Adsorption of an emerging contaminant (primidone) onto activated carbon: kinetic, equilibrium, thermodynamic, and optimization studies.

The current study addresses the removal of an emerging environmental contaminant (primidone) in batch adsorption experiments using commercial-grade powdered activated charcoal (PAC). The experiments for the removal of primidone were performed to identify the effect of various adsorption parameters. The second-order rate expression best represented the adsorption kinetics data. The Freundlich isotherm equation was best fitted to the experimental adsorption data at equilibrium for removal of primidone using PAC. The values for change in entropy (ΔSo) were positive, which indicates that the degree of freedom of the process increases. The negative values of change in enthalpy (ΔHo) and change in Gibb's free energy (ΔGo) indicate that the physical adsorption is a dominant phenomenon, and the process is feasible and spontaneous. The negative value of ΔHo also represented the exothermicity of the adsorption process. The Taguchi optimization technique calculated the influence of variation of different process parameters, viz., initial pH (pH0), PAC dosage (m), initial adsorbate concentration (C0), solution temperature (T), and process contact time (t), on the removal of primidone by adsorption from aqueous solution. Each of the above parameters was examined at three levels to study their effects on the adsorptive uptake of primidone using PAC (qe, mg g-1), and the optimum value necessary to maximize qe was determined. The findings from the ANOVA indicate that the PAC dose (m) is the most notable parameter contributing 62.16% to qe and a 71.96% to the signal to noise (S/N) ratio data, respectively. The confirmation experiments performed at the optimum parameter condition validated the applicability of the Taguchi design of experiments. The percent removal and adsorptive uptake at the optimal condition were 86.11% and 0.258 mg g-1, respectively.

Removal of 4-nitrophenol from aqueous solution by adsorption onto activated carbon prepared from Acacia glauca sawdust.

The present paper deals with a complete batch adsorption study of 4-nitrophenol (4NP) from aqueous solution onto activated carbon prepared from Acacia glauca sawdust (AGAC). The surface area of the adsorbent determined by methylene blue method is found to be 311.20 m(2)/g. The optimum dose of adsorbent was found to be 2 g/l with 4NP uptake of 25.93 mg/g. The equilibrium time was found to be 30 minutes with the percentage removal of 96.40 at the initial concentration of 50 ppm. The maximum removal of 98.94% was found to be at pH of 6. The equilibrium and kinetic study revealed that the Radke-Prausnitz isotherm and pseudo second order kinetics model fitted the respective data well. In the thermodynamic study, the negative value of Gibbs free energy change (-26.38 kJ/mol at 30°C) and enthalpy change (-6.12 kJ/mol) showed the spontaneous and exothermic nature of the adsorption process.

Adsorption of phenol using adsorbent derived from Saccharum officinarum biomass: optimization, isotherms, kinetics, and thermodynamic study.

The present research shows the application of Taguchi's design of experiment approach to optimize the process parameters for the removal of phenol onto surface of Saccharum officinarum biomass activated carbon (SBAC) from an aqueous solution to maximize adsorption capacity of SBAC. The effect of adsorption parameters viz. adsorbent dose (m), temperature (T), initial concentration (C0) and mixing time (t) on response characteristics i.e., adsorption capacity (qt) has been studied at three levels by using L9 orthogonal array (OA) which further analyzed by variance analysis (ANOVA) for adsorption data and signal/noise (S/N) ratio data by using 'larger the better' characteristics. Using ANOVA, the optimum parameters are found to be m = 2 g/L, C0 = 150 mg/L, T = 313 K and t = 90 min, resulting in a maximum adsorption capacity of 64.59 mg/g. Adopting ANOVA, the percentage contribution of each process parameter in descending order of sequence is adsorbent dose 59.97% > initial phenol concentration 31.70% > contact time 4.28% > temperature 4.04%. The phenol adsorption onto SBAC was best fitted with the pseudo-second-order kinetic model and follows the Radke-Prausnitz isotherm model. Thermodynamic parameters suggested a spontaneous, exothermic nature and the adsorption process approaches physisorption followed by chemisorption. Hence the application of Taguchi orthogonal array design is a cost-effective and time-efficient approach for carrying out experiments and optimizing procedures for adsorption of phenol and improve the adsorption capacity of SBAC.

Neutralization of red mud with pickling waste liquor using Taguchi's design of experimental methodology.

'Red mud' or 'bauxite residue', a waste generated from alumina refinery is highly alkaline in nature with a pH of 10.5-12.5. Red mud poses serious environmental problems such as alkali seepage in ground water and alkaline dust generation. One of the options to make red mud less hazardous and environmentally benign is its neutralization with acid or an acidic waste. Hence, in the present study, neutralization of alkaline red mud was carried out using a highly acidic waste (pickling waste liquor). Pickling waste liquor is a mixture of strong acids used for descaling or cleaning the surfaces in steel making industry. The aim of the study was to look into the feasibility of neutralization process of the two wastes using Taguchi's design of experimental methodology. This would make both the wastes less hazardous and safe for disposal. The effect of slurry solids, volume of pickling liquor, stirring time and temperature on the neutralization process were investigated. The analysis of variance (ANOVA) shows that the volume of the pickling liquor is the most significant parameter followed by quantity of red mud with 69.18% and 18.48% contribution each respectively. Under the optimized parameters, pH value of 7 can be achieved by mixing the two wastes. About 25-30% of the total soda from the red mud is being neutralized and alkalinity is getting reduced by 80-85%. Mineralogy and morphology of the neutralized red mud have also been studied. The data presented will be useful in view of environmental concern of red mud disposal.

Rice husk ash as an effective adsorbent: evaluation of adsorptive characteristics for Indigo Carmine dye.

Present study explored the adsorptive characteristics of Indigo Carmine (IC) dye from aqueous solution onto rice husk ash (RHA). Batch experiments were carried out to determine the influence of parameters like initial pH (pH(0)), contact time (t), adsorbent dose (m) and initial concentration (C(0)) on the removal of IC. The optimum conditions were found to be: pH(0)=5.4, t=8h and m=10.0 g/l. The pseudo-second-order kinetic model represented the adsorption kinetics of IC on to RHA. Equilibrium isotherms were analyzed by Freundlich, Langmuir, Temkin and Redlich-Peterson models using a non-linear regression technique. Adsorption of IC on RHA was favorably influenced by an increase in the temperature of the operation. The positive values of the change in entropy (DeltaS(0)) and heat of adsorption (DeltaH(0)); and the negative value of change in Gibbs free energy (DeltaG(0)) indicate feasible and spontaneous adsorption of IC on to RHA.