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Adsorption is one of the most versatile and widely used techniques for the removal of toxic metals from the aqueous solutions. Cadmium is the toxic metal selected for adsorption in this study and adsorbent of interest was activated carbon prepared from Bauhinia purpurea leaves as a plant biomass. The following process parameters were investigated during the batch adsorption process: The adsorption efficiency and cadmium deposition on the adsorbent surface were increased from 15.95 to 89.98%, 0.074 to 0.418 mg/g, and 7.27 to 89.97%, 0.034 to 0.418 mg/g with increasing contact time from 2 to 50 min and pH from 2 to 6.5, respectively. The adsorption efficiency was decreased from 89.98 to 45.96% and the amount of cadmium deposited on the surface of the ACBPL adsorbent was increased from 0.418 to 1.032 mg/g with an increase in solute concentration. The adsorption efficiency of cadmium decreased from 98.41 to 84.51% and 0.457 to 0.392 mg/L with an increase in particle size from 74 to 177 μm. The rate of adsorption of cadmium was increased from 61.31 to 96.34% with an increase in dosage of the ACBPL adsorbent from 0.05 to 0.15 g. The adsorption efficiency and cadmium deposition was decreased from 89.98 to 97.90%, 0.418 to 0.454 mg/g as the temperature increased from 303K to 323K. The variation of thermodynamic energy parameters (ΔG°, ΔH° and ΔS°) with the solution temperature described that the adsorption process is endothermic, spontaneous at high temperatures and non-spontaneous at low temperatures. The positive value of ΔS, reflecting the high degree of disorder in the adsorbent/adsorbate interface that is formed during the transition. [ABSTRACT FROM AUTHOR]

Biosorption is the attractive technique of wastewater treatment to retain the dyes. Biosorption of Malachite Green (MG) using leaf biomass Plumbago Zeylanica (PZ) from an aqueous solution was studied using the batch technique. The batch analysis was accessed by altering the variables like time, pH, dye concentration, biosorbent dosage, average biosorbent size and temperature. The % removal of 93% was attained at 25mg/L of concentration for 50ml of an aqueous solution with a time of 45min, pH 9, the dosage of 0.1g and average biosorbent size of 63 µm having 303 K as temperature. By utilizing four models the equilibrium data were reviewed. The Langmuir model was the best fit with an R² value of 0.998. The kinetics data were evaluated by three models. The data was suitable to Pseudo-second order kinetics. Thermodynamic parameters evaluated are enthalpy change (ΔH°), entropy change (ΔS°) and free energy (ΔG°). The negative value of (ΔH°) represents an exothermic reaction. The operating conditions are optimized using Response Surface Methodology (RSM). [ABSTRACT FROM AUTHOR]

Activated carbons prepared from waste rubber tires (RTAC) are used as practical adsorbents for the speedy evacuation and quick adsorption of lead ions from the wastewater effluents. Batch studies were done to evaluate the performance of RTAC for the adsorption of Pb+2 from aqueous solutions at various process parameters of pH (2-5), metal ion concentration (100 - 200 mg/L), the mass of the adsorbent (0.025 - 0.1 g), average particle size (85 - 200 Mesh) and solution temperature (308 - 323 K) at a maximum equilibrium agitation time of 60 minutes in an orbital shaker at 200 RPM. Taking into account exploratory results, Maximum evacuation of lead onto RTAC as adsorbent by 97.55 %. Optimized the adsorption efficiency using Central Composite Design (CCD) at pH = 4.98, Initial concentration 140.01 mg/L, the mass of the adsorbent is 0.12 grams and temperature of the metal solution is 314.46. Experimentation led above optimum conditions, the value of 3.64 % deviation is obtained with proposed value. Adsorption isothermal data were easily interpreted by Langmuir, Freundlich, Redlich-Peterson and Dubinin-Radushkevich (D-R), a Langmuir model with maximum adsorption capacity of 125 mg/g of lead ions on RTAC and kinetic data were appropriately equipped with the pseudo-second-order kinetic model. Consequences of thermodynamic investigations, properties of ΔH°, ΔG° and ΔS° are -63.976 KJ/mole, -5.787 KJ/mole and -0.196 KJ/mole.K, demonstrates the adsorption process is exothermic nature, feasible and spontaneous at lower temperature. [ABSTRACT FROM AUTHOR]