APPLICATION OF IRON NANOPARTICLES FOR INDUSTRIAL WASTEWATER TREATMENT. Martina SUKOPOVÁ*, Jana MATYSÍKOVÁ*, Ondřej ŠKORVAN*, **, Marek HOLBA*,***

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1 APPLICATION OF IRON NANOPARTICLES FOR INDUSTRIAL WASTEWATER TREATMENT Martina SUKOPOVÁ*, Jana MATYSÍKOVÁ*, Ondřej ŠKORVAN*, **, Marek HOLBA*,*** *ASIO, spol. s r.o., Brno, Czech Republic, EU ** VŠCHT Prague, Prague, Czech Republic, EU ***Institute of Botany Academy of Science of the Czech Republic, Brno, Czech Republic, EU Abstract Nanotechnology has widespread application potential and offers also the possibility of an efficient removal of pollutants and germs in the area of wastewater treatment. Recently, nanoparticles and nanomembrane are innovative technologies used for removal of chemical and biological substances, including metals, nutrients, cyanide, organics, viruses, bacteria and antibiotics. Our research focuses on zerovalent iron nanoparticles and its use for municipal and industrial wastewater treatment. Zerovalent iron is a strong reducing agent with high reactivity. Surface area of iron nanoparticles is in the range from 20 to 25 m 2 /g. Reaction products are mostly non toxic iron oxides. This environmentally friendly technology has great potential to combine redox processes with sorption and coagulation effect in one technological step in order to remove crucial pollutants. The aim of our study was to investigate the treatment efficiency of the wastewater from rinsing after copper plating by zerovalent iron nanoparticles (nzvi). Wastewater from metal finishing industry contains high concentrations of contaminants. Typical ones are cyanides and heavy metals. Removal of copper and nickel was observed in this study. Tests were carried out in lab-scale and performed on real wastewater from metal finishing. Metals were bound in complex compounds and difficult to remove from wastewater. nzvi showed possibility to solve this problem via environmentally friendly way. Keywords: Zerovalent iron nanoparticles, copper removal, nickel removal, industrial wastewater treatment 1. INTRODUCTION Nanotechnology is a branch with a great potential and boost today. Materials with dimensions nm offer wide range of applications. Water treatment applications can be divided into three categories, according to Cloete et. al [1]: treatment and remediation, sensing and detection, and pollution prevention. This article deals with use of nanoscale zerovalent iron (nzvi) for wastewater treatment and remediation. Nanoscale zerovalent iron has become a valuable material for its environmental remediation abilities [1, 2, 3]. Zerovalent iron is a particle with average particle size nm and a specific surface area of m 2 /g. Iron in oxidation state 0 is very unstable, thus reactive and represents one of the strongest reducers [2,4]. High reactivity and relatively large surface area facilitate to combine processes reduction, sorption and coagulation into one technological step. Reaction products are ferrous and ferric oxides and hydroxides that are commonly found in nature. Those advantages make the technology environmentally friendly. Continuous effort of sustainable environmental protection influences all types of industry in relation with produced waste, and thus discharge of contaminants into the environment. Process optimization or new technologies are necessary to fulfill more stringent outlet parameters. nzvi has been shown as an efficient tool for the treatment of various contaminants in aqueous systems [2, 4, 5, 6]. Removal efficiencies of heavy metals, organic compounds and nutrients show various ways of zerovalent iron applications. Successful in-situ remediation of groundwater contaminated with heavy metals were investigated in many studies [1, 2, 3, 5, 7]. Copper is characterized by reduction and precipitation mechanisms and typical interactions for nickel are reduction, adsorption and co-precipitation [2]. Reaction mechanism of nzvi with Ni 2+ has

2 described Li and Zhang [5]. First reaction step is physical sorption of cation onto the nzvi surface then it is strongly bound by chemisorption and reduced to Ni 0. Sorption of heavy metals is very fast, namely less than one minute [8]. Wastewater from metal finishing industry is usually treated by well-known principle of precipitation. This non-expensive technology is easy to operate and most of the metals are diverted into insoluble compounds that are well separated. Unfortunately, not all the contaminants can be removed under the required limits. Therefore another technological step is necessary to treat low concentrations, e.g. nzvi applications. Furthermore, important advantage of nzvi for heavy metal removal is a production of non-harmful compounds. Metals are reduced and adsorbed onto iron surface, thus easily separated from the treated water in the sludge of minimal volume compared to conventional methods. In our study we applied nzvi to remove Cu and Ni. We suppose reduction and adsorption reactions. 2 MATERIALS AND METHODS 2.1 Wastewater Real processing wastewater from metal finishing industry was used for the lab-scale testing. Technological wastewater from rinsing after cyanide copper plating contained high concentrations of copper, nickel and cyanides (see Tab. 1). Outlet limits for Cu and Ni are 0.5 mg/l, and 0.8 mg/l, respectively. Table 1 Rinsing water characteristics Parameter 2.2 nzvi Unit Non-filtered sample Limit according GD 23/2011 COD mg/l Cu mg/l Ni mg/l ph Tests were performed with aquatic dispersion of nzvi. Commercially available sample from nzvi, s.r.o. characterized by 17 wt.% of nzvi was used. nzvi have average diameter 50 nm. Due to the narrow size distribution of nzvi and stabilization process, the product exhibits a high reactivity and very low degree of agglomeration. Suspension must be stored in fridge/cold and when applied, the contact with the air should be minimized with regard to mentioned reactivity. It was necessary to homogenize the suspension sample before dosage to achieve accurate iron dose. 2.3 Methods Copper, nickel and COD concentrations were analyzed and reaction conditions were characterized by ph, temperature and conductivity. Samples were prepared for analyses by Crack Set LCW 902 from HACH Lange. This technique allows metals to be assessed as a sum of free and bounded ions. Analyses were provided by HACH tests LCK 329 for copper and LCK 337 for nickel with spectrophotometric detection by Spectrophotometer HACH DR COD was analyzed by test LCK 314 (HACH Lange). 2.4 Metal ions removal Optimal dosage The dose of nzvi was tested in the range of 0-4 g/l. 100 ml of wastewater was put into 250 ml erlenemyer s flasks and nzvi slurry was added while quick manual mixing. Closed flasks were slowly mixed on the shaking device in 200 rpm for 4 hours. Samples were filtered through filter from glass fibers with pore

3 size 0.45 µm after the reaction. The analyses for COD, copper and nickel were made in filtrates. This study does not concern with ph adjustment. Reaction conditions - ph, temperature and conductivity were monitored Kinetic test To make the metals removal effect more obvious, the initial nzvi dose was chosen as 3 g/l. For investigation of reaction kinetics under the specific reaction conditions 2.5 liters of processing wastewater were mixed in opened beaker for 73 hours. Samples were immediately filtered through filter of pore size 0.45 m and analyzed for COD, copper and nickel concentrations. Reaction conditions - ph, temperature and conductivity were monitored. 3. RESULTS AND DISCUSSIONS 3.1 Optimal dosage Results show considerable metals concentration decrease with nzvi used. There are slight concentration differences for doses of nzvi from 0.5, 0.8, 1, 2, 3 to 4 g/l. The lowest concentrations of both investigated metals were achieved for nzvi dose 4 g/l, therefore residual concentrations were 1.23 mg/l for copper and 0.11 mg/l for nickel (see Fig. 1). Nickel concentration has been decreased under the outlet limits even with small dosages. The removal efficiency almost 60 % was achieved with nzvi dose 0.5 mg/l. However, further increase of nzvi concentration did not cause increase of removal efficiency. As for copper, any of the tested nzvi doses did not decrease concentration under outlet limit. However, removal efficiencies increasing up to 95 % is quite satisfactorily. We expect to use nzvi as polishing step and such removal efficiency is very promising. In this study, reaction conditions were monitored only without any adjustment. Dependence of nzvi dose to ph or conductivity was not confirmed. COD removal was insignificant contrary to other nzvi studies [10, 11]. COD concentration in raw wastewater was 204 mg/l and decrease to 181 mg/l was achieved during nzvi dose was 4 g/l. Fig. 1 Removal efficiency of copper and nickel as a function of nzvi dose

4 3.2 Kinetic test The iron dose 3 g/l was chosen from previously tested concentrations as an optimal dose for copper and nickel removal. Copper removal as a function of time confirmed previous results when removal efficiencies over 90 % were achieved. Increase of the time of exposure caused increasing removal efficiency. Best results were thus achieved after 73 hours, namely 99 %. Removal efficiency of nickel does not show increase in time. Best removal was achieved after 6 hours, approximately 80 %, up to 0.07 mg/l. That is under outlet limit, thus the removal efficiency should be considered as sufficient. This is agreed with Li and Zhang [5], who have found no more nickel adsorbed between 3 and 7 hours. Reaction conditions were monitored only without any adjustment. COD removal was more significant than in previous test. COD concentration was decreased from 154 mg/l to 78 mg/l during the test. Fig. 2. Copper and nickel concentration as a function of time CONCLUSIONS Our study evaluated copper and nickel removal from metal finishing industry by using of nzvi. Lab-scale tests were performed with processing wastewater. Concentration of metals in raw wastewater was 22.4 mg/l for copper and 1.3 mg/l for nickel. 99 % of copper was removed by nzvi dose 3 g/l in 73 hours, likewise the highest removal efficiency of nickel was up to 80 % for the same nzvi dose in 6 hours. The removal efficiency 80 % for nickel was sufficient. The reaction seems to be relatively fast, high removal efficiencies were observed after 30 minutes. Further time of exposure was beneficial only for copper removal, nickel concentration become stable after 2 hours. Reaction conditions were monitored only but no effect of ph, temperature or conductivity was investigated. The results showed possibility to remove heavy metals from industrial wastewater in environmentally friendly way. Further research with real wastewater is necessary to get more reliable results. ACKNOWLEDGEMENT This research is supported by Ministry of Industry and Trade through Project FRTI3/ 196: Advanced technologies for hygienic and toxicology provisions of the wastewater treatment plant outlet. We would also like to acknowledge to the nzvi, s.r.o. company for providing samples of iron.

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