Christiana Mystrioti

Reduction of nitrate by copper-coated ZVI nanoparticles

abstract Nano zero-valent iron has been shown to be effective for the removal of nitrates from natural wastes and wastewaters. This work studies the application of surface-modified nano zero-valent iron as bimetallic Fe/Cu particles to remove high concentration of nitrates. Dispersed nano-Fe/Cu particles were synthesized by chemical reduction and examined by X-ray diffraction, scanning electron microscopy, and BET surface area analysis. Batch experiments were conducted to investigate the effectiveness of bimetallic particles on the reduction and removal of nitrates. The parameters investigated included the copper content (0.5, 5, 10, and 20% w/w) in zero-valent iron nanoparticles and the initial concentration of nitrates (100, 200, 300, and 500 mg/L). During the experiments, the aqueous solution was analyzed to determine the evolution of as well as , NH3, and which were produced as intermediate and final products. Based on the results obtained, it was concluded that the optimum coating rate was 5% w/w cop...

Comparative evaluation of five plant extracts and juices for nanoiron synthesis and application for hexavalent chromium reduction

The effectiveness of five plant extracts and juices, i.e. extracts of Camellia sinensis (green tea, GT), Syzygium aromaticum (clove, CL), Mentha spicata (spearmint, SM), Punica granatum juice (pomegranate, PG) and Red Wine (RW), for the production of nanoiron suspensions and their application for Cr(VI) reduction was investigated. Polyphenols contained in extracts act as reducing agents for iron ions in aqueous solutions, forming thus iron nanoparticles, and stabilize the nanoparticles produced from further oxidation and agglomeration. The maximum amount of polyphenols extracted per g of herbs was obtained at herb mass to water volume ratio varying from 10 to 20g/L. Suspensions of nanoparticles with sizes below 60nm were produced by mixing iron chloride solution with the plant extracts and juices investigated. The maximum concentration of nanoiron in suspensions was estimated to 22mM, obtained using RW and PG at a mixing ratio of iron solution to extract equal to 2. Lower concentrations, up to 18mM, were achieved using GT and CL extracts. Therefore, PG juice and RW were considered as more effective for nanoiron production, and, together with GT extracts, they were selected for the production of nanoiron suspensions, which have been proven effective for Cr(VI) reduction, reaching removal capacity as high as 500mg Cr(VI) per g of iron in nanoparticles.

Column study for the evaluation of the transport properties of polyphenol-coated nanoiron.

Injection of a nano zero valent iron (nZVI) suspension in the subsurface is a remedial option for obtaining the in situ reduction and immobilization of hexavalent chromium in contaminated aquifers. Prerequisite for the successful implementation of this technology is that the nanoparticles form a stable colloidal suspension with good transport properties when delivered in the subsurface. In this study we produced stable suspensions of polyphenol-coated nZVI (GT-nZVI) and we evaluated their transport behavior through representative porous media. Two types of porous materials were tested: (a) silica sand as a typical inert medium and (b) a mixture of calcareous soil and sand. The transport of GT-nZVI through the sand column was effectively described using a classic 1-D convection-dispersion flow equation (CDE) in combination with the colloid filtration theory (CFT). The calculations indicate that nZVI travel distance will be limited in the range 2.5-25cm for low Darcy velocities (0.1-1m/d) and in the order of 2.5m at higher velocities (10m/d). The mobility of GT-nZVI suspension in the soil-sand column is lower and is directly related to the progress of the neutralization reactions between the acidic GT-nZVI suspension and soil calcite.

Reduction of hexavalent chromium with polyphenol-coated nano zero-valent iron: column studies

AbstractNano zero-valent iron (nZVI) is considered as a highly efficient reductant with wide applicability in the remediation of contaminated sites, due to the small particle size, large specific surface area, and high reactivity. In this study, nZVI was synthesized by mixing Camellia Sinensis extract (green tea, GT) with a ferric iron solution. Polyphenols in the GT extract act as: (a) strong reductants, reducing thus Fe(III) to its elemental state and (b) capping agents that stabilize the Fe(0) nanoparticles and inhibit their potential rapid oxidation. The remediation potential of ZVI nanoparticles, produced with the Green Tea method (GT-nZVI), for hexavalent chromium (Cr(VI)) was evaluated by column tests. The tests were carried out using polyethylene columns, with 2.63 cm internal diameter and ~10 cm length. The columns were filled with 65 g of natural soil and pure silica sand at a ratio of 50% w/w. The reductive capacity of GT-nZVI was examined for high (5 mg L−1) concentration of hexavalent chromiu...

Fate of Green Tea Iron Nanoparticles in Calcareous Soils

A promising method for obtaining sterically and chemically stable nano zero valent iron (nZVI) suspensions is the use of green tea (GT) extract for the synthesis of iron nanoparticles. However, the stability of this suspension when delivered in the subsurface depends highly on the specific geochemistry of soil material. Current work was focused on studying the fate of green tea nZVI (GT-nZVI) suspensions in contact with calcareous soils, which are typical in many relatively arid areas. The experimental work involved the synthesis and characterisation of GT-nZVI suspensions and the implementation of column tests using mixtures of quartz sand and natural soil. The results of column tests indicated that the mobility of nZVI suspension is directly related to the progress of the neutralization reactions between the acidic GT suspension and soil calcite. Calcite neutralizes the acidic GT-nZVI suspension and causes the precipitation of aquatic Fe(III) in the form of ferric hydroxides. The ZVI nanoparticles are attached to the solid ferric hydroxides, and thus they are removed from the fluid phase.

Comparative Evaluation of Sulfuric and Hydrochloric Acid Atmospheric Leaching for the Treatment of Greek Low Grade Nickel Laterites

Greece is the only EU country with extensive nickel laterite deposits. Since the 1960s, the Greek laterites are treated for ferronickel production via a pyrometallurgical route, which involves pre-reduction of the ore in rotary kilns and reduction smelting in electric arc furnaces. Due to the rising cost of energy and the decreasing grade of mined laterites, the pyrometallurgical treatment is economically marginal. For this reason, alternative treatment processes are currently under investigation. Potential applicability of hydrometallurgical treatment, using either H2SO4 or HCl, under atmospheric pressure conditions, for Ni and Co extraction from two low grade laterite ores, was examined in the present work. The two samples were selected to represent the different mineralogical composition of the saprolitic and limonitic ore deposits of the Greek laterites. The investigated parameters were temperature (65–90 °C), acid concentration (1–4 N) and solid to liquid ratio (10–30% w/v). The results indicated that HCl was more efficient than H2SO4 for the treatment of the saprolitic ore; Ni and Co extractions were very high for both elements, up to 98% and 96% respectively, while H2SO4 could leach efficiently Ni, up to 100%, but extracted only 34% of Co. Hydrochloric acid was also more efficient for the treatment of the limonitic ore, with Ni and Co extractions up to 98.3% and 87.6% respectively. With H2SO4 the maximum extractions were 71.3% for Ni and 52.1% for Co.

Green Synthesis of Resin Supported Nanoiron and Evaluation of Efficiency for the Remediation of Cr(VI) Contaminated Groundwater by Batch Tests

In this study the fixation of nano zero valent iron (nZVI) on a polymeric matrix applying an environmentally friendly technique and the performance of this material for the treatment of Cr(VI) contaminated groundwater were evaluated. The investigated method could be applied in a pump & treat groundwater remediation system. A macroreticular cationic resin was selected as porous host material. It was found that green tea polyphenols were able to penetrate within the macroporous resin matrix and obtain the reduction of Fe(III) to the elemental state. The effectiveness of this composite material in removing Cr(VI) contaminated waters was evaluated by conducting batch tests. It was found that the reduction of Cr(VI) follows a kinetics law of first order with respect to the concentration of Cr(VI) and to the amount of nZVI per liter of solution. The kinetic constant varied between 5·10−3 and 0.5·10−3 per min and per mM of nZVI in the pH range 3.5–7.5.