高爐集塵灰以及脫硫渣礦物細料，係為鋼鐵產業之副產物，因含有高溫鐵水所析出之凝析石墨，故若能將凝析石墨從副產物之中有效富集回收，不但能使該類副產物後續資源化過程更不受限，亦能從中獲取高純度之石墨，提升資源循環之價值。本研究首先篩選出凝析石墨富集潛能最高之原料，而後利用石墨所具天然疏水性，以泡沫浮選作為初步富集凝析石墨之方法，並尋求其最佳物理操作以及加藥條件。此外，再以化學純化程序，探討酸純化凝析石墨之最適條件，並檢討不同純化流程對凝析石墨純化之影響，最後依純化後石墨含量及粒徑大小，評估高爐凝析石墨回收程序之可創造之價值。
本研究首先開發高爐凝析石墨定量技術，以更精確瞭解樣品之石墨含量，而後材料基本特性分析結果顯示，Dust 2含有約34 wt.%之石墨，為材料中最高者，故應具回收凝析石墨潛力，而Ca、Fe為主要雜質。凝析石墨泡沫浮選時，過高之礦漿濃度對於精礦中石墨含量以及回收率皆有負面影響。適當起泡劑能夠有效穩定泡沫層，但過多的起泡劑易造成夾帶機制發生，導致富含雜質之細小顆粒於泡沫浮選過程一併被夾帶至精礦，進而降低精礦之石墨含量；捕收劑能夠加強礦物表面之疏水特性，但添加量過高易影響泡沫穩定性，因此藥劑添加種類以及搭配劑量為影響浮選效果之關鍵因素。本研究在礦漿濃度10 %、攪拌轉速1200 rpm、攪拌時間3 min、浮選時間10 min，搭配加藥條件為MIBC 5 g/t、煤油1000 g/t之泡沫浮選條件下，能夠將精礦石墨含量由原34 wt.%提升至51 wt.%且回收率達98.36 %。以此條件經三段浮選後最終精礦石墨含量可達到約84 wt.%，此時精礦中主要剩餘雜質組成為Fe、Ca、Al及Si。
在凝析石墨之酸純化過程中，純化效果依序為HCl > HBF4 > HNO3 > H2SO4。於常溫下，較高HCl濃度有較佳之純化效果，當使用較高的酸濃度時，反應時間加長對石墨含量提升較為顯著；而當酸濃度越低時，提高液固比對純化效果之提升幅度越明顯。以HCl與HBF4形成混合酸溶液對提升凝析石墨純化效果並不十分顯著，但其Si去除效果隨HBF4比例提高而增加，Fe溶出部分亦有些微上升，顯示HBF4能夠有效提升Si及Fe之去除效果。
於反應條件為1.0 N HCl、L/S=10 L/kg、反應時間30 min下，使用平板加熱輔助酸純化時，石墨含量大致隨溫度提升而增加，約於80℃時可獲得石墨含量最高達到為97.06 wt.%。微波加熱輔助能於相對低溫下（40℃）完成反應，但石墨含量略低於平板加熱。超音波輔助酸純化之主要優勢為可降低反應時間，於條件1.0 N HCl、L/S=10 L/kg之下反應僅需2 mi即可得到與常溫下攪拌30 min之相近結果。
綜合而言，本研究透過泡沫浮選搭配酸純化之技術，可有效將高爐副產物中凝析石墨由約34 wt.%進行富集與純化後提升至~97 wt.%，除了能夠降低副產物後續資源化應用之限制，純化後之凝析石墨亦具有廣泛應用性及相當的價值。根據石墨之含量以及尺寸，本研究評估高爐集塵灰（Dust 2）之凝析石墨於三段浮選及不同化學純化方式之下，所得凝析石墨價值約可達到投入藥劑成本的4.7~6.8倍，應具工程應用性與經濟效益。

Blast furnace dust and slag are by-products of the steel industry. During the steelmaking process, kish graphite is created through precipitation from molten iron at high temperatures. In this study, based on the analysis of the basic characteristics of the material, it is found that Dust 2 contained about 34 wt.% of kish graphite, which is the highest among the materials. When the kish graphite is concentrated by froth flotation, the excessive pulp density has a negative impact on the graphite concentration and recovery in the concentrates. A suitable frother (methyl isobutyl carbinol (MIBC)) can effectively stabilize the froth layer, and the collector (kerosene) can impart enough hydrophobicity to the mineral surface. Using the froth flotation operating at pulp density = 10 %, rotary speed = 1200 rpm, flotation time = 10 min, MIBC = 5 g/t, and kerosene = 1000 g/t, the kish graphite concentration in Dust 2 increased from 33.90 wt.%. to 51.00 wt.%. After the three stages flotation, the concentrate containing 84.09 wt.% of graphite can be obtained. In the chemical purification of the kish graphite, the effect of four kinds of acid solutions on the graphite is HCl > HBF4 > HNO3 > H2SO4. When using 1.0 N HCl, L/S=10 L/kg, reaction time 30 min, and the heating temperature = 80℃, the final graphite concentration of the product can reach 97.06 wt.%. According to the concentration and size, the benefit of graphite product after acid leaching assisted with heating at 80℃ is 295.6 USD per ton of Dust 2.

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