Characterization and application of activated carbon prepared from waste coir pith

Transcription

1 Journal of Scientific & Industrial Research Vol. 65, December 2006, pp Characterization and application of activated carbon prepared from waste coir pith B Ash, D Satapathy, P S Mukherjee*, B Nanda, J L Gumaste and B K Mishra Regional Research Laboratory, Bhubaneswar Received 04 May 2006; accepted 24 July 2006 Activated carbon (AC) has been prepared from raw coconut pith and coconut pith impregnated with H 3 PO 4 and NaOH solutions separately. AC was characterized with SEM, particle size analyzer and proximate analyzer. Adsorption studies were carried out using UV and atomic absorption spectrophotometer to find its effectiveness. AC obtained from coconut pith treated with phosphoric acid was found comparable to the commercial grade samples. Keywords: Adsorption, Coconut pith, Metal ion, Particle size, Pyrolysis, SEM IPC Code: B01D17/05 Introduction Activated carbon (AC) has many applications 1-5, one of which is as an adsorbent for purification of water, air and many chemical products 6. AC has been an effective adsorbent for dye removal 7,8. Adsorption capacity of certain carbon is known to be a function of porous structure, chemical nature of the surface and ph of the aqueous solutions. Surface functional groups play an important role in deciding adsorption capacity and removal of the adsorbents 9. Coir pith is a soft biomass separated from coconut husk during extraction of coir fiber. Due to porous structure, organic nature and large-scale availability, it would be an ideal precursor for preparing AC 10, which has been found to be effective for the removal of metal ions and chlorophenols 11,12. Present work investigates the removal of metal ions and toxic colouring materials from the industrial effluents using AC prepared from coir pith. Materials and Methods Experimental Procedure AC was prepared by thermal pyrolysis of coconut pith waste at 823 K in carbonaceous atmosphere for 2 h. Before heat treatment, raw material was washed thoroughly with tap water to remove earthly matter and dried at 383 K in an electrical oven for 24 h. After cooling raw material to room temperature, aqueous impregnation treatment was carried out under three different conditions. Dried raw material was divided *Author for correspondence Tel: psmukherjee@rrlbhu.res.in into three parts on weight basis. One part was pyrolysed at 823 K in a carbonaceous atmosphere. Second part was mixed with 10 % H 3 PO 4 13 and the third with 10 % NaOH. These mixtures were separately pyrolysed at 823 K in CO 2 atmosphere for 1-2 h, after drying. They were then cooled to room temperature. Pyrolysed carbons were further leached with 5 % v/v HCl for 2-3 h, then filtered and rinsed with de-ionised water to neutral condition. Rinsed carbon paste was dried in an electrical oven at 383 K for 3 h. AC was grounded and sieved to fine agglomerates ( µ) for further studies. Decolorizing power of AC was measured by treating with standard solution of methylene blue (IS 877:1989). Muddy water (initial turbidity value, 431) was filtered through a composite bed of AC and sand in a vertical column in a dropwise manner, to render it free from suspended matter and adsorb pollutant ions. Colored effluent liquors from textile industries were passed through the column for decolourisation and adsorption of heavy toxic metal ion present in it. Some heavy toxic metal ions in aqueous solutions of 10 mg/l concentrations were treated in solid liquid suspension form through that column, for adsorption studies. Physico-chemical Characterization of Activated Carbon AC from coir pith carbon was characterized AC structure was examined by JEOL scanning electron microscope (SEM). Adsorption of colour matter studies was carried out by Systronics UV-VIS spectrophotometer 119 and PERKIN ELMER atomic absorption spectrophotometer (AAS) 3100 used for study of heavy metal ion adsorption. Particle size was

2 ASH et al: ACTIVATED CARBON FROM COIR PITH WASTE 1009 measured by MALVERN HYDRO 2000MU particle size analyzer. Proximate analysis was done by TGA- 601 LECO corporation, USA, to know moisture and ash content of the coir pith carbon. Results and Discussion Characterization of Coir Pith Physico-chemical composition of coir pith is as follows: bulk density, 0.2 g/cc; calorific value, 3400 kcal/kg; water holding capacity, 460 vol%; lignin, 30-35; cellulose, 20-25; organic carbon, 20-25; nitrogen, 0.3; phosphorus, 0.01; calcium, 0.4; magnesium, 0.36; iron, 0.07; manganese, 1.3; and zinc, 0.8 wt %. Coir pith having very low bulk density and porous structure is found to be one of the valuable raw materials for the production of highly porous AC. Other important factor is its high carbon content (25-30%). Characterization of Activated Carbon SEM photograph shows that wide variety of pores is present in AC along with fibrous structure. Phosphoric acid impregnated carbon consists of more canals like structure than the untreated carbon. NaOH treated carbon has also similar type of SEM photographs. In case of phosphoric acid and NaOH treated carbon, surfaces are pitted and fragmented (Fig. 1). Those imperfections were not found on the surface of the untreated carbon (Fig. 1). Particle size distribution of commercial grade AC (a product from E-Merck (India) Ltd. Mumbai) and AC from coir pith (d 10, d 50, d 90 ) is shown in Fig. 2. Average particle sizes of both the carbons show that d 10 and d 50 values are almost comparable with that of commercial grade AC (Table 1). However, d 90 values are higher for commercial grade AC than coconut pith carbon. Specific surface area of AC from coconut pith (0.52 m 2 /g) is higher than that of commercial grade AC. (0.48 m 2 /g.). Adsorption capacity of coir pith carbon will be better than that of commercial grade carbon due to larger specific area. Application of Coir Pith Carbon Thermal pyrolysis ( K) of dried and impregnated coconut pith in a carbonaceous atmosphere gives carbon (25-30 wt%) of the starting charge. Phase analysis of the leached AC shows: moisture, 11.0; ash, 9.8; water-soluble matter, 4.5; and acid soluble matter, 4.62 wt %. Bulk density of AC was 0.72% g/cc with overall porosity of 460% (v/v). Adsorption of dissolved cations from water to the surface of active carbon is brought about by Fig. 1 SEM analysis of a) untreated coir pith carbon, b) phosphoric acid impregnated carbon, and c) NaOH treated carbon Table 1 Average particle size and specific surface area of different activated carbons Type of AC D 10 D 50 D 90 Specific surface area, m 2 /g Coconut pith Commercial grade

3 1010 J SCI IND RES VOL 65 DECEMBER 2006 Fig. 2 Particle size distribution curve for a) commercial grade AC, b) untreated coir pith carbon, c) H 3 PO 4 impregnated coir pith carbon and d) NaOH treated coir pith carbon valence interactions of different cations. Turbid water (ph 5.8) before purification indicated presence of acidic cations and other acidic radicals. But the same water after filtration through a bed of AC showed a ph of 6.8, which strongly suggests that some dissolved impurities in water are effectively adsorbed by the carbon particles and are removed from water. Turbidity value from 431 ntu reduces to 001 ntu of collected muddy water. Active carbon obtained after pyrolysis of coconut pith waste in carbonaceous atmosphere at low temperature of 823 K shows nearly neutral interface whereas the same carbon obtained after pyrolysis of 973 K shows ph in the alkaline range (>8.2).

4 ASH et al: ACTIVATED CARBON FROM COIR PITH WASTE 1011 Table 2 Chemical analysis data of effluent from textile dye industries by activated carbon from coconut pith waste Individual elements Colored effluent water, mg/l Colored effluent water treated with activated carbon, mg/l Iron Lead Zinc Cadmium Chromium Calcium Fig. 3 UV-Visible spectrum of dye effluents; A=before treatment, B=after treatment Studies on the adsorption of pollutant metal radicals like Cd, Pb and As from dilute solutions showed effective reduction (from 10.0 mg/l to < 0.1 mg/l) in less than 5.0 min after passing through a bed of AC filled in a column (internal diam 5.0 cm and internal height of 20.0 cm) by drop wise manner. For this experiment, standard solution of 10 mg/l has been prepared separately for Cd, Pb and As. Analysis was done by AAS. This study was carried out at an initial metal ion solution at ph 5. Adsorption of these cations may be attributed to formation of metal complexes at the interface of carbon particles and release of acidic radicals to the bulk solution. Effective decolorizing power towards standard methylene blue solution (0.15 g methylene blue/ 100 ml water) of different ACs has been found as follows: commercial grade AC, 153; coconut pith carbon without treatment, 67.5; coconut pith carbon treated with H 3 PO 4, 168.0; coconut pith carbon treated with NaOH, 37.5 mg/g. Thus, H 3 PO 4 treated AC was found most effective. During purification treatment of waste colour effluent collected from a textile industry, it was observed that, almost all metal ions present were reduced to a greater extent (analyzed by AAS) when treated with AC prepared from coconut pith (Table-2). Purification was carried out by a bed of AC filled in a column (internal diam 5.0 cm and internal height of 20.0 cm). Adsorption by any surface was controlled by specific surface area and average particle size. Smaller the size of particle, higher is the adsorption capacity. AC prepared from coconut pith waste shows high decolourisation of effluent colour water and nearly wt% of coloring material is removed from matrix during decolourisation using the column described earlier (Fig. 3). Colour removal was studied calorimetrically at λ max = 450 nm and the experiment was carried out at a ph Simultaneously, turbidity value of effluent from 87 ntu was reduced to 14 ntu. Conclusions AC prepared from coir pith has been observed as an effective adsorbent for decolourisation of dye industry effluents and removal of toxic metals from their aqueous solutions. Thus it can be used effectively in water treatment plants. AC prepared from coir pith waste with phosphoric acid treatment displays better decolorizing power than commercially available AC. Specific surface area of coir pith AC is higher than that of commercial grade AC. SEM analysis shows the high porous nature of the coir pith carbon. Thus the coir pith, which is regarded as a waste and pollutant can be converted to a value added product-ac, which has extensive application for removing pollutants from wastes produced by various industries. Acknowledgements Authors thank Ministry of Environment and Forest, Govt. of India for financial support, and Director, RRL, Bhubaneswar for encouragement and kind permission to publish the work. References 1 Rangaraj S, Banumath A & Marugesan V J, Activated carbon from rubber sheed and palm seed coats: preparation and characterization, J Sci Ind Res, 57 (1998) Rangaraj S, Banumath A & Murugesan V, Preparation and characterization of activated carbon from agricultural waste, Indian J Chem Tech, 6 (1999) Krystyna Konieczny & Grzegorz Klomfas, Using activated carbon to improve natural water treatment by porous membrane, Desalination, 147 (2002) Dinesh M, Singh K P & Singh V K, Trivalent chromium removal from waste water using low cost activated carbon derived from agricultural waste material and activated carbon fabric cloth, J Hazardous Mat, B135 (2006) Stavropoulos G G, Precursor material suitability for super activated carbons productions, Fuel process Technol, 86 (2005) Hassler J W, Purification with Activated Carbon, 2 nd edn (Chemical Publishing Co Inc, New York) 1963,

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