The concentration of boron, an essential micronutrient for plants, presents a narrow range between deficiency and toxicity. In order to provide the boron requirement for plants, and to avoid toxicity problems, boron compounds are mixed with basic fertilizers. Sodium borate pentahydrate was used as a boron source. Ammonium orthophosphates fertilizers with boron were prepared by neutralizing phosphoric acid with ammonia and addition of variable amounts of sodium tetraborate pentahydrate to the reaction mixture at a NH3:H3PO4 molar ratio of 1.5. The fertilizers obtained with boron contents ranging from 0.05 to 1 % (w/w) were fully characterized by chemical analysis, thermal analysis, X-ray diffraction and infrared spectrophotometry. The studies showed that up to 500?C, regardless of the boron content, no significant changes concerning thermal stability and nutritional properties occurred. Above 500?C, an increase of thermal stability with an increase of the boron content was observed. X-ray diffraction of a heat-treated sample containing 5 % (w/w) boron indicated the appearance of boron orthophosphate, BPO4, as a new crystalline phase, and the disappearance of the previous structures above 500?C, which explains the increase in thermal stability.
The paper presents studies about the process of obtaining the fertilizers based on ammonium phosphates (NH 4 ) 2 HPO 4 and NH 4 H 2 PO 4 with boron added as micronutrient. As boron source was used boric acid, which has been introduced into the neutralization mass at various NH 3 :H 3 PO 4 molar ratio, in order to obtain thermal stable compounds, with a minimum loss of nutritional elements (N, P). The variation of pH, considered the process control parameter, as a function of NH 3 :H 3 PO 4 molar ratio was recorded during the neutralization.Specific analyses has been used in order to determine phosphorus, ammonia nitrogen and boron content in the obtained fertilizers. The thermal behaviour of the fertilizers was studied using TG and DTG. The lowest total mass loss was observed at a 1.5 NH 3 :H 3 PO 4 molar ratio.
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