Abstract:

Side reactions of gaseous product P₂O₅ with phosphate ores (so-called P₂O₅ back absorption) in rotary kiln produce large quantities of low melting point solid products, which could form a kiln ring, block material flow and cause unstable operation of the kiln. The back absorption of gaseous P₂O₅ with calcium phosphate was studied at different temperatures and the products were characterized for P₂O₅ content, morphology, phase composition, structure and thermal stability by chemical analysis and other techniques of SEM, XRD, IR, Raman, TG and DSC. The experimental results show that temperature significantly affected the back absorption, which was occurred above 500℃. Calcium metaphosphate was formed at 500-900℃ with almost pure calcium metaphosphate at 900℃. Calcium metaphosphate decomposed into calcium pyrophosphate and P₂O₅ at 1000-1300℃ with almost pure calcium pyrophosphate at 1300℃.

Key words: rotary kiln phosphoric acid, P₂O₅ back absorption, calcium metaphosphate, calcium pyrophosphate, fouling, sintering, chemical processes

摘要：

窑法磷酸生产中，气体产物P₂O₅与磷矿发生副反应（俗称P₂O₅反吸）生成大量低熔点物料，导致窑内结圈堵料，造成生产装置不能稳定运行。以磷酸钙与P₂O₅的反应为研究对象，采用化学分析与SEM、XRD、IR、Raman、TG及DSC等表征手段对不同温度下该反应产物的P₂O₅含量、形貌、物相组成、结构及热稳定性能等进行研究，探讨磷矿对P₂O₅的反吸行为。研究表明，反吸过程与反应温度密切相关，磷酸钙与P₂O₅在500℃以上发生反应，在500～900℃时，磷酸钙与P₂O₅反应生成偏磷酸钙，900℃反吸产物几乎为纯偏磷酸钙；在1000～1300℃时，反吸产物偏磷酸钙分解为稳定的焦磷酸钙，同时释放出P₂O₅气体，1300℃时反吸产物几乎为纯焦磷酸钙。

关键词: 窑法磷酸, P₂O₅反吸, 偏磷酸钙, 焦磷酸钙, 烧结, 结垢, 化学过程