Showing papers on "Freundlich equation published in 2006"

Study of the selection mechanism of heavy metal (Pb2+, Cu2+, Ni2+, and Cd2+) adsorption on clinoptilolite.

Abstract: The study was carried out on the sorption of heavy metals (Ni2+, Cu2+, Pb2+, and Cd2+) under static conditions from single- and multicomponent aqueous solutions by raw and pretreated clinoptilolite. The sorption has an ion-exchange nature and consists of three stages, i.e., the adsorption on the surface of microcrystals, the inversion stage, and the moderate adsorption in the interior of the microcrystal. The finer clinoptilolite fractions sorb higher amounts of the metals due to relative enriching by the zeolite proper and higher cleavage. The slight difference between adsorption capacity of the clinoptilolite toward lead, copper, and cadmium from single- and multicomponent solutions may testify to individual sorption centers of the zeolite for each metal. The decrease of nickel adsorption from multicomponent solutions is probably caused by the propinquity of its sorption forms to the other metals and by competition. The maximum sorption capacity toward Cd2+ is determined as 4.22 mg/g at an initial concentration of 80 mg/L and toward Pb2+, Cu2+, and Ni2+ as 27.7, 25.76, and 13.03 mg/g at 800 mg/L. The sorption results fit well to the Langmuir and the Freundlich models. The second one is better for adsorption modeling at high metal concentrations.

Phosphate adsorption on synthetic goethite and akaganeite.

Abstract: Low crystalline iron hydroxides such as goethite (alpha-FeOOH) and akaganeite (beta-FeOOH) were synthesized, and the selective adsorption of phosphate ions from phosphate-enriched seawater was examined. The results of the distribution coefficients (K(d)) of oxoanions in mixed anion solutions at pH 8 follow the selectivity order Cl-, NO3-, SO4(2-) << CO3(2-), HPO4(2-) for goethite, and Cl-, CO3(2-) < NO3- < SO4(2) << HPO4(2-) for akaganeite. In seawater, both adsorbents show high selectivity for phosphate ions despite the presence of large amounts of major cations and anions in seawater. The adsorption isotherms fitted better with the Freundlich equation and the maximum uptake of phosphate from phosphate-enriched seawater was 10 mg P/g at an equilibrium phosphate concentration of 0.3 mg P/L on both adsorbents. The phosphate adsorption/desorption cycles show that akaganeite is an excellent adsorbent even after 10 cycles and its chemical stability is good.

Application of zeolite MCM-22 for basic dye removal from wastewater

Abstract: MCM-22 was employed as an effective adsorbent for removal of basic dyes including methylene blue, crystal violet, and rhodamine B from aqueous solution. The adsorption kinetics and isotherms were investigated. The adsorption capacity of MCM-22 for three dyes follows an order of MB > CV approximately RB. Kinetic studies indicate that the adsorption follows the pseudo second-order kinetics and the adsorption is a two-step diffusion process with film diffusion dominating the process. The adsorption isotherm can be well fitted by both the Langmuir and the Freundlich models. Thermodynamic calculations suggest that the adsorption of basic dyes on MCM-22 is an endothermic reaction.

Removal and Recovery of the Hazardous Azo Dye Acid Orange 7 through Adsorption over Waste Materials: Bottom Ash and De-Oiled Soya

Abstract: An azo dye, Acid Orange 7 [p-(2-hydroxy-1 naphthylazo)benzene sulfonic acid] was removed by adsorption over two waste materials, namely, bottom ash, a power plant waste, and de-oiled soya, byproduct obtained during the processing of soybean in soya oil extraction mills. Both waste materials showed excellent adsorption abilities and can be treated as low-cost adsorbents. The adsorbents were characterized through IR spectroscopy and differential thermal analysis (DTA), and preliminary investigations were carried out by batch adsorption to examine the effects of pH, adsorbate concentration, sieve size, adsorbent dosage, contact time, and temperature. A plausible mechanism for the ongoing adsorption process and thermodynamic parameters were also obtained from Langmuir and Freundlich adsorption isotherm models. The kinetic measurements helped in determining the specific rate constant, confirming the applicability of the first-order rate expression. To identify whether the ongoing process is particle diffusion ...

Isotherms for the Sorption of Lead onto Peat: Comparison of Linear and Non-Linear Methods

Abstract: A comparison of the linear least-squares method and a trial-and-error non-linear method of three widely used isotherms (the Langmuir, Freundlich, and Redlich-Peterson) were examined in an experiment using lead ion sorption onto peat at different temperatures. The four Langmuir linear equations are discussed. Langmuir isotherm parameters obtained from the four Langmuir linear equations using the linear method differed but they were the same when using the non-linear method. Langmuir-1 is the most popular linear form, and it had the highest coefficient of determination compared with the other Langmuir linear equations. The Redlich-Peterson and Langmuir isotherms produced higher coefficients of determination. There are two separate regions depicting the Freundlich isotherm. The results show that that non-linear method may be a better way to obtain the parameters.