Porous phosphatic materials of agronomical interest:Synthesis and study of their dissolution
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Abstract
Phosphatic materials of agronomic interest were synthesised. These materials of good mechanical quality and of significant porosity show high P2O5 contents (up to 28%). They have been prepared by treatment of volcanic pumices with a solution of phosphoric acid (1N, 5N or 10N) at 200°C in a closed system for 72h using a mass solid/liquid ratio of 1:3.
After reaction, the precipitation of amorphous phosphates and crystalline aluminium phosphates has been detected by XRD both outside and inside of the material. The morphological study by SEM reveals several crystalline forms of aluminium phosphates: crystals of small size migrate into the internal porosity of the pumices and crystals of berlinite appear (AlPO4) well developed in a matrix of amorphous phosphate overlapping the initial material.
Normal tests of reactivity in water and in 2% citric acid show that the percentages of released P2O5 in solution are greater after treatment with weak concentrations of phosphoric acid. Lixiviation of treated materials with citric acid reagent shows that, after three days of reaction, losses in weight are considerable and the kinetic curves of phosphorus liberation present a linear evolution.
The fertilizing value of these materials did not decrease during the leaching; so phosphorus will be solubilized with time thus allowing these materials to gain a good agronomical availability and to propose their use as delayed fertilizer types for tropical agricultural soils.
Keywords
Citric Acid Phosphoric Acid P2O5 Normal Test P2O5 ContentPreview
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