Separation and Purification Technology 70 (2010) 329–337 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Perchlorate removal by activated carbon adsorption Rovshan Mahmudov, Chin Pao Huang ∗ Department of Civil and Environmental Engineering, University of Delaware, 301 DuPont Hall, Newark, DE 19702, USA article info Article history: Received 21 May 2009 Received in revised form 14 October 2009 Accepted 21 October 2009 Keywords: Perchlorate Activated carbon Adsorption Surface complexes abstract The adsorption of perchlorate on activated carbon was studied. A total of 10 types of commercial acti- vated carbons were tested for perchlorate adsorption characteristics using pH as the master variable. The activated carbons were made from different base materials such as wood, bituminous coal, and lignite coal and thus expressed different surface characteristics such as specific surface area and surface charge, e.g. pH zpc . Adsorption isotherms were obtained in the pH range from 3 to 10 and perchlorate concentra- tion from 0.01 to 1.0 mM. It was found that the adsorption isotherms followed the Langmuir type. Results showed that under the experimental conditions of the present study, surface charge not specific surface area was the most important factor governing perchlorate removal. All wood based activated carbons that had large variation in specific surface area, e.g. 3-fold, but very close pH zpc (surface charge) exhib- ited similar perchlorate adsorption capacity. On the other hand, the activated carbons having pH zpc >8 exhibited higher adsorption capacity than those with low pH zpc of 2–3. This provided strong evidence of electrostatic forces as responsible for perchlorate adsorption. However electrostatics alone failed to explain the better perchlorate removal compared to other anions such sulfate and phosphate. The per- chlorate adsorption on activated carbon was described by surface complexation model. Results of XPS and FT-IR studies showed that perchlorate adsorption at least partially occurs through specific inter- actions of perchlorate with surface functional groups. Results also demonstrated that specific chemical interactions between perchlorate and surface functional groups in combination with electrostatic forces were the major mechanism for perchlorate adsorption on activated carbon. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Perchlorate salts, highly soluble compounds, have raised pub- lic health concerns due to the potential toxicity of perchlorate recently. Perchlorate salts especially ammonium perchlorate are known to be most widely used as oxidant in solid rocket fuel propellants, explosives, pyrotechnics, and as chemical reagents. Perchlorate salts are also commonly used in the manufacture of many commercial products ranging from electronics to pharma- ceuticals. The toxicity of perchlorate was revisited in 1990 by USEPA after it was discovered that it could be potentially more toxic than was previously thought. Perchlorate has been suspected of disrupting the thyroid uptake of iodide, which is an essential nutrient for the synthesis of thyroid hormones, and subsequently causing the malfunction of metabolic processes [1]. USEPA has included per- chlorate in the Contaminants Candidate List (CCL) with a reference dose of 0.7 g/kg/day, which is corresponding to a drinking water equivalent level of 24.5 ppb [2]. Due to uncertainties in perchlo- ∗ Corresponding author. Tel.: +1 302 831 8428. E-mail address: huang@ce.udel.edu (C.P. Huang). rate toxicity the recommended levels vary between 1 and 20 ppb in several States in USA. Substantial advances in perchlorate treatment such as biological and chemical reduction have been made. However, these methods still have limited applications in wastewater treatment and drink- ing water purification due to either low reaction rate or the use of huge amount of metals as in the case of chemical reduction. Among alternatives for perchlorate removal, ion exchange is appar- ently the most efficient method. However, the strong and weak base anion exchange resins, though showed good perchlorate removal, were not efficient to deal with small concentration of perchlorate in natural waters, which is usually a few orders of magnitude lower than that of other common anions present [3,4]. Since the develop- ment of bifunctional perchlorate-selective ion exchange resins, ion exchange has become a method of choice. Gu et al. [5,6] have stud- ied the performance of perchlorate-specific ion exchange resins and reported that these ion exchange resins were efficient. However, in spite of the good affinity toward perchlorate, these bifunctional ion exchange resins required involved regeneration processes [6]. Activated carbon adsorption, on the other hand, is a cost effec- tive alternative to other perchlorate removal techniques. Contrary to the conventional belief that activated carbon is not effective for the removal of inorganic anions, several studies have shown that 1383-5866/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2009.10.016