高溫燒結含鎳鉻重金屬污泥之研究

Abstract

近年來利用污泥鐵氧磁體法處理含重金屬污泥的技術漸漸受到重視，此項技術分為濕式處理與乾式處理兩種方法，濕式處理是在液相中進行鐵氧磁體的合成，調整廢液的pH 值與提供曝氣將污水中的重金屬離子形成鐵氧磁體這種尖晶石結構。而乾式處理則是直接將含有重金屬的污泥利用高溫燒結的方式使重金屬氧化物互相結合成尖晶石結構。 本研究以高溫熱處理合成鐵氧磁體方式進行鎳鉻金屬污泥的安定化討論，分別控制燒結的溫度、反應氣氛、污泥含鹽程度以及重金屬Cr/Ni 莫耳配比，處理過後的污泥以TCLP 溶出試驗、XRD 晶相分析及SEM 表面分析探討各種操作因子對污泥安定化的影響。 研究結果發現，污泥經過1200℃高溫燒結三小時後，可以形成完整的鎳鉻尖晶石結構，且經過TCLP 溶出試驗鎳、鉻金屬的溶出量皆大幅的減少，其中鉻金屬的溶出量更可以低於法規管制標準5 mg/L。而由SEM觀察污泥顆粒的變化可以發現經過高溫污泥顆粒由鬆散的不規則破碎顆粒互相聚集黏結成結構完整的較大結晶。 反應氣氛對污泥安定化的影響並不明顯，無論是在有氧(air)還是無氧(N2)環境對污泥做高溫燒結後皆可形成鎳鉻尖晶石，代表污泥中的物種轉變並不會受到反應氣氛影響，且TCLP 溶出量皆可明顯的下降。 當污泥中有適當的鹽類含量存在，可以使燒結後的污泥形成較大的結晶顆粒，降低污泥中重金屬的溶出量，但當鹽類含量過高的時後，反而會阻礙金屬氧化物的結合，使污泥中有剩餘的三氧化二鉻無法形成鎳鉻尖晶石，且結晶顆粒會產生裂縫及破損，降低了結構的完整性，造成鎳、鉻金屬溶出量增加。 污泥中Cr/Ni 莫耳配比對鎳金屬影響較明顯，隨污泥中的鉻含量增多，鎳金屬形成鎳鉻尖晶石的數量較完全，故有較低的溶出量，但對鉻金屬而言較沒有明顯的相關性。

In recent years, ferrite synthesis method has been investigated for heavy metal sludge stabilization. The ferrite formation processes could be divided into two categories. The first one is wet process, aqueous divalent metal ions co-precipitate with iron ions to form hydrous iron oxides and then divalent metals are fixed onto the ferrite by dehygration process. The second one is high temperature ferritization, which is more simpler than wet process. In this study, high temperature spinel synthesis process is performed on chromium and nickel contained sludge. To understand the spinel synthesis stabilized efficiency, various operating parameters included sintering temperature, reaction ambient gas, salt quantity and Cr/Ni molar ratio were discussed. Stability of sintered specimens was evaluated by toxicity characteristic leaching procedure (TCLP). The crystalline phases of sintered specimens were studied using X-ray powder diffraction (XRD). The microstructural characteristics of the powders were examined by scanning electron microscopy (SEM). Chromium and nickel containing sludge could be more stable by thermal process. According to TCLP results and XRD patterns, chromium and nickel would be stabilized by inserting the chromium and nickel ion into the stable NiCr2O4 spinel crystalline structures during thermal treatment. When suitable quantity of salts exists in sludge, both of chromium and nickel would be more stable and the spinel crystalline structure could be more complete. Relationship between chromium stability and Cr/Ni molar ratio is hard to distinguish, but raise Cr/Ni molar ratio could improve nickel stability. The high-temperature spinel synthesis technique for chromium and nickel sludge stabilization is applicable.