Geochemical assessment of metal transport in glacial till during electrokinetic remediation

Abstract

This paper presents the chemical speciation and retention behavior of chromium (Cr), nickel (Ni), and cadmium (Cd) prior to and after the electrokinetic remediation in glacial till soil. The speciation of the metals was predicted using the chemical speciation program MINEQL(+). The simulations were performed for single-contaminant with only Cr(VI) or Ni, and multi-contaminants consisting of: (1) Cr(VI), Ni, and Cd; (2) Cr(III), Ni and Cd; (3) Cr(VI), Cr(III), Ni and Cd; (4) Cr(VI), Ni, and Cd with reducing agents; and (5) Cr(III), Ni, and Cd with oxidizing agent (Mn). The results showed that the speciation and distribution of cationic metals [Ni, Cd, and Cr(III)] in glacial till soil remain unaffected or slightly affected during electrokinetics. This is attributed to the high pH buffering capacity of the glacial till, leading the metals to precipitate in the soil prior to and after electrokinetics. This study showed that during electrokinetics, Cr(VI) existed as anionic complex and migrated towards the anode and the migration is maximum in case of a single-contaminant system. The study also showed that near the anode in the absence of any reducing and oxidizing agent, Cr(VI) mostly adsorbed, and some of Cr(VI) reduced to Cr(III) and migrated towards the cathode and finally precipitated due to high pH conditions. Ni and Cd remain adsorbed or precipitated due to the high pH conditions throughout the soil. Among the reducing agents, the sulfide had significant effect on the migration of metals compared to ferrous ions. While in the presence of oxidizing agent (Mn), no noticeable Cr(VI) was found in the soil sample indicating the reduction of Cr(VI) to Cr(III) and the predominance of reducing conditions due to the presence of naturally occurring iron in the glacial till soil. Overall, this study provides a reasonable explanation of the speciation and distribution of chromium, nickel and cadmium during the electrokinetic remediation of glacial till soil.

Particle morphology and mineral structure of heavy metal-contaminated kaolin soil before and after electrokinetic remediation

“…Geochemical modeling results [28][29][30] indicated that wherever the heavy metals existed, either they existed in the dissolved phase or they were adsorbed to the soil surface. The only exception was in Section 5 of the combined chromium, cadmium and nickel test, where the model predicted that nickel would exist in the precipitate form.…”

“…Geochemical modeling was performed to assess how the metal contaminants were bound to the soil after electrokinetic remediation [28][29][30]. This information is useful because it facilitates an understanding of the processes that take place during electrokinetic remediation.…”

“…Previous research on electrokinetics at UIC has helped to understand the effects of different contaminant types, single and multiple contaminants, different soil mineralogical compositions and different pore-fluid chemistries on electrokinetic remediation. Geochemical characterization [2] and modeling [28][29][30] have implied that adsorption and precipitation are the two dominant processes associated with immobilization of metal contaminants in kaolin soil during electrokinetic remediation. This paper presents complementary study which involves the use of TEM, EDX and XRD to provide a better understanding of contaminant distribution and changes in soil minerals.…”

Influence of nickel speciation on electrokinetic sediment remediation efficiency

“…There were no significant changes in the current density during the experiments. The overall pH in the sediment did not decrease significantly because of the high CEC and high buffer capacity (ANC) of the sediment [13,11], which decreased the dissolution and desorption rates of the adsorbed and/or complexed species in the sediment. During EXP III there is a much higher current density which was accomplished by lowering the cross-sectional area.…”

Behavior of zinc, nickel, copper and cadmium during the electrokinetic remediation of sediment from the Great Backa Canal (Serbia)

“…This behavior is probably due to the evolution of hydrogen at the cathode during the EK process. [18] The more positive ORP near the anode can be ascribed to oxygen generation. Figure 5 shows the results of the DOC measurements carried out during EXP I to determine the behavior of DOM during the EK process.…”