Experimento De Laboratorio

LABORATORY EXPERIMENT
pubs.acs.org/jchemeduc

Laboratory Experiments on the Electrochemical Remediation of the
Environment. Part 9: Microscale Recovery of a Soil Metal Pollutant and
Its Extractant
Jorge G. Ibanez,*,† Patricia Balderas-Hernandez,‡ Elizabeth Garcia-Pintor,† Sandy Nohemi Barba-Gonzalez,§
Ma. del Carmen Doria-Serrano,† Lorena Hernaiz-Arce,† Armando Diaz-Perez,† and AnaLozano-Cusi†
†

Centro Mexicano de Quimica Verde y Microescala, Departamento de Ingenieria y Ciencias Quimicas, Universidad Iberoamericana,
Prol. Reforma 880, 01219 Mexico, D. F. Mexico
‡
Facultad de Quimica, Centro Conjunto de Investigacion en Quimica Sustentable UAEM-UNAM, Universidad Autonoma del Estado de
Mexico, Carretera Toluca-Atlacomulco, Km 14.5, Toluca, Estado de Mexico, Mexico
§Departamento de Quimica, CUCEI, Universidad de Guadalajara, Boulevard Marcelino Garcia Barragan #1451, 44430 Guadalajara,
Mexico
S
b Supporting Information

ABSTRACT: Many soils throughout the world are contaminated with metal
salts of diverse toxicity. We have developed an experiment to demonstrate the
removal of a metal from an insoluble surrogate soil pollutant, CuCO3 3 Cu(OH)2,
bycomplexation followed by the simultaneous electrochemical recovery of the
ligand (i.e., EDTA) and of the metal in its elemental form (i.e., Cu0). We have
calculated speciation diagrams to predict appropriate conditions and to
interpret the results.
KEYWORDS: Upper-Division Undergraduate, Analytical Chemistry, Environmental Chemistry, Inorganic Chemistry, Laboratory Instruction, Hands-OnLearning/Manipulatives, Aqueous Solution Chemistry, Coordination Compounds, Electrochemistry, Microscale Lab
chelating agents can be difficult to biodegrade and may also
remove essential components and nutrients from the soil.11,12
Ongoing research focuses on the possibility of using natural,
biodegradable chelating agents from weak organic acids and their
salts (e.g., citrates) that have a lower tendency toform strong
chelates with Ca, Mg, and Fe and thus have less impact on soil
composition.13 Once the metal ions are extracted, the next step is
to recover the metal and the extracting agent, although this is
seldom achieved by chemical means. A promising alternative
consists of the paired electrochemical recovery of both components by the simultaneous electrodeposition of the metal and theliberation of the chelating agent.3,14
Because metal carbonates and other derivatives are known to
pollute soils,11 in this qualitative experiment, the metal part of a
pollutant (Cu2þ) will be extracted from one of its relatively
insoluble salts, copper(II) hydroxide carbonate, mixed with silica
gel to simulate the siliceous matrices commonly found in natural
soil environments. This mixture istreated with either (i) pure
water or (ii) a chelating agent (e.g., EDTA) to compare its
behavior in both media. Then, Cu0 (from the resulting CuEDTA
solution) is deposited on the cathode of an electrochemical cell,
and simultaneously, the EDTA contained in the remaining

oils are frequently the depositories of a wide range of wastes1,2
including atmospheric deposition. Preventionstrategies can
undoubtedly ameliorate this problem; however, remediation
technologies are of immediate urgency in many instances. For
example, a site located in a former battery recycling plant
contained over 5 Â 104 mg Pb/kg of soil.3
There are a wide variety of soil remediation technologies based
on physical, chemical, electrochemical, or biochemical principles.4À6
Physicochemical remediation ofmetal-polluted soils is fundamentally based on two principles:1À4,7 (i) immobilization of the metal
via retention increase by the soil matrix and (ii) removal of the metal
from the soil matrix, which involves transfer of metal ions into a
washing solution by desorption from the soil followed by dissolution. These washing solutions are frequently composed of acids
(mainly hydrochloric,...