| 摘要: | 本研究針對電弧爐集塵灰、高爐礦泥、鑄鐵集塵灰與熱軋礦泥等鋼鐵鑄造業副產物具有微細顆粒與含有大量氧化鐵之特性，以及晶圓廠廢磷酸的穩定化特性，經由化學計量式與試拌程序混合產製磷酸陶瓷固化劑，並探討磷酸濃度與硼酸劑量對固化體之性質影響實驗，獲得固液比等磷酸陶瓷固化劑配方；同時，以各類固化劑配方固化不同劑量的飛灰，探討飛灰固化量對磷酸陶瓷固化體的新拌與硬固性質，溶出特性，以及微結構的影響，藉此獲得各類磷酸陶瓷固化體的最佳飛灰固化量。最後，以水泥固化為比較基準對各類固化劑進行經濟效益評估。 實驗結果顯示電弧爐集塵灰、高爐礦泥、鑄鐵集塵灰與熱軋礦泥的化學組成會與磷酸產生明顯反應的氧化金屬總含量，以電弧爐集塵灰與熱軋礦泥為較高(達54%)，高爐礦泥次之(38%)，鑄鐵集塵灰最低(35%)。前述此四類磷酸陶瓷固化劑的配方：每克鋼鐵業副產物需要磷酸量分別為0.84克、0.68克、0.68克與0.98克，固液比分別為0.52、0.60、0.80與0.30；最佳的硼酸緩凝劑使用量為2wt.%。磷酸濃度過高可能因激烈發泡反應而對固化體的新拌與硬固性質產生不利影響，建議適當磷酸濃度應低於75%以下，而不宜過高。此四種磷酸陶瓷飛灰固化體之TCLP結果均符合法規值，對於Pb與Cu的穩定效果最佳，但部分固化體的抗壓強度低於法規值；電弧 爐集塵灰、高爐礦泥、鑄鐵集塵灰等磷酸陶瓷固化體之最大飛灰固化量分別為20%、25%、30%，而熱軋礦泥磷酸陶瓷固化體則不適合應用於固化飛灰。電弧爐集塵灰與鑄鐵集塵灰兩種磷酸陶瓷固化劑比傳統水泥固化劑 深具經濟性，因此具有資源化與市場競爭潛力。 Chemically bonded phosphate ceramics (CBPCs) are produced by acid-base reactions between an inorganic oxide and either phosphoric acid solution or an acid-phosphate solution. By taking the advantage of forming chemical phosphate bond and the ability to capsulate wastes, the CBPCs can be used to solidify and/or stabilize toxic wastes. Typical reactants of this acid-base process (i.e., MgO, Fe2O3, and phosphoric acid) can be provided with by industrial wastes: iron-oxide-containing wastes can be obtained from steel making plants, and waste phosphoric acid from IC foundry plants. Some of the iron oxide may also be obtained from the MSWI fly ash. These industrial wastes provide an excellent opportunity to evaluate the feasibility of developing phosphate ceramics from wastes (referred to as WDPCs), and to assess their further applicability to solidify and/or stabilize MSWI fly ash. Accordingly, this study investigated the feasibility of developing phosphate ceramics from wastes such as electric arc furnace dust (EAF dust), blast furnace wet dust (BF dust), cast iron dust (CI dust), and hot-roll wet dust (HR dust); as well as waste phosphoric acid. In this study, the waste-derived phosphate ceramics (WDPCs) were further evaluated by their capacity to solidify and/or stabilize MSWI fly ash. The results indicate that the reactive inorganic oxides, mainly iron (III) oxide, in EAF dust, BF wet dust, CI dust, and HR wet dust were found to be 54, 38, 35, and 54% (w/w), respectively. Each gram of the dusts, stoichiometrically, required 0.84, 0.68, 0,68, and 0.98 gram of phosphoric acid (pure) respectively to produce proper WDPCs, or 1.53, 1.24, 1.24, and 1.77 gram for phosphoric acid of averaged 55% concentration. The WDPCs were fabricated by adding water to the previous formula at a solid-to-liquid ratio as determined by a workable viscosity of the WDPC pastes. The determination resulted in an appropriate solid- to-liquid ratio of 0.52, 0.60, 0.80, and 0.30, respectively for the tested EAF dust, BF dust, CI dust, and HR dust respectively. Phosphoric acid concentration less than 75% was recommended to avoid vigorous acid-base reaction and the excessive forming, which adversely affected the quality of the WDPC pastes. For all WDPC samples, the leaching concentrations of the target metals resulting from the TCLP test were found to be in compliance with the US EPA's regulatory thresholds. The effect of solidification/stabilization for Pb and Cu was especially significant. However, some WDPCs failed to develop sufficient regulatory compressive strength for solidified monolith. One the other hand, of the four WDPCs tested, the maximum ratio for MSWI fly ash to be solidified was found to be 20, 25, and 30% (w/w) for phosphate ceramics derived from the corresponding EAF dust, BF dust, and CI dust; whereas that derived from HR wet dust failed in solidifying/stabiling MSWI fly ash. Solidification/stabilization of MSWI fly ash with WDPCs is economically competitive with other disposal methods such as traditional cement solidification process and can have the added attractiveness of being beneficial to the waste disposal. |
