CRYSTALLIZATION OF IRON(III) PHOSPHATE AT ROOM-TEMPERATURE

Ferric nitrate, sodium dihydrogen phosphate, and sodium hydroxide solutions were mixed in a variety of combinations and aged at room temperature. The results showed that, with solutions 0.001M in Fe, 0.0002 to 0.001M in phosphate, and NaOH/Fe molar ratios ranging from 0 to 3 (pH 2.6 to 7.8), all precipitates were amorphous basic iron(III) phosphates without any tendency to crystallize toward strengite-type compounds for up to at least 66 months. With 0.01M in Fe, metastrengite was observed from samples 0.03 to 0.06M in phosphate (pH 2.0 to 2.4) 24 months after preparation, but the reaction product was positively charged amorphous basic iron phosphate if the sample was dispersed in 0.01M in phosphate (pH 1.8) during the entire period of study. These positively charged particles were rapidly precipitable with sulfate. The sample 0.02M in phosphate was on the borderline for metastrengite formation. © 1982 Soil Science Society of America.