Browsing by Author "Pamukcu, Sibel"
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- Electrokinetic enhanced transport of zero valent iron nanoparticles for chromium(VI) reduction in soilsPublication . Gomes, Helena I.; Ferreira, Célia; Ribeiro, Alexandra B.; Pamukcu, SibelZero valent iron nanoparticles (nZVI) are a promising technology that could provide cost-effective solutions to soil and groundwater remediation. However, transport of nZVI is normally limited by their aggregation and settling, and with mobility being normally less than a few meters.The main research objective of this study is to find out if coupling electrokinetics and reactive iron nanoparticles can be an effective method for treating chromium contaminated clay soils. Direct current was used to enhance poly(acrylic acid), sodium salt (PAA) coated iron nanoparticles (PAA-nZVI) mobility in Cr(VI) spiked kaolin.A commercially available electrophoretic cell was modified for these experiments and equipped with internal auxiliary electrodes that allow to measure the redox potential directly in the clay. A constant potential of 5.0 V wasapplied across the test bed. Experimental results show that electrokinetics can enhance the delivery of nanoscale iron particles for the reduction of hexavalent chromium to the less toxic trivalent chromium. Direct current enhanced nZVI transport up to 74 % when compared with diffusion, maximum value found when comparing iron concentrations ratios. Activation of nZVI was also observed with a decrease in the redox potential of 531 mV, in average, after the injection point.
- Electrokinetics and zero valent Iron nanoparticles: experimental and modeling of the transport in different porous mediaPublication . Gomes, Helena I.; Rodríguez-Maroto, José M.; Ribeiro, Alexandra B.; Pamukcu, Sibel; Ferreira, Célia
- Enhanced transport and transformation of zero-valent nanoiron in clay using direct electric currentPublication . Gomes, Helena I.; Ferreira, Célia; Ribeiro, Alexandra B.; Pamukcu, SibelOne of the major obstacles to zerovalent iron nanoparticles (nZVI) application in soil and groundwater remediation is the limited transport, especially in low-permeability soils. In this study, direct current (constant potential of 5.0 V) was used to enhance polymer-coated nZVI mobility in different porous media, including a bed of glass beads and kaolin clay. The tests were conducted using a modified electrophoretic cell and with nZVI concentrations typical of field applications (4 g L−1 ). Experimental results indicate that the use of direct current can enhance the transport of the polymer-modified nanoparticles when compared with natural diffusion in low permeability or surface neutral porous medium. The applied electric field appeared to enhance the oxidation–reduction potential, creating a synergistic effect of nZVI usage with electrokinetics. Aggregation of the nanoparticles, observed near the injection point, remained unresolved.
- Influence of electrolyte and voltage on the direct current enhanced transport of iron nanoparticles in clayPublication . Gomes, Helena I.; Ferreira, Célia; Ribeiro, Alexandra B.; Pamukcu, SibelZero valent iron nanoparticles (nZVI) transport for soil and groundwater remediation is slowed down or halted by aggregation or fast depletion in the soil pores. Direct electric current can enhance the transport of nZVI in low permeability soils. However operational factors, including pH, oxidation–reduction potential (ORP), voltage and ionic strength of the electrolyte can play an important role in the treatment effectiveness. Experiments were conducted to enhance polymer coated nZVI mobility in a model low permeability soil medium (kaolin clay) using low direct current. Different electrolytes of varying ionic strengths and initial pH and high nZVI concentrations were applied. Results showed that the nZVI transport is enhanced by direct current, even considering concentrations typical of field application that favor nanoparticle aggregation. However, the factors considered (pH, ORP, voltage and electrolyte) failed to explain the iron concentration variation. The electrolyte and its ionic strength proved to be significant for pH and ORP measured during the experiments, and therefore will affect aggregation and fast oxidation of the particles.
- Numerical prediction of diffusion and electric field-induced iron nanoparticle transportPublication . Gomes, Helena I.; Rodríguez-Maroto, José Miguel; Ribeiro, Alexandra B.; Pamukcu, Sibel; Ferreira, CéliaZero valent iron nanoparticles (nZVI) are considered very promising for the remediation of contaminated soils and groundwaters. However, an important issue related to their limited mobility remains unsolved. Direct current can be used to enhance the nanoparticles transport, based on the same principles of electrokinetic remediation. In this work, a generalized physicochemical model was developed and solved numerically to describe the nZVI transport through porous media under electric field, and with different electrolytes (with different ionic strengths). The model consists of the Nernst–Planck coupled system of equations, which accounts for the mass balance of ionic species in a fluid medium, when both the diffusion and electromigration of the ions are considered. The diffusion and electrophoretic transport of the negatively charged nZVI particles were also considered in the system. The contribution of electroosmotic flow to the overall mass transport was included in the model for all cases. The nZVI effective mobility values in the porous medium are very low (10 7 –10 4 cm2V 1 s 1 ), due to the counterbalance between the positive electroosmotic flow and the electrophoretic transport of the negatively charged nanoparticles. The higher the nZVI concentration is in the matrix, the higher the aggregation; therefore, low concentration of nZVI suspensions must be used for successful field application.