Conceptual model and sensitivity analysis for simulating the extraction kinetics of soil washing

Abstract

Purpose Most previous studies focused on the metal extraction efficiency of chelant-enhanced soil washing under various operational conditions; however, one of the keys to cost-effective field application is to maintain a high throughput rate (i.e., short washing time) while achieving the treatment objectives. Therefore, this study presented a conceptual model for simulating the kinetic extraction of heavy metals and evaluated its sensitivity analysis to the predetermined parameter values in five soils with different initial metal distributions. Materials and methods The proposed conceptual model considered the initial metal distribution and the respective fast and slow first-order extraction rates as the predetermined input parameters. The sensitivity analysis was conducted by combined and individual variation of the parameter values by fixed percentages. An implicit assumption is that there is no interaction between the metal fractions and the parameters are independent of each other. All other parameters were kept constant. Such systematic testing of the model behaviour in reaction to changes in the input parameters helped us identify the parameters that are more sensitive and require particular attention in the modelling process. Results and discussionIn the sensitivity analysis of combined parameter groups, the fraction of fast extraction ( f ) was linearly and inversely correlated to the required washing time in two stages, in which the correlation was more significant at the lower range of f values. The first-order rate coefficients of fast extraction (k′) and slow extraction (k″) showed a nonlinear and negative relationship with the required washing time. The individual contributions of f i and k i ′ of the three fraction groups were then analysed. Although the fraction group 1 (exchangeable and carbonate) had the highest f i and k i ′ values, their importance was limited by relatively small proportion in the field-contaminated soils. The required washing time for Pb extraction was most sensitive to the fraction group 2 (Fe/Mn oxides).Conclusions The results of this study suggested that model simulations are less sensitive to f 1 and k 1 ′ values of exchangeable and carbonate fractions, which can therefore be considered constant. However, f 2 and k 2 ′ values of the oxide fraction are sensitive parameters and should be prudently justified, or even recalibrated, at different sites.

Humic substances from sewage sludge compost as washing agent effectively remove Cu and Cd from soil

“…In their study, equilibrium was reached within 6 h with most soils. Tsang et al (2011) found that heavy metals (Pb, Zn, Cu) removal from soil with EDTA followed 1st order kinetics; however, this proceeded in two phases, rapid extraction during the first few hours followed by gradual extraction.…”

Statistical Optimization of Heavy Metal (Cu2+ and Co2+) Extraction from Printed Circuit Boards and Mobile Batteries Using Chelation Technology

“…The chelation process works on the concept of coordinative incorporation of a metal ion into a heterocyclic ring structure in which monodentate ligands are replaced by multidentate ones to form a metal–ligand complex . The chelating agent-assisted metal extraction process takes place into two steps: formation of metal–ligand complexes on WEEE surfaces and then kinetic detachment of the complex from WEEE into aqueous solution to maximize the thermodynamic stability of the complex. − Mass transfer of liquid extractant from the solid–liquid interface to the inner zone of the WEEE particles and then mass transfer of the metal–ligand complex from the interior of WEEE to bulk of the liquid extractant exclusively depend upon external and internal diffusion mechanisms. External diffusion involves rapid extraction of metals from superficial sites of the solid surface, whereas internal diffusion suggests extraction of metals present on internal sites of particles.…”

Conceptual mechanism and kinetic studies of chelating agent assisted metal extraction process from spent catalyst

“…Chelating agent assisted metal extraction process starts with the formation of metal-ligand complexes on catalyst surfaces and then kinetic detachment of the complex takes place from catalyst surfaces into the solution (i.e. dissociation) to maximize the thermodynamic stability of the complex [15,18,[22][23][24][25]. The process commences with the mass transfer of liquid extractant from solid-liquid interface to inner zone of the catalyst particles and then mass transfer of metalligand complex from interior of catalyst particles to bulk of the liquid extractant.…”