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Studies of Aged OH‐Al Solutions using Kinetics of Al‐Ferron Reactions and Sulfate Precipitation
Author(s) -
Tsai Ping Ping,
Hsu Pa Ho
Publication year - 1984
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/sssaj1984.03615995004800010011x
Subject(s) - chemistry , reaction rate constant , precipitation , polymer , sulfate , monomer , kinetics , sodium , composition (language) , amorphous solid , crystallography , mineralogy , organic chemistry , linguistics , physics , philosophy , quantum mechanics , meteorology
A series of OH‐Al solutions (0.02 M in Al, NaOH/Al molar ratio = 1, slow neutralization) aged from 10 d to 55 months were all clear and had similar pH values and monomeric Al concentrations but reacted differently with sodium sulfate and with ferron. The addition of sodium sulfate yielded three kinds of basic aluminum sulfates: tetrahedral crystals of composition Na 0.08 Al(OH) 2.46 (SO 4 ) 0.31 · xH 2 O, x‐ray amorphous spherical particles of composition Al(OH) 2.34 (SO 4 ) 0.33 · xH 2 O, and irregular‐shaped crystals of composition Al(OH) 2.38 (SO 4 ) 0.31 · xH 2 O. The distribution of these sulfates is related to the aging of the parent OH‐Al solutions. The kinetics of Al‐ferron color development indicated that the OH‐Al polymers in the fresh solutions reacted with ferron rapidly, following a pseudo first‐order reaction (rate constant = 0.096 min −1 ). With increased aging, the rapidly reacting polymers slowly decreased, whereas another polymeric species that reacted with ferron slowly (rate constant = 0.00038 min −1 ) gradually developed. The results suggest that the polymers that reacted rapidly with ferron accounted for the formation of tetrahedral crystals and spherical particles, whereas those polymers that reacted slowly accounted for the formation of irregular‐shaped crystals.