br Ethical approval br Introduction The presence

Ethical approval
Introduction The presence of metal ions in the environment is of major concern due to their toxicity to many life forms. Unlike organic pollutants, the majority of which are susceptible to biological degradation, metal ions do not degrade into harmless end-products. The metals of most immediate concern are Cr, Mn, Fe, Zn, and Cd which are widely distributed in materials which make up the earth\'s surface. Among these heavy metals, chromium occurs in higher concentration in the wastes from electroplating, paints, dyes, chrome tanning, paper industries, etc. This metal is very toxic. Over exposure to high concentration of chromium can result in epigastric pain, nausea, vomiting, severe diarrhea and hemorrhage (Huang and Wu, 1977). Maximum contaminant level of chromium for the drinking water is 0.05 mg/L. Over the years, various conventional treatment methods such as chemical precipitation, rad001 exchange, electrolytic recovery, membrane separation, floatation and adsorption have been used to remove chromium from wastewater. Removal of chromium has also been investigated using phytoextraction, reverse osmosis, adsorption, precipitation, ion-exchange, membrane and biological processes (Sule and Ingle, 1996; Chiarle et al., 2000; Cengeloglu, 2003; Pehlivan and Arslan, 2006; Das and Mishra, 2010). These conventional methods are not suitable for the removal of metals when it is present at low concentrations. Thus, to reduce the heavy metal ion concentration to an environmentally acceptable level, a cost-effective and efficient separation method is to be developed. Of all the various water treatment techniques, adsorption is generally preferred for the removal of heavy metal ions due to its high efficiency, easy handling, availability of different adsorbents and cost effectiveness (Kimbrough et al., 1999; Lin and Juang, 2002; Bhattacharya et al., 2006). The uses of activated carbon as adsorbent in adsorption process are very popular for removal of metal ion from waste water, but are quite expensive and the regeneration of the carbon is not always possible (Lalvani et al., 1998). A considerable research work has been done in the search of inexpensive adsorbents especially developed from various industrial waste materials i.e. fly ash (Pollard et al., 1992; Ferraiolo et al., 1990), metal hydroxides (Namasivayam and Ranganathan, 1998), blast furnace slag (Gupta et al., 1998), biomass (Chang et al., 1997), peanut hull (Periasamy and Namasivayam, 1994), bagasse pith (Aly and Daifullah, 1998), carbonaceous material (Srivastava and Tyagi, 1995), bagasse fly ash (Dubey and Gopal, 2007), etc. In continuation it was decided to undertake a study to assess the potential of a sponge iron industry waste material such as dolochar, as an adsorbent for the removal of Cr (VI) from aqueous solution. As far as our knowledge goes this is the first time when dolochar is used for Cr (VI) removal from synthetic sample.
Materials and methods
Results and discussion
Adsorption isotherms Several models have been used to describe the experimental data of adsorption isotherms. The Freundlich and Langmuir models are the most frequently employed models. In the present work both models were used. The Freundlich isotherm model explains about the adsorption process wherein a heterogeneous adsorbent surface involves in the multilayer distribution of the adsorbate with interaction amongst adsorbed molecules (Maji et al., 2008; Baraka et al., 2012; Diwevdi et al., 2008; Sing et al., 2008). The relation between the metal uptake capacity qe (mg/g) of adsorbent and the residual metal ion concentration Ce (mg/l) at equilibrium is given bywhere the intercept ln k is a measure of adsorbent capacity, and the slope 1/n is the adsorption intensity. k is related to temperature and the chemical or physical characteristics of adsorbents, where as “n” is an indicator of the change of intensity of adsorption process and also a measure of the deviation from linearity of the adsorption. A higher value of n (n > 1) indicates favorable adsorption, whereas n < 1 represents poor adsorption characteristics (Yang et al., 2013). The value of n = 3.66 suggests favorable adsorption. The situation n > 1 is most common and may be due to a distribution of surface sites or any factor that cause a decrease in adsorbent–adsorbate interaction with increasing surface density. The isotherm data fit the Freundlich model (R2 = 0.987).