Occurrence and behavior of phosphorus-bearing minerals in metallurgical coke

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>The behavior of phosphorus‐bearing minerals is characterized from coking coals to the feed coke and the blast furnace (BF) coke using scanning electron microscope and thermodynamic calculations. In coals, they are represented mostly by apatite (major phase, used for thermodynamic calculations), crandallite, gorceixite, goyazite, monazite and xenotime. Apatite fully transforms to Ca₄P₂O₉ and Ca₃P₂O₈ at coking temperatures. In the samples of BF coke, phosphorus‐bearing phases are 5–30 μm in size. In the case of a closed system (inside pieces of coke, no gas), phosphorus is presented in the BF in the form of Ca₄P₂O₉ and Ca₃P₂O₈ up to 1250 °C. Above this temperature, it is transformed to Fe₃P (stable until 1495 °C). A further rise in temperature leads to the transformation of Fe₃P to Fe₂P (stable up to 1930 °C − tuyere level of the BF). In the case of an open system with intensive flow of BF gas, the formation of Fe₃P from Ca₄P₂O₉ and Ca₃P₂O₈ starts at 1178 °C. The Fe₂P appears near 1494–1495 °C, and after that it goes to a molten state.</p></div>