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Abstract: This study investigates the effect of nickel speciation and its equilibrium kinetics on the nickel toxicity to methylotrophic methanogenic activity. Toxicity tests were done with anaerobic granular sludge in three different media containing variable concentrations of complexing ligands. A correlation between nickel toxicity and the free nickel concentration failed, because not the equilibrium conditions, but the kinetics of the speciation processes taking place in the medium (precipitation, sorption, liquid speciation, etc.) determine nickel bio-uptake and its toxic effect. The latter was confirmed with an F-test (p-value always lower than 0.1). It was shown that the biological activity (methane production) took place within 3–20 days upon the start of methanogenic experiments, i.e. prior the chemical–physical equilibrium of nickel speciation was established in the methanogenic medium (10–20 days). The process of nickel sorption in the methanogenic granular sludge was limited by intra-particle diffusion and the experimental data fitted to the Weber–Morris sorption model. The other sorption kinetic models applied (pseudo-first order sorption kinetics, pseudo-second order sorption kinetics and first order reversible reaction kinetics) did not fit the experimental data satisfactorily. [Copyright &y& Elsevier]

Abstract: In the present work, potential of sunflower head (BSH) [an agricultural waste biomass] to remove Cr(VI) from simulated wastewater has been evaluated under different process conditions such as pH, metal concentration, adsorbent dose and contact time. A contact time of 120min and pH 2.0 were found to be optimum. Chromium removal decreased from 90.0 to 45.2% as its concentration increased from 10 to 70mg/L. The Cr(VI) removal increased from 31.4 to 52.4% as adsorbent dose increased from 4.0 to 20.0g/L using a test solution having 100mg/L Cr(VI) concentration. Adsorption isotherms were employed to evaluate the maximum adsorption capacity. Adsorption data fitted well to Langmuir isotherm and pseudo-second order model as indicated by high values of correlation coefficient (0.9882 and 0.999) respectively. The adsorption capacity calculated from Langmuir isotherm was 8.177mg/g. [Copyright &y& Elsevier]

Azadirachta indica leaves are converted to a fine powder for use as a biosorbent for the removal of metal ions in aqueous solution. In this work, the adsorptive interactions between Ni(II) and the powder were studied under a variety of conditions involving variations in pH, Ni(II) concentration, biosorbent amount, interaction time and temperature, all in single batch processes. The experimental data have been interpreted on the basis of existing mathematical models of equilibrium kinetics and thermodynamics. The biosorption of Ni(II) increased in the pH range of 2.0–5.0 with ∼92.6% adsorption at pH 5.0 for the highest amount of the biosorbent (4g/L). The biosorption followed second-order kinetics and intra-particle diffusion was likely to have significant influence in controlling the process. The Langmuir monolayer adsorption capacity varied from 2.4 to 9.1mg/g and the equilibrium coefficient from 1.09 to 2.78L/g with strong indication that the Ni(II) ions were held on the biosorbent surface by formation of an adsorption complex. The thermodynamic parameters showed the process to be exothermic in nature supported by appropriate ranges of values of enthalpy change, entropy change and Gibbs energy change. [Copyright &y& Elsevier]

The increase in the use of heavy metals has resulted in an increased flux of metallic substances into the aquatic environment which poses a danger to human health. The present work relates to the removal of cadmium ions by treatment with polyacrylamide grafted rice (Oryza sativa) husk/saguan (Tectona grandis) saw dust. The drinking water guideline value recommended by WHO for cadmium is 0.005ppm.The adsorbent has been prepared by treatment of rice husk/saw dust with acrylamide. Removal has been studied at various pH values for different times of contact and adsorbate concentrations and is found to be pH-dependent, maximum removal occurs at pH 9 and at a contact time of 180min for both the adsorbents. The results were found to be consistent with both the Langmuir and Freundlich isotherm models. The value of n (rate constant) determined at pH 9 has been found to be 1 (within experimental limits). This is further substantiated by applying the Lagergren model. The intra-particle diffusion constants were determined by the Morris–Weber model. Continous flow column studies have also been undertaken and the breakthrough characteristics were determined. Desorption has been affected with 0.5M HCl. The results suggest that both polyacrylamide grafted rice husk/saw dust can be used as efficient and cost effective adsorbents for cadmium ion removal. [Copyright &y& Elsevier]

In this paper, the potential of two low-cost adsorbents such as sunflower seed shells (SS) and mandarin peelings (MP) in the removal of the synthetic anionic dye Reactive Black 5 (RB5) from aqueous solutions was investigated. SS led to a percentage of dye removal higher than MP (85% and 71% after 210min, respectively, for an initial RB5 concentration of 50mgL−1 and an initial pH of 2.0). The rate of adsorption followed a pseudo-second-order kinetic model and the intra-particle diffusion was found to be the rate-controlling stage. In addition, the equilibrium data fitted well both the Freundlich and multilayer adsorption isotherm equations indicating the heterogeneity of the adsorbent surface. This was also corroborated by the SEM photographs. On the whole, the results in this study indicated that SS were very attractive materials for removing anionic dyes from dyed effluents. [Copyright &y& Elsevier]

The kinetics and mechanism of methylene blue adsorption on perlite have been studied. The effects of various experimental parameters, such as initial dye concentration, temperature and pH on the adsorption rate were investigated. Adsorption measurements show that the process is very fast and physical in nature. The extent of the dye removal increased with increase in the initial concentration of the dye and the initial pH and temperature of solution. Adsorption data were modelled using the first and second-order kinetic equations, mass transfer and intra-particle diffusion models. It was shown that the second-order kinetic equation could best describe the sorption kinetics. The diffusion coefficient, D, was found to increase when the initial dye concentration, pH and temperature were raised. Thermodynamic activation parameters, such as ΔG*, ΔS* and ΔH*, were calculated. [Copyright &y& Elsevier]