Study On Recovery Of Heavy Metals From Sludge Incineration Fly Ash

Sludge incineration is defined as a thorough way to deal with sludge due to the advantages of making sludge decrement, killing micro-organisms and saving energy. A lot of fly ash which contains different kinds of heavy metals would be produced by sludge incineration. A method which we can recover heavy metals from sludge fly ash that is produced by a sludge incineration power plant in Jiaxing was researched in this paper.The properties of sludge incineration fly ash including superficial characteristics, particle size composition, element composition and heavy metals content were analyzed by the experimental apparatus including inductively coupled plasma atomic emission spectrometer(ICP-AES), X-ray diffraction(XRD), Scanning electron microscopy(SEM), and Energy dispersive spectroscopy (EDS). The forms of heavy metals were analyzed by BCR sequential extraction method. It was proved that the main elements in fly ash are C, O, Ca, Fe, Al, S, Na, K and Cu, Zn and Pb have high content in fly ash and can be easily extracted. It was decided to recover Cu, Zn and Pb from fly ash due to these researches.In order to extract the soluble salt ions, a pretreatment that washing with deionized water was used in this research. It was shown that most soluble salt ions were extracted while few heavy metals were removed in this condition:liquid to solid ratio L/S=7 mL/g, time:40min, temperature:normal indoor temperature.Alkaline leaching using NaOH as leachate was carried out. It was found that alkaline leaching was effective that 60% of Pb,10% of Zn were extracted while most Cu stayed in fly ash in the condition:temperature=70℃, L/S=25 mL/g, time=lh. Sulfuric acid was used to wash fly ash that after alkaline leaching.72% of Cu and 70% of Zn were extracted by sulfuric acid washing when the condition was:time=20min, L/S=8mL/g. This investigation has shown that hydrometallurgical treatment of fly ash by means of acid washing followed alkaline leaching is a potential method which can separate the heavy metals you wanted to recover.Hydrogen peroxide was used to switch Fe2+ to Fe3+ and iron removal rate is 96% under the condition of pH=3.4. But it is hard to filtrate Fe(OH)3. Zn powder was used to recover Cu in solution. Cu reduction rate was over 99% at room temperature, with stirring and the amount of zinc is of 1.3 times in theory within 1 Omin of the reduction; Electrodeposition was used to recover Pb and Zn. It was shown that in this experiment more than 99% of Pb would be recovered when the condition:2V of cell voltage,30mm of electrode space and 3h was spent. And when the condition:3.4V of cell voltage, 30mm of electrode space and Ih was spent, the ratio of recovery of Cu would be more than 99%.