Abstract
This research presents the optimization of soil washing conditions in the removal of multiple heavy metals (Cu-Pb-Zn-Cd) under the using of ethylenediaminetetraacetic acid (EDTA). The optimum combination of washing parameters in a bench-scale soil washing experiments is determined by response surface methodology (RSM). Central composite design is applied after single factor experiment, EDTA concentration, solid-to-liquid ratio and washing time are evaluated variables for the removal processes, and the regression models of HMs are constructed. The results show that, EDTA concentration and solid-to-liquid ratio are significant factors for this process. Subsequently, 50% of Cu removal was set as the optimum target to optimize the combined conditions, through the building of multiple quadratic regression models, the optimal condition combination is determined that EDTA concentration is 0.0026 mol·L-1, solid-to-liquid ratio is 1:22, washing time is 3.89 h, the extraction rate of Pb, Zn, Cd is predicted to be 78%, 75% and 71%, respectively.
Highlights
Soil pollution caused by heavy metals (HMs) has become a widespread global problem for their non-biodegradation and long residence time (Wuana, Okieimen, & Imborvungu, 2010; Evangelou, Bauer, Ebel, & Schaeffer, 2007)
Single type of heavy metal has been intensively studied of late years, a number of HMs always co-exist in common types of contamination sites (Arao et al, 2010; Moutsatsou, Gregou, Matsas, & Protonotarios, 2006)
The purpose of this study was using central composite design (CCD) of response surface methodology (RSM) to optimize the conditions for the removal of Cu, Pb, Zn and Cd from the contaminated soils in the process of soil washing with ethylenediaminetetraacetic acid (EDTA)
Summary
Soil pollution caused by heavy metals (HMs) has become a widespread global problem for their non-biodegradation and long residence time (Wuana, Okieimen, & Imborvungu, 2010; Evangelou, Bauer, Ebel, & Schaeffer, 2007). Ex-situ soil washing process bases on the idea of water rinsing to remove pollutants from soil and to transfer them to a concentrated liquid phase (Mao, Jiang, Xiao, & Yu, 2015). Speaking, it includes either a physical separation, or a chemical extraction, both the physical and the chemical washing often coexist in most cases (Peters, 1999; Di Palma, Ferrantelli, & Medici, 2005). Many different chemicals like acid solutions, diluted acid solutions containing chloride salts, surfactants, reducing and oxidizing agents, and chelants are of high extraction efficiency for HMs in the soil (Dermont et al, 2008). For the purpose of removing various types of contaminant from soil, chemical-enhanced soil washing has been comprehensively studied in recent years (Lo, Tanboonchuy, Yan, Grisdanurak, & Liao, 2012; Gao, He, Ling, Hu, & Liu, 2003; Haapea & Tuhkanen, 2006)
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