Metal ions from solution, adsorption

As shown in Fig. 1 biosorption comprises a variety of processes including ion exchange, chelation, adsorption, and diffusion through cell walls and membranes all of which are dependent on the species used, the biomass origin and, and solution chemistry (Gavrilescu 2004). Biosorption is a fast and reversible process for removing toxic metal ions from solution. 

In their description of metal ion adsorption, Benjamin and Leckie used an apparent adsorption reaction which included a generic relationship between the removal of a metal ion from solution and the release of protons. The macroscopic proton coefficient was given a constant value, suggesting that x was uniform for all site types and all intensities of metal ion/oxide surface site interaction. Because the numerical value of x is a fundamental part of the determination of K, discussions of surface site heterogeneity, which are formulated in terms similar to Equation 4, cannot be decoupled from observations of the response of x to pH and adsorption density. As will be discussed later, It is not the general concept of surface-site heterogeneity which is affected by what is known of x> instead, it is the specific details of the relationship between K, pH and T which is altered. 

Among the different adsorptive materials that have conventionally been used to capture metal ions from solution are activated charcoal (2), zeolites (3, 4), and clays (5). 

In actual experiments, because adsorption is operationally defined as the removal of metal ions from solution, complexation and precipitation are not separated, and adsorption seems to continue to increase at high pH. 

They suggested that metal ion adsorption is initiated at a pH value corresponding to surface nucleation, which seems to relate to the reduction of cation-solvent interactions, as a result of hydrolysis or ligand complex formation, leading to conditions favorable to the adsorption of hydrated metal ions from solution. Their model suggests that metal ion hydrolysis enhances adsorption on Si02, whereas Schindler proposes direct participation by unhydrated ions. 

Coprecipitation processes tend to be more effective than adsorption processes at removing aqueous heavy metal ions from solution. This could be due to a much larger effective surface area becoming available as various "layers" of the colloid form. Alternatively, it may result from the formation of mixed metal hydroxide complexes (either in solution or as a solid) that exhibit greater adsorption characteristics than those of the individual metal ions. 

Experiments to remove metal ions from solution similar to those discussed in Sec. Ill were performed using Zn(II) and Ni(H) with HCO as the adsorbing or coprecipitating colloid. It is not possible to perform adsorption studies of Fe(III) with HCO, because the HFO forms at a lower pH than the HCO. 

When compared to the spheres, the microspheres presented higher adsorption capacity values indicating that the adsorption is possibly limited by external mass transfer resistance (boundary layer effect), reducing intra particle diffusion [141]. In principle, a more finely ground sample of a given cellulose-based material is expected to adsorb more metal ions from solution, under speeified conditions, compared to coarser particles. This statement has been proven in a few studies [5, 21]. When the particle size of sawdust was deereased Ifom 500 pm to 100 pm an increase in metal sorption eapaeity by only a factor of about 2 was observed [5]. 

Considering all we know up to now, the specific properties of zeolites can be summarized as follows. Zeolites are aluminosilicates with defined microporous channels or cages. They have excellent ion-exchange properties and can thus be used as water softeners and to remove heavy metal cations from solutions. Furthermore, zeolites have molecular sieve properties, making them very useful for gas separation and adsorption processes, e.g., they can be used as desiccants or for separation of product gas streams in chemical processes. Protonated zeolites are efficient solid-state acids, which are used in catalysis and metal-impregnated zeolites are useful catalysts as well. 

Abstract In this study, a new natural adsorbent (sumae leaves) for removing Cu (II) ion from the aqueous solutions has been investigated. Leaves of sumae were obtained from Siirt, Tmkey. The tannins were extraeted with acetone water (70 30, v/v) mixture from the leaves of sumac. For the total tannin determination Folin-Ciocalteu method was used and tannin content was found 27%. In batch experiments, pH profile, adsorption time, adsorbent/hquid ratio, initial concentration of metal ions, adsorbent amoimt, particle size of adsorbent and temperature were performed to determine binding properties of adsorbent for the Cu(II) ions. The concentrations of the metal ions in solutions before and after adsorption were measured with an atomic absorption spectrophotometer. 

The removal of metal ions from waste aqueous solutions is of importance to many countries of the world both environmentally and for water re-use. The application of low-cost sorbents including carbonacceous materials, agricultural products and waste by-products has been investigated [1], Several researchers employing wide variety techniques have attempted removal of metal ions from contaminated water bodies. Majorities of these are adsorption on various surfaces. In recent years, agricultured by products have been widely studied for metal removal from water. These include peat [2], pine bark [3], banana peat [4], peanut shells [5], sawdust [6] and leaves [7]. 

The effect of NaCl concentration on the rate of paraquat adsorption on activated clays is reported by Tsai et al. (2003). The rate constant increases with an increase of salts in the aqueous paraquat solution from 0.046 (g mg min at a NaCl concentration of 0.05 M, to 0.059 (g mg" min" at a solution concentration of 2.50 M NaCl. Studying the effect of various alkali metals ions on paraquat adsorption... 

After an extensive study of the adsorption of arsenious oxide by metallic hydroxides,3 Sen concluded that this type of adsorption resembles that of cations by manganese dioxide, and that the chemical affinity between the adsorbent and the substance adsorbed plays an important part, thus differing from adsorption by charcoal. It has been observed that soils having a high absorption capacity for bases also absorb the arsenite ion from solutions of 0-001 to 0-01X concentration.4 The absorption increases with time, without reaching an end-point, and the process follows the normal adsorption equation C1=kC1Jn. The addition of ferric oxide or calcium carbonate to the soil considerably increases the capacity for absorption, but such salts as calcium sulphate or copper sulphate have no effect. 

T1he adsorption of metal ions from aqueous solutions is a phenomenon of immediate interest to workers in many diverse disciplines. The incorporation of metals into geological sediments, removal of metal ions from industrial and civic effluent, interference of trace metal ions in analytical and electroanalytical chemistry, ore flotation, metallurgical leaching processes, and the stability of ceramic slips are all processes which are controlled to a large extent by interaction of metal ions with solid-liquid interfaces. 

The surface of the sample container may interact with the analyte. The surfaces can provide catalysts (e.g., metals) for reactions or just sites for irreversible adsorption. For example, metals can adsorb irreversibly on glass surfaces, so plastic containers are chosen for holding water samples to be analyzed for their metal content. These samples are also acidified with HNO3 to help keep the metal ions in solution. Organic molecules may also interact with polymeric container materials. Plasticizers such as phthalate esters can diffuse from the plastic into the sample, and the plastic can serve as a sorbent (or a membrane) for the organic molecules. Consequently, glass containers are suitable for organic analytes. Bottle caps should have Teflon liners to preclude contamination from the plastic caps. 

The relative equilibrium constants for the adsorption of alkenes on the surfaces of platinum metals are not available from static measurements. Accordingly, the kinetically derived constants have been compared with the association constants of alkenes with metal ions in solution. Of these, the measurements by Tolman are the most instructive. ... 

Cyclic voltammetry can also be used for investigating the influence of surface chemistry on the adsorption of selected heavy metal ions from aqueous solution... 

Faur-Brasquet, C., Kadirvelu, K., and Le Cloirec, P. (2002). Removal of metal ions from aqueous solution by adsorption onto activated carbon cloths adsorption competition with organic matter. Carbon, 40, 2387—92. 

The tendency for easily hydrolyzed metals to appear to be strongly adsorbed on soil minerals may be caused in part by the manner in which adsorption is traditionally measured. Typically, the pH is adjusted over a range, and the amount of metal removed from solution is calculated from the change in solution concentration. As the pH is raised from an acid value, chemisorption is initially favored, but even before adsorption sites become saturated, metal ions cluster into metal oxide or... 

Adsorption from solution—Adsorption is defined as the selective removal of metal salts or metal ion species from their solution by a process of either physisorption or chemical bonding with active sites on the support. Depending upon the strength of adsorption of the adsorbing species, the concentration of the active material through the support may be varied and controlled. 

Waste water treatment Recovery of heavy metal ions from effluent of the galvanizing process,36 treatment of waste from galvanizing baths (Cr, Zn, etc.),37 recovery of precious metals, regeneration of chemical plating baths,38 removal of radioactive elements,39 removal of ions such as chloride ions from a Kraft pulp mill,40 completion of closed system of waste water in factories,41 treatment of adsorption solution of flue gases,42 removal of salt from landfill leachate.43... 

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