Synthesis of tobermorite filter with desulfurization slag and its application in heavy metals recovery from wastewater

• Main Authors: Yu-RongJhou, 周鈺蓉
• Other Authors: Juu-En Chang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/68648573362015345944

碩士 === 國立成功大學 === 環境工程學系碩博士班 === 100 === High concentrations of heavy metals in industrial wastewater before discharge was common in Taiwan. The purpose of this study was to improve the water security by filtering. Literatures have indicated that crystalline phase of tobermorite (Ca5Si6O18H2 • 4H2O) is suitable for wastewater filtration treatment due to its high cation exchange capacity. In addition, desulfurization (DS) slag was a by-product of steel-making processes, which contained large amounts of Ca and Si; therefore, it has the potential to synthesize tobermorite filters, and can be applied in heavy metals removal and recovery from wastewater. This study used quartz (SiO2) and lime (CaO) as raw materials with different amount of reaction solutions. Afterward, the suitable autoclave reaction procedure was applied in order to synthesize pure oxides (PO) tobermorite filter (PO-tobermorite). According to the synthetic conditions of PO-tobermorite, synthesized DS tobermorite filter (DS-tobermorite) was obtained by adjusting DS slag ratio of raw materials and reaction conditions. Furthermore, the crystalline phase and microscopic structures were observed to assess the capability of tobermorite filters to remove and recover heavy metals from wastewater. The results showed that synthetic conditions of PO-tobermorite were controlled at 0.83 of CaO/SiO2 (C/S) ratio and 15 wt.% of deionized water. Moreover, the synthetic conditions of DS-tobermorite were controlled at 0.83 of CaO/ (SO2+Al2O3) (C/(S+A)) ratio and 15 wt.% of 2 N NaOH(aq). The synthesized DS-tobermorite filter had the best removal efficiency of Cu and Pb ions. The batch test showed that the DS-tobermorite filter could treat Cu (15 mg/L) and Pb (20 mg/L) wastewater to meet the Taiwan EPA’s effluent regulations of 3 mg/L for Cu and 1 mg/L for Pb, with the reaction pH = 7 and reaction time = 24 hours. Furthermore, using column-continuous flow test could get 217.03 mg/g (Cu) and 239.67 mg/g (Pb) of the balance removal capacity. Finally, the recovery experiments showed that under 1.5 N HNO3(aq), reaction time = 3 hours, and liquid to solid ratio = 100 L-HNO3(aq)/ kg-DS-tobermorite, the enrichment ratio of Cu and Pb could achieve at 11.49 and 15.32, respectively. However, with liquid to solid ratio = 200 L-HNO3(aq)/ kg-DS-tobermorite, the optimum recovery of Cu and Pb were 67.9% and 83.9%, respectively. It is concluded that DS-tobermorite had good ion-exchange properties, good removal efficiency in neutral environment, and could recovery heavy metals with the appropriate amounts of acids. Therefore, DS-tobermorite can achieve the goal of resource recycling and reuse.