Cláudia B. Lopes

Silica coated magnetite particles for magnetic removal of Hg2+ from water

The magnetic removal of Hg(2+) from water has been assessed using silica coated magnetite particles. The magnetite particles were first prepared by hydrolysis of FeSO(4) and their surfaces were modified with amorphous silica shells that were then functionalized with organic moieties containing terminal dithiocarbamate groups. Under the experimental conditions used, the materials reported here displayed high efficiency for Hg(2+) uptake (74%) even at contaminant levels as low as 50 μg l(-1). Therefore these eco-nanomagnets show great potential for the removal of heavy metal ions of polluted water, via magnetic separation.

Mercury pollution in Ria de Aveiro (Portugal): a review of the system assessment

The Ria de Aveiro (Portugal) is a coast al lagoon adjacent to the Atlantic Ocean and it has an inner bay (Laranjo bay) that received a highly contaminated effluent discharged by a mercury cell chlor-alkali plant from the 1950s until 1994. The aim of this study is to review in a holistic way several research studies that have been carried out in the Ria de Aveiro, in order to evaluate the remobilization of the mercury accumulated within the system and the recovery of the lagoon. The spatial distribution of the total mercury in the surrounding terrestrial environment has also been considered. Results indicate that the main mercury contamination problems in the Ria de Aveiro are confined to the Laranjo bay. Mercury export to the coastal waters and its impact on the nearshore compartments (water column, sediment and biota) are low. No direct effects of the mercury from nearby industrial activities were detected in Aveiro’s urban soils, although historical mercury contamination is still affecting soil quality in the immediate vicinity of the chlor-alkali plant, located in Estarreja. Moreover, macrophyte harvesting for human direct or indirect use and the consumption of mussels, crabs and the sea bass from the Laranjo bay may constitute a health risk. Further studies focusing on developing skills for the restoration of the ecosystem are presently underway.

Nanoscale materials and their use in water contaminants removal—a review

Water scarcity is being recognized as a present and future threat to human activity and as a consequence water purification technologies are gaining major attention worldwide. Nanotechnology has many successful applications in different fields but recently its application for water and wastewater treatment has emerged as a fast-developing, promising area. This review highlights the recent advances on the development of nanoscale materials and processes for treatment of surface water, groundwater and industrial wastewater that are contaminated by toxic metals, organic and inorganic compounds, bacteria and viruses. In addition, the toxic potential of engineered nanomaterials for human health and the environment will also be discussed.

Removal of mercury (II) by dithiocarbamate surface functionalized magnetite particles: Application to synthetic and natural spiked waters

In order to take advantage of the high affinity between mercury and sulphur, magnetite (Fe(3)O(4)) particles functionalized with dithiocarbamate groups (CS(2)(-)), were synthesized to be used as a new type of sorbent to remove Hg (II) from synthetic and natural spiked waters. The effectiveness of this type of sorbent was studied, and its potential as cleanup agent for contaminated waters was assessed. Batch stirred tank experiments were carried out by contacting a volume of solution with known amounts of functionalized Fe(3)O(4) particles, in order to study the effect of sorbent dose, salinity, and the kinetics and the equilibrium of this unit operation. A complete Hg (II) removal (ca. 99.8%) was attained with 6 mg/L of magnetic particles for an initial metal concentration of 50 μg/L. It was confirmed that highly complex matrices, such as seawater (ca. 99%) and river water (ca. 97%), do not affect the removal capacity of the functionalized magnetic particles. Concerning isotherms, no significant differences were observed between two- and three-parameter models (P = 0.05%); however, Sips isotherm provided the lowest values of SS and S(x/y), predicting a maximum sorption capacity of 206 mg/g, in the range of experimental conditions under study. The solid loadings measured in this essay surmount the majority of the values found in literature for other type of sorbents.

Efficient sorbents based on magnetite coated with siliceous hybrid shells for removal of mercury ions

New sorbents based on magnetite particles coated with siliceous shells were synthesized and tested in the removal of mercury ions from aqueous solutions by magnetic separation. Atomic fluorescence spectroscopy studies performed on water samples treated with these sorbents have shown that the metal ion concentration decreased to values lower than the guideline values for drinking water. The high adsorption affinity for mercury ions in these materials was attributed to dithiocarbamate groups grafted over the siliceous domains using a new surface modification method. Hence, the magnetic particles have been coated with amorphous silica shells that include thiolate moieties via a hydrolytic co-condensation process using tetraethoxysilane (TEOS) and siloxydithiocarbamate (SiDTC) as the sol–gel precursors. This one-step method for the surface modification of magnetite particles led to sorbents with extensive thiolate moieties that can be then collected by applying an external magnetic field.

Effect of pH and temperature on Hg2+ water decontamination using ETS-4 titanosilicate.

Batch stirred tank experiments were carried out to study the effect of pH (range 2-10, at 294 K) and temperature (277, 294 and 313 K, at pH 5) on the uptake of Hg(2+) ions by ETS-4 microporous titanosilicate. Changes in the pH have a significant effect on the ETS-4 uptake efficiency, the optimal range being 4-6. Due to competition effects, the chemical used to adjust the pH of the Hg(2+) solution also influences the uptake efficiency. Thermodynamic parameters for the uptake of Hg(2+) ions were calculated. For the temperature range studied, the Hg(2+) sorption increased with decreasing temperature.

Uptake of Hg2+ from aqueous solutions by microporous titano- and zircono-silicates

Being mercury one of the most toxic heavy metals present in the environment, it is of major concern to develop cleanup technologies to remove it from wastewater and recover mercury polluted ecosystems. In this context, we study the potential of some microporous titanosilicates and zirconosilicates for taking up Hg2+ from aqueous solutions. These materials have unique chemical and physical properties, and here we are able to confirm that they readily remove Hg2+ from aqueous solutions. Moreover, the presence of the competitive Mg2+ and Na+, which are some of the dominant cations in natural waters, does not reduce the uptake capacity of some of these materials. Thus, several inorganic materials reported here may have important environmental applications, efficiently removing Hg2+ from aqueous solutions.

Ferromagnetic sorbents based on nickel nanowires for efficient uptake of mercury from water.

This work reports the preparation of ferro-magnetic nickel nanowires (NiNW) coated with dithiocarbamate-functionalized siliceous shells and its application for the uptake of aqueous Hg(II) ions by magnetic separation. NiNW with an average diameter and length of 35 nm and 5 μm, respectively, were firstly prepared by Ni electrodeposition in an anodic aluminum oxide template. The NiNW surfaces were then coated with siliceous shells containing dithiocarbamate groups via a one-step procedure consisting in the alkaline hydrolytic co-condensation of tetraethoxysilane (TEOS) and a siloxydithiocarbamate precursor (SiDTC). A small amount of these new nanoadsorbents (2.5 mg·L(-1)) removed 99.8% of mercury ions from aqueous solutions with concentration 50 μg·L(-1) and in less than 24 h of contact time. This outstanding removal ability is attributed to the high affinity of the sulfur donor ligands to Hg(II) species combined with the high surface area-to-volume ratio of the NiNW.

Competitive Removal of Cd2+ and Hg2+ Ions from Water Using Titanosilicate ETS-4: Kinetic Behaviour and Selectivity

Mercury and cadmium are priority hazardous substances. Some titanosilicates have been tested for the removal of Cd2+ and Hg2+ from single solutions by ion exchange. In this work, the competition between both contaminants for the exchanger binding sites of titanosilicate Engelhard titanosilicate material number 4 (ETS-4) was studied by performing batch experiments with aqueous solutions containing the two counter ions. The results evidenced the large capacity of ETS-4 and shown that the cadmium(II) diffusivity through the sorbent is higher than that of mercury(II). Furthermore, the ETS-4 exhibited higher kinetic and equilibrium selectivities for Cd2+, which attained values in the ranges 8.9–12.5 and 7.9–12.8, respectively. With respect to modelling, the pseudo-second-order equation described successfully the competitive removal of Cd2+ and Hg2+.

Competitive effects on mercury removal by an agricultural waste: application to synthetic and natural spiked waters

In this work, the efficiency of a local and highly available agricultural waste, the raw rice husk, was used to remove mercury (Hg) from synthetic and natural waters, spiked with concentrations that reflect the contamination problems found in the environment. Different operating conditions were tested, including initial pH, ionic strength, the presence of co-ions (cadmium) and organic matter. The sorption efficiency of rice husk was slightly affected by the presence H+ ions (pH range between 3 and 9), but in the presence of NaNO3 and NaCl electrolytes and in binary solutions containing Cd2+ and Hg2+, the sorption efficiency was dependent on the nature and levels of the interfering ion and on the initial concentration of Hg2+ used. Nevertheless, in a situation of equilibrium the effect of those ions was negligible and the removal efficiency ranged between 82% and 94% and between 90% and 96% for an initial Hg2+ concentration of 0.05 mg L−1 and 0.50 mg L−1, respectively. In more complex matrices, i.e. in the presence of humic substances and in natural river waters, the speciation and dynamics of Hg was changed and a fraction of the metal becomes unavailable in solution. Even then, the values obtained for Hg removal were satisfactory, i.e. between 59% and 76% and 81% and 85% for an initial concentration of Hg2+ of 0.05 and 0.50 mg L−1, respectively.