廢棄物衍生鋁熱熔融劑處理鉻污泥; Waste derived thermite melting preparation to dispose of chromium sludge

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題名:	廢棄物衍生鋁熱熔融劑處理鉻污泥;Waste derived thermite melting preparation to dispose of chromium sludge
作者:	高國源;Kuo-Yuen Kao
貢獻者:	環境工程研究所
關鍵詞:	資源化;鉻回收;鉛回收;熔融;鋁熱反應;resources;chromium recycling;lead recycling;multing;thermite reaction
日期:	2008-12-18
上傳時間:	2009-09-21 12:18:52 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本研究利用電鍍工業副產物鉻電鍍污泥、鉻廢水污泥及機械工廠邊料鋁屑，配置成廢棄物鋁熱反應熔融劑，鋁熱反應可產生高溫將三種原料共同熔融，回收鉛金屬及鐵鉻合金，利用鉻廢水污泥含高濃度二氧化矽之特性作為玻璃形成劑，改善熔渣品質，提高分離效率。研究結果顯示，前處理溫度500℃時可使鉻電鍍污泥中氧化鉛、氧化鉻純度相對於100℃時，分別上升19%、14%，而結晶峰面積上升40%。將鉻電鍍污泥混合足量金屬鋁，進行鋁熱反應時，前處理溫度500℃時的DTA放熱鋒面積，較熱處理溫度100℃時增加59.5%。鉻電鍍污泥鋁熱處理最佳配比實驗中，鉻電鍍污泥與鋁屑以重量百分比4.53:1(鉻電鍍污泥80克和鋁屑17.64克)混合時，有最大放熱溫度1851℃，各組配比皆僅回收熔渣(含金屬)及飛灰，並無法回收金屬錠的部份。鉻污泥鋁熱處理—鉛、鉻回收實驗，鉻電鍍污泥：鋁屑：鉻廢水污泥=4.53:1:4.08 (鉻電鍍污泥80克、鋁屑17.64克和鉻廢水污泥72克)，能改善鋁熱反應放熱過於劇烈之特性，幫助鉛金屬錠與熔渣分離並改善熔渣品質，同時可熱處理鉻污泥，達到廢棄物無毒化、資源化之雙重功能。將回收鉛後的熔渣取20g研磨，混合3-5g的氧化鐵及足量鋁屑，反應可回收鐵鉻合金、鐵合金兩種金屬錠。以金屬回收率決定本研究的最佳配比，則最佳配比回收的鉛金屬佔總鉛的75%純度為95%；鐵鉻合金純度，鐵為32%、鉻為50%；鐵合金純度，鐵為88%；處理後的鉻污泥熔渣呈玻璃狀，毒性特性溶出合乎法規標準，化學抗蝕性皆低於0.2%，耐候性試驗於第八次循環方有重量損失。綜合上述結果，鋁熱熔融處理可將鉻污泥中的金屬回收同時將剩餘熔渣無害化且所得熔渣具有材料化之潛力。 It is beneficial to recover Cr and Pb from chromium plating sludge (referred to as CrPS) since it is primarily composed of PbCrO4 and PbO. This study investigated a novel technology for recovering chromium and lead from CrPS, by using thermite reaction between chromium oxide and aluminum (i.e., waste, parings and scrap). Sludge from Chromium wastewater treatment process (referred to as CrWS) , mainly composing of chromium oxide (Cr2O3) and silicon dioxide (SiO2), was also added in the recovering process to function as a glass-former that facilitate the separation of metal and slag and improves the quality of slag. In this study, the recovery process was divided into 3 stages: refinement of the CrPS, recovery of lead form the CrPS, and again, recovery of chromium as Cr-Fe alloy from the resultant slag. During the refinement of the starting CrPS, the sludge was heated at a temperature ranging from 100℃ to 600℃. It was found that the major species identified as PbCrO4, PbO, Cr3O4, and CrO were not changed; the total concentration of crystal phases, however, increased at 500℃. This suggests that the loss on ignition (i.e., 8.53 w/w% for CrPS) and the oxidized degree of thermit oxides might affect. The thermite reaction between chromium oxide and aluminum may proceed in a one-step path: CrO3+2Al→Al2O3+Cr, or in a two-step path: 2CrO3+2Al→Cr2O3+Al2O3 and CrO3+2Al→2Cr+Al2O3. The PbCrO4 in the starting CrPS might decompose into PbO and CrO3 when heated, which led to the activation of thermite reactions between PbO and Al, as well as between CrO3 and Al. However, the species, the oxidized degree, the reaction path, and the stoichiometry of Al were not clear. Therefore, the actual stoichiometry between CrPS and Al has to be determined experimentally by properly assuming what the thermit oxides are in the starting material. Several mixes of CrPS and Al, with Al in excess of its stoichiometry were tested. Thus, the highest reaction temperature developed would then determine the optimum mix of CrPS and Al, reflecting a mix under the balanced effects of factors such as species, oxidized degree, reaction path, impurities, non- reactive oxides, Al stoichiometry, and heat loss from the reactor wall. In this study, a mix ratio of CrPS:Al=4.53:1 showed the optimum mix for the CrPs and Al thermite. However, in this case, the recovered alloy and slag were not separated. In the recovering of Pb by thermite reactions, it was found that one kg of the above optimum mix, when added with 0.72 kg of CrWS, would result in a maximum recovery of lead alloy (18 w/w%), with 95.61% of Pb purity. The Pb recovery rate reached 76.79% as compared to initial Pb in the inputs. The 69 % of slag by weight of inputs was also recovered that retained most of the chromium oxides. In the subsequent recovery of chromium as Cr-Fe alloy, the above slag was further pulverized and mixed with Fe2O3-Al thermite with proper amount of Al stoichiometry. Optimum recovery of Cr-Fe alloy was achieved with Cr:Fe ranging from 4.61:1 to 1.55:1. Chromium recovery rate reached 80.78% as compared to the Cr input at second phase. This process also recovered 62.3 w/w% of slag compared to the inputs at second phase. The recovered slag was vitrified and stable. The results of this work suggest that to recover Pb and Cr from CrPS and CrWS using thermite reactions is a promising technology not only energy conservative but also recycling-beneficial.
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