| 摘要: | 都市垃圾焚化飛灰之反應灰含有大量的的氯鹽，如直接再利用會影響其在建築材料上之可行性，因此便必須針對反應灰氯鹽部份進行前處理才能進一步利用。前處理中以水洗為目前最為普遍之前處理方式，在水萃過程中，除了將氯鹽萃取出來之外，也會洗出大量的鈣離子。本研究除了利用通入CO2及添加石灰與蘇打進入水萃廢水來回收Ca之外，並同時也利用化學置換、化學沈降、電聚浮除法針對水萃廢水中重金屬去除效果進行探討，最後再將此兩程序進行整合並討論沉積物之特性。
由結果中可得知，通入CO2及直接添加石灰兩種方法對於Ca之回收效果有其限制；而直接添加蘇打加藥量達到理論值110％(64,181 mg/L)時，水萃廢水中之Ca回收率可達到98％。由於水萃廢水含有一定程度之重金屬，因此本研究也針對重金處之處理進行不同方法的測試。化學置換法對於水萃廢水重金屬去除效果不佳，而化學沈降法在pH調整為10之條件下，水中Pb已可去除99.69％以上，而電聚浮除系統在操作電壓為125V，水力停留時間為60秒時，處理後廢水之重金屬濃度皆可達到放流水標準。在經過化學沈降或是電聚浮除處理後，蘇打之加藥量只需理論值之100％即可達到99.95％以上之Ca回收率，廢水中重金屬多已無法測得或遠低於放流水標準；在沉積物部分，由產物之XRD晶格強度可確定前處理可提高碳酸鈣之純度。因此，本研究對於飛灰水萃廢液不但可有效回收廢水中之鈣，且具有處理或回收廢水之潛力。
MSWI fly ash contains a lot of chloride salt, if not be pre-treated properly, it will influence the feasibility of recovery as the construction materials. Water extraction is the most common operation, beside a lots of chloride salt could be removed; a large quantity of calcium ions will also be dissolute at the same time. In this study, CO2-sparging, lime softening and soda ash softening were exam in order to recovery the calcium carbonate from the extraction wastewater. Substitution, chemical precipitation and electro-aggregation method were discussed for the removal of heavy metals before the calcium recovery, in order to upgrading the characteristic of the product and satisfied the wastewater effluent standard.
The results showed that, the effects of CO2-sparging and lime softening methods for Ca recovery were limited. When dosing the soda ash at 110% of theoretical quantity, the recovery of Ca was up to 98%. For heavy metals removal, substitution with alumni powder was ineffective, while the chemical precipitation at pH 10, the Pb in the water could be removed more than 99％, and electro-aggregation method at 125V, hydraulic retention time 60s, all of the heavy metals could reach the effluent standards. After the operation of chemical precipitation or electro-aggregation for pre-treatment, the soda ash dosing 100% of theoretical quantity, Ca recovery could reach more than 99.95%, and heavy metals were not detectable or far below the effluent standards. The XRD analysis showed that, pre-treatment of heavy metals could improve the purity of calcium carbonate product evidently. |
