Stabilization of Heavy Metal-Containing Sludge by Ferrite Process

• Main Authors: Chia-Yu Ko, 柯家宇
• Other Authors: Juu-En Chang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/05113573227314608225

碩士 === 國立成功大學 === 環境工程學系碩博士班 === 92 === 　　Chemical precipitation is the most popular process in wastewater treatment among the available heavy metal removal processes. Generally, the heavy metals are precipitated in alkaline solution to form metal hydroxide sludge. But metals in the sludge may be released under acidic conditions and cause environmental hazards. Consequently, further treatments for the hazardous sludge are needed. Cement solidification is in common use for the harzardous sludge treatment. Nevertheless, a landfill site is needed for the final disposal of the cement solidification derivatives. Limited by the availability of landfill space, the cement solidification process becomes more and more expensive. Also, the cement solidification process always causes a negative effect of waste volume expansion, which is opposite to the reduction strategy in the integrated solid waste management. Therefore, the reuse of metal-containing sludge is a better alternative than the cement solidification process for the management of heavy metal-containing sludges. In this research, the actual sludge(high iron-containing) is utilized. The aim of this study is to use two different ferrite process, high temperature ferrite process and hydrothermal reaction ferrite process, to treat the sludge and compare the stability effect of two methods. High temperayure ferrite process is also utilized to treat single heavy metal simulated sludge (Cu-series、Zn-series、Ni-series、Cr-series) and multiple heavy metal simulated sludge to discuss the stability effect of simulated sludge. 　　By TCLP (Toxicity Characteristic Leaching Procedure), XRD (X-ray diffraction) and saturated magnetization (Ms), the experimental results show that the hydrothermal reaction ferrite process, under the operational condition (T=70℃、pH=11、air flow rate=4L/min and Fe/metal (w/w) ratio=4、8、12、16), is applicable to the transformation of actual sludge into ferrite. The TCLP result of actual sludge after hydrothermal reaction ferrite process treatment is still over the regulatory standard (Cu: 15 mg/l). By high temperature (800 °C) ferrite process, the heavy metals in sludge are transferred to a more stabilized ferrite form. Ferrite forms has the advantages of high chemical stability and ferromagnetic property, which not only prevent the heavy metals from leaching out, but also could be used as environmental friendly materials. After high temperature ferrite process (800℃, Fe/metal molar ratio=1.7、3.5、5.5、7.5 and different isothermal time) treated, TGA results show that after the ramping step the weight is equilibrium. TCLP , XRD and Ms results show that the actual sludge is transformed into ferrite and possess magnetic properties, and the magnetic properties decrease as the Fe/metal molar ratio increases. After the high temperature ferrite process in specific operational condition (Fe/metal>3.5, isothermal time=15 hr) treated, the Cu TCLP results of actual sludge is all below the regulatory standard. 　　The results also show that the high temperature ferrite process（800℃, Fe/metal=3.5） is applicable to the transformation of single heavy metal simulated sludge(Cu-series、Zn-series and Ni-series) and multiple heavy metal simulated sludge into ferrites. All the crystalline phases of these ferrites could be observed in the XRD patterns of sintered materials. And the TCLP results show that the heavy metal concentrations in leachate are below the regulatory standard. The simulated Cr-series sludge formed (Fe0.6Cr0.4)2O3 after the high temperature ferrite process treatment, and the TCLP value of Cr appears slightly increase as the increased isothermal time. After the high temperature ferrite process treated, the multiple heavy metal simulated sludge is transformed into ferrite and TGA results also show that the weight is equilibrium. After the high temperature ferrite process treated, both simulated copper sludge and actual sludge（Fe/metal =3.5） are transformed into ferrite and possess magnetic properties. By increasing the isothermal time, the stability effect is better. When the isothermal time is more than 3 hours, the Cu TCLP results of simulated Cu-series sludge is all below the regulatory standard, but when the isothermal time is more than 10 hours, the Cu TCLP results of actual sludge is just below the regulatory standard. According to these experimental results, ferrite process is applicable to treat the actual sludge and the magnetic properties can improve the application value.