Mechanisms of tripolyphosphate adsorption and hydrolysis on goethite

Jordan G Hamilton; David Hilger; Derek Peak

doi:10.1016/j.jcis.2016.12.036

Mechanisms of tripolyphosphate adsorption and hydrolysis on goethite

J Colloid Interface Sci. 2017 Apr 1:491:190-198. doi: 10.1016/j.jcis.2016.12.036. Epub 2016 Dec 19.

Authors

Jordan G Hamilton¹, David Hilger², Derek Peak²

Affiliations

¹ Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A8, Canada. Electronic address: Jordan.Hamilton@usask.ca.
² Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A8, Canada.

PMID: 28033517
DOI: 10.1016/j.jcis.2016.12.036

Abstract

Linear tripolyphosphates (TPP) are used extensively in liquid fertilizers though little is known about their chemical fate after sorption on mineral surfaces. The initial rapid adsorption of TPP to metal oxide surfaces has been observed, but it is not known whether this adsorption will catalyze or inhibit TPP hydrolysis. To determine the effects of adsorption upon TPP hydrolysis, batch reactors were set up with two surface loadings of TPP adsorbed on goethite (α-FeOOH) for up to 3months at pH 4.5, 6.5 and 8.5. Samples were analyzed for; adsorbed phosphorus (P), P speciation via both P K-edge XANES and FTIR vibrational spectroscopies. Additionally, it was learned through in-situ ATR-FTIR that drying of adsorbed TPP in the presence of Ca results in the formation of a Ca-trimetaphosphate type of surface complex. The rates of adsorbed TPP hydrolysis as measured with ex-situ FTIR were most rapid at pH 4.5 with 100% of the TPP fully hydrolyzed by 3months. Slower rates were observed at pH 6.5 and 8.5 through 3months. Compared to published rates of aqueous TPP hydrolysis, adsorption to mineral surfaces catalyzes TPP hydrolysis.

Keywords: ATR-FTIR spectroscopy; Hydrolysis rates; Phosphorus XANES; Tripolyphosphate adsorption; Tripolyphosphate hydrolysis.