Hilmi Önder Özbelge

Removal of mercury from aqueous solutions via polymer-enhanced ultrafiltration

Separation of mercury from aqueous solutions by continuous polymer-enhanced ultrafiltration (PEUF) was investigated. Polyethyleneimine (PEI) was added to the solutions as the complexing agent before circulating the solution in a laboratory-scale continuous ultrafiltration system. Effects of mercury-to-polymer ratio, pressure drop and feed solution circulation rate on retention of mercury and permeate flux were studied. Constant retention values close to unity were obtained until a critical mercury-to-polymer ratio was exceeded. For higher metal loadings, retention values decreased linearly. Permeate flux increased linearly with pressure drop and was not affected by other parameters such as metal loading and feed circulation rate. Therefore, concentration polarization was not a problem for the studied range of variables.

Effect of operating parameters on selective separation of heavy metals from binary mixtures via polymer enhanced ultrafiltration

Performance of continuous polymer enhanced ultrafiltration (PEUF) method was investigated for removal of mercury and cadmium from binary mixtures. This method includes the addition of polyethyleneimine (PEI) as a water soluble polymer to bind the metals, which was followed by ultrafiltration operation performed on both laboratory and pilot scale systems. The influence of various operating parameters such as temperature, metal/polymer ratio, presence of calcium ions and pH on retention of metals and permeate flux was investigated. To investigate the possibility of selective separation of mercury and cadmium, experiments were conducted for binary solutions at different pH and loading ratios. It was seen that the retention of mercury decreased and permeate flux increased when the temperature increased. The increased pH and decreased metal/polymer ratio, loading (L), resulted in higher retention of both metals. Shapes of retention vs. pH or L curves were very similar for both metals. Retentions stay almost constant at a value very close to unity until a critical L or pH value was reached, then, R decreases almost linearly with L or pH. However, retention of cadmium was affected more than that of mercury as the pH decreased and L increased. This leads to the selective separation of mercury and cadmium. At low pH values (about 5) and at high L values (about 0.3), mercury was removed by ultrafiltration operation while almost all cadmium passed through the membrane. At pH 5.5 and cadmium/polymer ratio about 0.35 and mercury/polymer ratio about 0.39, the highest separation factor was obtained as 49.

Removal of boron from aqueous solutions by continuous polymer-enhanced ultrafiltration with polyvinyl alcohol

Boron is a highly contaminating metal due to its toxic effects for plants even at very low concentrations. Continuous polymer-enhanced ultrafiltration (PEUF) was applied for removal of boron from aqueous solutions. The effects of operating parameters on the performance of PEUF were investigated. A commercial polymer, polyvinyl alcohol (PVA) was used as the boron-complexing agent. The methodology consists of two steps: complexing boron with PVA following separation of boron and polymer complexes by ultrafiltration process. The pilot scale system utilized for the PEUF process accommodates a spiral-wound cellulose cartridge with 10,000 Da MWCO. The experimental parameters studied are metal/polymer ratio (loading) (0.01–0.5), pH (7–10), and the polymer characteristics such as molecular weight (M n) of the polymer and degree of hydrolysis (DoH). The results showed that PEUF could be a successful alternative method for removal of boron. The permeate flux remained constant at around 19 L/m2 hr throughout the runs and the fluxes were not affected by the operating parameters studied and by the polymer characteristics. When the loading values were decreased, the retention of boron was increased. Also, pH had an important influence as increase in pH resulted in increase in retention of boron. The polymeric M n of the polymer did not have any influence on the retention of boron while an increase in DoH caused a decrease in retention of boron.

Development of a Precipitation Based Separation Scheme for Selective Removal and Recovery of Heavy Metals from Cadmium Rich Electroplating Industry Effluents

Abstract The treatment of electroplating wastes is a serious worldwide problem, because of their high content of many different heavy metals. Chemical precipitation based treatment methods could be an important alternative for fractional selective separation of heavy metals if they are systematically developed by sequencing of pH, adjusting the added portions of precipitating agents, and selecting the optimum time period before removing the precipitate from the solution. In this study, for selective removal and recovery of Cd from real electroplating bath wastewater (containing high amounts of Cd, medium amounts of Zn, Cu, Fe and small amounts of Ni, Co, Mn), a precipitation based separation scheme was developed. The scheme comprised of three consecutive steps: 1) Acid treatment with nitric acid (HNO3). Cyano‐metal complexes were decomposed in acidification step and complete removal of iron was achieved. 2) Alkali precipitation by sodium hydroxide (NaOH). Large portion of Cd was recovered as pure Cd(OH)2. 3) As a polishing step sulfide precipitation by sodium sulfide (Na2S) was applied. pH was the critical parameter in sulfide precipitation. Addition of sodium sulfide in alkali pH range led to cadmium precipitation whereas copper was totally precipitated in acidic pH range. The sulfide precipitation step may be replaced by more environmentally friendly steps (e.g. polymer enhanced ultrafiltration) until the heavy metal concentrations were reduced down to suitable discharge limits.

Determination of heavy metal concentration in feed and permeate streams of polymer enhanced ultrafiltration process

Polymer enhanced ultrafiltration (PEUF) is a newly developed method for the removal of heavy metals from aqueous solutions. This method was applied for the removal of mercury and cadmium with the presence of polyethyleneimine (PEI) as a water soluble polymer. After ultrafiltration experiments for metal-polymer mixtures, two separate streams, namely, retentate and permeate, former of which contains mainly metal-polymer complex and free polymer molecules while latter of which mainly contains free metal ions, were obtained. At the end of PEUF experiments, performance of operation was determined by concentration analyses which was achieved by atomic absorption spectroscopy (AAS) applied in a different way for permeate and retentate streams considering the effect of presence of polymer. For mercury analysis, cold vapor AAS was applied. It was observed that the presence of PEI did not affect the atomic absorption signal when 10% HCl was added to the sample solutions. For calcium and cadmium, flame AAS was used. It was observed that change in PEI concentration results in change in measured concentration of calcium and cadmium. Therefore, two new approaches were developed for accurate measurement of concentrations of calcium and cadmium. It was also observed that presence of other metals did not affect the accuracy of the measurement of a particular metal in the concentration range studied.

Heat and mass transfer mechanisms in drying of a suspension droplet: A new computational model

A new computational single-droplet drying model is presented. The model considers heat and mass transfer simultaneously together with the receding evaporation front approach. A spherical droplet under constant drying conditions is considered. Computations are performed to predict the drying of colloidal silica-water suspension and skimmed milk. It is shown that the results agree well with those of experimental observations available in the literature.

CVD of boron and dichloroborane formation in a hot-wire fiber growth reactor

Abstract Chemical vapor deposition (CVD) of boron by hydrogen reduction of BCl3 on a hot tungsten substrate was investigated in a parallel flow reactor. Effect of substrate temperature (1100–1250°C) on the relative rates of formation of BHCl2 and boron was observed by the on-line analysis of the reactor effluent stream composition using an FT-IR spectrophotometer. It was concluded that BHCl2 was majorly formed in the gas phase within the thermal boundary layer adjacent to the substrate with possible contribution of surface reactions at higher temperatures. Comparison of results obtained in the impinging jet and parallel flow reactors indicated the significance of diffusion resistance in the parallel flow system. Tubular flow reactor experiments indicated that BHCl2 formation reaction started at temperatures as low as 350°C and reached equilibrium in less than a second at temperatures over 420°C.

Mechanism And Characterization Studies on Boron Carbides Deposited by Chemical Vapor Deposition Technique

Boron carbide was produced in an impinging jet CVD reactor from a gas mixture of BCl 3 , CH 4 and H 2 . The mass transfer limitations on the reaction kinetics were minimised by the jet impingement on the substrate surface. XPS characterization of the produced deposits revealed a nearly pure boron carbide phase containing small amounts of oxy-boron and oxy-carbon species. After a detailed kinetic study, a reaction model was proposed to predict the rates of boron carbide and dichloroborane formation reactions. In this model, boron trichloride is adsorbed on the surface non-dissociatively, whereas hydrogen and methane are adsorbed dissociatively. BC is formed on the solid surface through the reaction of adsorbed boron trichloride with adsorbed methane in the form of CH 3 (s) (adsorbed CH 3 on the surface). Produced BC is reacted in successive series reactions including adsorbed boron trichloride and adsorbed hydrogen. In the proposed mechanism, dichloroborane is produced only through the gas phase reaction between boron trichloride and hydrogen. The simultaneous fit of the experimental data to the model expression gave good fits for the boron carbide and dichloroborane formation reactions with the high correlation coefficient values.