Multi-metal Systems Research Articles

Removal and recovery of copper (II) ions by bacterial biosorption.

Studies were conducted to investigate the removal and recovery of copper (II) ions from aqueous solutions by Micrococcus sp., which was isolated from a local activated sludge process. The equilibrium of copper biosorption followed the Langmuir isotherm model very well with a maximum biosorption capacity (q(max)) of 36.5 mg of Cu2+/g of dry cell at pH 5.0 and 52.1 mg of Cu2+/g of dry cell at pH 6.0. Cells harvested at exponential growth phase and stationary phase showed similar biosorption characteristics for copper. Copper uptake by cells was negligible at pH 2.0 and then increased rapidly with increasing pH until 6.0. In multimetal systems, Micrococcus sp. exhibited a preferential biosorption order: Cu approximate to Pb > Ni approximate to Zn. There is virtually no interference with copper uptake by Micrococcus sp. from solutions bearing high concentrations of Cl-, SO4(2-), and NO3- (0-500 mg/L). Sulfuric acid (0.05 M) was the most efficient desorption medium, recovering >90% of the initial copper sorbed. The copper capacity of Micrococcus sp. remained unchanged after five successive sorption and desorption cycles. Immobilization of Micrococcus sp. in 2% calcium alginate and 10% polyacrylamide gel beads increased copper uptake by 61%. Biomass of Micrococcus sp. may be applicable to the development of potentially cost-effective biosorbent for removing and recovering copper from effluents.

Zinc(II), Cadmium(II), Mercury(II), and Lead(II) Complexes of N-Carboxymethyl-D,L-threonine in Aqueous Solution

The formation of complexes of Zn(II), Cd(II), Hg(II), and Pb(II) and N-carboxymethyl-D,L-threonine (H2CMT, H2L) in aqueous solutions has been studied by spectrophotometric and potentiometric methods. The complexation model for each system has been established by the HYPERQUAD program from the potentiometric data. Three different behaviors are found: ML2H, MLH, ML, MLOH, and ML2 complexes are formed by Zn(II) and Cd(II) ions, ML2H, ML, MLOH, and ML2 are formed by Hg(II) ion, and only 1/1 complexes MLH, ML, and MLOH are formed by the Pb(II) ion. The formation constants determined for all these complexes allow simulation of experimental titration curves with good agreement. The speciation of multimetal systems with H2CMT shows that this compound is a good and selective ligand at low pH for the Hg(II) ion.

Isotherm Model Analysis for the Adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) on Anaerobically Digested Sludge

Adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) from aqueous solutions on anaerobically digested sludge has been investigated. Experimental data has been fit to Langmuir, Freundlich, and Redlich-Peterson isotherms to obtain the characteristic parameters of each model. Based on the maximum adsorption capacity obtained from the Langmuir and the Redlich-Peterson isotherm the affinity of the studied metals for the sludge has been established as Cu (II)>Cd (II)>Zn (II)>Ni (II). Adsorption tests from multimetal systems confirm the affinity order obtained in the individual metal tests. The adsorption capacity for Cu (II) measured in individual tests is not reduced by the presence of the other above referred metals. Desorption of Zn (II) and Cd (II) previously bound to the sludge in front of Cu (II) and HCl solutions is also reported.

Influence of co-cations on biosorption of lead and zinc – a comparative evaluation in binary and multimetal systems

The influence of co-cations (cadmium, copper, cobalt and nickel) on lead and zinc biosorption by Streptoverticillium cinnamoneum and Penicillium chrysogenum in binary and multimetal systems was evaluated. The metal sorption capacity of S. cinnamoneum was higher than P. chrysogenum for all the metals tested. Both the biomasses exhibited preferential uptake of lead in a multimetal situation. Even though mutual inhibition was seen for all binary systems containing zinc, systems containing lead exhibited unequal inhibition. The extent of metal sorption was dependent on metal chemistry, affinity for binding sites and the type of metal binding. In multimetal systems, S. cinnamoneum and P. chrysogenum exhibited preferential sorption orders: Pb 2+ > Zn 2+=Cu 2+ > Cd 2+ > Ni 2+ > Co 2+ and Pb 2+ > Cu 2+ > Zn 2+ > Cd 2+ > Ni 2+ > Co 2+. The order of metal biosorption in a multimetal system could be predicted well on the basis of Langmuir parameters evaluated in binary metal systems.

Quantitative Analysis and Equilibrium Models of Selective Adsorption in Multimetal Systems Using a Bacterial Biosorbent

ABSTRACT This study investigated the behavior of selective adsorption on the biomass of Pseudomonas aemginosaPU21 (Rip64) with solutions containing Pb, Cu, and Cd. Experiments were designed to quantitatively justify the biosorption preference of the biomass for the three metals. The multimetal adsorption equilibria were described by three models, two of which originated from single-component Langmuir isotherm, and the third one was established empirically. The multimetal adsorption results show that lead and copper significantly inhibited the adsorption of cadmium, while the effects of Cd on the adsorption of Cu and Pb were limited. Lead was found to exhibit a slightly higher inhibition effect on Cu when the two adsorbate coexisted. The data obtained from the ion-exchange systems indicate that Pb and Cu appreciably replaced the preadsorbed Cd ions from the biosorbent, but the competition of Pb and Cu for the adsorption sites was comparative. For three-metal biosorption with equal initial molar concentrations, the relative surface coverage of Pb, Cu, and Cd on the biomass was approximately 55, 40, and 5%, respectively. A modified Langmuir-type model (Model 2), which took account of the heterogeneity and specificity of the adsorption sites, described the experimental results better than the traditional Langmuir isotherm (Model 1) did. Of the three models examined, the empirical one (Model 3) showed the best fits for the two-metal adsorption data, whereas Model 2 had better prediction for the ternary adsorption results. In Model 3 the parameters determined from binary systems can be extrapolated to predict the adsorption equilibria of three-metal adsorption systems satisfactorily.

Excited-state energy- and electron-transfer reactions in multimetal systems

The ability of scientists to convert light into stored chemical potential energy has increased over the past ten years.1 A critical component of this development has been the sophistication of the synthesis of multi metal systems.1~2 Conceptually, the design of individual, but coupled, components in supramolecular systems with specific properties such as light absorption, light emission, chemical reaction, charge storage and conductivity are now possible through elaborate synthetic schemes.2 However, little is known about the coupling of these components. Extensive electronic coupling may perturb the desired characteristics of the mononuclear fragments. On the other hand, minimal coupling may preclude energyor electron-transfer processes within the lifetime of the excited state of the molecular ensemble. Our goal in this paper is to outline some of the design constraints present in supramolecular systems in terms of the coupling of metal centers in excited-state, energyand electrontransfer processes. Metal azine systems have been used extensively in the design of multimetal complexes. 13 One reason for this extensive use in the longlived excited state of complexes such as Ru(bpy)$+, where bpy = 2,2’bipyridine. Another reason is that polyazaaromatic ligands form stable, chelating, bridging ligands. The azines used as bridging and terminal ligands in this work are pictured in Figure 1.

A Spectroscopic Monitor for Sputter-Etching Processes

Sputter-etching is a convenient technique for metal pattern generation on complex integrated circuits. It is particularly advantageous for multimetal systems because it completely eliminates the possibility of undercutting of the lower metal layers as can occur with chemical etching. A real-time monitoring system has been developed for monitoring the sputter-etching process when it is used for metal pattern generation with a beam lead metallization system consisting of titanium, platinum (or palladium), and gold. The intensity of the uv atomic radiation emitted by sputter-etched atoms which are excited in the sputtering discharge is monitored. The system has been used with both triode and diode types of sputter-etching systems and can reliably be used to tell when a given metal layer has been completely removed. A detailed description of the monitoring system and its performance is given.