Enhancing Electrokinetic Remediation of Cadmium- Contaminated Soils with Stepwise Moving Anode Method

Abstract

This paper proposed an innovative approach by stepwise moving anode towards cathode to enhance the cadmium (Cd) removal from soil during the process of electrokinetic (EK) remediation. Fixed anode tests and moving anode tests were carried out for 60 hours to compare their performances. The anode-cathode spacing was 21 cm. Constant voltage grade of 1.0 V cm(-1) was applied in this study. The parameters included pH, electrical conductivity, current, Cd concentration and speciation distributions, energy consumptions, etc. It was found that the pH values in the moving anode tests were relatively lower than those of the fixed tests. In the moving anode test, the removal efficiency of Cd in the soils at the fraction of S4 was enhanced by 54.9% compared with that of the fixed anode tests. After 60 hours of treatment, approximately 80% of the spiked soils (100.63 mg x kg(-1) of Cd) in the system were successfully remedied in the moving anode tests; and the mean removal efficiency was 73% for actual field-contaminated soil (54.26 mg x kg(-1) of Cd). It is effective to remedy actual contaminated soils. In addition, the cumulative energy consumptions were 59.29 kWhm(-3) and 31.52 kWhm(-3) for the fixed and moving tests, respectively. The results revealed that the Cd removal efficiency was improved by the moving anode method. Moreover, less energy was consumed in the moving test. The proposed approach does not need to introduce extra chemicals nor adjust the pH in the system to enhance the Cd removal by EK remediation. The basic idea proposed in this paper provides a novel and environmental friendly method to enhance the EK remediation of heavy metals contaminated soils.

Effects of electrokinetic treatment of contaminated sludge on migration and transformation of Cd, Ni and Zn in various bonding states

“…2b and c). These trends were expected due to the higher mobility of the exchangeable and reducible fractions than that of the immobile forms such as residual and oxidizable (Chen et al, 2006). Li et al (2008) have also stated that the residual and organic fractions of heavy metals are immobile and exhibit lower toxicity.…”

“…Since the constant voltage during this EK process was maintained, the resistance was directly affected by the current in this system. According to Chen et al (2006), current is an indication of the amount of mobile ions under electromigration. Therefore, the transformation of Zn might be related to the amount of mobile ions in the sludge system.…”

Electrokinetic remediation of wood preservative contaminated soil containing copper, chromium, and arsenic

“…Although, most of the investigations were done on soils contaminated with single metallic species [4][5][6][7][8][9][11][12][13][14][15][16][17][18][19][20][21]26,38], limited tests have been done on soils contaminated with multiple metallic species [10,[22][23][24][25][27][28][29][30][31][32][33][34][35][36][37]. Previous tests conducted on soils contaminated with multiple species have shown that, the presence of multiple metals had an impact on the removal efficiencies [34].…”

A Review Article: Electrokinetic Bioremediation Current Knowledge and New Prospects

“…The conventional techniques include the use of an ion selective membrane such as cation-exchange membrane, which prevents the transport of the hydroxide ions from the cathode to the soil as shown in Figure 1 [57], continuous changing/removing of the solution in the electrode compartments [58], addition of chemical conditioning agents such as ethylenediaminetetraacetic (EDTA) [59] [60], acetic acid [55], and nitric acid [61]. Innovative techniques on the other hand include a stepwise moving anode [62] [63], polarity exchange [12] [64], circulation of an electrolyte (anolyte and catholyte) solution in the electrode compartments (see Figure 2) [35] [43] [65], and the two anodes technique (TAT) (see Figure 3) which has investigated the control of the advancement of the acid and the base fronts. The soil type (mostly buffer capacity) and the presence of anions which contribute to the buffer capacity (besides carbonates, hydrocarbonates and hydroxides): borates, phosphates, silicates and organic acids anions influence the pH changes and should be taken into account when choosing the right pH-regulation technique [63].…”