Thermal treatment of aluminous phosphates of the crandallite group and its effect on phosphorus solubility

Abstract

Optimization in the use of phosphate rocks is important and the residues of fertilizer production in the form of crandallite may be suitable for agronomic use after calcination. With the objective of evaluating the effect of thermal treatment of the aluminous phosphates of the crandallite group as related to solubility, crystalline structure and morphology, samples from the mine residues of three Brazilian phosphate deposits (Tapira-MG, Catalão-GO, and Juquiá-SP) were collected, air-dried, and screened to 100 mesh. Sub samples were thermally treated at 300, 500, 700, and 900°C for 2 hours. Treated and untreated materials were analyzed by X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectrometry, and for the total and soluble P contents. The treatment of samples: (i) raised P solubility in neutral ammonium citrate solution, (ii) caused the disorganization of the crystalline structure of crandallite at 500°C and above, and (iii) altered their morphology (cracking and rounding). The increase in P solubility of samples after calcination indicates that the agronomic utilization of these marginal P sources may be of interest since plant growth may be favored due to higher P availability. New studies to evaluate these materials in order to determine their agronomic effectiveness must be carried out to establish adequate conditions that favor their use by plants. Key words: calcination, phosphate fertilizer, phosphate impurities TRATAMENTO TÉRMICO DE FOSFATOS ALUMINOSOS DO GRUPO DA CRANDALLITA E SEU EFEITO NA SOLUBILIDADE DO FÓSFORORESUMO: A otimização do uso de rochas fosfáticas é importante e resíduos da indústria de fertilizantes fosfatados na forma de crandallita poderão ser agronomicamente eficientes após calcinação. Com o objetivo de avaliar o efeito do tratamento térmico em fosfatos aluminosos do tipo crandallita quanto à solubilidade, estrutura cristalina, e morfologia, amostras do rejeito de mineração de três depósitos fosfáticos brasileiros (Tapira-MG, Catalão-GO e Juquiá-SP) foram coletadas, secas ao ar e separadas por peneiramento 100 mesh. Sub-amostras foram submetidas ao tratamento térmico a 300, 500, 700 e 900°C durante 2 horas. Os materiais tratados e não-tratados foram analisados por difratometria de raios X, observados por microscopia eletrônica de varredura e espectrometria por energia dispersiva, e seus teores de fósforo total e solúvel determinados. O tratamento térmico das amostras: (i) elevou, consideravelmente, a solubilidade em CNA dos materiais; (ii) promoveu a desorganização da estrutura cristalina da crandallita a temperaturas de 500°C e superiores; e (iii) causou alterações morfológicas (fraturamento e arredondamento) nas amostras. O aumento na solubilidade das amostras após o tratamento térmico indica que a utilização agronômica destas fontes marginais de P pode ser de interesse, uma vez que o crescimento das plantas pode ser favorecido pela maior disponibilidade de P. Estudos de avaliação desses materiais a fim de determinar sua eficiência agronômica...

Hillslope curvature, clay mineralogy, and phosphorus adsorption in an Alfisol cultivated with sugarcane

“…Therefore, the convex area has a highest proportion of gibbsite and smaller kaolinite crystals when compared to the concave area. The convex area favors the formation of gibbsite, demonstrating that the relief may indicate the boundaries between the environments and specific areas for the management and transfer of information (Marques Júnior & Lepsch, 2000;Franzen et al, 2006).…”

“…The hillslope curvatures and steepness make up a complex pattern of water and solute transportation in a soil landscape (Marques Júnior & Lepsch, 2000;Franzen et. al., 2006).…”

“…Similarities between the spatial distribution of the soil clay minerals and their chemical properties may explain the cause/effect relationship between these properties and the relief curvature (Franzen et al, 2006). This relationship is important because it can guide farm management decisions, such as the number of soil samples necessary to characterize an area (Souza et al, 2006) and the required amount of fertilizer.…”

“…Improving the efficiency of phosphate fertilization has been objective of many researchers (Francisco et al, 2007;Nogueira & Cardoso, 2007;Galvani et al, 2008). Most crops in Brazil respond positively to the application of phosphorus.…”

Application of Gettering Process on the Improvement of the Structural and Mineralogical Properties of Tunisian Phosphate Rock

“…This scanning procedure consisted of looking for structure alterations, agglutination, porosity, morphology, compaction, and distribution, with qualitative and semi quantitative identification of elements [35].…”