Considering the harmful effects of heavy metals, it is necessary to remove them from liquid waste... more Considering the harmful effects of heavy metals, it is necessary to remove them from liquid wastes at least to a limit accepted by regulatory agencies before their discharge to the environment – i.e. there is a need for a capable, cost-effective treatment method. The application of an innovative, simple and low cost method was tested for the preparation of nanocrystalline iron hydroxides and oxyhydroxides; different iron precursors have been earlier used and combined to different volatile precipitating agents. The examined in the present product, akaganéite [beta- FeO(OH)], had high surface area and definite pore size distribution. Main aim of this study was to evaluate the efficiency of the prepared material in the removal of heavy metal ions, like cadmium cations and arsenate oxyanions, metals that constitute priority pollutants. Batch and column experiments were conducted in current research to investigate metal ions removal.
The investigated hybrid cell combines the advantages of both flotation and membrane separation, w... more The investigated hybrid cell combines the advantages of both flotation and membrane separation, while overcoming their limitations and having as an outcome clean water from a industrial wastewater. Hence, metals recovery from dilute aqueous solutions was a promising application of this innovative process, further to solid/liquid separation. The specific objective was to apply the process for the efficient separation of effluents containing metals (here, zinc). The main examined parameters were the following: the metal initial concentration, flotation surfactant applied, and air flowrate. The successful contribution of precipitate flotation was highlighted, while the observed metal removals were of the order of 100%.
The current research focuses on removal of arsenite ions from aqueous solutions by a new adsorben... more The current research focuses on removal of arsenite ions from aqueous solutions by a new adsorbent, surfactant modified akaganeite (Akm), prepared after the adsorption of the cationic surfactant, hexadecyl trimethyl ammonium bromide (N‐Cetyl‐N,N,N‐Trimethylammonium Bromide) onto akaganeite. The new adsorbent was investigated with Fourier transform infrared spectra and X‐ray photoelectron spectroscopy methods for a better understanding of the effects of surface
... Edwards and Benjamin[11]11. Edwards, M. and Benjamin, MM 1989. Regeneration and reuse of iron... more ... Edwards and Benjamin[11]11. Edwards, M. and Benjamin, MM 1989. Regeneration and reuse of iron hydroxide adsorbents in the treatment of metal bearing wastes. J. Water Pollut. Control Fed. ... Lehmann et al.[15]15. Lehmann, M., Zouboulis, AI and Matis, KA 2001. ...
A large number of techniques have been used today to limit the membranes fouling and among them, ... more A large number of techniques have been used today to limit the membranes fouling and among them, certainly is air bubbling constituting also the transport medium in flotation, as applied in wastewater treatment; flotation is suitable as a pretreatment stage for microfiltration. Ceramic flat-sheet membrane modules were used in this paper, of multi-channel geometry and mainly their fouling tendency and
In this study, phosphates removal from aqueous solutions was investigated using synthetic prepare... more In this study, phosphates removal from aqueous solutions was investigated using synthetic prepared nanocrystalline oxyhydroxide material in unmodified and surfactant modified form. Equilibrium and kinetic studies were carried out to determine the sorption capacity of akaganéite and the rate of phosphate ions uptake. Equilibrium data were analyzed by Langmuir and Freundlich isotherms. The sorption capacity was found to be 59.62 mg P g −1 for pure nanocrystalline akaganéite and 451.20 mg P g −1 for hybrid surfactant-akaganéite. Kinetic data followed a pseudo-secondorder kinetic model. FT-IR spectra indicate the presence of inner-sphere complexes. Desorption studies showed entirely different behaviour between the two materials.
Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydr... more Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydroxides, followed by hydrothermal processing and freeze-drying. The synthesis involves the hydrolysis of aqueous metal precursors by using ammonia as precipitating agent. The chlorine ion concentration in the solution and the pH of the precipitation, are shown to play a crucial role in retaining the initial stoichiometry of the solution to the nanoparticles. The obtained products exhibited some interesting and unique features: they consisted of nanoparticles with sizes ranging from 5 to 25 nm, they had surface areas between 60 and 110 m 2 g À1 and pore sizes in the mesopore region (i.e. 8-20 nm). The produced materials were examined by powder X-ray diffraction for crystalline phase identification, scanning electron microscopy for grain morphology, high resolution transmission electron microscopy for particle size distribution and nitrogen sorption for surface area, pore volume and pore size distribution determination. The sintering of the ferrite powders was also studied by thermogravimetric analysis and dilatometry of the powders mixed with an organic binder to improve their compaction properties.
The possibility of using iron-based adsorbents (i.e. akaganéite or goethite) to remove heavy meta... more The possibility of using iron-based adsorbents (i.e. akaganéite or goethite) to remove heavy metal ions from aqueous solutions was the aim of the present review paper. Synthesized material was used in two forms, i.e. in fine powder of nanocrystals and in the form of grains (as granular). The main examined parameters were the quantity of sorbent, the presence of ionic strength, the pH value of solution and the metals speciation, including the presence of complexing agents. The removal efficiency of the packed-bed column was examined and compared. Typical adsorption models were discussed and the bed depth-service time equation has been applied to the sorption results in order to model the column operation.
Batch and column experiments were conducted to investigate zinc removal from dilute aqueous solut... more Batch and column experiments were conducted to investigate zinc removal from dilute aqueous solution (i.e. effluent) by sorption onto synthetic nanocrystalline akaganéite. Due to favorite characteristics, this material was shown to be a promising inorganic adsorbent prepared in the laboratory, following a new method of synthesis-previously published. The effects of adsorbent amount, zinc concentration, solution pH value, ionic strength and temperature variation on the treatment process were mainly investigated during this study. Typical adsorption models were determined searching the mechanism of sorption while the bed depth-service time model was applied to column (with granular material) experiments.
The concept of unit operations, over time, and subsequent concepts in chemical technology have ev... more The concept of unit operations, over time, and subsequent concepts in chemical technology have evolved into a unified field of separation processes. Sustainability in this field and its significance for the chemical and process industry will be commented, because the need for fresh sources of drinking water is becoming urgent worldwide. The biosorption of metal ions via residual biomass will be specifically examined in this review paper, as a separation technique. It has been recognized that the increased application of ion exchange and also membrane processes for producing potable water necessitates the use of advanced technologies as well as combinations of these. Therefore, a new hybrid cell of microfiltration combined with flotation will be also described in the present and applied effectively downstream for the same purpose (i.e., metals removal). Flotation is a separation process originated from minerals processing.
In this study, the recovery of copper ions from simulated and real wastewaters of a mine and mine... more In this study, the recovery of copper ions from simulated and real wastewaters of a mine and minerals processing plant was investigated. The separation process employed was flotation, which was applied in three different mechanisms: (i) ion flotation using xanthates, (ii) precipitate flotation generating copper hydroxide and (iii) sorptive flotation using zeolites as sorbent material. Under the studied conditions, ion and sorptive flotation were found to be effective methods for copper removal with almost 100% Cu removal achieved, while the precipitation method failed. The copper removal was always higher in simulated mixture than in real effluents; it may be due to the presence of other minor constituents that they have not taken into account in simulated mixture (e.g. organic compounds). The bubble generation method was that of dispersedair flotation. Reference is also given to economic aspects. An economic study of sorptive flotation showed that the capital investment for a 10 m 3 /h plant would be of the order of US$1.15 million dollars. The operating costs are about US$1.76 million per year. The total revenues from water recycling and reuse are US$68,800 per annum, without calculating the benefits of copper recovery. D
Air bubbling is one of the techniques used to limit membrane fouling. Under appropriate condition... more Air bubbling is one of the techniques used to limit membrane fouling. Under appropriate conditions, it could be used also as the transport means for flotation, which is another efficient separation method applied in water treatment. The present paper reviews briefly the integration of both processes in the same tank, taking advantage of dispersed-air flotation combined with microfiltration (MF) by submerged membranes. Process parameters investigated were the nature, size and concentration of solid particles (zeolite, hydrotalcite, zinc hydroxide and iron colloidal particles), the type and concentration of selected ions (Zn 2+ , P-PO 4 3À ), the effect of gas flow rate, as well as the frequency and length of backflushing, which reduces the fouling of membranes.
Phosphates removal from aqueous solutions was investigated using three different inorganic materi... more Phosphates removal from aqueous solutions was investigated using three different inorganic materials: laboratory synthesized goethite, commercial alumina and commercial hydrotalcite. Equilibrium and kinetic studies were carried out to determine their sorption capacity and the rate of phosphate ions uptake. Equilibrium data were analyzed by Langmuir and Freundlich isotherms. The maximum sorption capacity at 25EC was found to be 244.58 mg g !1 for calcined hydrotalcite at 500EC, 192.9 for calcined hydrotalcite at 400EC, 144 mg g !1 for goethite, 60 mg g !1 for hydrotalcite and 34.57 mg g !1 for aluminumoxid S. Kinetic data followed a pseudo-second-order kinetic model.
Several industrial wastewater streams may contain heavy metal ions, which must be effectively rem... more Several industrial wastewater streams may contain heavy metal ions, which must be effectively removed, before the discharge or reuse of treated waters could take place. Different bonding materials, presenting selectivity and fast reaction kinetics for the removal of metals, have been examined for this purpose. The objective of the present paper was to investigate the application of dispersed-air flotation for the separation of metal-loaded sorbents. Two similar zeolite samples were applied as effective bonding agents for the removal of zinc, a toxic metal commonly found in many industrial wastewaters. This combined process, termed sorptive flotation, involves the preliminary scavenging of metal ions, by using the appropriate sorbent particles (usually present as ultrafine particulates), followed by flotation for the effective separation of them. The obtained results were very promising, as both metal and sorbent were effectively removed/separated from the dispersion.
Considering the harmful effects of heavy metals, it is necessary to remove them from liquid waste... more Considering the harmful effects of heavy metals, it is necessary to remove them from liquid wastes at least to a limit accepted by regulatory agencies before their discharge to the environment – i.e. there is a need for a capable, cost-effective treatment method. The application of an innovative, simple and low cost method was tested for the preparation of nanocrystalline iron hydroxides and oxyhydroxides; different iron precursors have been earlier used and combined to different volatile precipitating agents. The examined in the present product, akaganéite [beta- FeO(OH)], had high surface area and definite pore size distribution. Main aim of this study was to evaluate the efficiency of the prepared material in the removal of heavy metal ions, like cadmium cations and arsenate oxyanions, metals that constitute priority pollutants. Batch and column experiments were conducted in current research to investigate metal ions removal.
The investigated hybrid cell combines the advantages of both flotation and membrane separation, w... more The investigated hybrid cell combines the advantages of both flotation and membrane separation, while overcoming their limitations and having as an outcome clean water from a industrial wastewater. Hence, metals recovery from dilute aqueous solutions was a promising application of this innovative process, further to solid/liquid separation. The specific objective was to apply the process for the efficient separation of effluents containing metals (here, zinc). The main examined parameters were the following: the metal initial concentration, flotation surfactant applied, and air flowrate. The successful contribution of precipitate flotation was highlighted, while the observed metal removals were of the order of 100%.
The current research focuses on removal of arsenite ions from aqueous solutions by a new adsorben... more The current research focuses on removal of arsenite ions from aqueous solutions by a new adsorbent, surfactant modified akaganeite (Akm), prepared after the adsorption of the cationic surfactant, hexadecyl trimethyl ammonium bromide (N‐Cetyl‐N,N,N‐Trimethylammonium Bromide) onto akaganeite. The new adsorbent was investigated with Fourier transform infrared spectra and X‐ray photoelectron spectroscopy methods for a better understanding of the effects of surface
... Edwards and Benjamin[11]11. Edwards, M. and Benjamin, MM 1989. Regeneration and reuse of iron... more ... Edwards and Benjamin[11]11. Edwards, M. and Benjamin, MM 1989. Regeneration and reuse of iron hydroxide adsorbents in the treatment of metal bearing wastes. J. Water Pollut. Control Fed. ... Lehmann et al.[15]15. Lehmann, M., Zouboulis, AI and Matis, KA 2001. ...
A large number of techniques have been used today to limit the membranes fouling and among them, ... more A large number of techniques have been used today to limit the membranes fouling and among them, certainly is air bubbling constituting also the transport medium in flotation, as applied in wastewater treatment; flotation is suitable as a pretreatment stage for microfiltration. Ceramic flat-sheet membrane modules were used in this paper, of multi-channel geometry and mainly their fouling tendency and
In this study, phosphates removal from aqueous solutions was investigated using synthetic prepare... more In this study, phosphates removal from aqueous solutions was investigated using synthetic prepared nanocrystalline oxyhydroxide material in unmodified and surfactant modified form. Equilibrium and kinetic studies were carried out to determine the sorption capacity of akaganéite and the rate of phosphate ions uptake. Equilibrium data were analyzed by Langmuir and Freundlich isotherms. The sorption capacity was found to be 59.62 mg P g −1 for pure nanocrystalline akaganéite and 451.20 mg P g −1 for hybrid surfactant-akaganéite. Kinetic data followed a pseudo-secondorder kinetic model. FT-IR spectra indicate the presence of inner-sphere complexes. Desorption studies showed entirely different behaviour between the two materials.
Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydr... more Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydroxides, followed by hydrothermal processing and freeze-drying. The synthesis involves the hydrolysis of aqueous metal precursors by using ammonia as precipitating agent. The chlorine ion concentration in the solution and the pH of the precipitation, are shown to play a crucial role in retaining the initial stoichiometry of the solution to the nanoparticles. The obtained products exhibited some interesting and unique features: they consisted of nanoparticles with sizes ranging from 5 to 25 nm, they had surface areas between 60 and 110 m 2 g À1 and pore sizes in the mesopore region (i.e. 8-20 nm). The produced materials were examined by powder X-ray diffraction for crystalline phase identification, scanning electron microscopy for grain morphology, high resolution transmission electron microscopy for particle size distribution and nitrogen sorption for surface area, pore volume and pore size distribution determination. The sintering of the ferrite powders was also studied by thermogravimetric analysis and dilatometry of the powders mixed with an organic binder to improve their compaction properties.
The possibility of using iron-based adsorbents (i.e. akaganéite or goethite) to remove heavy meta... more The possibility of using iron-based adsorbents (i.e. akaganéite or goethite) to remove heavy metal ions from aqueous solutions was the aim of the present review paper. Synthesized material was used in two forms, i.e. in fine powder of nanocrystals and in the form of grains (as granular). The main examined parameters were the quantity of sorbent, the presence of ionic strength, the pH value of solution and the metals speciation, including the presence of complexing agents. The removal efficiency of the packed-bed column was examined and compared. Typical adsorption models were discussed and the bed depth-service time equation has been applied to the sorption results in order to model the column operation.
Batch and column experiments were conducted to investigate zinc removal from dilute aqueous solut... more Batch and column experiments were conducted to investigate zinc removal from dilute aqueous solution (i.e. effluent) by sorption onto synthetic nanocrystalline akaganéite. Due to favorite characteristics, this material was shown to be a promising inorganic adsorbent prepared in the laboratory, following a new method of synthesis-previously published. The effects of adsorbent amount, zinc concentration, solution pH value, ionic strength and temperature variation on the treatment process were mainly investigated during this study. Typical adsorption models were determined searching the mechanism of sorption while the bed depth-service time model was applied to column (with granular material) experiments.
The concept of unit operations, over time, and subsequent concepts in chemical technology have ev... more The concept of unit operations, over time, and subsequent concepts in chemical technology have evolved into a unified field of separation processes. Sustainability in this field and its significance for the chemical and process industry will be commented, because the need for fresh sources of drinking water is becoming urgent worldwide. The biosorption of metal ions via residual biomass will be specifically examined in this review paper, as a separation technique. It has been recognized that the increased application of ion exchange and also membrane processes for producing potable water necessitates the use of advanced technologies as well as combinations of these. Therefore, a new hybrid cell of microfiltration combined with flotation will be also described in the present and applied effectively downstream for the same purpose (i.e., metals removal). Flotation is a separation process originated from minerals processing.
In this study, the recovery of copper ions from simulated and real wastewaters of a mine and mine... more In this study, the recovery of copper ions from simulated and real wastewaters of a mine and minerals processing plant was investigated. The separation process employed was flotation, which was applied in three different mechanisms: (i) ion flotation using xanthates, (ii) precipitate flotation generating copper hydroxide and (iii) sorptive flotation using zeolites as sorbent material. Under the studied conditions, ion and sorptive flotation were found to be effective methods for copper removal with almost 100% Cu removal achieved, while the precipitation method failed. The copper removal was always higher in simulated mixture than in real effluents; it may be due to the presence of other minor constituents that they have not taken into account in simulated mixture (e.g. organic compounds). The bubble generation method was that of dispersedair flotation. Reference is also given to economic aspects. An economic study of sorptive flotation showed that the capital investment for a 10 m 3 /h plant would be of the order of US$1.15 million dollars. The operating costs are about US$1.76 million per year. The total revenues from water recycling and reuse are US$68,800 per annum, without calculating the benefits of copper recovery. D
Air bubbling is one of the techniques used to limit membrane fouling. Under appropriate condition... more Air bubbling is one of the techniques used to limit membrane fouling. Under appropriate conditions, it could be used also as the transport means for flotation, which is another efficient separation method applied in water treatment. The present paper reviews briefly the integration of both processes in the same tank, taking advantage of dispersed-air flotation combined with microfiltration (MF) by submerged membranes. Process parameters investigated were the nature, size and concentration of solid particles (zeolite, hydrotalcite, zinc hydroxide and iron colloidal particles), the type and concentration of selected ions (Zn 2+ , P-PO 4 3À ), the effect of gas flow rate, as well as the frequency and length of backflushing, which reduces the fouling of membranes.
Phosphates removal from aqueous solutions was investigated using three different inorganic materi... more Phosphates removal from aqueous solutions was investigated using three different inorganic materials: laboratory synthesized goethite, commercial alumina and commercial hydrotalcite. Equilibrium and kinetic studies were carried out to determine their sorption capacity and the rate of phosphate ions uptake. Equilibrium data were analyzed by Langmuir and Freundlich isotherms. The maximum sorption capacity at 25EC was found to be 244.58 mg g !1 for calcined hydrotalcite at 500EC, 192.9 for calcined hydrotalcite at 400EC, 144 mg g !1 for goethite, 60 mg g !1 for hydrotalcite and 34.57 mg g !1 for aluminumoxid S. Kinetic data followed a pseudo-second-order kinetic model.
Several industrial wastewater streams may contain heavy metal ions, which must be effectively rem... more Several industrial wastewater streams may contain heavy metal ions, which must be effectively removed, before the discharge or reuse of treated waters could take place. Different bonding materials, presenting selectivity and fast reaction kinetics for the removal of metals, have been examined for this purpose. The objective of the present paper was to investigate the application of dispersed-air flotation for the separation of metal-loaded sorbents. Two similar zeolite samples were applied as effective bonding agents for the removal of zinc, a toxic metal commonly found in many industrial wastewaters. This combined process, termed sorptive flotation, involves the preliminary scavenging of metal ions, by using the appropriate sorbent particles (usually present as ultrafine particulates), followed by flotation for the effective separation of them. The obtained results were very promising, as both metal and sorbent were effectively removed/separated from the dispersion.
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