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ABSTRACT: Cyanide is found as free cyanide and metal–cyanide complexes in metal finishing rinse wastewaters. Experiments were performed
to seek removal of cyanide in Ni(II)–cyanide and Ni(II)–cyanide–ethylenediaminetetraacetate (EDTA) solutions by the environmentally
friendly oxidant, ferrate(VI) (FeO42−, Fe(VI)) as a function of pH (8.0–11.0). Incomplete removal of cyanide in Ni(II)–cyanide solutions (≤60%) was observed at
the studied pH range. However, cyanide removal efficiency approached to 100% in Ni(II)–cyanide–EDTA solutions. Formation of
Ni(II)–cyanide and Ni(II)–EDTA complexes and relative rates of the reactions of Fe(VI) with various species (water, cyanide,
Ni(II)–cyanide, and EDTA) present in solutions were responsible for the variation in removal efficiencies in mixtures at various
pH. The oxidation of cyanide by Fe(VI) produced cyanate. Tests using electroplating rinse wastewaters demonstrated that Fe(VI)
was highly effective in removing cyanide.
KeywordsFerrate–Removal–Metal finishing–Rinse water–Speciation–Rates
Water Air and Soil Pollution 04/2012; 219(1):527-534. · 1.63 Impact Factor
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ABSTRACT: Knowledge of sorption and transport of heavy metals in soils in the presence of other metals is crucial for assessing the environmental risk of these metals. Competitive sorption and transport of four metals, Pb(2+), Ni(2+), Zn(2+), and Mn(2+), were investigated using multi-metal column experiments with lateritic soils obtained from a gold mine impacted by acid mine drainage. Based on Pb(2+) breakthrough time for single-metal system at a pH of approximately 5, the sorption capacity of Pb(2+) was estimated to be higher in lateritic soil than the other metals. For multi-metal systems, the estimated retardation factors for the metals from highest to lowest were: Pb(2+)>Zn(2+)∼ Ni(2+)>Mn(2+), suggesting the mobility of metals through lateritic soil for a multi-metal system would be in the order of Mn(2+)>Ni(2+)∼ Zn(2+)>Pb(2+). For binary and multi-metal systems, the estimated sorption capacities of individual metals were found to be lower than the sorption capacities in single metal system - indicating possible competition for sorption sites. Mass recoveries estimates showed that the sorption of metals was more reversible under competitive multi-metal systems than in single metal systems.
Journal of hazardous materials 06/2011; 190(1-3):391-6. · 4.14 Impact Factor
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ABSTRACT: a b s t r a c t Knowledge of sorption and transport of heavy metals in soils in the presence of other metals is crucial for assessing the environmental risk of these metals. Competitive sorption and transport of four metals, Pb 2+ , Ni 2+ , Zn 2+ , and Mn 2+ , were investigated using multi-metal column experiments with lateritic soils obtained from a gold mine impacted by acid mine drainage. Based on Pb 2+ breakthrough time for single-metal system at a pH of approximately 5, the sorption capacity of Pb 2+ was estimated to be higher in lateritic soil than the other metals. For multi-metal systems, the estimated retardation factors for the metals from highest to lowest were: Pb 2+ > Zn 2+ ∼ Ni 2+ > Mn 2+ , suggesting the mobility of metals through lateritic soil for a multi-metal system would be in the order of Mn 2+ > Ni 2+ ∼ Zn 2+ > Pb 2+ . For binary and multi-metal systems, the estimated sorption capacities of individual metals were found to be lower than the sorption capacities in single metal system – indicating possible competition for sorption sites. Mass recoveries estimates showed that the sorption of metals was more reversible under competitive multi-metal systems than in single metal systems.
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ABSTRACT: This study investigated the effects of pH on the transport of Pb2+, Mn2+, Zn2+ and Ni2+ through lateritic soil columns. Model results by fitting the symmetric breakthrough curves (BTCs) of bromide (Br-) with CXTFIT model suggested that physical non-equilibrium processes were absent in the columns. The heavy metal BTCs were, however, asymmetrical and exhibited a tailing phenomenon, indicating the presence of chemical non-equilibrium processes in the columns. The retardation factors of Pb2+ were the largest of the four metal ions at both pH 4.0 (33.3) and pH 5.0 (35.4). The use of Langmuir isotherm parameters from batch studies with HYDRUS-1D did not predict the BTCs well. Rather the two-site model (TSM) described the heavy metal BTCs better than the equilibrium linear/nonlinear Langmuir model. The fraction of instantaneous sorption sites (f) of all four metal ions on the lateritic soil was consistently about 30%-44% of the total sorption sites.
Journal of Environmental Sciences 01/2011; 23(4):640-8. · 1.66 Impact Factor
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ABSTRACT: The effect of ethylenediaminetetraacetate (EDTA) on the removal of cyanide (CN(-)) from electroplating wastewater was investigated using an electrochemical process. Decay of 100 mg/L CN(-) was carried out as a function of electrical current (I = 0.5-5.0 A) and molar ratios of EDTA to CN(-) (2.6-15.7) at pH 13.0. The experiments showed that electrooxidation of CN(-) follows first-order kinetics with respect to CN(-) ion. The first-order rate constant, k, showed linearity with the applied current (r(2) = 0.99). At a molar ratio of 2.6 ([EDTA]: [CN(-)]) and electric current, I = 2.5 A, the oxidation of CN(-) proceeded by a slower rate than in the absence of EDTA. Under similar conditions, the oxidation rate of cyanide increased at molar ratios ranging from 5.2 to 15.7. Consequently, the energy consumption for the electrooxidation of CN(-) varies with the amount of EDTA present in the solution.
Journal of Environmental Science and Health Part A 03/2008; 43(3):295-9. · 1.19 Impact Factor
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ABSTRACT: Zinc-cyanide complexes are found in gold mining effluents and in metal finishing rinse water. The effect of Zn(II) on the oxidation of cyanide by ferrate(VI) (Fe(VI)O(4)(2-), Fe(VI)) was thus investigated by studying the kinetics of the reaction of Fe(VI) with cyanide present in a potassium salt of a zinc cyanide complex (K(2)Zn(CN)(4)) and in a mixture of Zn(II) and cyanide solutions as a function of pH (9.0-11.0). The rate-law for the oxidation of Zn(CN)(4)(2-) by Fe(VI) was found to be -d[Fe(VI)]/dt=k[Fe(VI)][Zn(CN)(4)(2-)](0.5). The rate constant, k, decreased with an increase in pH. The effect of temperature (15-45 degrees C) on the oxidation was studied at pH 9.0, which gave an activation energy of 45.7+/-1.5kJmol(-1). The cyanide oxidation rate decreased in the presence of the Zn(II) ions. However, Zn(II) ions had no effect on the cyanide removal efficiency by Fe(VI) and the stoichiometry of Fe(VI) to cyanide was approximately 1:1; similar to the stoichiometry in absence of Zn(II) ions. The destruction of cyanide by Fe(VI) resulted in cyanate. The experiments on removal of cyanide from rinse water using Fe(VI) demonstrated complete conversion of cyanide to cyanate.
Chemosphere 11/2007; 69(5):729-35. · 3.21 Impact Factor
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ABSTRACT: The sorption and transport of three pharmaceutical compounds (acetaminophen, an analgesic; nalidixic acid, an antibiotic; and 17alpha-ethynyl estradiol, a synthetic hormone) were examined by batch sorption experiments and solute displacement in columns of silica, alumina, and low organic carbon aquifer sand at neutral pH. Silica and alumina were used to represent negatively-charged and positively-charged fractions of subsurface media. Column transport experiments were also conducted at pH values of 4.3, 6.2, and 8.2 for the ionizable nalidixic acid. The computer program UFBTC was used to fit the breakthrough data under equilibrium and nonequilibrium conditions with linear/nonlinear sorption. Good agreement was observed between the retardation factors derived from column model studies and estimated from equilibrium batch sorption studies. The sorption and transport of nalidixic acid was observed to be highly pH dependent, especially when the pH was near the pK(a) of nalidixic acid (5.95). Thus, near a compound's pK(a) it is especially important that the batch studies be performed at the same pH as the column experiment. While for ionic pharmaceuticals, ion exchange to oppositely-charged surfaces, appears to be the dominant adsorption mechanism, for neutral pharmaceuticals (i.e., acetaminophen, 17alpha-ethynyl estradiol) the sorption correlated well with the K(ow) of the pharmaceuticals, suggesting hydrophobically motivated sorption as the dominant mechanism.
Water Research 05/2007; 41(10):2180-8. · 4.86 Impact Factor
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ABSTRACT: Two pure minerals and a hydrophobic medium were selected to study sorption of pharmaceuticals. The sorption of four pharmaceuticals, acetaminophen (analgesic), 17alpha-ethynyl estradiol (synthetic hormone), nalidixic acid (antibiotic), and norfloxacin (antibiotic), was evaluated with silica, alumina, and Porapak P (a hydrophobic medium). Alumina and silica were selected to represent positively charged and negatively charged aquifer mineral surfaces at neutral pH, respectively, while Porapak P was selected to represent the hydrophobic organic content of an aquifer medium. At neutral pH, acetaminophen, the least hydrophobic pharmaceutical, showed no significant sorption to any of the media, while 17alpha-ethynyl estradiol, the most hydrophobic pharmaceutical, showed significant sorption to Porapak P. Nalidixic acid, which has a carboxyl functional group that is anionic at neutral pH, showed significant adsorption to the positively charged alumina. Norfloxacin, with both a carboxyl (anionic) and a piperazynyl (cationic) group, can exist in four forms (neutral, cationic, anionic, and zwitterionic) depending on the aqueous pH. Norfloxacin also showed significant adsorption than nalidixic acid. Both nalidixic acid and norfloxacin adsorbed to silica and Porapak P to a much lower extent. The pH dependence of nalidixic acid and norfloxacin adsorption to silica and alumina was also studied by varying the pH between 4 and 11. The maximum adsorption of nalidixic acid to alumina occurred near its pKa (pH approximately 6), where the combination of cationic alumina and anionic nalidixic produced maximum adsorption. The maximum adsorption of norfloxacin to alumina was observed at pH approximately 7, which was the region where the zwitterionic form dominated. This research demonstrates that the adsorption of ionizable pharmaceuticals is strongly dependent on the system pH, the pharmaceutical properties (pKa and hydrophobicity), and the nature of the surface charge (point of zero charge). For pharmaceuticals that are uncharged at environmentally relevant pH values, the main sorption factor is their solubility or hydrophobicity; for charged forms, ion exchange is also an important adsorption mechanism.
Water Research 05/2006; 40(7):1481-91. · 4.86 Impact Factor
