• Journal of Korean Society on Water Environment
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• v.26 no.4
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• pp.687-690
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• 2010

The objective of this study is to investigate the effect of aldehyde compounds and ploysulfide as accelerating agents on removal of heavy metals and CN in plating wastewater. As a results of the experiments, the removal efficiency of cyanide using the formaldehyde type of aldehydes was the highest at pH 9. Next types were sodium formaldehyde bisulfite addut> paraldehyde> paraformaldehyde. Also, optimum pH and dosage for treating the residual heavy metals by using polysulfide were pH 9 and 30 mg/L, respectively. The removal efficiencies of cyanide, chromium, zinc and copper were above 96.7% at optimum condition.

• Journal of the Mineralogical Society of Korea
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• v.27 no.4
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• pp.223-233
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• 2014

Cyanidation method has been used to extract high-purity gold and silver in mining industry. Such mining activities have used a large amount of cyanide, and the mine wastewater contained a high level of cyanide has brought about pollution of surrounding aqueous environments. This research was initiated to study $TiO_2$-catalytic UV-LED photo-oxidation to remove cyanide from the mine wastewater. UV lamp has been generally used as a light source in conventional photo-oxidation so far, but it shows numerous drawbacks. For this reason, this study focused on the evaluation of applicability of UV-LED as an alternative light source in cyanide photo-oxidation process. Three types of $TiO_2$ photo-catalyst were compared in terms of performance of photo-oxidation of cyanide, and the results show that Degussa P25 was the most efficient. In addition, four types of UV-LED were tested to compare their efficiencies of cyanide photo-oxidation, and their efficacy was increased in the order of 365 nm lamp-type > 365 nm can-type > 280 nm can-type > 420 nm lamp-type. Not only did this study demonstrate that UV-LED can be used in the photo-oxidation of cyanide as an alternative light source of UV lamp, but also confirmed that the performance of photo-oxidation was significantly influenced by the type of $TiO_2$ catalysts.

• Environmental Engineering Research
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• v.11 no.6
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• pp.318-324
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• 2006

The higher valence state of iron i.e., Fe(VI) was employed for the oxidation of one of an important toxic ion, cyanide in the aqueous medium. Cyanide was oxidized into cyanate, which is 1,000 times less toxic to cyanide and often accepted for its ultimate disposal. It was to be noted that Fe(VI) is a very powerful oxidizing agent and can oxidize most of the cyanide within few minutes i.e., ca 5 mins of contact. The data was obtained by the UV-Visible measurements for the Fe(VI) decomposition. The UV-Visible data was used to evaluate the overall rate constant for second order redox reaction between ferrate(VI) and cyanide. Also the pseudo first order rate constant was calculated as keeping the cyanide concentration in excess.

• Journal of Environmental Science International
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• v.17 no.12
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• pp.1343-1351
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• 2008

The activated sludge obtained from wastewater coke oven plant was immobilized by entrapment with polyethylene glycol (PEG). The effects of several factors on the biodegradation of $CN^-$ from. synthetic wastewater were investigated using batch and continuous reactors. The degradation rate of $CN^-$ increased with increasing of the immobilized bead volume in the reactor. Approximately 7.65mg/L of $NH_4-N$ was produced upon the degradation of 35mg/L of $CN^-$. When high concentrations of the toxic cyanide complex were used in the testing of cyanide degradation, the free activated sludge could be inhibited more than that of the immobilized activated sludge. When the phenol concentration was higher than 400mg/L in the synthetic wastewater, approximately 98.4% of $CN^-$ was removed within 42 hours by the immobilized activated sludge. However, the cyanide was not completely degraded by the tree activated sludge. This indicates that high phenol concentrations can act as a toxic factor for the free activated sludge. A $CN^-$ concentration of less than 1mg/L was achieved by the immobilized sludge at the loading rate of 0.025kg $CN^-/m^3-d$. Moreover, it was found that the HRT should be kept for 48 hours in order to obtain stable treatment conditions.

• Membrane and Water Treatment
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• v.11 no.3
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• pp.217-222
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• 2020

An electrochemical oxidation process was applied to remove cyanide (CN^-) from real plating wastewater. CN^- removal efficiencies were investigated under various operating factors: current density and electrolyte concentration. Electrolyte concentration positively affected the removal of both CN^- and Chemical Oxygen Demand (COD). As the electrolyte concentration increased from 302 to 2,077 mg Cl^-/L, removal efficiency of CN^- and COD increased from 49.07% to 98.30% and from 23.53% to 49.50%, respectively, at 10 mA/㎠. Current density affected the removal efficiency in a different way. As current density increased at a fixed electrolyte concentration, CN^- removal efficiency increased while COD removal efficiency decreased, this is probably due to lowered current efficiency caused by water electrolysis.

• Environmental Engineering Research
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• v.8 no.2
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• pp.82-90
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• 2003

• Journal of Korean Society of Environmental Engineers
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• v.29 no.12
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• pp.1381-1389
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• 2007

Wastewater discharged by industrial activities of metal finishing and electroplating units is often contaminated by a variety of toxic or otherwise harmful substances which have a negative effects on the water environment. The treatment method of heavy metal-cyanide complexes wastewater by alkaline chlorination have already well-known($1^{st}$ Oxidation: pH 10, reaction time 30 min, ORP 350 mV, $2^{nd}$ Oxidation: ORP 650 mV). In this case, the efficiency for the removal of ferro/ferri cyanide by this general alkaline chlorination is very high as 99%. But the permissible limit of Korean waste-water discharge couldn't be satisfied. The initial concentration of cyanide was 374 mg/L(the Korean permissible limit of cyanide is 1.0 mg/L max.). So a particular focus was given to the treatment of heavy metal-cyanide complexes wastewater by $Zn^{+2}/Fe^{+2}$ ion and coprecipitation after alkaline chlorination. And we could meet the Korean permissible limit of cyanide(the final concentration of cyanide: 0.30 mg/L) by $Zn^{+2}/Fe^{+2}$ ion and coprecipitation(reaction time: 30 min, pH: 8.0, rpm: 240). The removal of Chromium ion by reduction(pH: 2.0 max, ORP: 250 mV) and the precipitation of metal hydroxide(pH: 9.5) is treated as 99% of removal efficiency. The removal of Copper and Nickel ion has been treated by $Na_2S$ coagulation-flocculation as 99% min of the efficiency(pH: $9.09\sim10.0$, dosage of $Na_2S:0.5\sim3.0$ mol). It is important to note that the removal of ferro/ferri cyanide of heavy metal-cyanide complexes wastewater should be employed by $Zn^{+2}/Fe^{+2}$ ion and coprecipitation as well as the alkaline chlorination for the Korean permissible limit of waste-water discharge.

• Journal of Korean Society on Water Environment
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• v.30 no.3
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• pp.292-297
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• 2014

We synthesized the self-organized nanoporous oxide with potentiostatic anodization of iron foil. The iron oxide nanocomposite (INCs) were fabricated in 1M $Na_2SO_4$ containing 0.5wt% NaF electrolyte holding the potential at 20, 40 and 60 V for 20min, respectively. Field Emmision Scanning Electron Microscopy (FESEM) and X-ray Diffractometer (XRD) were used to evaluate the micromorphology and crystalline structure of INC film. Also, this study was performed to evaluate the fenton reaction using INC film with hydroperoxide for degradation of cyanide dissolved in water. In case of INC-40V in the presence of $H_2O_2$ 3%, the first-order rate constant was found to be $1.7{\times}10^{-2}min^{-1}$, and indicated to be $1.2{\times}10^{-2}min^{-1}$ on commercial hematite powder. This result is shown to be good performance enough to replace the powder type for treatment of wastewater.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.5
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• pp.524-533
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• 2008

Industrial wastewater generated in the electroplating and metal finishing industries typically contain toxic free and complex metal cyanide with various heavy metals. Alkaline chlorination, the normal treatment method destroys only free cyanide, not complex metal cyanide. A novel treatment method has been developed which destroys both free and complex metal cyanide as compared with Practical Plant(I). Prior to the removal of complex metal cyanide by Fe/Zn coprecipitation and removal of others(Cu, Ni), Chromium is reduced from the hexavalent to the trivalent form by Sodium bisulfite(NaHSO$_3$), followed by alkaline-chlorination for the cyanide destruction. The maximum removal efficiency of chromium by reduction was found to be 99.92% under pH 2.0, ORP 250 mV for 0.5 hours. The removal efficiency of complex metal cyanide was max. 98.24%(residual CN: 4.50 mg/L) in pH 9.5, 240 rpm with 3.0 $\times$ 10$^{-4}$ mol of FeSO$_4$/ZnCl$_2$ for 0.5 hours. The removal efficiency of Cu, Ni using both hydroxide and sulfide precipitation was found to be max. 99.9% as Cu in 3.0 mol of Na$_2$S and 93.86% as Ni in 4.0 mol of Na$_2$S under pH 9.0$\sim$10.0, 240 rpm for 0.5 hours. The concentration of residual CN by alkaline-chlorination was 0.21 mg/L(removal efficiencies: 95.33%) under the following conditions; 1st Oxidation : pH 10.0, ORP 350 mV, reaction time 0.5 hours, 2nd Oxidation : pH 8.0, ORP 650 mV, reaction time 0.5 hours. It is important to note that the removal of free and complex metal cyanide from the electroplating wastewater should be employed by chromium reduction, Fe/Zn coprecipitation and, sulfide precipitation, followed by alkaline-chlorination for the Korean permissible limit of wastewater discharge, where the better results could be found as compared to the preceding paper as indicated in practical treatment(I).

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1998.11a
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• pp.240-244
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• 1998

This study was carried out to investigate the efficiency of steel mill slag and sludge in removing heavy metals and cyanide in metal plating wastewater. Laboratory experiments were peformed with jar tester, The tests were peformed at ambient temperature. The results of tests showed that overall rates metals removed were greater than 90 %. Metals were removed from solution as the combined effects of adsorption and precipitation in alkaline condition. The removal efficiency of cyanide by steel mill wastes was above 90 % at optimum conditions. In view of the test results and other engineering characteristics of steel mill slag and sludge, these industrial by-products from steel industry have a high potential to be used in metal plating wastewater treament and were particularly beneficial.