A combined scanning Auger, XPS, scanning SIMS, and TEM (electron diffraction) investigation of naturally‐occurring goethite surfaces in contact with 10 −3 M KH 2 PO 4 solution for 90 d at 60 °C has shown that isolated crystallites of the mineral griphite, Fe 3 Mn 2 (PO 4 ) 2.5 (OH) 2 , are formed by reprecipitation from solution. No adsorbed phosphate can be detected on the goethite surface above 0.1 atomic % and there is no phosphate penetration of the goethite crystals. Evidence concerning initial adsorption of phosphate, before recrystallization, is reconsidered. The results suggest that phosphate retention in Fe oxide systems may be due primarily to precipitation rather than adsorption.
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Martin et al. (1988) studied this question.