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Calcium Ion Complexation by Fulvic Acid Extracted from Sewage Sludge‐soil Mixtures
Author(s) -
Sposito Garrison,
Holtzclaw Kenneth M.,
LeVesqueMadore C. S.
Publication year - 1978
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/sssaj1978.03615995004200040013x
Subject(s) - chemistry , potentiometric titration , titration , inorganic chemistry , calcium , ion , sewage sludge , sewage , organic chemistry , engineering , waste management
The complexes formed between Ca 2+ and fulvic acid extracted from sewage sludge were investigated by potentiometric titration of K/H‐fulvate with Ca(NO 3 ) 2 at pH 7 and 25°C, in an ionic medium of 0.1 N KNO 3 . Formation functions, giving the number of moles of Ca bound per mole of K/H‐fulvate, were calculated from the titration data and plotted against the concentration of Ca 2+ , with the concentration of K/H‐fulvate being a fixed parameter for each plot. The molarity of K/H‐fulvate, which was held rigorously constant during each titration, was determined with the help of separate experiments in which the number‐average molecular weight of the K/H‐fulvate sample employed was measured by vapor pressure osmometry. The formation functions were interpreted as evidence of: (i) a relatively strong ion pair that is formed between Ca 2+ and the most acidic functional groups in fulvic acid, and (ii) a weaker ion pair that is formed between Ca 2+ and the more weakly acidic functional groups. The properties of the latter complex depend both on pH and on the concentration of fulvic acid, since these variables in part determine the number of ionized, weakly acidic functional groups that can react with Ca 2+ . The Ca 2+ ion was shown to have a modest ability to displace protons from undissociated acidic functional groups in sludge‐derived fulvic acid.