Comparative Sorption Properties of Metal(III) Phosphates

Easily synthesized mesoporous aluminum phosphate for the enhanced adsorption performance of U(VI) from aqueous solution

High-yield selective adsorbents and suitable modification methods are both significant for the efficient treatment of U-contaminated wastewater. In this work, a rich-mesoporous aluminum phosphate adsorbent (APO-10) was synthesized by simply increasing the mass of reactants under a fixed solvent volume. After increasing the mass of reactants ten times, APO-10 has the added defect level, the increased specific surface area, and mesoporous structure, and the increased number and enhanced adsorption ability of adsorption active sites (phosphorus-oxygen groups) on the surface, resulting in an enhanced adsorption performance of U(VI) in various environmental conditions. Its ultrahigh adsorption capacity calculated by the Langmuir model can reach 826.44 mg g^-1 at pH = 5.5 and T = 298 K. Its crystal structure did not change after adsorption and remained at 584.40 mg g^-1 after 6 cycles. Additionally, APO-10 shows an excellent uranium-selectivity over 68% from a mixed aqueous solution and has excellent applicability in the acidic and alkaline environment based on dynamic adsorption and desorption column experiments. This study not only provides a high-yield efficient selective adsorbent (APO-10) with excellent anti-radiation structure stability for the treatment of radioactive contamination but also provides a feasible modification method by simply increasing the mass of reactants.

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.

Exchange Behaviour of Amorphous AlPO4 towards Cu2+ Ions

Sorption studies of Cu2+ ions onto AlPO4 were carried out as a function of pH (3–5) and temperature (303–323 K). The extent of sorption was found to increase with an increase in Cu2+ ion concentration, pH and the temperature of the system. The Kurbatov equation along with a new equation based on the law of mass action were found applicable to the sorption data. The sorption mechanism was found to consist of an exchange between the H+ ions from the exchanger and Cu2+ ions from the aqueous solution. The thermodynamic parameters evaluated showed that the process was endothermic and non-spontaneous in nature. FT-IR spectroscopy was also employed to evaluate the mechanism of Cu2+ ion sorption.

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.

Separation of platinum and rhodium from chloride solutions containing aluminum, magnesium and iron using solvent extraction and precipitation methods

The solvent extraction and precipitation methods have been used to develop a process to separate platinum and rhodium from a synthetic chloride solutions containing other associated metals such as (mg/L): Pt-364, Rh-62, Al-13880, Mg-6980, Fe-1308 at <1M HCl acidity. At pH 3.4, the quantitative precipitation of Al and Fe was achieved using 10 wt% Na(3)PO(4)·12H(2)O, with ~4% loss of Pt and Rh due to adsorption phenomenon. The selective separation of platinum was carried out with 0.01 M Aliquat 336 (a quaternary ammonium salt) at an aqueous to organic ratio (A/O) of 3.3 in two stages. Stripping of Pt from loaded organic (LO) at O/A ratio 6 with 0.5 M thiourea (tu) and HCl indicated that ~99.9% stripping efficiency. In stripping studies, needle like crystals of Pt were found and identified as tetrakis (thiourea) platinum (II) chloride ([Pt(tu)(4)]Cl(2)). The selective precipitation of rhodium was performed with (NH(4))(2)S from platinum free raffinate with a recovery of >99%.

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.

Sorption of divalent metal ions on CrPO4

The divalent metal ion sorption (Cu(2+), Cd(2+), Ni(2+), and Pb(2+)) on chromium phosphate (CrPO(4)) was studied as a function of pH, temperature, and concentration of metal ions. The sorption of metal ions is observed to increase with the increase in pH, temperature, and concentration of metal ions in solution. The mechanism of sorption is found to be the exchange of the hydrolyzed metal cations with the protons from solid at high temperature. The sorption at low temperature is found to be accompanied by the precipitation of the corresponding metal phosphates such as Pb(3)(PO(4))(2).

Surface charge properties of Fe2O3 in aqueous and alcoholic mixed solvents

Iron oxide (Fe2O3) was identified and characterized by surface area, X-ray diffractometry, and FTIR analyses. Surface charge densities, point of zero charge (PZC), and surface ionization constants were determined from the potentiometric titration data in various aqueous and aqueous organic mixed solvents in the temperature range 293-313 K. The surface charge densities were observed to decrease with the increase in temperature and concentration of metal ions in both the aqueous and aqueous organic mixed solvents. The absolute values of the surface charge density were found to change in the order aqueous > aqueous/methanol > aqueous/ethanol. Further, the PZC of the iron oxide was observed to shift to the higher pH values in the order ethanol > methanol > aqueous solution, which indicated a decrease in the acidity of the surface -OH groups. The pKa1 and pKa2 values of iron oxide were also determined and then used for determination of the surface potential (psi0) of the solid in aqueous and aqueous organic mixed solvents. The surface potential-surface charge curves generally supplemented the results derived from psi0-pH curves.

Degradation of the textile dyes Basic yellow 28 and Reactive black 5 using diamond and metal alloys electrodes

Basic yellow 28 (SLY) and Reactive black 5 (CBWB), which are respectively methine and sulfoazo textile dyes were individually exposed to electrochemical treatment using diamond-, aluminium-, copper- and iron-zinc alloy electrodes. The generated current was registered with time during electrolysis of the dye solutions and the color variation and the formation of degradation products were followed using HPLC with diode array detection. Four different electrodic materials were tested by applying different potentials in the range -1.0 to -2.5 V and presented 95% color removal and COD removal of up to 65-67% in the case of CBWB dye solution treated with the copper and iron electrodes. Efficiency was enhanced with stirring and flow in relation to the stationary regime. The kinetic parameter reaction rate was used to establish the effect of flow, potential, electrode nature and pH. The formation and characterization of the precipitate formed under certain conditions is reported and discussed.

The mechanisms of Ni2+ ions sorption by AlPO4

Sorption of Ni2+ ions by AlPO4 is studied as a function of concentrations and temperature at pH 7. Potentiometric titration, dissolution and FTIR studies are employed to determine the mechanism of the process of the uptake of Ni2+ ions which is found to be both the ion exchange and the surface precipitation of the corresponding metal phosphates. Freundlich equation is found applicable to the sorption data, and is employed to evaluate the thermodynamic parameters deltaH(o) and deltatS(o).

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.

The Sorption of Divalent Metal Ions on AlPO4

The sorption of Cu(2+), Pb(2+), Ni(2+), and Cd(2+) ions on the aluminum(III) phosphate was observed to increase with increases in the concentration, temperature, and pH of the system. The apparent dissociation (pK(a)), binding (pK(b)) and exchange (pK(ex)) constants of aluminum(III) phosphate were evaluated and found to be dependent upon the temperature and nature of the metal cations. The values of the dissociation constants (pK(a)) followed the order Pb(2+)<Cu(2+)<Cd(2+)<Ni(2+)<K(+), opposite to the values of the binding constants and selectivity shown by the solid. Ion exchange between protons from the surface and metal cations from aqueous solution was found to be responsible for the metal ions sorption by AlPO(4). The values of the dissociation (pK(a)) and exchange (pK(ex)) constants were used to estimate the corresponding apparent thermodynamic parameters (DeltaH(o)(diss), DeltaS(o)(diss) and DeltaH(o)(exch), DeltaS(o)(exch)). The values of DeltaH(o)(diss) and DeltaH(o)(exch) were found to be positive, which showed that both the dissociation and exchange processes were endothermic in nature. The DeltaS(o)(diss) and DeltaS(o)(exch) were also found to be positive, which showed that both the deprotonation and exchange processes on the AlPO(4) were entropy driven and spontaneous.

The effect of metal cations on the phase behavior and hydration characteristics of phospholipid membranes

To characterize the specificity of ion binding to phospholipids in terms of headgroup structure, hydration and lyotropic phase behavior we studied 1-palmitoyl-2-oleoyl-phosphatidylcholine as a function of relative humidity (RH) at 25 degrees C in the presence and absence of Li+, Na+, K+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Zn2+ and Cu2+ ions by means of infrared (IR) spectroscopy. All divalent cations and Li+ shift the gel-to-liquid crystalline phase transition towards bigger RH values indicating stabilization of the gel state. The observed shift correlates in a linearly fashion with the electrostatic solvation free energy for most of the ions in water that in turn, is inversely related to the ionic radius. This interesting result was interpreted in terms of the excess chemical potential of mixing of hydrated ions and lipids. Calcium, zinc and partially lithium, cause a positive deviation from the linear relationship. IR spectral analysis shows that the carbonyl groups become more accessible to the water in the presence of Mg2+, Ca2+, Sr2+ and Ba2+ probably because of their involvement into the hydration shell of the ions. In contrast, Be2+, Zn2+ and Cu2+ dehydrate the carbonyl groups at small and medium RH. The ability of the lipid to take up water is distinctly reduced in the presence of Zn2+ and, partially, of Cu2+ meaning that the headgroups have become less hydrophilic. The binding mode of Be2+ to lipid headgroups involves hydrolyzed water. Polarized IR spectra show that complex formation of the phosphate groups with divalent ions gives rise to conformational changes and immobilization of the headgroups. The results are discussed in terms of the lyotropic Hofmeister series and of fusogenic activity of the ionic species.