Available online at www.sciencedirect.com Journal of Hazardous Materials 157 (2008) 137–145 Environmentally stable adsorbent of tetrahedral silica and non-tetrahedral alumina for removal and recovery of malachite green dye from aqueous solution Chellapandian Kannan a,∗ , Thiravium Sundaram a , Thayumanavan Palvannan b a Department of Chemistry, Periyar University, Salem 636011, Tamilnadu, India b Department of Biochemistry, Periyar University, Salem 636011, Tamilnadu, India Received 2 April 2007; received in revised form 12 December 2007; accepted 26 December 2007 Available online 17 January 2008 Abstract The conventional adsorbents like activated carbon, agricultural wastes, molecular sieves, etc., used for dye adsorption are unstable in the environment for long time, and hence the adsorbed dyes again gets liberated and pollute the environment. To avoid this problem, environmentally stable adsorbent of silica and alumina should be employed for malachite green adsorption. The adsorbents were characterized by Fourier transformed infrared spectroscopy (FT-IR) to confirm the tetrahedral framework of silica and non-tetrahedral framework of alumina. The adsorption equilibrium of dye on alumina and silica were 4 and 5 h, respectively, this less adsorption time on alumina might be due to the less activation energy on alumina (63.46 kJ mol -1 ) than silica (69.93 kJ mol -1 ). Adsorption increased with increase of temperature on silica, in alumina, adsorption increased up to 60 ◦ C, and further increase of temperature decreased the adsorption due to the structural change of non-tetrahedral alumina in water. The optimum pH for dye adsorption on alumina was 5 and silica was 6. The dye adsorptions on both adsorbents followed pseudo-second-order kinetics. The adsorption well matched with Langmuir and Freundlich adsorption isotherms and found that adsorption capacity on alumina was more than silica. The thermodynamic studies proved that the adsorption was endothermic and chemisorptions (H ◦ > 40 kJ mol -1 ) on alumina and silica. Recovery of dye on alumina and silica were studied from 30 to 90 ◦ C and observed that 52% of dye was recovered from alumina and only 3.5% from silica. The less recovery on silica proved the strong adsorption of dye on silica than alumina. © 2008 Elsevier B.V. All rights reserved. Keywords: Malachite green; Adsorption; Thermal desorption; Tetrahedral silica; Non-tetrahedral alumina 1. Introduction The organic dyes discharged (12%) from cosmetics, rub- ber, plastics, paper-manufacturing industries and textile dyeing industries are the main source for polluting surface water, ground water and soil [1,2]. To avoid this problem, the physico-chemical techniques like oxidation, flotation, coagulation, photochemical destruction and biodegradation were studied [3–8]. All these process required additional chemicals, which causes environ- mental pollution, corrosion and results the process was more expensive [3–8]. The fact nessaciates to find out an environmen- tally stable adsorbent to uptake organic dyes from dye effluent. ∗ Corresponding author. Tel.: +91 427 2345766x252; fax: +91 427 2345124. E-mail address: chellapandiankannan@gmail.com (C. Kannan). Malachite green (MG) is a common (cationic) dye for dyeing wool, silk, leather, cotton, jute and fungicide, ectoparasiti- cide in aquaculture and fisheries [9,10]. Though it effectively controls the infection of bacteria, protozoans, cestodes, trema- todes, nematodes and crustaceans in aquaculture [11], MG was found to cause muscle glycogenolysis, impairs protein synthe- sis, severe damage to gills and degenerative changes in fishes [12–14]. The dye MG is also harmful to symbiotic bacteria present in water and tumor promoter to human beings [15–19]. Biodegradation of MG was also studied by using some bacteria: Kocuria rosea MTCC 1532 [8]; fungi: Fomes sclerodermeus, Phanerochaete chrysosporium [20], Trametes trogii [21]; algae: Cosmarium, Chlorella, Chlamydomonas and Euglena [22]. The biodegradation of MG requires suitable condition for the growth of micro-organisms and was not effective for higher concentra- tions of dye [8,20–22]. Hence, it is an expensive and not a viable process for bulk dye effluent treatment. 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2007.12.116