Extraction Of Ferromagnetic Material From MSWI Bottom Ash And Preliminary Studyon The Removal Of Trichloroethylene

The Municipal solid waste incineration(MSWI) plant generated about more than 11.7 million tons bottom ash every year, in china. Although the MSWI bottom ash could be used in many fields effectively through the physical treatment-process(classification, magnetic separation, weathering and etc), all of that has been treated as reclamation of the landfill until now. The MSWI bottom ash is one catagerie of resource. If the MSWI bottom ash which contaims various materials, such as silicate, aluminate, hematite and magnetite can be separated respectively and be used, it would obtatain the high-value products in recycling field. Especially, in the case of the ferromagnetic material(FM), it accounts for approximately 5% of the bottom ash and is easy to be removed by magnetic separation. So, the MSWI bottom ash was taken as the research object and the TCE was chosed as the target material in this study, and we investigated the characteristic and the chemical reaction of the FM from MSWI bottom ash using wet magnetic separator. The conclusion is as follows:1) The main particle size dictribution of the MSWI botton ash is above 0.45 mm and accounts for approximately 97% of the bottom ash and the content of the botton ash is 35.83% in the > 4mm fraction. The p H value of the MSWI bottom ash is 12.78. The loss-on-ignition is 2.23% at 600℃ and 3.76% at 950 ℃. It was revealed that MSWI bottom ash mainly consists of assorted silicate-based glass phases and mineral phases including melilites, pseudowollastonite, spinels, and metallic inclusions.2) Nowadays, the FM is usually recovered from MSWI bottom ash by magnetic separation. To our knowledge, such a physical technique has been applied to raw MSWI bottom ash, not processing MSWI bottom ash. However, this study focuses on the applicability of magnetic separation on the smash bottom ash. Different types of purification steps and solvents are used to extract the FM. Among the different extraction ways, we propose the following order based on their direct FM uptake capacity: two-step extraction > one-step extraction> dry extraction. Two-step extraction was found to be the best effective extraction way of the FM. The experiment results revealed that the Fe% were 4~6 times higher in the FM after two-step extraction than that in the raw bottom ash and 2~2.5 times higher than that derived from one-step extraction. The iron-rich matters characterize the composition of more than 40% of the FM, and reaches 375.66g/kg. Other metals(such as Cu、Zn、Ni、Mn and Ni,) and non-metals(such as K、Na、P, Si, Al,S and Cl) with variable amounts incorporated in the FM from MSWI bottom ash after two-step extraction though they are enriched in Fe, are composed of similar elements to the raw ashes. However the FM contained magnetite(Fe3O4), hematite(Fe2O3), metallic iron(Fe), and, to a lesser extent, quartz, gehlenite and mullite after two-step extraction, as detected by XRD. About mental release, chemical analyses revealed that solubility of Cu、Zn、Pb、Cr、Cd and Ni were higher in the FM than that in the raw MSWI bottom ash, while they were composed of similar elements to the raw MSWI bottom ash.3) Pure water, ethanol and acetone were selected and utilized in this study for wet magnetic separation of the FM from MSWI bottom ash,we proposed the following order based on their direct FM uptake capacity: ethanol > acetone > pure water. The Fe% in the FM were 375.66g/kg, 365.79g/kg, 344.59g/kg, and extraction efficiency were 63.57%, 72.53%, 67.67% by the two-step extraction for water, ethanol and acetone respectively. Pure water might have altered chemical forms of Fe during separation of the FM, so the Fe0 accounts for approximately 12% of the iron-rich maters by the two-step extraction for ethanol. XPS analysis of the FM after two-step extraction disclosed that the Fe0:Fe2+:Fe3+ ratios were 10:35:55, 12:43:45 and 9:33:59 for water, ethanol and acetone respectively.4) Reduction of aqueous trichloroethene(TCE) by FM was studied in anaerobic batch systems. The MSWI bottom ash had an effect on the reductive dechlorination of TCE and the principal degradation product was ethane and the matters whose chemical formula is C8H27O2. It is proposed that not only the Fe0, but also a lot of iron-rich maters played an important part in the reaction of TCE. The removal efficiency of the TCE observed to be reach 40% in the anaerobic batch experiments.5) Although a decreasing rate of dechlorination is to be expected, the TCE removal efficiency is nearly affected by the presence of difference valence conditions of irons and other catalytic matters. It was observed that reaction temperature at 37℃ had a fiercer detrimental effect on the volatilization of TCE than that at 22 ℃. The experimental results showed that increasing p H slightly increased the removal efficiency of TCE. The results indicated the reaction process to be relatively insensitive to the initial concentration of TCE over the range from about 100 to 400 ug/L.