Linear tripolyphosphates (TPP) are used extensively in slow release liquid fertilizers, but little is known about the chemical fate of TPP after sorption on mineral surfaces. Rapid adsorption of TPP to metal oxide surfaces has been observed, but whether this adsorption will catalyze or inhibit TPP hydrolysis has not been studied. To determine the effects of adsorption upon TPP hydrolysis, batch reactors were set up to adsorb TPP on goethite (α-FeOOH) for up to 3 months at pH 4.5, 6.5 and 8.5. Speciation of adsorbed TPP samples was determined via both P K-edge XANES and FTIR spectroscopies. Adsorbed TPP hydrolysis rates measured with <i>ex-situ</i> FTIR were most rapid at pH 4.5 with 100% of the TPP hydrolyzed by 3 months. Slower rates were observed at pH 6.5 and 8.5 through 3 months. Compared to published rates of aqueous TPP hydrolysis, adsorption to mineral surfaces catalyzes TPP hydrolysis at pH 6.5 and 8.5. Application of TPP to calcareous soils resulted in rapid adsorption of TPP to soil mineral surfaces (&lt;48hrs) and persisted without hydrolyzing to ortho-P or precipitating as a calcium phosphate mineral species. Further large-scale field applications of TPP found that, over a one year period, TPP increased the relative fraction of adsorbed P from ~10-15% to 60% while also increasing total soil P concentration. This research demonstrates that TPP will rapidly adsorb to mineral surfaces with hydrolysis rates largely reliant on pH. However, adsorption to mineral surfaces has shown to catalyze subsequent TPP hydrolysis at alkaline pH conditions.<br/>

Mechanisms of tripolyphosphate adsorption and hydrolysis on mineral surfaces

255th National Meeting (2018)

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