Irene Cano-Aguilera

Kinetic and Thermodynamic Modeling of Cd+2 and Ni+2 Biosorption by Raw Chicken Feathers

Batch experiments were performed to model kinetic and thermodynamic data for Cd+2 and Ni+2 biosorption by raw chicken feathers (CFs) under different conditions. Results indicated that Cd+2 and Ni+2 sorption onto CFs occurred on the external surface of the biosorbent. Ion removal increased with pH, whereas both endothermic and exothermic stages where observed depending on temperature. Our calculated thermodynamic parameters showed that, below the temperature of 30°C, the metal uptake of Cd+2 and Ni+2 ions may be mainly controlled by a chemisorption process. However, for temperatures higher than 30°C, it is likely that sorption of both metals onto CFs is caused by a combination of both physical and chemical processes, especially for Ni+2 ions. Maximum sorption capacities were of 0.039 (Cd+2 ) and 0.065 mmol/g (Ni+2) at pH 5 and 30°C. Using 0.1 M HCl or CH3COOH as desorbing agents, approximately a 50% recovery for Cd+2 was achieved. The pseudo-second order and the general rate law models best fit the sorption kinetics data. The equilibrium metal uptake data was best described by the Sips isotherm.

Role of ethylenediaminetetraacetic acid on lead uptake and translocation by tumbleweed (Salsola kali L.)

Tumbleweed plants (Salsola kali L.) grown in agar and liquid media demonstrated a high capacity to accumulate Pb in their different parts without affecting biomass. Whereas shoot elongation and biomass were not significantly affected by high tissue concentrations of Pb, root growth was significantly affected relative to controls. Roots, stems, and leaves demonstrated Pb concentrations of 31,000, 5,500, and 2,100 mg/kg dry weight, respectively, when plants were grown in the agar medium containing 80 mg Pb/L. Application of ethylenediaminetetraacetic acid (EDTA) to Pb-contaminated media dramatically reduced the total acquisition of Pb from both types of media. However, EDTA significantly increased the translocation of Pb from roots to the aerial parts, as evidenced by a multifold increase (23- and 155-fold for agar and liquid media, respectively) in the translocation concentration factor. The concentration of the antioxidant thiol compounds significantly increased (p < 0.05) in plants grown with uncomplexed Pb treatments relative to control plants. Scanning-electron microscopy and electron dispersive x-ray spectroscopic evaluation of leaf samples demonstrated an interesting pattern of Pb translocation in the presence or absence of EDTA. Large Pb crystals were found across the leaf tissues (palisade, spongy parenchyma, and conducting tissues) in the absence of EDTA. Lead nanoparticles also were seen when plants were grown in Pb-EDTA solution. Ultramicroscopic features of tumbleweed provide clear evidence for the unrestricted conduction of Pb from the root to the aerial parts, and this property makes the plant a good candidate for phytoremediation.

Heavy Metal Binding by Inactivated Tissues of Solanum Elaeagnifolium: Chemical and Subsequent XAS Studies

Contamination caused by heavy metals as well as their toxic effects on the environment and mankind is well known. However, it has been observed that some native plants have survived within areas polluted with heavy metals. This has been the case with the woody subshrub Solanum elaeagnifolium. It is possible to take advantage of this singular feature by using its inactivated tissues as a biofiltration system. In this work we characterized the mechanism of the binding between the biomass tissues with heavy metals by using chemical modification techniques. These techniques included chemical esterification and hydrolyzation of carboxylic groups and methyl esters, respectively. These studies have shown an overall decrease in metal binding for the esterified biomass, and an overall increase in metal binding for the hydrolyzed biomass as compared with the unmodified biomass. These experiments were performed with Cu(II), Pb(II), Cr(III), Zn(II) and Ni(II). In addition, experiments conducted with modified biomass at different pH conditions were done in order to corroborate the biomass modification results. Also, we used X-ray absorption spectroscopy techniques (XANES and EXAFS) to elucidate the mechanism(s) of metal ion binding.

Factors controlling the release of arsenic from mining tailings.

Some mine tailings pools in the Mine District of Guanajuato, Mexico, present a varied distribution and temporal and spatial concentration of elements that are potentially toxic, such as manganese, cadmium and zinc. These elements were detected in majority concentrations, and arsenic was present in the two major oxidation states As(III) and As(V). The highest arsenic concentration in the surrounding surface water reservoirs was detected when a rainy seasons occurred, which in turn is mainly a function of pH and the presence of bicarbonate ions. The conceptual model to describe the mobilization of arsenic from mining tailings towards the aqueous systems proposes a scenario where oxidation, the neutralization of acid drainage by carbonates, and arsenic desorption by bicarbonates takes place in different steps and at different times.