• 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.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 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 the Korean Chemical Society
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• v.20 no.4
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• pp.280-289
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• 1976

The silver selenide electrode has been prepared and its properties as an indicating electrode for silver ion have been investigated. Epoxy resin was used as a filler of silver selenide electrode. Silver metal plate was directly connected with the membrane of the electrode and the silver paste was used as its binder. The sintered electrode was more sensitive and stable than the pressed electrode, and the silver selenide electrode more sensitive than the silver sulfide electrode to silver ion. The linear relationship between the electrode potential and logarithmic concentration of silver ion has been observed down to 10-6 M for the electrode. Several heavy metal ions except mercuric ion did not interfere this linearity, but halide, cyanide, and thiocyanate ions did intensively interfere owing to the formation of silver compounds and complexes. This electrode has been applied to the potentiometric titration for determining halide ion. It is concluded that interferences from ,$CN^-, SCN^-, S^-, I^-, Br^-, Cl^- and Hg^{2+}$ ions are detrimental to the practical use of the electrodes for measuring pAg.