Oxidation of high iron content electroplating sludge in supercritical water: stabilization of zinc and chromium
- 106 Downloads
The stabilization of heavy metals (zinc and chromium) and the degradation of organic pollutants during supercritical water (SCW) and supercritical water oxidation (SCWO) treatment of electroplating sludge (EPS) with a high iron content were studied. Experiments were performed in a batch reactor at temperatures in the range from 623.15 to 823.15 K with an oxygen coefficient (OE) from 0 to 2.0, a reaction time of 7 min and pressure of 25 MPa to examine the effect of the operation conditions. Chemical oxygen demand (COD) and total organic carbon (TOC) in raw sludge and liquid products under different reaction conditions were detected. The results indicated that more organic pollutant degradation occurred under supercritical conditions than in subcritical water. Additionally, as the temperature and amount of oxidant increased, the organic pollutant removal rate increased. In addition, the Zn and Cr removal efficiency from sludge was more than 98% under all conditions. Temperatures under 773.15 K had a positive effect, whereas the oxygen ratio was more significant than the other factors above 773.15 K. Furthermore, leaching toxicity tests of the heavy metals in solid products were conducted based on the toxicity characteristic leaching procedure (TCLP). All heavy metals showed greatly reduced leaching toxicity due to their stabilization. The Zn in the EPS is more easily converted into a solid product after SCWO treatment; however, Cr is more difficult to leach from the solid product. Oxides of iron, zinc, and chromium were detected by X-ray diffraction and an electron probe microanalyzer, and the yield of the oxides increased with increasing temperature and oxidant amount. Using the obtained data and analysis results, the effect of Fe on the stabilization of Zn and Cr was studied.
KeywordsElectroplating sludge High iron content SCWO Zinc Chromium Stabilization mechanism
This project was supported by the National Natural Science Foundation of China (No. 41673105), the BaGui Scholars Program Foundation (No. 2014BGXZGX03), and the Youth Fund Project of Guangxi Natural Science Foundation (No. 2016GXNSFBA380239).
- Apj S, Cardozo FL, Dcc M, Tkfs F, Garcia JC, Crg T (2018) Combined processes of ozonation and supercritical water oxidation for landfill leachate degradation. Waste Manag 466–476Google Scholar
- Chen G, Chen S, Song Z, et al. (2015) Lignite sulfur transformation during the supercritical water gasification process[J]. J Anal Appl Pyrolysis 116(6):161–167Google Scholar
- Chinese Ministry of Environmental Protection (1997) Test standard for leaching toxicity of solid wastes using horizontal vibration extraction procedure. Chinese Environmental Science Press, Beijing (in Chinese)Google Scholar
- Kriksunov LB, Macdonald DD (1995) Corrosion in supercritical water oxidation systems: a phenomenological analysis. Chemphyschem A European J Chem Phys Phys Chem 142(12):4069–4073Google Scholar
- Langton CA (1989) Slag-based materials for toxic metal and radioactive waste stabilization[C]//Google Scholar
- US Environmental Protection Agency (1992) Method 1311 – toxicity characteristic leaching procedure (TCLP), 35 pGoogle Scholar
- Zan YF, Wang SZ, Zhang QM, Shen LH, Duan BQ, Lin ZH (2006) Experimental studies on the supercritical water oxidation of municipal sludge and its reaction heat. J Chem Eng Chinese Universities 20(3):379–384 (In Chinese) Google Scholar
- Zou D, Chi Y, Dong J, Fu C, Ni M (2015) Supercritical water oxidation of MSW leachate: factor analysis and behavior of heavy metals. Environ Prog Sustain 33:1117–1124Google Scholar