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Calcium Phosphate Precipitation: Identification of Kinetic Parameters in Aqueous Limestone Suspensions
Author(s) -
Brown J. L.
Publication year - 1981
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1981.03615995004500030006x
Subject(s) - fluorapatite , phosphate , apatite , aqueous solution , calcium , precipitation , phosphorite , mineralogy , chemistry , phosphate minerals , crystal (programming language) , molar concentration , nuclear chemistry , inorganic chemistry , biochemistry , organic chemistry , physics , meteorology , computer science , programming language
Phosphate disappearance from aqueous calcitic limestone suspensions was described using an equation for interface‐, controlled crystal growth following addition of hydroxyapatite seed crystals. Phosphate removal from solution exhibited second order dependence on the phosphate concentration. Hydroxyapatite seed crystals were more important than limestone in governing phosphate removal. Limestone functioned primarily to buffer the activities of (Ca 2+ ) and (OH ‐ ). At pH 8.5, an increase of 0.1‐millimolar (m M ) NaF caused a fivefold increase in the rate constant. Twenty successive reactions of limestone with phosphate caused a fourfold increase in the phosphate removal rate. A portion of freshly precipitated calcium phosphate probably served as seed for development of new crystals. Participation of both (F ‐ ) and hydroxyapatite crystals suggests a mixture of fluorapatite and hydroxyapatite, or an apatite precursor formed in the experiments.