In this work, we prepared a heterojunction anode with a surface layer of SnO2-Sb-Ni (SSN) on a Ti/IrO2 electrode by thermal decomposition to improve the electrochemical activity of the Ti/IrO2 electrode. The Ti/IrO2-SSN electrode showed significantly improved electrochemical activity compared with Ti/IrO2. For the 0.1 M NaCl and 0.1 M Na2SO4 electrolytes, the onset potential of the Ti/IrO2-SSN electrode shifted in the positive direction by 0.1 VSCE and 0.4 VSCE, respectively. In 2.0-2.5 V voltages, the concentration in Ti/IrO2-SSN was 2.59-214.6 mg/L Cl2, and Ti/IrO2 was 0.55-49.21 mg/L Cl2. Moreover, the generation of the reactive chlorine species and degradation of Eosin-Y increased by 3.79-7.60 times and 1.06-2.15 times compared with that of Ti/IrO2. Among these voltages, the generation of the reactive chlorine species and degradation of Eosin-Y were the most improved at 2.25 V. Accordingly, in the Ti/IrO2-SSN electrode, it can be assumed that the competitive reaction between chlorine ion oxidation and water oxidation is minimized at an applied voltage of 2.25V.

1970년대 수출주도 고도성장을 위해 정부는 조선･철강･기계 등의 중화학공업을 선택적으로 집중육성 하였다. 그 결과 일반기계산업은 1970년 수출 8백만불에서 2015년 현재 218,262백만불로 약 27,000배 이상 성장하였다. 일반기계산업에 있어 금속가공 공정은 필수적이며, 금속가공 공정에서 필요로 하는 것이 공작기계(Mother machine)와 절삭유(Soluble Cutting Fluids, SCF)이다. 절삭조건 개선에 사용되는 절삭유는 첨가제, 사용용도 등에 따라 원액으로 사용하는 비수용성과 물로 희석해서 사용하는 수용성으로 나뉜다. 국내 절삭유 이용량의 60%이상이 수용성 절삭유로 비수용성 절삭유의 오일미스트(Oil-mist), 폐유처리과정에서 유독성 물질 발생 등의 문제로 수용성 절삭유 사용량이 점차 증가하였다. 또한 절삭 성능 향상을 위한 방부제, 윤활제, 방청제, 부식방지제, 세정제, 극압 첨가제 등 각종 화학물질 첨가로 인해, 노출될 경우 췌장, 피부, 담낭, 방광, 소화기계 등 인체의 여러 조직에 암을 유발할 수 있으며, 각종 호흡기계 질환과 피부질환을 초래하는 것으로 알려져 있다. 인체에 미치는 영향 외에도 수용성 절삭유에는 고농도의 유기성분과 질소화합물 등이 함유되어 있어 적절한 처리 없이 수계로 유출시 부영양화, 녹조현상 등과 같은 문제를 일으킬 수 있으며 산화반응에 의해 수계의 용존산소를 감소시키므로 그 처리의 중요성이 부각되고 있다. 본 연구에서는 실공정에서 발생한 폐수용성절삭유를 원시료로 하여 대표적인 불용성 전극인 Ti/IrO2 전극을 이용하여 전기화학적 처리를 진행하였으며 연구에 사용한 장치의 모식도를 Fig. 1에, 시료의 성상을 Table 1에 나타내었다.

Soluble Cutting Fluids (SCFs) have been used in metal machining processes to improve the quality of metal processing equipment and products. Although SCFs are useful and essential material, wasted soluble cutting fluids are harmful in hydroecological systems because of the high concentration of COD and nitrogen material. If discharged to hydroecological systems without specific treatment, they may cause eutrophication in rivers and lakes. Therefore, the removal efficiency of the COD contained in the SCFs is investigated in this study using electrochemical treatment with an insoluble electrode. The electrode was made of titanium with iridium plating, made from a perforated metal sheet to agitate the sample in the reactor. Cathode and anode electrodes were inserted into acrylic reactor alternately and the reaction time was one hour. The experimental results were as follows: First, for 60 A/m2, 80 A/m2, and 100 A/m2 current densities, the COD removal efficiencies were 42.0%, 63.9%, and 78.4%, respectively.

As industry continues to develop, the contents of various recalcitrant substances that are not removed by conventional wastewater treatment have increased in modern society. The metal working fluids (MWFs) used in the metal working process contain chemical substances, such as mineral oils, anticorrosive agents, extreme-pressure additives, and stabilizers, as well as high concentrations of organics and ammonia-nitrogen. Accordingly, MWFs are required to develop advanced treatments to conserve hydro-ecological resources. This study investigated the removal efficiency of ammonia nitrogen from MWFs according to operating time, applied voltage, and NaCl concentration using a Ti/IrO2 electrode in a batch-type reactor. The experimental results showed that ammonia-nitrogen removal efficiencies without NaCl were 89% and 92% when voltage was adjusted to 15 and 20 V for 60 min and removal efficiency was 90% at 25 V for 40 min. Removal efficiencies of 10 mM NaCl were 4% and 2% greater than those of not adding NaCl at 15 V for 50 min and 20 V for 30 min.