Synthesis, Characterization, and Agronomic Evaluation of Iron Phosphate Impurities in Superphosphates
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Date
2003
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Abstract
Two of the most common impurities found in superphosphates processing marginal-grade PR was reported by Bartos (single superphosphate [SSP] and triple superphosphate [TSP]) in et al. (1992), Mullins et al. (1995), Mullins and Sikora the forms of Fe3KH8(PO4)6·6H2O and Fe3KH14(PO4)8·4H2O were syn- (1995), and Prochnow et al. (1998). The results showed thesized (H8-syn and H14-syn, respectively), characterized, and agro- that water solubility of these acidulated P fertilizers nomically evaluated to investigate cost-effective means to optimize required for maximum crop yield was lower than that the utilization of phosphate rocks (PRs) containing Fe impurities. A accepted by some legislation (Official Journal of the solubility study showed that more P was released from both com- European Communities, 1975; Brasil, 1982). However, pounds as pH increased in the 0.01 M KCl solutions (pH 3.0–7.5) and little attempt has been made to adequately characterize more P was released from H14-syn than H8-syn. The two Fe-K-P the impurity compounds present in acidulated P fertiliz- compounds were mixed and compacted with monocalcium phosphate ers, especially in SSP and TSP or to produce large quan- (MCP) at 0, 25, 50, 75, and 100% of total P as MCP. In a greenhouse tities under laboratory conditions for agronomic eval- study, rates of P were applied at 0, 10, 20, 40 and 80 mg P kg 1 from H8-syn, H14-syn, and MCP, while the compacted mixtures were uation. applied only at 40 mg P kg 1 to an Ultisol (thermic Rhodic Kanhaplu- In SSP and TSP, two of the most common waterdults, pH 5.3) cropped with upland and flooded rice (Oryza sativa insoluble P impurities are the generic compounds H8 L.) for 65 d. The results showed that P uptake and dry-matter yield and H14 (Lehr et al., 1967; Frazier et al., 1991). These were greater with H14-syn than H8-syn for both crops and both compounds preferentially form the K-containing com- compounds were more effective for flooded rice than upland rice. pounds, but in the absence of K in solution, Na-con- The calculated values of relative agronomic effectiveness (RAE) of taining compounds will form [(Fe,Al)3NaH8(PO4)6·6H2O H8-syn and H14-syn with respect to MCP were 32 and 72% in dry- or (Fe, Al)3NaH14(PO4)8·4H2O] or even as the analog H9 matter yield for upland rice and 55 and 102% for flooded rice, respec- or H15 members [(Fe, Al)3H9(PO4)6·6H2O or (Fe,Al)3 tively. To reach 90% of maximum dry-matter yield obtained with H15(PO4)8 MCP, it required approximately 43 and 35% of total P as water- ·4H2O] (Frazier et al., 1991; Sullivan et al., soluble P (WSP) in the mixtures of H8-syn and H14-syn with MCP 1991). According to Lehr et al. (1967) and Frazier et for upland rice and only 17 and 11% for flooded rice, respectively.
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Soil, Plants
Citation
Prochnow, L.I., S.H. Chien, E.F. Dillard,E.R. Austin, G. Carmona, J. Henao, U. Singh and R.W. Taylor. 2003. “Synthesis, Characterization, and Agronomic Evaluation of Iron Phosphate Impurities in Superphosphates,” Soil Sci. Soc. Am. J., 67:1551-1563.