IDENTIFICATION OF COMPOUNDS PRESENT IN SINGLE SUPERPHOSPHATES PRODUCED FROM BRAZILIAN PHOSPHATE ROCKS USING SEM, EDX, AND X-RAY TECHNIQUES

Abstract

Scanning electron microscope (SEM), energy dispersive X-ray (EDX) and X-ray techniques were used to obtain data about the mineralogical composition of single superphosphates (SSP) produced from apatite concentrates originating from Araxa, Jacupiranga, Catalao, and Tapira igneous phosphate rock deposits. The SSP samples were investigated both in their original form and after leaching with water to remove water-soluble compounds. Results of chemical analysis and instrumental techniques showed that P compounds were still present in the water-leached material. Anhydrite (CaSO 4 with no hydration water) was the main Ca-S component in the SSP samples. Monocalcium phosphate monohydrate [Ca(H 2 PO 4 ) 2 .H 2 O] was identified in the original but not in the water-leached samples. Results of SEM, EDX, and X-ray confirmed the presence of crystals of triiron (III) potassium octahydrogen hexaphosphate hexahydrate [Fe 3 KH 8 (PO 4 ) 6 .6H 2 O] in the SSP. The results of SEM and EDX analyses suggested that the compounds triiron (III) nonahydrogen hexaphosphate hexahydrate [Fe 3 H 9 (PO 4 ) 6 .6H 2 O], triiron (III) 15-hydrogen octaphosphate tetrahydrate [Fe 3 H 15 (PO 4 ) 8 .4H 2 O], triiron (III) potassium 14-hydrogen octaphosphate tetrahydrate [Fe 3 KH 14 (PO 4 ) 8 .4H 2 O], and barium sulfate (BaSO 4 ) were present in some of the SSP samples. Use of SEM, EDX, and X-ray techniques was shown to be adequate for precise characterization of compounds present in the SSP studied, which will help to understand further the plant availability of the phosphorus contained (especially) in the water-insoluble P fraction of this fertilizer.