The Sorption of Divalent Metal Ions on AlPO4

Functionalized Carbon Nanotubes Encapsulated Alginate Beads for the Removal of Mercury Ions: Design, Synthesis, Density Functional Theory Calculation, and Demonstration in a Batch and Fixed-Bed Process

Various nanomaterials have been envisaged mainly through batch studies for environmental remediation application. The real utilization of these new generation adsorbents in large scale pose a difficulty due to its low density and small size which makes it difficult for isolation after application. In this context, nanoadsorbents polymer composite beads can be seen as a way out. Here, functionalized CNTs (carbon nanotubes) have been fabricated into micro beads with sodium alginate. The alginate-functionalized CNT (Alg-f-CNT) beads were then comprehensively evaluated for batch and fixed-bed column separation of divalent mercury ions from an aqueous medium. The effects of process parameters such as pH, contact time, feed Hg2+ concentration, and temperature were studied. Simulation of the experimental data suggested that adsorption is an endothermic spontaneous process which follows the pseudo-second-order kinetic and Langmuir isotherm model. The desorption of the Hg2+ ion from used adsorbent was possible with 1 M HNO3. The breakthrough curves at different process parameters were investigated during fixed-bed column separation and found to be in good agreement with Thomas model. The regeneration and reusability of the adsorbent were tested up to five cycles without a significant decrease in the removal performance. Density functional theory studies revealed stronger interaction of Alg-f-CNT with Hg compared to free alginic acid and established the role of carboxyl and oxo groups present in the adsorbent in the coordination of the Hg2+ ions. The experimental results demonstrate that functionalized CNT-encapsulated alginate beads are a promising alternate material, which can be used to remove mercury in the fixed-bed column mode of the operation.

Sorption performances of TiO(OH)(H2PO4)·H2O in synthetic and mine waters

The first report on sorption behaviour of a titanium phosphate sorbent containing entirely –H₂PO₄ groups reveals a high exchange capacity and fast kinetics.

Temperature and pH Effect on the Sorption of Divalent Metal Ions by Silica Gel

The sorption of Zn2+, Ni2+ and Cd2+ ions by silica gel was studied as a function of ion concentration, pH and temperature. An increase in all three parameters led to an increase in the extent of sorption for all the metal cations studied. The selectivity of the solid was observed to be in the order Zn2+ > Ni2+ > Cd2+. Sorption of the metal cations was accompanied by the release of H+ ions into the bulk phase. On average two moles of H+ ions were released per mole of metal cation sorbed. The sorption data fitted the linear forms of both the Kurbatov and Langmuir adsorption equations. The values of the binding constants were used to estimate the apparent thermodynamic parameters, ΔH and ΔS, for the adsorption process. FT-IR spectroscopic studies also showed that the uptake of metal cations by the silica gel occurred via a cation-exchange process.

Cation-Exchange Properties of CrPO4

Alkali metal ion exchange (Li+, Na+ and K+) on chromium phosphate (CrPO4) was studied potentiometrically as a function of temperature and metal ion concentration. The shift in the potentiometric titration curves corresponding to the exchange of alkali metal cations increased with increasing pH and concentration of the metal ions, while the opposite results were obtained by increasing the temperature of the system. The affinity of the exchanger for alkali metal ions was also found to be in the order Li+ > Na+ > K+. The data were employed to evaluate the apparent deprotonation constants of CrPO4 and the corresponding thermodynamic parameters ΔH0, ΔS0 and ΔG0.

Equilibrium and kinetics studies of arsenate adsorption by FePO(4)

The present work is focusing on removal of arsenate from aqueous solution using FePO4. The equilibrium study regarding the removal of arsenic by FePO4 was carried out at 298, 308, 318 and 328K. Langmuir parameters were found to increase with the increase in temperature indicating that the adsorption is favorable at high temperature. Kinetic study of arsenate adsorption on FePO4 was also carried out at different temperatures and at pH 6 and 8. Different kinetic models were used to the kinetic data amongst which pseudo second order model was best fitted. The mechanism of the adsorption kinetics was investigated by employing intraparticle diffusion and Richenberg models. The energy of activation (Ea) was found to be 30 and 35.52kJmol(-1) at pH 6 and pH 8, respectively, suggesting chemisorption nature of the adsorption process. The negative entropic values of activation signified the existence of entropy barrier while the positive ΔG(#) values indicated the existence of energy barrier to be crossed over for the occurrence of a chemical reaction. Both the spectroscopic studies and increase in equilibrium pH reveal the anion exchange removal of arsenate from aqueous solution to the solid surface.

Metals removal from soil, fly ash and sewage sludge leachates by precipitation and dewatering properties of the generated sludge

This study concerns the treatment by precipitation of three acidic and metal-rich leachates by using various reagents. Two treatment modes (simple and combined precipitation) have been performed to evaluate the metals removal efficiency and the dewatering ability of the generated sludge. It appears that for the three leachates used, the Ca(OH)(2) addition gave better metals removal at pH 10.0 than the use of NaOH at the same pH. Moreover, the combination of NaOH and Na(2)S allows better removal for Pb(2+), Zn(2+), Cu(2+) and Mn(2+) ions than with NaOH/Na(2)CO(3) or NaOH/Na(2)HPO(4). The dewaterability (vacuum filtration) of precipitates produced during the treatment of soil leachate was established as follows on the basis of the specific resistance to filtration (SRF) values: sulphides (4.3 x 10(12)mkg(-1))<phosphates (6.4 x 10(12) m kg(-1))<hydroxides [Ca(OH)(2)] (14.2 x 10(12) m kg(-1))<hydroxides [NaOH] (19.7 x 10(12) m kg(-1))<carbonates (26.5 x 10(12) m kg(-1)). For the fly ash leachate treatment, the obtained results were quite similar no matter the treatment mode used; the SRF values were in a range of 5-7 x 10(12) m kg(-1), while sludge volume index (SVI) ranged from 39 to 50 mL g(-1). The sludge generated during the treatment of sewage sludge filtrate using phosphate salt gave the best results regarding to SVI and SRF parameters (180 mL g(-1) and 7.6 x 10(12) m kg(-1), respectively). Experimental results show that whatever precipitating agent is used, vacuum filtration is more efficient in water elimination [total solids: 11-73% (ww(-1))] than in centrifugation [5-11% (ww(-1))] from sludge.

An investigation of Cu(II) adsorption by raw and acid-activated bentonite: a combined potentiometric, thermodynamic, XRD, IR, DTA study

Adsorption of Cu(II) by raw bentonite (RB) and acid-activated bentonite (AAB) samples was investigated as a function of the initial Cu(II) concentration, solution pH, ionic strength, temperature, the competitive and complexation effects of ligands (Cl-, SO4(2-), PO4(3-)). Langmuir monolayer adsorption capacity of the RB (42.41 mg g(-1)) was found greater than that of the AAB (32.17 mg g(-1)). The effect of structural charges on the reactivity of the edge groups was evidenced by the particular proton adsorption behaviour of the bentonite samples. The spontaneity of the adsorption process is established by decrease in DeltaG which varied from -0.34 to -0.71 kJ mol(-1) (RB), -1.13 to -1.49 kJ mol(-1) (AAB) in temperature range 303-313 K. Infrared (IR) spectra of the bentonite samples showed that the positions and shapes of the fundamental vibrations of the OH and Si-O groups were influenced by the adsorbed Cu(II) cations. Differential thermal analysis (DTA) results showed that adsorbed Cu(II) cations have a great effect on the thermal behaviour of the bentonite samples. The X-ray diffraction (XRD) spectra indicated that the Cu(II) adsorption onto the bentonite samples led to changes in unit cell dimensions and symmetry of the parent bentonites.

Temperature effect on xanthate sorption by chalcopyrite

Xanthate ions sorption on copper ore (chalcopyrite) is studied as a function of temperature (273-293 K) in the pH range (8-11). The sorption of xanthate ions at all the pH values is observed to increase with the increase in temperature. The changes in pH, dissolution studies of the ore, SO2(4)- concentration determinations, and FTIR studies were employed to probe the mechanism of the process of adsorption. The results are found to fit successfully to the linear form of the Freundlich equation. The isosteric heats of adsorption (DeltaHi) are also calculated and show that the adsorption of xanthate on copper ore under the given experimental condition is endothermic in nature. The values of DeltaHi found are in conformity with the ion exchange sorption of xanthate by the chalcopyrite.

Selective removal of Pb2+ by AlPO4

Aluminium(III) phosphate was observed to have a very high selectivity towards Pb2+ ions. Under similar conditions, the sorption capacities of the exchanger were observed to follow the order: Pb2+ > Zn2+ > Ni2+ > Co2+. The potentiometric titration data were used to determine the deprotonation constants (pKa) of AlPO4, which were dependent upon the temperature and nature of the metal cations present in the aqueous phase. Different physical methods i.e. FTIR, EPM and the wet chemical analyses were used to investigate the uptake mechanism of Pb2+ by the solid, which showed that no new solid phases were present in the solid residue after sorption of Pb2+ at pH 5. The exchange between protons from the surfaceand Pb2+ from solutions was found to be responsible for Pb2+ sorption by aluminum(III) phosphate.