courtie mahamadi | Bindura University of Science Education (original) (raw)

Papers by courtie mahamadi

Water hyacinth (Eichhornia crassipes), has attracted significant attention as the world's worst i... more Water hyacinth (Eichhornia crassipes), has attracted significant attention as the world's worst invasive aquatic plant due to its extremely rapid proliferation and congest growth, presenting serious challenges in navigation, irrigation, and power generation. Attempts to control the weed have proved to be costly with minimum results. However, the same plant has demonstrated an amazing ability to absorb and concentrate many toxic metals from aquatic environments. Consequently, research activity on utilization of the plant has been registered over the last few decades. This article reviews literature related to the utilization of E. crassipes in the biosorption and recovery of metals from aquatic environments. Availability in large quantities, high biosorption capacity, renewability and low cost determine the extent to which biosorbents can be adapted technologically. Sorption dynamics through classical and competitive models, effect of physical and chemical treatment, pH, temperature, initial metal concentration and biosorbent dose on metal removal by water hyacinth is discussed.

Preconcentration of cadmium(II) by adsorption onto untreated Saccharomyces cerevisiae, was invest... more Preconcentration of cadmium(II) by adsorption onto untreated Saccharomyces cerevisiae, was investigated. The study was carried out at 25 0 C, with a low initial metal concentration (2 mg/L), and under varying conditions of initial pH (buffered and uncontrolled-pH), sorbent doses (0.250-1.00 g) as well as water hardness. Cadmium uptake was observed to increase with yeast biomass, exhibiting an equilibrium that was well described by the Langmuir adsorption model, thus suggesting monolayer coverage of the yeast cell wall. The uptake of Cd 2+ was a rapid process, with over 60% sorption in the first 15 min, following a pseudo-second order adsorption with a maximum rate constant of 36.32 g/mg min. Yeast sorption capacity increased with pH, with a maximum value of 0.7428 mg/g at pH 7.3. Three sorption phases were observed at the initial Cd 2+ concentration of 2 mg/L (200 ml), 0.400g yeast, shaking rate of 150 rpm, thus suggesting involvement of at least three different functional groups in the adsorption process. Cd 2+ uptake was depressed by a factor of 10 as water hardness was varied from 9.45 to 133.09 mg CaCO 3 /L, suggesting that competition with calcium ions strongly reduces the affinity of the biomass for cadmium. The results of this study are important for optimizing conditions for removal of toxic trace metals from aqueous environments.

Inductively coupled plasma atomic emission spectrometry (ICP-AES) is one of the most widely used ... more Inductively coupled plasma atomic emission spectrometry (ICP-AES) is one of the most widely used and extremely important tools for trace element analysis today. The technique however still suffers from matrix effects, especially those due to easily ionizable elements (EIEs). Current theory of atomic spectrometry assumes Local Thermal Equilibrium (LTE), and EIE interference effects cannot be explained fully as long as all the electrons in the plasma are regarded as equivalent in accordance with the LTE theory. If however it is assumed that electronic collisions with heavy particles can occur before or after thermal equilibration, then electrons can be expected to experience different activation energies depending on whether collisions occurred before or after thermal equilibration. This paper reviews recent work carried out to characterize EIE interference effects during ICP-AES, flame AAS and flame AES in terms of ion-electron collisional radiative recombination activation energy. The work is based on a simplified rate model showing that when analytes are determined by atomic spectrometry in the absence and then in the presence of EIEs as interferents, the change in collisional radiative recombination activation energy, ∆E a , is zero when the system conforms to LTE. Several analyte-interferent systems have been studied, and results obtained so far lead to the conclusion that departure from LTE results from collisions involving electrons in the ambipolar diffusion state. Factors affecting both pre-LTE and LTE collisions, as well as a possible collisional radiative recombination mechanism designed to account for the ∆E a values obtained are discussed.

Cadmium biosorption properties of non-living, dried river green alga from a river source, and wat... more Cadmium biosorption properties of non-living, dried river green alga from a river source, and water hyacinth weed, Eichhornia crassipes from a lake in Zimbabwe have been investigated. The cadmium uptake was found to depend on initial pH, uptake being apparently minimal at low pH values and increasing with an increase in pH. Cadmium biosorption kinetics by both samples is fast, with 80% of total uptake occurring within 60 min. The effect of initial solution pH and initial cadmium concentration on cadmium biosorption from a cadmium solution has been studied. The data for algal biomass fitted the Langmuir monolayer adsorption isotherm, while the biosorption of the metal by water hyacinth weed fitted the Freundlich adsorption isotherm with 1/n values all less than 1. Maximum metal uptake capacities were recorded using 0.35 g of biomass and a 250 mg L −1 cadmium solution at pH 6.5 and at 25°C and these were about 85 and 50 mg L −1 for water hyacinth weed and green alga, respectively, showing that water hyacinth weed offered a greater potential for cadmium uptake. The absorption was described by pseudo-second order rate model and the rate constant and equilibrium sorption capacity are reported.

The thermodynamic parameters relating to the activated complex for the heterogeneous dilute acid ... more The thermodynamic parameters relating to the activated complex for the heterogeneous dilute acid hydrolysis of the difficultly accessible portions of microcrystalline cellulose, ΔH 0 ‡ and ΔS 0 ‡ were determined from the measured apparent rate constants k c in 0.3 M, 1.0 M and 1.3 M HCl containing 0.00 M, 0.08 M and 0.20 M KBr at 60, 70, 75, and 80 0 C using a loss-in-weight method. When hydrolysis was carried out in 0.3 M HCl only, ΔH 0 ‡ and ΔS 0 ‡ values of +105 kJ moland +549 Jk -1 , respectively, were obtained. These values decreased with increasing concentration of inert electrolyte. However when the measurements were made at higher HCl concentration of 1.0 M, the values of the parameters increased with added salt concentration. Two possible mechanisms are presented, to account for the differences in variation of the thermodynamic parameters.

Removal of Methylene Blue (MB) and Crystal Violet (CV) dyes from monocomponent and binary aqueous... more Removal of Methylene Blue (MB) and Crystal Violet (CV) dyes from monocomponent and binary aqueous solutions by water hyacinth-E. Crassipes roots fixed on alginate (a low-cost adsorbent) has been investigated. The extent of adsorption was evaluated as a function of solution pH, initial dye concentration, and bead biomass loading. Kinetic sorption data were analysed by widely used models: pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The results showed that pseudo-second-order model better described the biosorption experimental data than the pseudo-first-order kinetic model for both dyes, whilst the Elovich model fitted the biosorption experimental data at lower dye concentrations. The intraparticle diffusion model indicated that sorption of CV and MB was characterized by rapid surface adsorption coupled with slow film diffusion process at higher initial dye concentration and at all initial bead biomass loading. The range of mean free energy values confirmed physical adsorption as the mechanism for dye removal from solution.

Temnocalyx obovatus is widely found in many areas in Zimbabwe, Nigeria and Zambia where it is use... more Temnocalyx obovatus is widely found in many areas in Zimbabwe, Nigeria and Zambia where it is used to treat a variety of ailments. Phenolic compounds in T. obovatus assessed by Folin-Ciocalteu method varied from 1.18 to 2.89 mg tannic acid g -1 . Acetone extract showed the greatest flavonoids, flavonols and proanthocyanidins content 5.12, 4.13 and 3.07 mg catechin g -1 respectively. 2, 2-diphenyl-1picrylhydrazyl radical (DPPH . ) scavenging effect, Ferric reducing ability and egg lipid peroxidation inhibition assays were adopted to evaluate antioxidant activity. Acetone extracts exhibited the greatest antioxidant activity for all the assays, followed by methanol extracts. Hexane extracts showed the weakest activity. Correlation studies showed that antiradical activity is explained more by flavonols and proanthocyanidins (73%) and flavonoids (71%) and weakly by phenolic contents (43%). The results revealed significant phenolic capacity and antioxidant potential of T. obovatus to warrant its use as a source of antioxidants. It can be added to foods, such as, meat and soups for enhancement of nutritional content and promotion of health.

A simplified rate model for the interference effects of easily ionized elements on analyte absorb... more A simplified rate model for the interference effects of easily ionized elements on analyte absorbance and emission signals in Flame atomic absorption spectroscopy, FAAS, is presented showing that when the analyte is determined in the absence and presence of the interferent, the change in the collisional radiative recombination activation energy, DE a , is zero when the systems conform to local thermal equilibrium. The proposed model also shows that DE a can be calculated from the slope of the plot of A 0 =A or I 0 =I versus the interferent-to-analyte ion number density ratio, where A and I denote absorbance and emission signal intensities, respectively, and the prime denotes presence of the interferent. DE a values of À1.5168 and À1.6924 eV where obtained when Mg was determined by FAAS in the presence of excess Ca and Sr respectively, and values of À6.62, À9.83, and À13.52 eV were obtained when CaI, CaII, and MgII respectively were determined in the presence of excess Li, confirming that these systems are not in LTE. Possible causes for departure from LTE and possible collisional radiative recombination mechanisms consistent with the results are discussed.

The occurrence of toxic metals in waters is a major health issue. Polluted waters can be cleaned ... more The occurrence of toxic metals in waters is a major health issue. Polluted waters can be cleaned by biosorption, which uses organisms such as algae, bacteria, fungi and plants that adsorb metals. In particular, water hyacinth-Eichhornia crassipes-is a promising biosorbent. Here we tested novel alginate-immobilised water hyacinth beads for the removal of Cu from aqueous solutions. Results show that successful service and regeneration continuous cycles were performed using a packed-bed, flow-through column of fixed internal diameter 1.2 cm, at room temperature and pH 5.1, with variation in initial metal concentration, bed depth and flow rate. The eluant used was 1 % w/v CaCl2 acidified at pH 3. A concentration factor of 12 and elution efficiency up to 98 % were observed in five service and regeneration cycles performed. The equilibrium adsorption capacity of Cu remained almost constant at about 29 mg/g. To conclude, we show for the first time that alginateimmobilised water hyacinth beads can uptake and adsorb Cu very efficiently in a continuousflow mode, hence highlighting their great potential for removal of toxic metals from aquatic environments.

Pollution from synthetic dyes has emerged to be a significant environmental issue over the past f... more Pollution from synthetic dyes has emerged to be a significant environmental issue over the past few decades. This has mainly been triggered by the increasing global dye production, possible toxic effects, undesirable colour and high persistence in the environment. Biosorption, which involves dye removal from aqueous solution by passive linkage in live and dead biomass, has shown great potential in removing dyes from aquatic environments. Among aquatic macrophytes, water hyacinth, Eichhornia crassipes, has shown great potential as a biosorbent. In this work, we investigated the removal of two basic dyes, methylene blue and crystal violet, using E. crassipes immobilized on alginate. Results showed that the Langmuir model better described the equilibrium sorption data when compared to the Freundlich model. Optimum amounts of methylene blue and crystal violet dyes were adsorbed in the alkaline pH range (8-10), 8 % biomass dose, and the amount of dye removed increased with increasing initial dye concentration. The equilibrium monocomponent adsorption capacities for the dyes were 111.1 and 43.5 mg/g, while the binary adsorption capacities were 26.1 and 11.6 mg/g for methylene blue and crystal violet, respectively. To conclude, we show for the first time that E. crassipes fixed on alginate beads can uptake and adsorb methylene blue and crystal violet dyes very effectively in batch systems and show great potential for dye removal from aquatic environments.

Phenolic compounds yield in plant extracts depend on the method employed in the extraction proces... more Phenolic compounds yield in plant extracts depend on the method employed in the extraction process. In this study, we investigated systematically, a method of determination of extraction yield of antioxidant compounds from Temnocalyx obovatus. A sample treatment and preparation protocol that employs strict statistical treatment to ensure sample homogeneity was applied. As preliminary indicator of homogeneity, total nitrogen and phosphorus were determined and an iterative process using Levene test was applied to statistically test the homogeneity of the ground T. obovatus leaves. At p = 0.01, homogeneity of the plant material was achieved on the third ground sample. Among the six solvents used, methanol gave the best yield of extractable phytochemicals and a butylated hydroxytoluene-spike recovery of 77%, whereas diethyl ether gave the lowest yield and a butylated hydroxytoluene-spike recovery of 63%, suggesting that optimal yields tended to be favoured by more polar solvents.

In this paper, batch kinetic studies and quantitative structure-activity relationships (QSARs) mo... more In this paper, batch kinetic studies and quantitative structure-activity relationships (QSARs) models were used to determine the effect of initial pH, biomass loading and initial metal ion concentration on the kinetics and equilibrium behavior of metal adsorption onto immobilized Eichhornia crassipes beads. Linear regression indicated that chemisorption was the main sorption mechanism under optimum operating conditions. The highest rate constants were 0.016 (mg g-1 min-1) for Cd2+ ions at pH 6.5 and 0.035 (mg g-1 min-1) at pH 4.5 for Pb2+ ions. When conditions were varied the sorption mechanism became more complex with intraparticle diffusion affecting the rate at low pH, high biomass loading and high initial metal ion concentration. The values of qmax (mg/g) and hence the preference of the biomass for binding were found to follow the order: class B (Soft ions: Pb2+ and Ag+)>borderline ions (Cr3+, Cd2+, Cu2+, Zn2+, Co2+)>Class A (hard ions: Sr2+ and K+). It was concluded that covalent bonding played a significant role in biosorption of soft metal ions and ionic bonding for borderline and hard ions.

The biosorption of different metal ions (Cu 2+ , Zn 2+ , Ni 2+ , Pb 2+ and Co 2+ ) by dried roots... more The biosorption of different metal ions (Cu 2+ , Zn 2+ , Ni 2+ , Pb 2+ and Co 2+ ) by dried roots of Canna indica biomass was investigated using a batch sorption technique. The equilibrium retention capacities of the metal ions determined from the Langmuir isotherm showed that C. indica had the largest sorption capacity for Pb 2+ ions and the least sorption for Ni 2+ . The results also showed that garlic-treatment of C. indica biomass enhanced its sorption capacity for the divalent metal ions, with the enhancement factor varying from 1.22 to 1.44. The biosorption process was found to be exothermic for all metal ions studied (∆H values varying from -4.438 to -12.716 kJ mol -1 ), with physisorption being the most likely mechanism of uptake. In conclusion, studies on biosorption of heavy metals by C. indica are important because they may contribute in aiding the innovative removal of metal ions from contaminated industrial effluents. @JASEM

A simplified rate model is presented showing that when analytes are determined by atomic spectros... more A simplified rate model is presented showing that when analytes are determined by atomic spectroscopy first in the absence, and then in the presence, of easily ionizable elements (EIEs) as interferents, the change in collisional radiative recombination activation energy, ∆Ea, is zero when the system conforms to local thermal equilibrium (LTE). ∆Ea values of -7.462, -7.925, and -8.898 eV were obtained when Ca(II), Mg(II), and Sr(II), respectively, were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES) in the absence and presence of excess Li, while ∆Ea values of -6.477 and -7.481 eV were obtained when Mg(II) and Sr(II), respectively, were determined in the absence and presence of excess K as interferent. A value of -2.223 eV for ∆Ea was obtained when Mg(I) was determined by air-acetylene flame atomic emission spectrometry (FAES) in the absence and presence of excess K. The data confirm that all the systems studied were not in LTE, and suggest pre-LTE collisional radiative recombination in the absence of the interferent in all cases, and that collisional radiative recombination involving electrons from the interferent can occur from the ambipolar diffusion state or the LTE state. Possible causes for departure from LTE, and a possible collisional radiative recombination mechanism to account for the ∆Ea values obtained, are discussed.

In this study, heat and chemically treated sand was applied as an adsorbent for the removal of fl... more In this study, heat and chemically treated sand was applied as an adsorbent for the removal of fluoride ions from aqueous solutions. The influence of different parameters such as calcination time, dosage, initial fluoride concentration and pH were evaluated. Results indicated that activated sand can be used for defluoridation of water. This can be achieved by coating sand with 10% Fe 2 O 3 , a calcination time of 3 h and pH around 6. The adsorption also increased with initial fluoride concentration and adsorbent dose. This study also showed that up to 90% of fluoride was adsorbed with 12 g of adsorbent in 50 ml of 10 mg/L fluoride solution. The sorption data were best described by the Freundlich isotherm. The maximum adsorption capacity was found to be 10.3 mg/g. According to these findings, physicochemically modified sand has potential application as an adsorbent for fluoride ions removal.

The potential of water hyacinth-Eichhornia crassipes biomass immobilized in calcium alginate for ... more The potential of water hyacinth-Eichhornia crassipes biomass immobilized in calcium alginate for the adsorption of Ni(II) from water was studied using the Langmuir and Freundlich adsorption models. The equilibrium adsorption data were obtained at different initial Ni(II) concentrations = 0.05 -2 mg/L, temperature = 30˚C ± 0.2˚C, agitation rate = 150 rpm, equilibration time = 3 hr, biosorbent dose = 4 g/L, and pH range = 4 -7.4. Langmuir isotherms gave monolayer sorption capacities ( ) of 26.5, 44.3 and 53.0 mg/g for the removal of Ni(II) in the presence of methanol, without added organic substance, and in the presence of acetonitrile, respectively. These findings were also confirmed by the trend in the Freundlich isotherm parameter ( m q 1 n < 1). Interpretation of the sorption data in terms of the separation factor, S F , suggested that the removal of Ni(II) from water mainly occurred through a chemisorption mechanism. Desorption experiments to recover Ni(II) from the adsorbent showed that highest amounts of the metal could be removed from the adsorbent when previously adsorbed in the presence of 1-(2-Thiazolylazo)-2-naphtol (TAN) (>90%). The results from these studies indicated that E. crassipes fixed on calcium alginate beads is a viable metal enrichment media that can be used freely immersed in solution to achieve very high adsorption capacities and possible preconcentration of Ni(II) in aquatic environments.

In this paper, we have presented the results of Cu(II) removal by alginateimmobilized water hyaci... more In this paper, we have presented the results of Cu(II) removal by alginateimmobilized water hyacinth beads. Batch equilibrium and kinetic experiments were conducted to determine maximum adsorption capacity under various experimental conditions. A sorption capacity of 61.0 mg/g was obtained using a biosorbent dose of 0.5 mg/l. The hyacinth-alginate beads formed were considerably resistant to swelling in acidic and aqueous media, but were less resistant in alkaline media. Sulphuric acid and calcium chloride solutions were effective desorbing agents, achieving up to 100% desorption, with the acid showing faster kinetics. Sorption capacity decreased slightly after 5 sorptiondesorption cycles indicating that both agents could be used as effective eluting agents. However, strong complexing agents such EDTA were found to be unsuitable for regeneration as they destroy the beads. In conclusion, entrapment of water hyacinth biomass in alginate improves both its sorption capacity and mechanical properties, thus presenting the biosorbent as a possible ingredient for continuous flow reactors.

Environmental protection requires the use of natural products instead of chemicals to minimize po... more Environmental protection requires the use of natural products instead of chemicals to minimize pollution and adsorption has now been recognized as an effective and economic method. This investigation utilized adsorption capacity ratios,

Water hyacinth (Eichhornia crassipes), has attracted significant attention as the world's worst i... more Water hyacinth (Eichhornia crassipes), has attracted significant attention as the world's worst invasive aquatic plant due to its extremely rapid proliferation and congest growth, presenting serious challenges in navigation, irrigation, and power generation. Attempts to control the weed have proved to be costly with minimum results. However, the same plant has demonstrated an amazing ability to absorb and concentrate many toxic metals from aquatic environments. Consequently, research activity on utilization of the plant has been registered over the last few decades. This article reviews literature related to the utilization of E. crassipes in the biosorption and recovery of metals from aquatic environments. Availability in large quantities, high biosorption capacity, renewability and low cost determine the extent to which biosorbents can be adapted technologically. Sorption dynamics through classical and competitive models, effect of physical and chemical treatment, pH, temperature, initial metal concentration and biosorbent dose on metal removal by water hyacinth is discussed.

Preconcentration of cadmium(II) by adsorption onto untreated Saccharomyces cerevisiae, was invest... more Preconcentration of cadmium(II) by adsorption onto untreated Saccharomyces cerevisiae, was investigated. The study was carried out at 25 0 C, with a low initial metal concentration (2 mg/L), and under varying conditions of initial pH (buffered and uncontrolled-pH), sorbent doses (0.250-1.00 g) as well as water hardness. Cadmium uptake was observed to increase with yeast biomass, exhibiting an equilibrium that was well described by the Langmuir adsorption model, thus suggesting monolayer coverage of the yeast cell wall. The uptake of Cd 2+ was a rapid process, with over 60% sorption in the first 15 min, following a pseudo-second order adsorption with a maximum rate constant of 36.32 g/mg min. Yeast sorption capacity increased with pH, with a maximum value of 0.7428 mg/g at pH 7.3. Three sorption phases were observed at the initial Cd 2+ concentration of 2 mg/L (200 ml), 0.400g yeast, shaking rate of 150 rpm, thus suggesting involvement of at least three different functional groups in the adsorption process. Cd 2+ uptake was depressed by a factor of 10 as water hardness was varied from 9.45 to 133.09 mg CaCO 3 /L, suggesting that competition with calcium ions strongly reduces the affinity of the biomass for cadmium. The results of this study are important for optimizing conditions for removal of toxic trace metals from aqueous environments.

Inductively coupled plasma atomic emission spectrometry (ICP-AES) is one of the most widely used ... more Inductively coupled plasma atomic emission spectrometry (ICP-AES) is one of the most widely used and extremely important tools for trace element analysis today. The technique however still suffers from matrix effects, especially those due to easily ionizable elements (EIEs). Current theory of atomic spectrometry assumes Local Thermal Equilibrium (LTE), and EIE interference effects cannot be explained fully as long as all the electrons in the plasma are regarded as equivalent in accordance with the LTE theory. If however it is assumed that electronic collisions with heavy particles can occur before or after thermal equilibration, then electrons can be expected to experience different activation energies depending on whether collisions occurred before or after thermal equilibration. This paper reviews recent work carried out to characterize EIE interference effects during ICP-AES, flame AAS and flame AES in terms of ion-electron collisional radiative recombination activation energy. The work is based on a simplified rate model showing that when analytes are determined by atomic spectrometry in the absence and then in the presence of EIEs as interferents, the change in collisional radiative recombination activation energy, ∆E a , is zero when the system conforms to LTE. Several analyte-interferent systems have been studied, and results obtained so far lead to the conclusion that departure from LTE results from collisions involving electrons in the ambipolar diffusion state. Factors affecting both pre-LTE and LTE collisions, as well as a possible collisional radiative recombination mechanism designed to account for the ∆E a values obtained are discussed.

Cadmium biosorption properties of non-living, dried river green alga from a river source, and wat... more Cadmium biosorption properties of non-living, dried river green alga from a river source, and water hyacinth weed, Eichhornia crassipes from a lake in Zimbabwe have been investigated. The cadmium uptake was found to depend on initial pH, uptake being apparently minimal at low pH values and increasing with an increase in pH. Cadmium biosorption kinetics by both samples is fast, with 80% of total uptake occurring within 60 min. The effect of initial solution pH and initial cadmium concentration on cadmium biosorption from a cadmium solution has been studied. The data for algal biomass fitted the Langmuir monolayer adsorption isotherm, while the biosorption of the metal by water hyacinth weed fitted the Freundlich adsorption isotherm with 1/n values all less than 1. Maximum metal uptake capacities were recorded using 0.35 g of biomass and a 250 mg L −1 cadmium solution at pH 6.5 and at 25°C and these were about 85 and 50 mg L −1 for water hyacinth weed and green alga, respectively, showing that water hyacinth weed offered a greater potential for cadmium uptake. The absorption was described by pseudo-second order rate model and the rate constant and equilibrium sorption capacity are reported.

The thermodynamic parameters relating to the activated complex for the heterogeneous dilute acid ... more The thermodynamic parameters relating to the activated complex for the heterogeneous dilute acid hydrolysis of the difficultly accessible portions of microcrystalline cellulose, ΔH 0 ‡ and ΔS 0 ‡ were determined from the measured apparent rate constants k c in 0.3 M, 1.0 M and 1.3 M HCl containing 0.00 M, 0.08 M and 0.20 M KBr at 60, 70, 75, and 80 0 C using a loss-in-weight method. When hydrolysis was carried out in 0.3 M HCl only, ΔH 0 ‡ and ΔS 0 ‡ values of +105 kJ moland +549 Jk -1 , respectively, were obtained. These values decreased with increasing concentration of inert electrolyte. However when the measurements were made at higher HCl concentration of 1.0 M, the values of the parameters increased with added salt concentration. Two possible mechanisms are presented, to account for the differences in variation of the thermodynamic parameters.

Removal of Methylene Blue (MB) and Crystal Violet (CV) dyes from monocomponent and binary aqueous... more Removal of Methylene Blue (MB) and Crystal Violet (CV) dyes from monocomponent and binary aqueous solutions by water hyacinth-E. Crassipes roots fixed on alginate (a low-cost adsorbent) has been investigated. The extent of adsorption was evaluated as a function of solution pH, initial dye concentration, and bead biomass loading. Kinetic sorption data were analysed by widely used models: pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The results showed that pseudo-second-order model better described the biosorption experimental data than the pseudo-first-order kinetic model for both dyes, whilst the Elovich model fitted the biosorption experimental data at lower dye concentrations. The intraparticle diffusion model indicated that sorption of CV and MB was characterized by rapid surface adsorption coupled with slow film diffusion process at higher initial dye concentration and at all initial bead biomass loading. The range of mean free energy values confirmed physical adsorption as the mechanism for dye removal from solution.

Temnocalyx obovatus is widely found in many areas in Zimbabwe, Nigeria and Zambia where it is use... more Temnocalyx obovatus is widely found in many areas in Zimbabwe, Nigeria and Zambia where it is used to treat a variety of ailments. Phenolic compounds in T. obovatus assessed by Folin-Ciocalteu method varied from 1.18 to 2.89 mg tannic acid g -1 . Acetone extract showed the greatest flavonoids, flavonols and proanthocyanidins content 5.12, 4.13 and 3.07 mg catechin g -1 respectively. 2, 2-diphenyl-1picrylhydrazyl radical (DPPH . ) scavenging effect, Ferric reducing ability and egg lipid peroxidation inhibition assays were adopted to evaluate antioxidant activity. Acetone extracts exhibited the greatest antioxidant activity for all the assays, followed by methanol extracts. Hexane extracts showed the weakest activity. Correlation studies showed that antiradical activity is explained more by flavonols and proanthocyanidins (73%) and flavonoids (71%) and weakly by phenolic contents (43%). The results revealed significant phenolic capacity and antioxidant potential of T. obovatus to warrant its use as a source of antioxidants. It can be added to foods, such as, meat and soups for enhancement of nutritional content and promotion of health.

A simplified rate model for the interference effects of easily ionized elements on analyte absorb... more A simplified rate model for the interference effects of easily ionized elements on analyte absorbance and emission signals in Flame atomic absorption spectroscopy, FAAS, is presented showing that when the analyte is determined in the absence and presence of the interferent, the change in the collisional radiative recombination activation energy, DE a , is zero when the systems conform to local thermal equilibrium. The proposed model also shows that DE a can be calculated from the slope of the plot of A 0 =A or I 0 =I versus the interferent-to-analyte ion number density ratio, where A and I denote absorbance and emission signal intensities, respectively, and the prime denotes presence of the interferent. DE a values of À1.5168 and À1.6924 eV where obtained when Mg was determined by FAAS in the presence of excess Ca and Sr respectively, and values of À6.62, À9.83, and À13.52 eV were obtained when CaI, CaII, and MgII respectively were determined in the presence of excess Li, confirming that these systems are not in LTE. Possible causes for departure from LTE and possible collisional radiative recombination mechanisms consistent with the results are discussed.

The occurrence of toxic metals in waters is a major health issue. Polluted waters can be cleaned ... more The occurrence of toxic metals in waters is a major health issue. Polluted waters can be cleaned by biosorption, which uses organisms such as algae, bacteria, fungi and plants that adsorb metals. In particular, water hyacinth-Eichhornia crassipes-is a promising biosorbent. Here we tested novel alginate-immobilised water hyacinth beads for the removal of Cu from aqueous solutions. Results show that successful service and regeneration continuous cycles were performed using a packed-bed, flow-through column of fixed internal diameter 1.2 cm, at room temperature and pH 5.1, with variation in initial metal concentration, bed depth and flow rate. The eluant used was 1 % w/v CaCl2 acidified at pH 3. A concentration factor of 12 and elution efficiency up to 98 % were observed in five service and regeneration cycles performed. The equilibrium adsorption capacity of Cu remained almost constant at about 29 mg/g. To conclude, we show for the first time that alginateimmobilised water hyacinth beads can uptake and adsorb Cu very efficiently in a continuousflow mode, hence highlighting their great potential for removal of toxic metals from aquatic environments.

Pollution from synthetic dyes has emerged to be a significant environmental issue over the past f... more Pollution from synthetic dyes has emerged to be a significant environmental issue over the past few decades. This has mainly been triggered by the increasing global dye production, possible toxic effects, undesirable colour and high persistence in the environment. Biosorption, which involves dye removal from aqueous solution by passive linkage in live and dead biomass, has shown great potential in removing dyes from aquatic environments. Among aquatic macrophytes, water hyacinth, Eichhornia crassipes, has shown great potential as a biosorbent. In this work, we investigated the removal of two basic dyes, methylene blue and crystal violet, using E. crassipes immobilized on alginate. Results showed that the Langmuir model better described the equilibrium sorption data when compared to the Freundlich model. Optimum amounts of methylene blue and crystal violet dyes were adsorbed in the alkaline pH range (8-10), 8 % biomass dose, and the amount of dye removed increased with increasing initial dye concentration. The equilibrium monocomponent adsorption capacities for the dyes were 111.1 and 43.5 mg/g, while the binary adsorption capacities were 26.1 and 11.6 mg/g for methylene blue and crystal violet, respectively. To conclude, we show for the first time that E. crassipes fixed on alginate beads can uptake and adsorb methylene blue and crystal violet dyes very effectively in batch systems and show great potential for dye removal from aquatic environments.

Phenolic compounds yield in plant extracts depend on the method employed in the extraction proces... more Phenolic compounds yield in plant extracts depend on the method employed in the extraction process. In this study, we investigated systematically, a method of determination of extraction yield of antioxidant compounds from Temnocalyx obovatus. A sample treatment and preparation protocol that employs strict statistical treatment to ensure sample homogeneity was applied. As preliminary indicator of homogeneity, total nitrogen and phosphorus were determined and an iterative process using Levene test was applied to statistically test the homogeneity of the ground T. obovatus leaves. At p = 0.01, homogeneity of the plant material was achieved on the third ground sample. Among the six solvents used, methanol gave the best yield of extractable phytochemicals and a butylated hydroxytoluene-spike recovery of 77%, whereas diethyl ether gave the lowest yield and a butylated hydroxytoluene-spike recovery of 63%, suggesting that optimal yields tended to be favoured by more polar solvents.

In this paper, batch kinetic studies and quantitative structure-activity relationships (QSARs) mo... more In this paper, batch kinetic studies and quantitative structure-activity relationships (QSARs) models were used to determine the effect of initial pH, biomass loading and initial metal ion concentration on the kinetics and equilibrium behavior of metal adsorption onto immobilized Eichhornia crassipes beads. Linear regression indicated that chemisorption was the main sorption mechanism under optimum operating conditions. The highest rate constants were 0.016 (mg g-1 min-1) for Cd2+ ions at pH 6.5 and 0.035 (mg g-1 min-1) at pH 4.5 for Pb2+ ions. When conditions were varied the sorption mechanism became more complex with intraparticle diffusion affecting the rate at low pH, high biomass loading and high initial metal ion concentration. The values of qmax (mg/g) and hence the preference of the biomass for binding were found to follow the order: class B (Soft ions: Pb2+ and Ag+)>borderline ions (Cr3+, Cd2+, Cu2+, Zn2+, Co2+)>Class A (hard ions: Sr2+ and K+). It was concluded that covalent bonding played a significant role in biosorption of soft metal ions and ionic bonding for borderline and hard ions.

The biosorption of different metal ions (Cu 2+ , Zn 2+ , Ni 2+ , Pb 2+ and Co 2+ ) by dried roots... more The biosorption of different metal ions (Cu 2+ , Zn 2+ , Ni 2+ , Pb 2+ and Co 2+ ) by dried roots of Canna indica biomass was investigated using a batch sorption technique. The equilibrium retention capacities of the metal ions determined from the Langmuir isotherm showed that C. indica had the largest sorption capacity for Pb 2+ ions and the least sorption for Ni 2+ . The results also showed that garlic-treatment of C. indica biomass enhanced its sorption capacity for the divalent metal ions, with the enhancement factor varying from 1.22 to 1.44. The biosorption process was found to be exothermic for all metal ions studied (∆H values varying from -4.438 to -12.716 kJ mol -1 ), with physisorption being the most likely mechanism of uptake. In conclusion, studies on biosorption of heavy metals by C. indica are important because they may contribute in aiding the innovative removal of metal ions from contaminated industrial effluents. @JASEM

A simplified rate model is presented showing that when analytes are determined by atomic spectros... more A simplified rate model is presented showing that when analytes are determined by atomic spectroscopy first in the absence, and then in the presence, of easily ionizable elements (EIEs) as interferents, the change in collisional radiative recombination activation energy, ∆Ea, is zero when the system conforms to local thermal equilibrium (LTE). ∆Ea values of -7.462, -7.925, and -8.898 eV were obtained when Ca(II), Mg(II), and Sr(II), respectively, were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES) in the absence and presence of excess Li, while ∆Ea values of -6.477 and -7.481 eV were obtained when Mg(II) and Sr(II), respectively, were determined in the absence and presence of excess K as interferent. A value of -2.223 eV for ∆Ea was obtained when Mg(I) was determined by air-acetylene flame atomic emission spectrometry (FAES) in the absence and presence of excess K. The data confirm that all the systems studied were not in LTE, and suggest pre-LTE collisional radiative recombination in the absence of the interferent in all cases, and that collisional radiative recombination involving electrons from the interferent can occur from the ambipolar diffusion state or the LTE state. Possible causes for departure from LTE, and a possible collisional radiative recombination mechanism to account for the ∆Ea values obtained, are discussed.

In this study, heat and chemically treated sand was applied as an adsorbent for the removal of fl... more In this study, heat and chemically treated sand was applied as an adsorbent for the removal of fluoride ions from aqueous solutions. The influence of different parameters such as calcination time, dosage, initial fluoride concentration and pH were evaluated. Results indicated that activated sand can be used for defluoridation of water. This can be achieved by coating sand with 10% Fe 2 O 3 , a calcination time of 3 h and pH around 6. The adsorption also increased with initial fluoride concentration and adsorbent dose. This study also showed that up to 90% of fluoride was adsorbed with 12 g of adsorbent in 50 ml of 10 mg/L fluoride solution. The sorption data were best described by the Freundlich isotherm. The maximum adsorption capacity was found to be 10.3 mg/g. According to these findings, physicochemically modified sand has potential application as an adsorbent for fluoride ions removal.

The potential of water hyacinth-Eichhornia crassipes biomass immobilized in calcium alginate for ... more The potential of water hyacinth-Eichhornia crassipes biomass immobilized in calcium alginate for the adsorption of Ni(II) from water was studied using the Langmuir and Freundlich adsorption models. The equilibrium adsorption data were obtained at different initial Ni(II) concentrations = 0.05 -2 mg/L, temperature = 30˚C ± 0.2˚C, agitation rate = 150 rpm, equilibration time = 3 hr, biosorbent dose = 4 g/L, and pH range = 4 -7.4. Langmuir isotherms gave monolayer sorption capacities ( ) of 26.5, 44.3 and 53.0 mg/g for the removal of Ni(II) in the presence of methanol, without added organic substance, and in the presence of acetonitrile, respectively. These findings were also confirmed by the trend in the Freundlich isotherm parameter ( m q 1 n < 1). Interpretation of the sorption data in terms of the separation factor, S F , suggested that the removal of Ni(II) from water mainly occurred through a chemisorption mechanism. Desorption experiments to recover Ni(II) from the adsorbent showed that highest amounts of the metal could be removed from the adsorbent when previously adsorbed in the presence of 1-(2-Thiazolylazo)-2-naphtol (TAN) (>90%). The results from these studies indicated that E. crassipes fixed on calcium alginate beads is a viable metal enrichment media that can be used freely immersed in solution to achieve very high adsorption capacities and possible preconcentration of Ni(II) in aquatic environments.

In this paper, we have presented the results of Cu(II) removal by alginateimmobilized water hyaci... more In this paper, we have presented the results of Cu(II) removal by alginateimmobilized water hyacinth beads. Batch equilibrium and kinetic experiments were conducted to determine maximum adsorption capacity under various experimental conditions. A sorption capacity of 61.0 mg/g was obtained using a biosorbent dose of 0.5 mg/l. The hyacinth-alginate beads formed were considerably resistant to swelling in acidic and aqueous media, but were less resistant in alkaline media. Sulphuric acid and calcium chloride solutions were effective desorbing agents, achieving up to 100% desorption, with the acid showing faster kinetics. Sorption capacity decreased slightly after 5 sorptiondesorption cycles indicating that both agents could be used as effective eluting agents. However, strong complexing agents such EDTA were found to be unsuitable for regeneration as they destroy the beads. In conclusion, entrapment of water hyacinth biomass in alginate improves both its sorption capacity and mechanical properties, thus presenting the biosorbent as a possible ingredient for continuous flow reactors.

Environmental protection requires the use of natural products instead of chemicals to minimize po... more Environmental protection requires the use of natural products instead of chemicals to minimize pollution and adsorption has now been recognized as an effective and economic method. This investigation utilized adsorption capacity ratios,