• Applied Chemistry for Engineering
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• v.20 no.3
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• pp.301-306
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• 2009

This research was carried out to establish the effective treatment condition and characteristic of wastewater from the electroplating plant of cold rolling mill by using microorganism. Alkaline wastewater and acidic heavy metal wastewater accounted for 64%, 30%, respectively, of the total wastewater. Highly concentrated thiocyanate was 53890 mg/L as COD and it was 53% of total COD, even though it was 0.03% of wastewater from the electroplating plant. When treating mixed wastewater with microorganism, it was easy to remove when SCN concentrations of mixed wastewater was 200 mg/L or less. While the treatment effect of COD-causing materials was low at the concentration of 400 mg/L or less, it implies that highly concentrated thiocyanate contains a large amount of slowly biodegradable organics. When treating with mixed wastewater, pH was 7.33 at the beginning, but after 8 hours it increased to 7.99. This is caused by ammonia which is generated when SCN of highly concentrated thiocyanate was degraded by microorganism.

• Journal of the Korean Professional Engineers Association
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• v.14 no.1
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• pp.22-29
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• 1981

This study concernes the decomposition of cyanide ion in electroplating plant wastewater and COD variation of photodeveloping wastewater under various conditions. Determinations of CN- concentration were carried out by AgNO$_3$ titration method. The sample solutions were pretreated by passing ozone and decompositions were checked as a function of time for ozone treatment. Analysis of film developing wastewater was carried out by KMnO$_4$ method. Electroplating plant wastewater was also examined at various pH; decomposition rate of cyanide ion was found to increase at higher pH. Time required for the decomposition could be shortened by removing the heavy metal ions under alkaline condition. The effect of temperature on decomposition was studied at 40$^{\circ}$ and 60$^{\circ}C$. The result was better at 40$^{\circ}C$ although time for decomposition was almost same at both temperatures. Analysis of film developing wastewater revealed that COD decrease was faster during the first 1 to 2 hours. However, further decrease could not be effected. The existence of unknown special organics resistant to the decomposition was believed to be the reason.

• Analytical Science and Technology
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• v.25 no.3
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• pp.159-163
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• 2012

A spectrofluorimetric method has been developed for the determination of free $CN^-$ in real samples with fluorescent safranine-O. When safranine-O interacts electrostatistically with $CN^-$, the fluorescent intensity of safranine-O is decreased. Several experimental conditions such as pH of the sample solution and the amount of safranine-O were optimized. $Ag^+$ interfered higher than any other ions. Interference of $Ag^+$ could be disregarded because $Ag^+$ was scarcely contained or mostly complexed with $CN^-$ in selected real samples. With this proposed method, the linear range of $CN^-$ was from 5.0 to 110 ng/mL and the detection limit of $CN^-$ was 2.9 ng/mL. For validating this technique, real samples (Cu, Ag, Au electroplating wastewater, and untreated wastewater in university and in sewage treatment plant) were used. Recovery yields of 91.5%~106.0% were obtained. Based on experimental results, it is proposed that this technique can be applied to the practical determination of free $CN^-$.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.4
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• pp.204-209
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• 2015

The effluent limit of nickel from electroplating wastewater has been strengthened from 5 mg/L to 3 mg/L from 2014. However, currently applied treatment process for nickel plating wastewater is unable to meet the effluent limit, most of the treatment concept conducted by treatment plant is dilution with other metal bearing wastewater. This can cause very significant impact to the environment of nickel contamination. With this connection, the feasibility test has been conducted with the use of electrolysis by using sacrificial electrodes. Experiments were conducted in synthetic and electroless nickel plating wastewater. Optimal condition of current density, pH were derived from the synthetic wastewater. It was found that the removal efficiency of nickel exceeded 94% at the operation condition of at pH 9 and the current density of $1{\sim}2mA/cm^2$. At this conditions, the iron sludge was generated very low amount. However, it was unsuccessful to meet the effluent limit by applying these treatment conditions to the real electroplating wastewater. This can be explained due to the matrix effect of other metals and anions contained real electroplating wastewater. From the result of further study, the optimal conditions for the real wastewater treatment were found out to be at pH 9, current density $6{\sim}7mA/cm^2$, for 5 minutes of operating time. At these conditions, 88% removal of nickel was achieved, which results the residual nickel concentration was below 3 mg/L.

• 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).

• 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.