium nitrate or aluminum potassium sulfate (alum) was added. The relatively high temperature was chosen to minimize the formation of crystal aggregates, which would otherwise complicate study of morphology. Crystallization kinetics was determined by pH recording, and the resulting crystals were studied by polarization microscopy. The main effect of Al observed was formation of small, irregular crystals. In contrast, Ca had little or no effect on morphology, but in three cases at intermediate additive concentrations kinetics changed from the usual combination of spiral growth and surface nucleation to pure spiral growth. It is proposed that the screw dislocations leading to growth spirals originate either from calcium phosphate crystallites acting as heteronuclei or from nuclei containing both Fe and Ca and with structure deviating from that of pure vivianite.

AB - The iron(II) phosphate vivianite, Fe3(PO4)2·8H2O, has been precipitated at 37 °C from solution of ammonium iron(II) sulfate (Mohr's salt) and ammonium phosphate, to which a small amount of calcium nitrate or aluminum potassium sulfate (alum) was added. The relatively high temperature was chosen to minimize the formation of crystal aggregates, which would otherwise complicate study of morphology. Crystallization kinetics was determined by pH recording, and the resulting crystals were studied by polarization microscopy. The main effect of Al observed was formation of small, irregular crystals. In contrast, Ca had little or no effect on morphology, but in three cases at intermediate additive concentrations kinetics changed from the usual combination of spiral growth and surface nucleation to pure spiral growth. It is proposed that the screw dislocations leading to growth spirals originate either from calcium phosphate crystallites acting as heteronuclei or from nuclei containing both Fe and Ca and with structure deviating from that of pure vivianite.

KW - A1. Environment

KW - A2. Growth from solution

KW - B1. Minerals

KW - B1. Phosphates

U2 - 10.1016/j.jcrysgro.2019.125242

DO - 10.1016/j.jcrysgro.2019.125242

M3 - Journal article

AN - SCOPUS:85072270129

VL - 526

JO - Journal of Crystal Growth

JF - Journal of Crystal Growth

SN - 0022-0248

M1 - 125242

ER -