Cyanide In Industrial Wastewater Research Articles

A catalytic ozonation process using MgO/persulfate for degradation of cyanide in industrial wastewater: mechanistic interpretation, kinetics and by-products.

Cyanide-laden wastewaters generated from mining and electroplating industries are extremely toxic and it is of vital importance to treat them prior to discharge to receiving water resources. The present study aims to oxidize cyanide using an ozonation process catalyzed by MgO and persulfate (PS). A MgO nanocatalyst was synthesized using the sol–gel method and characterized. The results show that the synthesized catalyst had a BET surface area of 198.3 m2 g−1 with a nanocrystalline particle size of 7.42 nm. In the present study, the effects of different operational parameters were investigated, and it was found that the MgO/O3/PS process is able to oxidize 100 mg L−1 of cyanide after 30 min under optimum operational conditions. Cyanide degradation mechanisms in the MgO/O3/PS process were completely investigated and the main radical species were identified using scavenging experiments. It was found that sulfate and hydroxyl radicals both contributed to the cyanide degradation in the MgO/O3/PS process. Cyanide degradation by-products were also tracked and it was found that cyanate and ammonium species are primarily generated during the oxidation, but increase of reaction time allowed their conversion to much less toxic compounds such as nitrate and bicarbonate. Cyanide degradation was also conducted in real industrial wastewater containing 173 mg L−1 of cyanide. Although there was a reduction in cyanide removal rate, the MgO/O3/PS process was able to completely oxidize cyanide within 70 min. Finally, it can be concluded that the ozonation process catalyzed by MgO and persulfate is an efficient and reliable advanced oxidation process for removal of cyanide from industrial wastewater.

Comparing the efficacy of catalytic ozonation and photocatalytical degradation of cyanide in industrial wastewater using ACF-TiO2: catalyst characterisation, degradation kinetics, and degradation mechanism

ABSTRACTIn the present study, the ACF-TiO2 catalyst was synthesised and used as a catalyst for the destruction of toxic cyanide in both synthetic and real industrial wastewaters. The ACF-TiO2 catalyst was found to be micro-porous with the BET surface area of 163 m2/g. The effect of different operational parameters such as catalyst concentration, cyanide concentration, operation time, and ozone concentration were target parameters in the present study. The findings show that 500 mg/L of catalyst is the optimum value for the photocatalytical process to completely oxidise 25 mg/L of cyanide within 10 min. While it was found that 300 mg/L of catalyst in the presence of 200 mg/h ozone is enough to remove 25 mg/L cyanide within operation time of 24 min. Degradation of the cyanide in both investigated processes follow the pseudo-first-order kinetic and the reaction rate constant is almost 2 times higher in the photocatalytical process compared with catalytic ozonation process. Furthermore, the quenching tests using salicylic acid demonstrated the hydroxyl radical generation in the investigated process. Generation of highly oxidising hydroxyl radical makes the photocatalytical process a promising process for the transformation of noxious cyanide to much less toxic compounds (ammonia and nitrate). Accordingly, it can be concluded that ACF-TiO2 could be a catalyst for degradation and detoxification of cyanide.

A Potentiometric Biosensor for Cyanide Detection using Immobilized Whole Cell Cyanide Dihydratase of Flavobacterium indicum MTCC 6936

A potentiometric biosensor for cyanide detection has been developed using whole cell cyanide dihydratase activity of Flavobacterium indicum coupled to an ammonium ion selective electrode. The cyanide dihydratase activity was optimum when 2% agar and cells in the amount of 0.175 mg/mL dry cell weight (dcw) were used for immobilization. The free and immobilized whole cell cyanide dihydratase of F. indicum exhibited maximum activity (0.192 U/mg dcw and 0.175 U/mg dcw, respectively) in 0.1 M sodium phosphate buffer (pH 8.0) at 35°C with 5 mM potassium cyanide. KM and Vmax for free and immobilized whole cell cyanide dihydratase were 5.25 mM, 0.33 U/mg dcw and 6.25 mM, 0.25 U/mg, respectively. The agar immobilized whole cell cyanide dihydratase was used as a biocomponent coupled to a potentiometer. A linear relationship was observed between response time and cyanide concentration. The cyanide concentration of 0.06 ppm could be detected using this potentiometric biosensor with a response time of 2 min. The developed potentiometric biosensor could be used for the detection of cyanide in industrial wastewater and food samples.

Investigating the aerated VUV/PS process simultaneously generating hydroxyl and sulfate radicals for the oxidation of cyanide in aqueous solution and industrial wastewater

The present study was designed to investigate the cyanide oxidation by the aerated VUV/S2O82- (VUV/PS) advanced process. The effect of persulfate concentration, cyanide concentration, aeration and nitrogen gas blowing in the batch experiments and of hydraulic retention time and presence of radical scavengers in the continuous-flow experiments were investigated. It was found that cyanide oxidation in the aerated VUV/PS process followed a pseudo-first order reaction kinetic. Complete destruction of 50 mg/L cyanide was achieved in the aerated VUV/PS batch process in the presence of 200 mg/L persulfate within the reaction time of 10 min. The scavenging tests indicated that both hydroxyl and sulfate radicals were simultaneously generated in the aerated VUV/PS process contributed in the cyanide oxidation. It was also found that the aeration could enhance performance of the process in oxidation of cyanide due to the generation of ozone. The presence of water anions considerably decreased the cyanide removal efficiency in the aerated VUV/PS process and carbonate had the highest interference. Carbonate, ammonium, and nitrate were the main by-products of cyanide oxidation in the aerated VUV/PS process showing that cyanide was completely oxidized to much less noxious compounds. The complete oxidation of 50 mg/L cyanide in the continuous-flow aerated VUV/PS process at a hydraulic retention time of 20 min indicates the potential of its field-scale application. A real industrial wastewater sample containing high concentration of cyanide, Cr(VI) and organic content was also efficiently treated in the aerated VUV/PS process. Therefore, it is concluded that the aerated VUV/PS process is a promising process for complete destruction of cyanide in industrial wastewater.

Ligand displacement, headspace single-drop microextraction, and capillary electrophoresis for the determination of weak acid dissociable cyanide

A new method involving ligand displacement, headspace single-drop microextraction (SDME) with in-drop derivatization and capillary electrophoresis (CE) was developed for the determination of weak acid dissociable (WAD) cyanide. WAD metal–cyanide complexes (Ag(CN) 2 −, Cd(CN) 4 2−, Cu(CN) 3 2−, Hg(CN) 2, Hg(CN) 4 2−, Ni(CN) 4 2− and Zn(CN) 4 2−) are decomposed with ligand-displacing reagent and the released hydrogen cyanide is extracted from neutral solution (pH 6.5) with an aqueous microdrop (5 μl) containing Ni(II)–NH 3 as derivatization agent. The hydrogen cyanide extracted reacts with Ni 2+ to form a stable and highly UV absorbing tetracyanonickelate anion which is then determined by CE. Among the three different ligand-displacing reagents (i.e., ethylenediamine, dithizone and polyethileneimine) studied none of the reagents used alone releases cyanide completely from all WAD cyanide complexes. Complete recoveries were obtained by the extraction of WAD cyanide from 0.4 mol l −1 ethylenediamine chloride buffer (pH 6.5) containing 0.001% (wt) dithizone. Proposed system was applied to determine WAD cyanide in industrial wastewater and river waters samples with spiked recoveries in the range of 95.8–104.7%.

Flow injection analysis–flame atomic absorption spectrometry system for indirect determination of cyanide using cadmium carbonate as a new solid-phase reactor

A new and simple flow injection system procedure has been developed for the indirect determination of cyanide. The method is based on insertion of aqueous cyanide solutions into an on-line cadmium carbonate packed column (25% m/m suspended on silica gel beads) and a sodium hydroxide with pH 10 is used as the carrier stream. The eluent containing the analyte as cadmiumcyanide complexes, produced from reaction between cadmium carbonate and cyanide, measured by flame atomic absorption spectrometry. The absorbance is proportional to the concentration of cyanide in the sample. The linear range of the system is up to 15 mg L −1 with a detection limit 0.2 mg L −1 and sampling rate 72 h −1. The method is suitable for determination of cyanide in industrial waste waters with a relative standard deviation better than 1.22%.

Use of arylidenerhodanines for the determination of Cu(II), Hg(II) and CN −

Arylidenerhodanines have been synthesized as reagents for the spectrophotometric determination of Cu(II) and Hg(II). 5-(4-Hydroxy-3-methoxybenzylidene)rhodanine (HMBR) and 5-(3,4-dihydroxybenzylidene)rhodanine (3,4-DHBR) form colored complexes of maximum absorbance with these metal ions, in the presence of polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB), respectively. In the pH ranges 9.7−10.6 and 9.6−10.6, the molar absorptivities of Cu- and Hg-HMBR-PVP systems are 4.55 × 10 4 and 9.52 × 10 4 l mol −1 cm −1 at 535 and 525 nm, respectively. The corresponding Cu- and Hg-3,4-DHBR-CTAB ternary complexes are formed in the pH ranges 9.8−10.4 and 9.9−10.8 with molar absorptivities of 5.4 × 10 4 and 1.05 × 10 5 1 mol −1 cm −1 at 562 and 535 nm. The effect of reagents, PVP and CTAB concentrations, pH, standing time and diverse ions have been studied. The ionization constants of reagents, and the stoichiometry and stability constants of complexes were evaluated. The proposed methods have been used to determine copper in aluminium metal, aluminium and gold alloys, steels and waters, and to the determination of mercury in muscle tissue of Mackerel fish. Moreover, indirect methods for determining CN − have been developed, based on measuring the decrease in absorbance of Hg-HMBR-PVP and Hg-3,4-DHBR-CTAB systems by the addition of CN −. The calibration graphs are rectilinear for 0.02−0.40 ppm of CN −. The methods have been used to determine total cyanide in industrial wastewater.

Kinetics of enzymatic degradation of cyanide

Cyanidase is a new enzyme preparation capable of degrading cyanide in industrial wastewaters to ammonia and formate in an apparently one-step reaction, down to very low concentrations. This enzyme has both a high selectivity and affinity toward cyanide. A granular form of the biocatalyst was used in a recirculation fixed bed reactor in order to characterize the new biocatalyst with respect to pH, ionic strength, common ions normally present in wastewaters, mass transfer effects, and temperature. Long term stability was investigated. The kinetics of the enzymatic degradation of cyanide were studied in a batch reactor using the powdered immobilized enzyme preparation and modeled using a simple Michaelis-Menten equation.

Determination of cyanide by a highly sensitive indirect spectrophotometric method

Complexation of Pd 2+ with cyanide inhibits the extraction of the palladium complex of 5-phenylazo-8-aminoquinoline. This effect is used for the indirect spectrophotometric determination of cyanide at the μg level. Cyanide in industrial waste water and in sea-water is determined after distillation as HCN from the sample and collection in sodium hydroxide solution.

Electron-capture gas chromatographic determination of cyanide as pentafluorobenzyl cyanide

A simple, sensitive and specific method was established for the determination of cyanide as pentafluorobenzyl cyanide, based on the derivatization of cyanide anion in an alkaline medium with pentafluorobenzyl bromide. The derivative formed in the reaction solution was injected directly into a gas chromatograph equipped with an electron-capture detector. The detection limit was about 0.2 ng of cyanide anion in 0.1 ml of aqueous sample (2 ppb). The effects of base, amount of pentafluorobenzyl bromide, solvents, reaction temperature and reaction time on the derivatization were investigated, and the optimal derivatization conditions were established. Interferences due to some anions commonly found in wastewater were examined and were found to be minimal except for thiocyanate ion. The proposed method was applied to the determination of cyanide in industrial wastewater and the results agreed well with those obtained using the pyridine—pyrazolone spectrophotometric method.

Determination of cyanide by an indirect spectrophotometric method using 5-Br-PADAP

Complexation of Ni 2+ with cyanide inhibits its colour reaction with 5-Br-PADAP and this reaction is used in the spectrophotometric determination of cyanide at the ug level. Cyanide in industrial waste waters is determined after an initial transfer as hydrogen cyanide from the sample into sodium hydroxide solution with a stream of air.