**2. Experimental procedure**

Stripping voltammetric measurements were carried out using the potensiostat / galvanostat Epsilon modular electrochemical analysis system. Three-electrode electrochemical cell (Figure 4) was used with glassy carbon electrode as working electrode, a platinum wire as auxiliary electrode and an Ag/AgCl as reference electrode (Pineda et al, 2009; Anguiano et al, 2012; Bustos, 2012). Glassy carbon electrode was polished in cloth with an alumina suspension of 1, 0.3 and 0.05 µm. Between each polish it was rinsed with deionized water, and then it was sonicated during 5 min in deionized water to eliminate any residual alumina.

Electrochemical Detection of Mercury Removal from Polluted Bentonite and Quartz using Different Removing Agents http://dx.doi.org/10.5772/57446 385

**Figure 4.** Scheme of a 3-electrode cell used in voltammetry techniques, where gas inlet is used for bubbling electro‐ lyte solution with an inert gas and with controlled temperature.

#### **2.1. Reagents and solutions**

**Removing agent Concentration Sample Removed Metal η / %**

Polluted

Polluted water

Polluted

Table 2 contains references about different removing agents reported to remove different metals. These studies analyzed the removal of metals from different samples, obtaining the highest efficiencies using removing and complexing agents by exchanging charges of cations to remove mercury in the first case, or coordinating cations in the second case (Wypych,

Stripping voltammetric measurements were carried out using the potensiostat / galvanostat Epsilon modular electrochemical analysis system. Three-electrode electrochemical cell (Figure 4) was used with glassy carbon electrode as working electrode, a platinum wire as auxiliary electrode and an Ag/AgCl as reference electrode (Pineda et al, 2009; Anguiano et al, 2012; Bustos, 2012). Glassy carbon electrode was polished in cloth with an alumina suspension of 1, 0.3 and 0.05 µm. Between each polish it was rinsed with deionized water, and then it was

**Potassium iodide (KI)** 0.1 M Polluted soil Hg 99

2004; Montuenga, 1979; Přibil, 1982; Buffle, 1990; Spencer et al. 2000; Malone, 1999).

sonicated during 5 min in deionized water to eliminate any residual alumina.

1.2 mMg Cu Co (11) -1 (Cr3+)

soil Hg

0.1 M 75

soil Cu, Pb

(Cu)- EDTA (84), NTA (66)

EDDS (67)

(Pb)- EDTA (94), NTA (65),

EDDS (67)

62

Co, Ca, Cr, Cu (53),

0.5 % Respectively

0.4 and 4 mM

0.02 mMg-1 (Co2+ and Ca2+)

2 mMg-1 (Cr3+)

**Table 2.** Scientific publications about metal extractions facilitated by removing agents.

**(EDTA +Cys+NaCl)**

384 Environmental Risk Assessment of Soil Contamination

**Ethylenediamine tetraacetic acid (EDTA)**

**Ethylenediamine disuccinicacid (EDDS) Iminodisuccinicacid**

**Ácidometilglicindi acetic**

**Potassium iodide (KI)** 0.1 M

**2. Experimental procedure**

**Nitrilotriacetic acid**

**Ethylenediamine tetraacetic acid (EDTA)**

**(IDSA)**

**(MGDA)**

**(NTA)**

**Chitosan**

Reagents used in this study were: potassium chloride, potassium iodide, potassium hydroxide, sodium hydroxide, etilendiamintetracetic acid, and hydrochloric acid obtained from J. T. Baker; sodium chloride from Sigma Ultra; chitosan from crab shells practical grade, βciclodextrin hydrate, L-cysteine were obtained from Aldrich. For mercury pollution were used mercury chloride (II) from Merk, and mercury oxide (II) obtained from Hach. Calcium bentonite from Lodbent Bentonite, and sand white quartz from Sigma Aldrich.

Removing agents tested were 0.1 M potassium iodide (KI), 0.1 M potassium chloride (KCl), 0.1 M potassium hydroxide (KOH), 0.1 M hydrochloric acid (HCl), 0.1 M ethylenediaminetetra‐ acetic acid (EDTA), 10% hydroxypropyl-β-cyclodextrine (HPCD) in deionized water, 0.01 M chitosan and a mixture of 275 mgL-1 EDTA, 1.15% cysteine and 0.5% sodium chloride (NaCl). All of the agents, with the exception of chitosan, had previously been tested for the ability to remove metals in soil samples. Control experiments were carried out with water. Solutions were prepared using water type I, according to ASTM-D1193-99. Chitosan were dissolved in acetic acid. Samples of quartz and calcium bentonite were polluted with mercuric chloride (HgCl2) and mercuric oxide (HgO) at concentrations of 10 and 25 mgL-1. Eight removing agents were tested to find the most effective. The percentage of mercury removed was quantified by ASV after extracting the liquid from the bentonite/quartz samples.

#### **2.2. Techniques and procedures**

Electrochemical techniques as Anodic Stripping Voltammetry (ASV), Differential Stripping Pulse Voltammetry (DSPV) and Square Wave Stripping Voltammetry (SWSV) were tested to select adequate technique to quantify mercury removal efficiency. After select adequate technique, calibration curves were created for all different removing agents for the addition of both HgCl2 and HgO.

Experimental conditions for ASV were as follows: pre-concentration potential –0.6 V vs. Ag/ AgCl, deposition time 6 min, quiet time 30 s, scan rate 20 mV s-1. An increase in signal due to increasing mercury was monitored and recorded along with the increment in current associ‐ ated with the concentration addition. For SWSV were used an initial potential of -0.2 mV, a deposition potential of -0.6 V for a deposition time of 10 s; a quiet time of 5 s, a SW frequency of 50 Hz, a potential step of 0.005 V. For DSPV were used an initial potential of -0.2 mV, a deposition potential of -0.6 V for a deposition time of 10 s; a quiet time of 5 s, a potential step of 4 mV, a pulse width of 50 ms, a pulse period of 200 ms, pulse amplitude of 50 mV. All experiments were carried out at room temperature (25±1°C) (Anastasiadou et al, 2010). Calibration curves for mercuric quantification were done using electrochemical techniques to select the best.
