폐자원 재활용 담체를 적용한 도금폐수 내 시안 및 중금속 처리 공정의 개발: 과산화수소 촉매 산화 및 흡착 시스템

Abstract

In this study, the treatment process for effective removal of both cyanide and heavy metals from real plating wastewater by using waste–reclaimed materials were developed. Above all, two type of waste-reclaimed materials such as waste-reclaimed (WR) and soil mineral (SM) were investigated, and the applicability of two composites (WR and SM) on cyanide removal and heavy metals removal was investigated. Briefly, for the physicochemical characteristics of composites, both WR and SM were mesoporous material. Pore diameter of the WR was similar to that of the SM while the Brunauer-Emmett–Teller (BET) surface area of WR was larger than those of SM. Results of X-ray diffraction (XRD) pattern mostly indicated the complexity of waste reclaimed composite (WR and SM), even though quartz (SiO2, ID 01–0649) was identified as the most common crystalline. For the WR, hercynite (FeAl2O4, ID 34–0192) was potentially identified because of detection of Fe by energy dispersive X-ray spectroscopy (EDS). WR showed higher cyanide (CN–) adsorption than the SM in both artificial solution and plating wastewater. For the CN– oxidation, the injection of H2O2 (1%) increased CN– removal, especially with WR. The behavior of cyanate (CNO–) production indicated the catalytic role of WR (Fe2O3 composite). Also, the partial conversion of CN– to CNO– could indicate that cyanide was removed by both adsorption and oxidation in WR/H2O2 system. On the other hand, for adsorption behavior of heavy metals (both Cu(II) and Zn(II)) of WR, experimental data was well predicted by both Langmuir and Freundlich models. Kinetically, adsorption of both Cu(II) and Zn(II) was predicted by pseudo-second order model. The highest qe of Cu(II) and Zn(II) were 1.6 × 10-1 and 8.1 × 10-2 mg/g, respectively. Moreover, the initial adsorption rate, h (k2qe2), was increased when initial concentrations of metal ions increased. The effect of pH on the removal of Cu(II) and Zn(II) revealed that some degrees of Cu(II) and Zn(II) were removed at the acidic condition. Moreover, all Cu(II) was removed at pH 7, while Zn(II) was completely removed at pH 9. Therefore, those results indicated that the surface characteristics, specifically both the surface charge and chemical compositions, could make WR a potential adsorbent. The use of WR showed that removal of heavy metals satisfy the regulatory requirements (i.e. under 3.0 mg/L of Cu(II) and 5.0 mg/L of Zn(II)) in Korea when experiments using large-scale reactors were conducted 20 times in plating wastewater. For the development of treatment processes to treat real plating wastewater (cyanide and heavy metals) in pilot–scale, combined two processes of cyanide oxidation (reactor I) and heavy metals adsorption (reactor II or III) system were used. From the reactor I, cyanide removal was achieved when using the WR/H2O2 system with removal capacity less than 1 mg/L (CN–). Sequentially, using reactor II or III, heavy metals (main Cu, Cr, and Cr6+) were eliminated with a removal capacity of the regulation in Korea.