爐石是煉鋼過程中不可避免的副產物，其中大部分元素有再利用價值，可用作建築和道路工程材料，甚至可作為精煉助熔劑和高爐煉鐵原料再利用。然而，轉爐石中磷含量高，會對鋼鐵產品產生不利影響，從而限制其回收應用。當煉鋼爐渣回爐時，磷還原並溶解在鐵水中，隨著這個程序反覆的進行，磷濃縮和積累在鐵水中，最終導致鐵脆化。為了提高煉鋼爐渣的回收利用能力，對爐渣中的磷進行脫磷是必要的。本研究以碳氯化法和兩階段還原法對轉爐石進行脫磷可行性探討，石墨為主要還原劑，鋁為次要還原劑，氯化鈣為氯化劑以促進揮發行為。關鍵參數包括渣鹽基度、氯化劑劑量、二階還原劑劑量，並在1300及1400℃下反應。空氣採樣濾膜用於收集磷蒸氣，XRF和ICP-OES用於測定爐渣元素組成，元素分佈圖和磷的遷移濃縮由EPMA和SEM-EDS分析。實驗結果顯示，碳熱還原的最佳脫磷條件為添加6 wt%的C及20 wt%的SiO2，鐵還原率92.45%，脫磷率51.92%。爐渣的熔點隨著CaCl2的增加而降低，提升爐渣和還原劑的質傳速率，同時也促進了爐渣再磷化。兩階段還原的最佳脫磷條件為添加6 wt%的C，9 wt%的CaCl2，3.4 wt%的Al及20 wt%的SiO2，鐵還原率為55.16%，脫磷率為54.73%。發現添加Al會抑制爐渣的鐵還原率，並使還原的鐵珠傾向於富集爐渣中的礦物質而不是磷，顯示兩階段還原抑制了再磷化反應。此外，Al生成的Al2O3促進渣中金屬相的分離，進一步優化爐渣兩階段還原脫磷程序。

Slag is an inevitable by-product from steelmaking process. Due to the most of elements in the slag is valuable and reusable, the slags can be utilized as construction materials and road engineering materials, even is reused as refining flux and ironmaking feedstock in blast furnace. However, presence of high contents of phosphorus in the BOF slags restricts the recycling applications due to the detrimental effects on iron products. When steelmaking slags are recovered to the blast furnace, the phosphorus is reduced and dissolved into molten iron, resulting in concentrating and accumulating in the molten iron. In order to promote the recycling amounts of steelmaking BOF slags, it is indispensable to eliminated phosphorus from slags. In this study, dephosphorization of slags by using carbo-chlorination and two-step reduction is investigated. Graphite is used as primary reductants, Al as secondary reductants, CaCl2 as chlorination agents to promote volatilization behavior. The operation parameters include basicity, chlorination doses, two-step reduction agent doses, and reaction temperatures (i.e., 1300 and 1400℃). Air sampling filter is utilized to collect the phosphorus vapor. XRF and ICP-OES is employed to evaluate the slag elemental compositions. Elemental mapping and phosphorus migration/concentration is determined by EPMA and SEM-EDS. As a result, optimal dephosphorization condition for carbothermic reduction is 6 wt% of C and 20 wt% of SiO2. The iron reduction rate of 92.45% and dephosphorization rate of 51.92% can be obtained. The melting point of slags decreases with increased CaCl2 which enhances the mass transfer of slags and reductants but increases slag re-phosphorization as well. Optimal dephosphorization condition for two-step reduction is 6 wt% of C, 9 wt% of CaCl2, 3.4 wt% of Al, 20 wt% of SiO2. The iron reduction rate of 55.16% and dephosphorization rate of 54.73% can be attained. Iron reduction rate of slag is found to suppressed by Al addition. In addition, the reductive iron droplets tend to absorb the minerals in the slags instead of together with phosphorus. Meanwhile, re-phosphorization reaction can be inhibited by two-step reduction. Furthermore, separation of metallic phase from slags enhanced by Al2O3 (generated from Al) can further optimize the two-step reduction of slag dephosphorization process.

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