Browsing by Author "Unuabonah, Emmanuel"

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    Adsorption Kinetics of 4-Nitrophenol onto a Cellulosic Material, Mansonia Wood Sawdust and Multistage Batch Adsorption Process Optimization.
    (Elsevier, 2010-09-18) Unuabonah, Emmanuel
    The kinetics of 4-nitrophenol biosorption from aqueous solution using mansonia wood sawdust, a cellulosic material at different dose is probably a two step mechanism involving the adsorption of a hydrogen ion from solution onto the biosorbent surface followed by electrostatic attraction between the positive surface and the anionic adsorbate. The Wu’s expression for the initial biosorption showed that limitations to intraparticle diffusion were higher for higher biosorbent dose. The switch of the rate-controlling step to intraparticle diffusion was observed in the pattern of the intraparticle diffusion plots as three distinct sections. Multistage optimization studies suggested that 193.8 g of Mansonia wood sawdust, three countercurrent batch adsorption stages and 12 min 48 s are required for the removal of 99.5% of 120 mg dm−3 of 4-nitophenol from aqueous solution. The minimum contact time for removal of 4-nitrophenol in each stage is independent of the percentage removal for each stage.
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    Adsorption of Lead and Cadmium Ions from Aqueous Solutions by Tripolyphosphate-Impregnated Kaolinite Clay
    (Elsevier, 2006-06) Unuabonah, Emmanuel
    The pretreatment of Kaolinite clay with tripolyphosphate (TPP) increased the cation exchange capacity (CEC) of Kaolinite clay from 13.45 meq/100 g to 128.7 meq/100 g. The equilibrium adsorption capacity of TPP–Kaolinite clay for Pb2+ and Cd2+ was 126.58 mg/g and 113.64 mg/g, respectively. The presence of Na- and Ca-electrolytes and with increase in their concentrations reduced the selectivity of TPP–Kaolinite clay for Pb2+ than Cd2+. TPP–Kaolinite clay showed higher selectivity for Pb2+ in the presence of these electrolytes and at all concentrations of these electrolytes used for the study. Binary mixtures of Pb2+ and Cd2+ in various concentrations caused a decrease in the adsorption capacity of TPP–Kaolinite for either metal ion. However, this may have caused the adsorption of Cd2+ onto high energy sites on the surface of the TPP–Kaolinite clay. Non-linear Chi-square model analysis of adsorption data using Langmuir, Langmuir–Freudlich, Freudlich, Toth and Temkin isotherms reveals that the adsorption of Pb2+ and Cd2+ by TPP–Kaolinite clay were best described by the Toth and Freudlich isotherms, respectively. At low concentrations (≤500 mg/L) the adsorption of these metal ions showed better fits to the five models with Langmuir–Freudlich and Freudlich isotherms giving the best fits for Pb2+ and Cd2+, respectively.
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    Adsorption of Pb (II) and Cd (II) from Aqueous Solution onto Sodium Tetraborate-modified Kaolinite Clay: Equilibrium and Thermodynamic Studies
    (Elsevier, 2008) Unuabonah, Emmanuel
    Kaolinite clay sample obtained from Ubulu-Ukwu in Delta State of Nigeria was modified with sodium tetraborate to obtain NTB-modified kaolinite clay. XRD measurements of NTB-modified kaolinite adsorbent showed no observable change in the d-spacing of its crystal lattice. Also, the data of XRD confirmed that this kaolinite clay sample is a mixture of kaolinite and Illite clay minerals. The SEM of modified and unmodified samples showed irregular crystal structures. FTIR results proved the surface modification of the kaolinite at –Al–O and –Si–O centers. The NTB-modified adsorbent presented with broader peaks of inner –OH. Modification of kaolinite clay sample with sodium tetraborate decreased its PZC from pH 4.40 to 3.70 while its Specific Surface Area (SSA) was increased from 10.56 m2 g−1 to 15.84 m2 g−1 . Modification with sodium tetraborate reagent increased the adsorption capacity of kaolinite clay from 16.16 mg/g to 42.92 mg/g for Pb (II) and 10.75 mg/g to 44.05 mg/g for Cd (II) at 298 K. Increasing temperature was found to increase the adsorption of both metals onto both adsorbents suggesting an endothermic adsorption reaction. The simultaneous presence of electrolyte in aqueous solution with Pb and Cd (II) was found to decrease the adsorption capacity of NTB-modified adsorbent for Pb and Cd (II). Using the Pearson's Hard and Soft Lewis Acid and Base (HSAB) theory the higher selectivity of unmodified kaolinite clay adsorbent for Pb and NTB-modified kaolinite clay for Cd (II) was justified. The thermodynamic calculations for the modified kaolinite clay sample indicated an endothermic nature of adsorption (ΔHmean + 4.35 kJ mol−1 for Pb(II) and +3.79 kJ mol−1 for Cd (II)) and an increase in entropy as a result of adsorption of Pb (II) and Cd (II) (ΔSmean −21.73 J mol−1 K for Pb (II) and −18.30J mol−1 K for Cd (II)). The small positive values of free energy change (ΔGmean) indicated that the adsorption of Pb (II) and Cd (II) onto the modified adsorbent may require some small amount of energy to make it more feasible. Modeling equilibrium adsorption data obtained suggested that NTB-modified adsorbent sample has homogeneous adsorption sites and fit very well with Langmuir adsorption model. Regeneration studies suggest that ≈85% of the metals were desorbed from both adsorbents. On reuse of the adsorbents only ≈80% of metals were adsorbed. NTB-modified kaolinite clay sample show some very good potentials as a low-cost adsorbent for the adsorption of Pb (II) and Cd (II) from aqueous solutions
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    Adsorption of some heavy metal ions on sulfate- and phosphate-modified Kaolin
    (Elsevier, 2004) Unuabonah, Emmanuel
    Kaolin (bright white lumps) from Ubulu-Ukwu in Delta State of Nigeria was modified with 200 µg mL-1 of phosphate and sulphate anions to give phosphate- and sulfate-modified adsorbents, respectively. The adsorption of four metal ions (Pb2+, Cd2+, Zn2+, and Cu2+) was studied as a function of metal ions concentration. The metal ions showed stronger affinity for the phosphate-modified adsorbent with Pb2+, Cu2+, Zn2+, and Cd2+ giving an average of 93.28%, 80.94%, 68.99%, and 61.44% uptake capacity. The order of preference for the various adsorbents shown by the metal ions was as follows: Pb2+>Cu2+>Zn2+>Cd2+. Desorption studies showed that the phosphate-modified adsorbent had the highest affinity for the metal ions, followed by the sulfate-modified clay while the unmodified clay had the least affinity. The experimental data were fitted by both the Langmuir and Freundlich models
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    Adsorption of Zn2+ and Cu2+ onto sulphate and phosphate-modified Bentonite
    (Elsevier, 2010) Unuabonah, Emmanuel
    The modification of bentonite with sulphate and phosphate increased the cation exchange capacity (CEC) and adsorption of Cu2+ and Zn2+ but decreased the specific surface area (SSA). Phosphate modified bentonite had the highest adsorption capacity for both metal ions. The Fourier transformed infrared spectra indicated the bonding of sulphate and phosphate bentonite with sulphate and phosphate by the hypochromic and hyperchromic shifts are typical of physisorption and chemisorption mechanisms. Phosphate and sulphate were adsorbed through inner-sphere and outer-sphere complex formation. The isotherms were better fitted by the Langmuir model than the Freundlich model.
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    Comparison of sorption of Pb2+ and Cd2+ on kaolinite clay and polyvinyl alcohol-modified kaolinite clay.
    (Elsevier, 2008) Unuabonah, Emmanuel
    Kaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with polyvinyl alcohol (PVA) reagent to obtain PVA-modified Kaolinite clay adsorbent. Scanning Electron Microscopy (SEM) of the PVA-modified adsorbent suggests that Kaolinite clay particles were made more compact in nature with no definite structure. Modification of Kaolinite clay with PVA increased its adsorption capacity for 300 mg/L Pb2+ and Cd2+ by a factor of at least 6, i.e., from 4.5 mg/g to 36.23 mg/g and from 4.38 mg/g to 29.85 mg/g, respectively, at 298 K. Binary mixtures of Pb2+ and Cd2+ decreased the adsorption capacity of Unmodified Kaolinite clay for Pb2+ by 26.3% and for Cd2+ by 0.07%, respectively. In contrast, for PVA-modified Kaolinite clay, the reductions were up to 50.9% and 58.5% for Pb2+ and Cd2+, respectively. The adsorption data of Pb2+ and Cd2+ onto both Unmodified and PVA-modified Kaolinite clay adsorbents were found to fit the Pseudo-Second Order Kinetic model (PSOM), indicating that adsorption on both surfaces was mainly by chemisorption and is concentration dependent. However, kinetic adsorption data from both adsorbent generally failed the Pseudo-First order Kinetic model (PFOM) test. Extents of desorption of 91% Pb2+ and 94% Cd2+ were obtained, using 0.1 M HCl, for the Unmodified Kaolinite clay adsorbent. It was found that 99% Pb2+ and 97% Cd2+, were desorbed, for PVA-modified Kaolinite clay adsorbents within 3 min for 60 mg/L of the metal ions adsorbed by the adsorbents.
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    Comparison of Two-Stage Sorption Design Models for The Removal of Lead Ions by Polyvinylalcohol Modified Kaolinite Clay.
    (Elsevier, 2009) Unuabonah, Emmanuel
    Kaolinite clay obtained from Ubulu-Ukwu, Delta State in Nigeria was modified with polyvinyl-alcohol (PVA) reagent to obtained PVA-modified Kaolinite clay. Kinetic and equilibrium data were obtained for the batch adsorption of Pb2+ onto PVA-modified Kaolinite clay. Time-dependent Langmuir and pseudo-second order kinetic models (TDLM and PSOM) were developed to predict the optimized minimum operating time for the adsorption of Pb2+ onto PVA-modified Kaolinite clay in a two-stage batch adsorber system. Results obtained suggest that the two-stage batch adsorber process leads to improved contact time and increased percentage Pb2+ removal. Data from both models (TDLM and PSOM) were compared using t-test and F-test and were found to be precise enough for use in the optimization of kinetic data for a two-stage adsorption of Pb2+ ions from aqueous solution.
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    Competitive Modeling for the Biosorptive Removal of Copper and Lead Ions from Aqueous Solution by Mansonia Wood Sawdust.
    (Elsevier, 2010) Unuabonah, Emmanuel
    Mansonia wood sawdust is applied as a biosorbent for the removal of copper and lead ions from single and binary aqueous solution. The effect of solution pH, electrolyte, metal ion competition and temperature were examined to obtain insight of its application for industrial waste water treatment. The Langmuir isotherm provided a better fit to experimental data for lead ion sorption with a higher monolayer capacity, while copper ion sorption was best described by the Freundlich and BET isotherms. The combined effect of adsorbing one metal ion in the presence of the other metal ion reduced the adsorption capacity of either metal ion. In a binary solution, removal of lead ions in the presence of copper ions followed the Langmuir isotherm model while the removal of copper ions in presence of lead ions followed both the Langmuir and BET isotherm models.
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    Continuous Synthesis of Multi-Walled Carbon Nanotubes from Xylene Using the Swirled Floating Catalyst Chemical Vapour Deposition Technique
    (Springer, 2011) Unuabonah, Emmanuel
    This work reports the continuous and large-scale production of multiwalled carbon nanotubes (MWCNTs) from xylene/ferrocene in a swirled floating catalyst chemical vapor deposition reactor using argon as the carrier gas. The concentration of ferrocene used was 0.01 g/mL of xylene. In every run, 50-mL xylene gas was used together with xylene/ferrocene mixture injected into the reactor by means of a burette. The MWCNTs produced were characterized using the transmission electron microscopy (TEM) and Raman spectra. TEM analysis showed a poor production rate at 850 °C and a good production in the range of 900–1000 °C with optimal production rate at 950 °C. Furthermore, xylene/ferrocene mixture produced more MWCNTs at 950 °C with H:Ar (1:7) as the carrier gas. The diameters of the MWCNTs in the temperatures studied ranged from 15 to 95 nm with wall thicknesses between 0.5 and 0.8 nm.
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    The Effect of some Operating Variables in the Adsorption of Lead and Cadmium ions unto Modified Kaolin Clay
    (Elsevier: Journal of Hazardous Materials, 2005-12-15) Unuabonah, Emmanuel
    Modification of kaolinite clay mineral with orthophosphate (p-modified sample) enhanced adsorption of Pb and Cd ions from aqueous solutions of the metal ions. Increasing pH of solutions of metal ions, increasing adsorbent dose and increasing concentration of metal ion, increased the adsorption of metal ions. Adsorption of both metal ions simultaneously on both unmodified and p-modified samples indicates that adsorption of one metal ion is suppressed to some degree by the other. The presence of electrolyte and their increasing concentration reduced the adsorption capacities of both unmodified and p-modified samples for the metal ions. Ca-electrolytes had more negative effect on the adsorption capacities of the adsorbents than Na-electrolytes. Ca-electrolytes reduced adsorption capacities of the adsorbents for Pb and Cd ions. From Langmuir plots it was observed that these electrolytes increased the binding energy constant of the metal ions unto the adsorbents especially on the p-modified samples. The rate of adsorption of Pb and Cd ions on p-modified adsorbent were increased and equilibrium of metal ion solution were more quickly reached (8 min for Pb ions and 12 min for Cd ions) with p-modified adsorbent as against 20 min for adsorption of both metal ions on unmodified adsorbent when 200 mg/L of metal ion solutions were used during the kinetic studies. When adsorption data were fitted against Langmuir, Freundlich, Toth and Langmuir–Freundlich isotherms, satisfactory fits were found with the Freundlich isotherm. However, at low concentration of metal ions, data also showed satisfactory fits to Langmuir isotherm.
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    Equilibrium, Kinetic and Sorber Design Studies on the Adsorption of Aniline Blue Dye by Sodium Tetraborate-modified Kaolinite Clay adsorbent.
    (Elsevier: Journal of Hazardous Materials, 2008-01) Unuabonah, Emmanuel
    Raw Kaolinite clay obtained Ubulu-Ukwu, Delta State of Nigeria and its sodium tetraborate (NTB)-modified analogue was used to adsorb Aniline blue dye. Fourier transformed infrared spectra of NTB-modified Kaolinite suggests that modification was effective on the surface of the Kaolinite clay with the strong presence of inner –OH functional group. The modification of Kaolinite clay raised its adsorption capacity from 1666 to 2000 mg/kg. Modeling adsorption data obtained from both unmodified and NTB-modified Kaolinite clay reveals that the adsorption of Aniline blue dye on unmodified Kaolinite clay is on heterogeneous adsorption sites because it followed strongly the Freundlich isotherm equation model while adsorption data from NTB-modified Kaolinite clay followed strongly the Langmuir isotherm equation model which suggest that Aniline blue dye was adsorb homogeneous adsorption sites on the NTB-modified adsorbent surface. There was an observed increase in the amount of Aniline blue adsorbed as initial dye concentration was increased from 10 to 30 mg/L. It was observed that kinetic data obtained generally gave better robust fit to the second-order kinetic model (SOM). The initial sorption rate was found to increased with increasing initial dye concentration (from 10 to 20 mg/L) for data obtained from 909 to 1111 mg kg−1 min−1 for unmodified and 3325–5000 mg kg−1 min−1 for NTB-modified adsorbents. Thereafter there was a decrease in initial sorption rate with further increase in dye concentration. The linearity of the plots of the pseudo-second-order model with very high-correlation coefficients indicates that chemisorption is involved in the adsorption process. From the design of a single-batch adsorber it is predicted that the NTB-modified Kaolinite clay adsorbent will require 50% less of the adsorbent to treat certain volumes of wastewater containing 30 mg/L of Aniline blue dye when it is compared with the unmodified adsorbent. This will be cost effective in the use of NTB-modified adsorbent for the adsorption of Aniline blue dye from water and wastewater.
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    Kinetic and Thermodynamic Aspects of the Adsorption of Pb2+ and Cd2+ Ions on Tripolyphosphate-Modified Kaolinite Clay.
    (Elsevier: Chemical Engineering Journal, 2007) Unuabonah, Emmanuel
    Kaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with tripolyphosphate reagent to obtain TPP-modified Kaolinite clay. The kinetics and thermodynamics of the adsorption of Pb2+ and Cd2+ by TPP-Kaolinite clay were studied. Increasing temperature and initial metal ion concentration increased the sorption capacity of the adsorbent. The rates of adsorption of both Pb2+ and Cd2+ increased with increasing temperature but decreased with increasing initial metal ion concentration and time. The pseudo-second-order initial sorption rates for the sorption of Pb2+ were found to be higher than those of Cd2+. Pseudo-first-order model was found to only describe well, the data obtained in the first 8 min of the adsorption process. The sorption of both metal ions was endothermic and spontaneous with H◦ values of +13.94 kJ mol−1 and +24.93 kJ mol−1 for Pb2+ and Cd2+, respectively. Activation energy values obtained were between +8 kJ mol−1 and +22 kJ mol−1. These values suggest that the rate-controlling step in the adsorption of Pb2+ and Cd2+ by TPP-Kaolinite clay was diffusion-controlled. The sorption of metal ions from binary solutions of both metal ions at different initial metal ion concentrations reduced the initial sorption rates of the adsorption of Pb2+ by TPP-Kaolinite clay and increased that for Cd2+. The adsorption capacity of TPP-Kaolinite clay for both metal ions was also decreased by simultaneous presence of both metal ions.
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    Kinetic and Thermodynamic Studies of the Adsorption of Lead (II) ions onto Phosphate-modified Kaolinite Clay
    (Elsevier, 2007) Unuabonah, Emmanuel
    This study is on the kinetics and thermodynamics of the adsorption of Pb2+ onto phosphate-modified and unmodified kaolinite clay obtained from Ubulu-Ukwu in Delta State of Nigeria. Increasing initial Pb2+ concentration increased the rate of Pb2+ adsorbed with increase in initial Pb2+ concentration from 300 to 1000 mg/L. Increasing Pb2+ concentration also increased the initial sorption rate h, from 1.404 to 13.11 mg g−1 min−1 for phosphate-modified kaolinite clay and 1.04–3.48 for unmodified kaolinite clay as Pb2+ concentration. Increase in temperature was found to increase the initial sorption rate of Pb2+ adsorption onto phosphate-modified adsorbent from 3.940 to 8.85 and 2.55 to 4.16 mg g−1 min−1 for the unmodified adsorbent. The overall sorption rate k, increased only slightly from 5.1 × 10−2 to 9.7 × 10−2 g mg−1 min−1 for phosphate-modified adsorbent, 3.8 × 10−2 to 5.4 × 10−2 g mg−1 min−1 for unmodified adsorbent. The adsorption reaction on both adsorbents was found to be chemically activated reaction and endothermic with energy of activation, E, at 500 mg/L of Pb2+ in solution as 19 and 10.68 kJ mol−1 for phosphate-modified and unmodified adsorbents, respectively. The positive values of both H◦ and S◦ obtained suggest an endothermic reaction and in increase in randomness at the solid–liquid interface during the adsorption of Pb2+ onto the adsorbents. G◦ values obtained were all negative indicating a spontaneous adsorption process. The presence of Cd2+ decreased both initial sorption rate and the amount of Pb2+ adsorbed on phosphate-modified and unmodified adsorbents at equilibrium. The adsorption process follows a pseudo-second-order reaction scheme.
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    Kinetic and Thermodynamics of the Removal of Zn2+ and Cu2+ from Aqueous Solution by Sulphate and Phosphate Modified Bentonite Clay
    (Elsevier, 2010) Unuabonah, Emmanuel
    The modification of pristine Bentonite clay with sulphate and phosphate anions was found to increase its cation-exchange capacity (CEC), adsorption capacity and overall pseudo-second order kinetic rate constant for the adsorption of Cu2+ and Zn2+. Modification with sulphate and phosphate anion decreased the specific surface area of pristine Bentonite clay. Phosphate-modified Bentonite clay was found to give the highest adsorption capacity for both metal ions. The adsorption process was observed to be endothermic and spontaneous in nature for both metal ions with Zn2+ being more adsorbed. Modification with phosphate anion increased the spontaneity of the adsorption process. The effective modification of pristine Bentonite clay with sulphate anion was confirmed from hypochromic shifts in the range of 13–18 cm−1 which is typical of physisorption while modification with phosphate anion was confirmed by its hyperchromic shifts typical of chemisorption in the infrared red region using Fourier transformed infrared spectroscopy (FTIR). Using the model efficiency indicator, kinetic data were found to show very strong fit to the pseudo-second order kinetic model implying that the adsorption of Cu2+ and Zn2+ were basically by chemisorption.
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    Modeling of Fixed-bed Column Studies for the Adsorption of Cadmium onto Novel Polymer–clay Composite Adsorbent.
    (Elsevier, 2010-03) Unuabonah, Emmanuel
    Kaolinite clay was treated with polyvinyl alcohol to produce a novel water-stable composite called polymer–clay composite adsorbent. The modified adsorbent was found to have a maximum adsorption capacity of 20,400 ± 13 mg/L (1236 mg/g) and a maximum adsorption rate constant of ≈7.45 × 10−3 ± 0.0002 L/(min mg) at 50% breakthrough. Increase in bed height increased both the breakpoint and exhaustion point of the polymer–clay composite adsorbent. The time for the movement of the Mass Transfer Zone (ı) down the column was found to increase with increasing bed height. The presence of preadsorbed electrolyte and regeneration were found to reduce this time. Increased initial Cd2+ concentration, presence of preadsorbed electrolyte, and regeneration of polymer–clay composite adsorbent reduced the volume of effluent treated. Premodification of polymer–clay composite adsorbent with Caand Na-electrolytes reduced the rate of adsorption of Cd2+ onto polymer–clay composite and lowered the breakthrough time of the adsorbent. Regeneration and re-adsorption studies on the polymer–clay composite adsorbent presented a decrease in the bed volume treated at both the breakpoint and exhaustion points of the regenerated bed. Experimental data were observed to show stronger fits to the Bed Depth Service Time (BDST) model than the Thomas model.
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    Optimization of Kinetic Data for Two-Stage Batch Adsorption of Pb(II) Ions onto Tripolyphosphate-Modified Kaolinite Clay.
    (Society of Chemical Industry, 2009) Unuabonah, Emmanuel
    Most adsorption studies consider only the adsorption of pollutants ontolow cost adsorbentswithout considering how equilibrium and kinetic data can be optimized for the proper design of adsorption systems. This study considers the optimization of kinetic data obtained for the removal of Pb(II) from aqueous solution by a tripolyphosphate modified kaolinite clay adsorbent. Modification of kaolinite clay with pentasodium tripolyphosphate increases its cation adsorption capacity (CEC) and specific surface area (SSA) from 7.81 to 78.9 meq (100 g)−1 and 10.56 to 13.2 m2 g−1 respectively. X-ray diffraction patterns for both unmodified and tripolyphosphate-modified kaolinite clay suggest the modification is effective on the surface of the clay mineral. Kinetic data from the batch adsorption of Pb(II) onto the tripolyphosphate-modified kaolinite clay adsorbent were optimized to a two-stage batch adsorption of Pb(II) using the pseudo-second-order kinetic model. Mathematical model equations were developed to predict the minimum operating time for the adsorption of Pb(II). Results obtained suggest that increasing temperature and decreasing percentage Pb(II) removal by the adsorbent enhanced operating time of the adsorption process. The use of two-stage batch adsorption reduces contact time to 6.7 min from 300 min in the single-stage batch adsorption process for the adsorption of 2.5 m3 of 500 mg L−1 Pb(II) under the same operating conditions. Results show the potential of a tripolyphosphate-modified kaolinite clay for the adsorption of Pb(II) from aqueous solution and the improved efficiency of a two-stage batch adsorption process for the adsorption of Pb(II) even at increased temperature.
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    Pb/Ca Ion Exchange on Kaolinite Clay Modified with Phosphates
    (Journal of Soils and Sediments, 2010) Unuabonah, Emmanuel
    Pollution of soils by heavy metal ions has attracted global concern because of the subsequent translocation into food chain which when taken up to a certain level can cause serious health problems. The influence of preadsorbed calcium by kaolinite clay modified with orthophosphate and tripolyphosphate reagents on the mobility of Pb2+ in kaolinitic soil system is studied. This is with the view to understand the fate of Pb2+ in phosphate-fertilized kaolinitic soils that are subsequently limed. Potassium dihydrogen phosphate (98%) and sodium tripolyphosphate (87%) were purchased from Aldrich and Merck, respectively. They were used to modify locally obtained kaolinite clay. These adsorbents were further pretreated with 0.1 M Ca(NO3)2. These phosphate-modified kaolinite clay adsorbents pretreated with Ca2+ were used in the adsorption of Pb2+ from aqueous solution in a batch mode. X-ray diffraction spectra of the various adsorbents indicated that modification of kaolinite clay with the reagents were effective on the surface of the clay mineral and not on the crystal structure of the clay mineral. Treatment with 0.1 M Ca(NO3)2 gave K–Ca (for unmodified kaolinite clay), K–O–Ca (for potassiumdihydrogen-phosphate-modified kaolinite clay), and K– TPP–Ca (for sodium-tripolyphosphate-modified Kaolinite clay) samples. The pHPZC of the adsorbents before pretreatment with Ca2+ decreased when compared with the unmodified kaolinite clay. Further pretreatment of these adsorbents with Ca2+ largely decreased the adsorption capacity of all three adsorbents for Pb2+ from aqueous solution due to the higher reactivity of Ca2+ compared with Pb2+. Data from all three adsorbents failed the nonlinear single Langmuir model fit while data from K–O–Ca adsorbent failed the competitive Langmuir model fit. ΔSo data were used to support the proposed structures of adsorbed Pb2+ on the various adsorbents. ΔHo for Pb/Ca exchange was endothermic in nature for K–O–Ca adsorbent and K–TPP–Ca adsorbents. However, it was exothermic for K–Ca adsorbent. ΔGo for Pb/Ca exchange on modified adsorbents was nonspontaneous but was spontaneous for K–Ca adsorbent. With increasing temperature, ΔGo for the ion exchange reaction became more spontaneous for all adsorbents. Pb/Ca ion exchange on phosphate-modified kaolinite clay adsorbents is endothermic in nature and nonspontaneous. However, with increase in temperature, spontaneity of the ion exchange reaction increased. This study suggests that liming of kaolinitic soils will decrease strongly the adsorption capacity of the soil for Pb2+, especially when they have initially adsorbed phosphates.
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    Removal of Cu2+ and Cd2+ from aqueous solution by Bentonite clay modified with binary mixture of Goethite and Humic Acid.
    (Springer, 2010) Unuabonah, Emmanuel
    Pre-modification of bentonite clay with goethite, humic acid, and a binary mixture of goethite and humic acid reagents increased its cation exchange capacity from 95 to 105.32, 120.4, and 125.8 meq/ 100 g of bentonite clay, respectively. The effective pre-modification of bentonite clay with goethite, humic acid, and goethite–humic acid reagents was confirmed from their Fourier transform infrared spectra which suggested that modification was effective on the AlAlOH and Si–O sites for goethite and humic acid modification and AlAlOH for goethite– humic acid modification. The presence of 0.001 M NaNO3 electrolyte increased the adsorption capacity of bentonite clay. Temperature was observed to favor the adsorption of Cu2+ and Cd2+ onto both the raw and modified bentonite clay samples. The goethite– humic acid-modified bentonite gave the best adsorption capacity of ≈10 and 16 mg/g at 30 and 50°C, respectively, for both metal ions. The inner sphere complexation mechanism was suggested for the adsorption of both metal ions onto the modified adsorbents. Modifying bentonite clay with a binary mixture of goethite and humic acid reduced the selectivity of bentonite clay for either Cu2+ or Cd2+. Preadsorbed goethite and humic acid on bentonite clay will further reduce the mobility of heavy metal ions in soils and in aquatic environments
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    Removal of Lead and Cadmium from aqueous solution by Polyvinyl alcohol-modified Kaolinite clay: a novel nanoclay adsorbent.
    (Multi-Science Publishing Co. Ltd, 2008) Unuabonah, Emmanuel
    Kaolinite clay was modified with polyvinyl alcohol (PVA) to obtain a PVA–nano-clay adsorbent. X-Ray diffraction measurements of the adsorbent showed no observable change in the d-spacing of its crystal lattice. Scanning electron microscopy of the PVA-modified nano-clay adsorbent indicated the presence of irregular crystal structures. Infrared spectroscopy suggested that the PVA–nano-clay adsorbent basically possessed outer –OH functional groups. This adsorbent was found to have an adsorption capacity of 56.18 mg/g for Pb2+ ions and 41.67 mg/g for Cd2+ ions. The adsorption data obtained was well explained by the Diffuse Layer Model (DLM), which implies that the adsorption of both metal ions onto the modified adsorbent was via an inner-sphere surface complexation mechanism. The ∆H0 values for the adsorption of both metal ions onto the PVA–nano-clay were –12.48 kJ/mol for Pb2+ ions and –13.49 kJ/mol for Cd2+ ions, with both ions exhibiting negative adsorption entropies. Data-fitting indicated that both the PVA–nano-clay and the unmodified adsorbent possessed homogeneous and heterogeneous adsorption sites. Virtually complete desorption (ca. 99%) of both metal ions occurred from PVA–nano-clay within 3 min.
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    Removal of Lead from Aqueous Solution by Palm Kernel Fibre
    (SABINET, 2005) Unuabonah, Emmanuel
    The sorption of lead on palm kernel fibre, an agricultural waste product, has been studied. The sorption process was studied as a function of initial lead concentration and initial solution pH. The percentage lead removal was found to increase with increasing initial solution pH up to pH 5 and then to decrease as pH was increased to 6. The pseudo-second order kinetic rate model was employed in the analysis of the kinetics of lead uptake onto the palm kernel fibre. The results show that the pseudo-second order model fits the experimental data with high coefficients of determination (r2). The equilibrium sorption capacity was found to be 33.33 mg g–1 when 1.0 g of fibre was contacted with 90 mg dm–3 of lead solution at pH 5. Mathematical expressions were derived to relate the pseudo-second order rate constant, k, and the change in solution pH with initial lead concentration.