Biosorption Performance of Two Brown Marine Algae for Removal of Chromium and Cadmium Ping Xin Sheng, Lai Heng Tan, J. Paul Chen, * and Yen-Peng Ting Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore ABSTRACT The brown marine algae Sargassum sp. and Padina sp., harvested locally, are used for the removal of cations (Cd 2þ and Cr 3þ ) and anion (Cr 2 O 7 22 ) from dilute aqueous solutions. It is found that the biosorption capacities are significantly affected by solution pH. Higher pH favors higher cation removal, whereas higher uptake of anion is observed as the pH is decreased, with the optimal uptake at pH 2. It is demonstrated that the removal rate of the cations is much faster than that of the anion. For cations, 90% of the total adsorption occurs within 60 min, but it takes 360 min for the Cr 2 O 7 22 to reach 90% of the maximum uptake. A series of isotherm experiments are carried out at the optimal pH of 5.5 for Cd 2þ , 3.8 for Cr 3þ , and 2.0 for Cr 2 O 7 22 . The results are well represented by Freundlich and Langmuir equations. Finally, it is observed that reduction of Cr(VI) to Cr(III) and biosorption of these two species occur simultaneously during the process. Key Words: Biosorption; Chromium; Marine algae; Reduction. INTRODUCTION The widespread use of heavy metals in various industries has created a series of environmental problems due to their nonbiodegradability and hazardous char- acteristics. Chronic exposure to elevated levels of cadmium is known to cause renal dysfunction, bone degeneration, liver damage, and blood damage. The US Department of Health and Human Services has reported that there is sufficient evidence in humans for the carci- nogenicity of cadmium and cadmium compounds. [1] Chromium in the industrial effluent is primarily present in the hexavalent form as chromate (CrO 4 22 ) and dichro- mate (Cr 2 O 7 22 ) ions. Cr(III) is less harmful and mobile, 681 DOI: 10.1081/DIS-200027327 0193-2691 (Print); 1532-2351 (Online) Copyright # 2004 by Marcel Dekker, Inc. www.dekker.com * Correspondence: J. Paul Chen, Department of Chemical and Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore; Fax: þ1-831-303-8636, þ65-6872-5483; E-mail: checjp@nus.edu.sg or jchen. enve97@gtalumni.org. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 LDIS27327 LDIS_025_005 Techset Composition Ltd, Salisbury, U.K. 8/12/2004 JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY Vol. 25, No. 5, pp. 681–688, 2004