Journal of Hazardous Materials B137 (2006) 591–602 Batch and bulk removal of hazardous dye, indigo carmine from wastewater through adsorption Alok Mittal ∗ , Jyoti Mittal, Lisha Kurup Department of Applied Chemistry, Maulana Azad National Institute of Technology, Bhopal 462 007, India Received 4 January 2006; received in revised form 25 February 2006; accepted 27 February 2006 Available online 9 May 2006 Abstract An inexpensive adsorption method has been developed for the removal of indigo carmine, a highly toxic indigoid class of dye from wastewater. Waste materials—bottom ash, a power plant waste and de-oiled soya, an agricultural waste have been used as adsorbents. Attempts have been made through batch and bulk removal of the dye and both the adsorbents have been found to exhibit good efficiency to adsorb indigo carmine. Under batch technique effect of temperature, pH, concentration, dosage of adsorbents, sieve size of adsorbents, etc. have been observed. The dye uptake on to both the adsorbents is found to validate Langmuir and Freundlich adsorption isotherms models. Different thermodynamic parameters, like Gibb’s free energy, enthalpy and entropy of the on-going adsorption process have also been evaluated. Batch technique has also been employed for the kinetic measurements and the adsorption follows a first order rate kinetics for both the adsorbents. The kinetic investigations also reveal for both the adsorbents film diffusion and particle diffusion mechanisms are operative in the lower and higher concentration ranges, respectively. Under the bulk removal, indigo carmine has been adsorbed through the column beds of bottom ash and de-oiled soya and more than 90% of the dye material has been recovered by eluting dilute NaOH solution through exhausted columns. © 2006 Published by Elsevier B.V. Keywords: Adsorption; Bottom ash; De-oiled soya; Indigo carmine; Waste materials 1. Introduction Indigo carmine (IUPAC name 3,3 ′ -dioxo-2,2 ′ -bis-indolyden- 5,5 ′ -disulfonic acid disodium salt) is popularly known as dis- odium salt of Indigotin 5,5 disulphonic acid, FD & C Blue 2 or Acid Blue W. Apart from its use as textile colouring agent and additive in pharmaceutical tablets and capsules as well as in confectionery items, indigo carmine is also used for medi- cal diagnostic purposes. In conjunction with acetic acid the dye facilitate diagnosis of Barrett’s esophagus [1]. It can also help to target biopsies even better, since inhomogeneously stained or unstained areas seem to correlate with intraepithelial neoplasia [2]. Indigo carmine, however, is not readily metabolized but is rather freely filterable by the kidneys. Giving intravenous injec- tion of indigo carmine for intra-operative cystoscopy is a safe technique that can detect otherwise undetected intra-operative compromise of the urinary tract [3]. It also contributes to intra- ∗ Corresponding author. Tel.: +91 9425025427; fax: +91 755 2670904. E-mail address: aljymittal@yahoo.co.in (A. Mittal). vital staining for contrasting and accentuating changed mucosal processes [4]. The dye indigo carmine is considered a highly toxic indigoid class of dye and its touch can cause skin and eye irritations to human being. It can also cause permanent injury to cornea and conjunctiva. The consumption of the dye can also prove fatal, as it is carcinogenic in nature and can lead to reproductive, develop- mental, neuro and acute toxicity [5]. It has also been established that the dye leads to tumors at the site of application [6]. When administered intravenously to determine potency of the urinary collecting system, it has also been reported to cause mild to severe hypertension, cardiovascular and respiratory effects in patients [7–9]. It may also cause gastrointestinal irritation with nausea, vomiting and diarrhea [10,11]. The toxicity tests of the 0304-3894/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.jhazmat.2006.02.047