Kinetics of mixed Ni-Al precipitate formation on a soil clay fraction

Journal Article · Mon Nov 01 04:00:00 EST 1999 · Environmental Science and Technology

DOI:https://doi.org/10.1021/es990235e· OSTI ID:20000698

Roberts, D R; Scheidegger, A M; Sparks, D L

The kinetics of mixed Ni-Al layered double hydroxide (LDH) precipitate formation on a soil clay fraction was monitored using X-ray absorption fine structure (XAFS) spectroscopy. The kinetic behavior was monitored at pH 6.0, 6.8, and 7.5 in order to determine the effect of reaction pH on precipitate formation. XAFS analyses were performed on a Ni-reacted whole soil at pH 7.5 to determine the effect of metal oxides and organic matter on mixed Ni-Al LDH formation. The initial Ni concentration was 3 mM with a solid/solution ration of 10 g L{sup {minus}1} in 0.1 M NaNo{sub 3}. Initial Ni sorption kinetics on the soil clay were rapid at all pH values but differed at each pH for longer reaction times. The sorption kinetics at pH 7.5 were characterized by an extremely rapid initial step with nearly 75% of Ni sorbed within 20 h, followed by a slower step with nearly 100% of the Ni removed from solution within 150 h. XAFS analysis of the pH 7.5 sorption samples indicated the formation of a mixes Ni-Al LDH within 15 min. The sorption kinetics at pH 6.8 were initially rapid, followed by a slow step, and SAFS revealed the formation of a Ni-Al LDH within 2 h. At pH 6.0, Ni sorption did not exceed 20% and SAFS analysis for the whole soil indicated a mixed Ni-Al phase formed at pH 7.5 after 24 h of reaction. These findings indicate that mixed metal precipitate formation occurs in heterogeneous clay systems and whole soils; therefore, they should be considered when predicting and modeling the fate of metals in subsurface environments.

• Research Organization: Univ. of Delaware, Newark, DE (US)
• OSTI ID: 20000698
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 21 Vol. 33; ISSN ESTHAG; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ALUMINIUM
CLAYS
ENVIRONMENTAL TRANSPORT
NICKEL
PRECIPITATION
SOIL CHEMISTRY
SORPTION
X-RAY SPECTROSCOPY