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The present study examines the adsorption of pyridine (Py) from aqueous solutions, using bagasse fly ash (BFA), which is a solid waste that is generated from bagasse-fired boilers, as an adsorbent. Batch adsorption studies have been performed to evaluate the influence of various parameters, such as initial pH (pH 0 ), adsorbent dose (m), contact time (t), initial concentration (C 0 ), and temperature (T), on the removal of Py from the aqueous solutions. The maximum removal of Py is determined to be 99% at lower concentrations (<50 mg dm -3 ) and 95% at higher concentrations (600 mg dm -3 ), using a BFA dosage of 25 kg m -3 at normal temperature. Studies on Py adsorption equilibrium and kinetics by BFA also have been conducted. The adsorption equilibrium analyses also are performed, using the Langmuir, Freundlich, Redlich-Peterson, and Temkin isotherm equations. The Langmuir equation is determined to best represent the equilibrium sorption data. Thermodynamic studies revealed that the adsorption of Py on BFA is endothermic in nature and that the isosteric heat of adsorption decreases as the equilibrium uptake of Py on the BFA surface increases. The desorption of Py from Py-loaded BFA with several solvents shows that only 68.70% and 51% of Py could be recovered, using ethyl alcohol and 0.1 N H 2 SO 4 , respectively.

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In this study, feasibility of using seawater to neutralize alkaline red mud for its safe disposal has been studied using Taguchi's design of experimental methodology. Parameters such as weight of red mud, volume of seawater, stirring time and temperature were tested at three levels to study their effect on response characteristic, i.e., pH of the neutralized slurry. The analysis of variance showed that volume of seawater added and quantity of red mud are the two significant parameters with 53.59 and 44.92 % contribution each, respectively. Under the optimized parameters, pH value of red mud slurry reaches to about 8.0 which is within disposable limits. When seawater or other Ca-and Mg-rich brines are added to caustic red mud, the pH of the mixture is reduced causing hydroxide, carbonate or hydroxy carbonate minerals to be precipitated. This mechanism of neutralization process has been explained with emphasis on chemical analysis, mineralogy and morphology of the neutralized red mud. The process improved the physical characteristics of red mud with entrained liquor becoming non-hazardous water with reduced alkalinity. The results would be extremely useful in the process of safe disposal of red mud.