以微波輔助重金屬污泥回收再利用之研究

Abstract

重金屬污泥在台灣為一產量甚大的有害事業廢棄物，其中以含銅污泥產 量為最大宗。若未加以處理而棄置，則會造成土壤及地下水的污染並危害人 體健康。本研究嘗試以微波輻射程序進行重金屬污泥之安定化，期望達到無 害化及資源化之目標。 實驗中探討之影響因子為：微波誘發程序影響、安定劑劑量與種類、微 波時間及功率、反應氣氛、微波吸收質、微波混成程序及溫度之影響。除了 探討其重金屬溶出濃度及安定化效率，並研究其固相化學反應。而安定化污 泥亦進行資材化之研究，探討其對於金屬離子的吸附性質與吸附量。 結果顯示不同的處理程序當中，以同時添加還原性金屬安定劑並供給微 波輻射方能有效達到含銅重金屬污泥之安定化，且還原性金屬添加劑量與該 金屬之反應性成反比。當微波功率越強或微波時間越長時都有較佳之安定化 效果。但在高功率微波照射下，樣品間會產生較大之之熱壓力造成顆粒之間 的裂隙進而降低安定化的穩定性。 當無添加安定劑時，以空氣做為反應氣體及冷卻氣體(Air/Air)會造成污 泥中的有機物完全燃燒並使銅大量溶出；而填充氮氣(N2/N2)則能阻隔有機物 與氧氣接觸，因此銅溶出濃度較低。若同時添加安定劑與控制反應氣氛，實 廠污泥填充氮氣(N2/N2)能有效的增進安定化效率，縮短安定化所需的時間； 若配合空氣進行冷卻(N2/Air)，則可使高能鋁粉氧化釋出氧化熱，促成銅物 種脫水反應及CuO 的生成。而無機污泥(De10)方面，在(Air/Air)環境鋁粉會 逐漸釋出氧化熱，安定化效率會逐漸上升；而N2/N2 組電弧程序的產生應為 主要污泥安定化的方式。 而在微波程序中，有機物的悶燒與否將微影響污泥安定化之穩定性。但 若污泥中的有機物及水分一併去除而僅添加安定劑，則會使得安定化效果不 IV 佳。當添加吸收微波能力較強的微波吸收質於污泥中時，微波安定化之效率 有明顯的提升。而在銅污泥安定時卻造成Al 及Fe 的溶出濃度增加，可能是 Al0 可在微波提供能量的狀況下，直接或間接將Fe3+及Cu2+還原成Fe2+ (或其 他溶解性較高的鐵氧化物)及Cu0 或CuO，而本身則氧化為Al3+。 在微波混成程序中添加活性碳收並控制反應環境(N2/N2)，仍能達到安定 化之效果；安定化反應包括脫水反應、物種轉換、玻璃化、還原反應及硫化 物生成。高溫固相化學反應方面，當溫度高達900 ℃時，CuAl2O4 有較高的 轉換率。當混合Cu4SO4(OH)6 與α-Al2O3 進行高溫鍛燒時，顯示溫度升高有 助於CuO 的生成，但是CuO 與α-Al2O3 的顆粒可能只在表面層生成 CuAl2O4，因此無法明確地以XRD 鑑定。以CuO 與α-Al2O3 混合，反應轉換 率不高；若以CuO 與γ-Al2O3 混合，在800 ℃有大量CuAl2O4 生成，因為 γ-Al2O3 有較鬆散之結晶結構，有助於CuO 與γ-Al2O3 嵌合及CuAl2O4 生成。 資材化研究方面，當溶液的pH 範圍在2-11 之間時，安定化污泥表面的 電荷皆為負電，因此適合作為陽離子之吸附劑。動力學研究中，吸附實驗數 據較符合pseudo-second order model，顯示銅離子與安定化污泥之間的吸附 可視為一種活性吸附機制。而等溫吸附實驗(Isotherm)數據與Langmuir equation 有較高的相關係數。從熱力學的參數中可得知銅離子於安定化污泥 表面的吸附為吸熱反應。但是整體的吸附現象確有可能包含物理性及化學性 吸附。而銅離子於安定化污泥表面的吸附容量分別約為23 mg/g (SL07-FeA) 及15.5 mg/g (SL07-AlA), 此吸附容量大於許多其他固體廢棄物吸附劑的吸 附容量。因此安定化污泥可被應用於含重金屬廢水吸附的資材化物質。

The leaching concentration of heavy metal sludge is above the TCLP criteria for land disposal (< 15 mg/L) and regarded as a hazardous solid waste. Without proper treatments, the hazardous sludge would contaminate the soil and ground water and even human health. Therefore, a stabilizing process for the tremendous amount of heavy metal sludge is required before land disposal and reuse. In this study, microwave processes were conducted for the stabilization of heavy metal sludge. The effects different processes, stabilizing agents, process time, microwave power, reaction atmosphere, microwave adsorbents, microwave hybrid process and temperature variation were investigated. The solid state reaction and adsorption study of stabilized sludge were also discussed. Results indicated that better stabilization ratio was reached when microwave radiation was applied coincided with the addition of reductive metal powder. The adding dose of metal powder at same stabilization ration was in reverse order of metal reactivity. As copper was stabilized, Fe and Al also leached out during TCLP process. Al3+, Fe2+ and Cu0 (or CuO) was formed as redox reaction was occurred. The stabilization efficiency improved at higher microwave power, but the thermal pressure caused by higher microwave power could decline the VI reproducibility of experimental data. For raw heavy metal sludge (TD10), the sludge would smolder under oxygen atmosphere leading to the leaching of metal ions when only microwave radiation was applied. Moreover, as microwave radiation was served coupled with stabilizing agent to TD10, an inert reaction atmosphere (N2) during heating and oxidizing atmosphere (air) for cooling gave better performance. Oxidation heat released from the oxidation of aluminum powder may be attributed to the formation of CuO. When metal powder was added into inorganic sludge (De10) with microwave radiation at N2/N2, the microarcing process may be responsible for the dehydration reaction of sludge. Appropriate amounts of microwave adsorbents in the sludge would increase the homogeneity of microwave energy to increase the reactions between stabilizing agents and copper. In Hybrid Microwave process, when processing time was longer than 18 min and AC dosage was more than 3 g, a minor portion of the De10 was vitrified and leading to low copper leachability. Adding carbonaceous materials in the samples would enhance the transformation of copper into CuAl2O4 due to the additional burning heat. Also, in this process, the reduction reaction may be attributed to the formation of Cu2S. In the solid state reaction, the transformation of CuAl2O4 was higher at 900 ℃. Calcination of mixture of CuO and γ-Al2O3 gave better transformation ratio of CuAl2O4 when VII compared with mixture of CuO and α- Al2O3. The diffusion rate of solid particles, formation of surface layer, lattice structure, and amorphous intermediate product may be attributed to the differences of transformation ratio. In the adsorption study, the surface charge of stabilized-sludge was negative at the pH range of 2-11. The removal of copper ions increased as the initial pH rose, and the final pH maintained at a constant of pH 7.2 while the initial pH is from 6 to 8. In the kinetic study, the adsorption of copper ions onto adsorbent was fitted to the pseudo-second order model with great correlation coefficient (R2 = 0.994). This result shows the adsorption of copper ions onto stabilized-sludge to be an activated adsorption mechanism. The experimental data was also analyzed by the isotherm equations and correlation coefficient of the Langmuir equation was better than that for the Freundlich equation. In isotherm experiment, both the Q0 and b increased as the temperature ure rose from 15℃ to 55℃. This implies that this adsorption reaction was an endothermic reaction which can also be demonstrated by the thermodynamic study with the parameters, ΔG0, ΔH0 and ΔS0. The adsorption capacity of copper ions onto stabilized-sludge was around 15-23 mg/g, which was greater than that on many other solid wastes.