Removal of Arsenic in Soil Washing Water Using GAC Coated with Fe(III)

Transcription

1 2012 International Conference on Environmental Science and Technology IPCBEE vol.30 (2012) (2012) IACSIT Press, Singapore Removal of Arsenic in Soil Washing Water Using GAC Coated with Fe(III) Heehun Chae 1, Wan-Hyup Kang 1, Jun-Gyo Cheong 1, Joo-Yang Park 2 and Chung-Hee Chang 1 1 Hyndai Engineering & Construction Co. Ltd., Yongin, , Korea 2 Hanyang University, Seoul, , Korea Abstract. Arsenic has been found frequently in environment and lead to the risk of cancer. GAC(granulatr activated carbon) is widely used as a reactive adsorbent for wastewater treatment because it has a high surface area 2). The GAC that coated with Fe(III)(FeCl 3 ) was used to remove arsenic in contaminated washing water. The objectives of this study is to find the effective method to remove arsenic by Fe(III)-GAC and develop design factors of recycle facility of soil washing water. Comparative experiments were conducted to evaluate systems containing GAC with or without Fe(III). A combination of the GAC and Fe(III) showed a potential to be developed as a reactive material to treat arsenic. And batch test, column test(lab scale and pilot scale) for adsorption capacity was carried out using GAC and Fe(III)-GAC. And pilot scale recycle facility of soil washing water was operated by operation factor from the result of column test. Final concentrations of arsenic in batch test are 0.03(Fe(III)-GAC) and the removal rate was 99.4%. The result of Fe(III)-GAC is below Korean allowable standards of arsenic for drinking water. The adsorption capacity of Fe(III)-GAC was 23mg/g in the lab column test, but the capacity was decreased to 18mg/g in the pilot scale facility. It means that the adsorption capacity of Fe(III)-GAC was affected by suspended solids in soil washing water. These results showed the Fe(III)-GAC can be effective adsorbent for arsenic removal of contaminated soil washing water. And the treatment by Fe(III)-GAC can be very effective and cheap recycling method for arsenic contaminated washing water Keywords: GAC(Granular activated carbon), Fe(III), coated, Arsenic, soil washing water 1. Introduction Heavy metal contaminations of groundwater and soils are usually related to mining activities. Arsenic is one of the most acute contaminants in the mine tailings 3). The toxicity of inorganic arsenic are considered harmful material for human, associated with increased risk of skin cancer, liver disease or other diseases 4). The Korean ministry of environment has imposed regulation which set the legal maximum contaminant level (MCL) of arsenic for drinking water(0.25mg/l), and the World Health Organization (WHO) recommended MCL for arsenic in drinking water of 0.01 mg/l. Arsenic contaminated wastewater can be treated by different kinds of techniques like, ion exchange, activated carbon, activated alumina, reverse osmosis, nano-filtration, etc 3). Previous research has been done on arsenic removal through adsorption because the system can be simple and cost-effective to operate. Use of activated carbon for water treatment is a mature technology for removal of synthetic and natural organic compounds, odor and taste and trace metals, with numerous treatment processes because of its large specific surface area and well-developed pore structures 5). Recently, several iron-based granular activated carbon or processes have been developed and applied for arsenic removal 6). The objective of this study is the effective method to remove arsenic by Fe(III)-GAC and develop design factors of recycle facility of soil washing water. Various test from batch test to field test at pilot facility were performed to check the ability of Fe(III)-GAC. Corresponding author. Tel.: ; fax: address: jkjung@hdec.co.kr 10

2 2. Materials and Methods 2.1. Materials The GAC(SYL0830, Samchully Carbotech Co. Ltd. Korea) was prepared by sieving for the size of 20~40 mesh. FeCl3 (FeCl3, SHOWA) was used for coating the GAC. The soil was sampled in the contaminated site. The soil was contaminated by heavy metals(as, Pb, Cd, etc.), and the arsenic is the representative heavy metal. The arsenic concentration of repared soils were over than 25mg/kg(The Korean allowable standards for soil contamination) 2.2. Experimental methods Three type of FeCl3 solution was used to find the effective synthesis concentration of Fe(III) coated GAC. Artificial As(V) solution was used for the experiments. And Fe(III)-GAC was made by 0.1M FeCl3 solution as the further test. Each sample contained 1g of Fe(III)-GAC or GAC, and 50 ml of 5 mg/l As(V) solution. The sample was mixed by Hag rotator (Vision Co.). After mixing, each sample were filtered with a syringe filter(0.45 μm) and were measured the concentration. Lab scale column test were endorsed for kinetics of arsenic removal. Pyrex column was packed with 40g of Fe(III)-GAC. And the solution flew up from bottom to top of column. Artificial As(V) solution(50mg/l) was used for the experiments. Columns were measured until the column went pass the breakthrough point. Pilot scale column test were endorsed to develop design factors. Acrylic column was packed with Fe(III)-GAC. Artificial As(V) solution(5mg/l) was used for the experiments. And the solution flew up from bottom to top of column. Columns were measured until the column went pass the breakthrough point. Field application at pilot scale facility were endorsed for field application. Pilot scale facility test is ongoing in the contaminated site in Korea. Steel column(6m3) was packed with Fe(III)-GAC. And real soil washing water was used for the experiments. Table 1. Test set for arsenic removal using Fe(III)-GAC Batch test Lab scale column Pilot scale column Pilot scale facility 2.3. Analyses As(V) concentration of samples were measured with atomic adsorption spectrophotometer (AAS, Vario 6, Analytik Jena) which combined with hydride generator (HS-55, Analytik Jena). Arsenic-hydride generation-atomic absorption spectrophotometry was based on measuring pyrolysis of As(III). Therefore, As(III) was converted to quantifiable hydride though pre-reduction process As(V) to As(III). The pre-reduction treatment was carried out by mixing KI (SHOWA) and L(+)-Ascorbic acid (C6H8O6, SHOWA) in deionized water. Hydrochloric acid(hcl) and pre-reduction solution was added. Samples were closed with lid and heated in water bath at 50 for 15 min and was diluted up to mark. Samples were aged for 1 hour, then analyzed for As(V) using AAS. Ionic coupled plasma-optical emission spectroscopy(icp-oes, Perkin elmer) was used to analyse other heavy metal concentration for reference and further study. 3. Results and Discussion The kinetic experiment of As(V) removal was performed with synthesized Fe-GAC with different concentration of FeCl3(0.1, M). The results of arsenic removal kinetic experiments are showed in Fig 11

3 1. Arsenic removal rate by Fe(III)-GAC was very rapid, within 24 hours. The hightst removal efficiency was occurred in 0.1 M FeCl 3 sample (80%). 1 M FeCl 3 sample showed less arsenic removal efficiency. This result means that Fe(III)-GAC with 0.1M FeCl 3 has more effective character in arsenic removal and cost. In order to compare the adsorption capacity, experiments were carried out for GAC and Fe(III)-GAC. In the Batch test for adsorption capacity, two GAC test set was performed different results. The adsorption approached equilibrium within 2 hours. Fe(III)-GAC removed 99.4% of arsenic in initial concentration(5mg/l Arsenic), but GAC removed just 76% of same condition. And the final concentration of arsenic in test solution reached 0.03mg/L(Fe(III)-GAC) and 1.2mg/L(GAC). Only Fe(III)-GAC was performed the adsorption capacity could be below the Korean allowable standards of arsenic for drinking water. As Conc.(mg/L) Fe-GAC GAC Time(min) Fig. 1: Adsorption capacity as concentratioin of Fe(III). Fig. 2: Removal rate of arsenic of Fe(III)-GAC. Lab scale column tests were endorsed using of Fe(III)-GAC and GAC. Initial arsenic concentration was 50 mg/l. The GAC column showed that the concentrations of arsenic were over the Korean allowable standards of arsenic for drinking water from the initial time of test. But the result of Fe(III)-GAC column test showed that the concentrations of arsenic were much more below the standards until 700 pore volumes of Fe(III)-GAC. The adsorption capacity of arsenic of Fe(III)-GAC was showed 23mg/g. Fig. 1: Arsenic adsorption in lab scale Fe(III)-GAC column. Pilot scale column tests were endorsed under similar conditions of lab scale column test. But initial arsenic concentration was 5 mg/l and the suspended solid was about 10mg/L. Pilot scale column designed as the field condition of soil washing plant. The real soil washing water contain a little portion of fine soil 12

4 particle. And this particle can be checked by suspended solid. Pilot scale column tests were performed the effect of suspended solid in soil washing water treatment using Fe(III)-GAC. The GAC column showed that the concentrations of arsenic were over the Korean allowable standards of arsenic for drinking water from the initial time of test. But the result of Fe(III)-GAC column test showed that the concentrations of arsenic were much more below the standards until 400 pore volumes of Fe(III)-GAC. Fig. 2: Arsenic adsorption in lab scale Fe(III)-GAC column. Field test with pilot scale water recycle facility were endorsed in heavy metal contaminated site of Korea. The arsenic removal ability of Fe(III)-GAC and design factors of wastewater recycle facility using Fe(III)- GAC were tested in the facility. In the lab test, the Fe(III)-GAC column was removed arsenic under Korean allowable standard until 700pore volumes. The adsorption capacity of Fe(III)-GAC was 23mg/g, and the replacement period of Fe(III)-GAC was designed to 233hr. But, the pilot scale facility was removed arsenic until 560 pore volumes. And the adsorption capacity of Fe(III)-GAC was 18mg/g, the replacement period of Fe(III)-GAC was fixed to 187hr. The ability of treatment of soil washing water were decreased than lab scale column test. This result showed that the adsorption capacity of pilot scale facility were affected by suspended solids in soil washing water. It means that solid control of washing water is very important factor in the operation of recycle facility of soil washing water. 4. Conclusions The GAC is generally used as a reactive material for heavy metal removal in wastewater because it has high adsorption capacity due to its high surface area 6). In this study, GAC which coated with Fe(III) was selected to remove arsenic in contaminated water from the soil washing facility. Initially, comparative experiments were conducted to evaluate the effect of Fe(III)-GAC. The test investigated removal efficiencies of arsenic by Fe(III)-GAC. Final concentrations of arsenic in batch test are 0.03(Fe(III)-GAC) and 1.2mg/L(GAC). The result of Fe(III)-GAC is below Korean allowable standards of arsenic for drinking water. It means the adsorption capacity of the Fe(III)-GAC is higher than the GAC, and Fe(III)-GAC is profitable adsorbent to removal of arsenic in soil washing water. We expect that the Fe(III)-GAC is a useful adsorbent for recycling of soil washing water. The treatment by Fe(III)-GAC can be very effective and cheap recycling method for arsenic contaminated washing water. 5. Acknowledgements This subject is supported by Korea Ministry of Environment as The GAIA Project. 6. References [1] H.H. Chae, W.H. Kang, J.G. Cheong, J.Y. Park, C.H. Chang, Treatment of arsenic contaminated water from soil washing process using surface modified activated carbon. KSEE conference. 2011, [2] Y.R. Park, S.H. Hong, J.H. Kim, J.G. Cheong, J.Y. Park, The surface modified granular activated carbon for arsenic removal. IWA-ASPIPE conference

5 [3] R. Kim, H.M. Park, J.Y. Park, A study on surface modified activated carbon for the treatment of arsenate wastewater. KSWQ & KSWW joint conference. 2011, 1: [4] Choong T.S.Y., Chuah T.G., Robiah Y., Gregory Koay F.L & Azni I., Arsenic toxicity, health harzards and removal techniques from water : an overview. Desalination. 2007, 217(1-3): [5] Zhang W., Chang Q. G., Liu W.D, Li B. J., Jiang X & Fu L. J. Selecting activated carbon for water and wastewater treatability studies. Environ. Prog. 2007, 26(3): [6] S.H. Hong, H.M. Park, W.H. Choi, J.Y. Park, Characteristics of arsenic removal using surface modified activated carbon. KSWQ & KSWW joint conference. 2010, 1: