Courtie Mahamadi

Utilization of water hyacinth weed (Eichhornia crassipes) for the removal of Pb(II), Cd(II) and Zn(II) from aquatic environments: an adsorption isotherm study

The potential of Eichhornia crassipes biomass for the adsorption of three metal ions, Pb(II), Cd(II) and Zn(II), from aqueous solution was studied using five two‐parameter adsorption isotherm equations – Langmuir, Freundlich, Flory‐Huggins, Temkin and Redlich–Peterson isotherms. The equilibrium adsorption data were obtained at different initial metal ion concentrations (Co = 10–60 mg/L), 3 h contact time, 30 °C temperature, a dosage of 2 g/L, agitation rate of 150 rpm and buffered at pH 4.84. Langmuir isotherms gave monolayer sorption capacities (qm ) of 26.32, 12.60 and 12.55 mg/g for Pb(II), Cd(II) and Zn(II) metal ions, respectively. The same trend of metal uptake was indicated by plots of sorption favourability (SF ). Negative values of indicated that the adsorption was spontaneous and exothermic in nature, and values from the Temkin isotherm constant, bT , suggested a mechanism consistent with an ion‐exchange process. The results from these studies indicated that E. crassipes biomass has promising potential for the removal of toxic metals from aquatic environments.

Modelling the kinetics and equilibrium properties of cadmium biosorption by river green alga and water hyacinth weed

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.

Interference Effects from Easily Ionizable Elements in Flame AES and ICP‐OES: A Proposed Simplified Rate Model Based on Collisional Charge Transfer Between Analyte and Interferent Species

Abstract The effects of excess Na and K on K and Mg atom line emission in the air‐acetylene flame and of excess Li and K on Ca, Mg, and Sr atom and ion lines in inductively coupled plasma spectroscopy were studied using emission signal ratios, I′/I as probes, where I′ and I are the emission readings in the presence and absence of the interferent respectively. The I′/I plots as a function of analyte concentration in the test solution for the ICP experiments were similar to those obtained for the flame experiments in the analytical range 0–10 mg/L. A simplified rate model based on analyte excitation via charge transfer between analyte ions and activated interferent atoms is proposed to account for the emission signal enhancement observed at low analyte concentrations (<1 mg/L) for both ICP‐AES and flame atomic emission spectroscopy (AES). Data are presented showing good agreement between experimental E′ calibration curves and theoretical E′ calibration curves computed using the simplified rate model.

Determination of cadmium, lead, nickel, and zinc in Micropterus salmoides and Oreochromis niloticus by flame atomic absorption spectrometry after cloud point extraction

The levels of cadmium, lead, nickel, and zinc in muscle, intestine, gills, and liver of two fish species (largemouth bass Micropterus salmoides and bream Oreochromis niloticus) collected from Acadia Dam, Bindura, Zimbabwe, were determined by flame atomic absorption spectrometry after cloud-point extraction (CPE) using 1-(2-thiazolylazo)-2-naphthol as a complexing agent and Triton X-114 as a surfactant. The CPE procedure was optimized with respect to ligand concentration and surfactant concentration, pH, equilibration time, and temperature. Enrichment factors of 26, 20, 31, and 32 were obtained for Cd, Pb, Ni, and Zn, respectively. The metal concentrations in most of the fish tissues were found to generally follow the order: Zn > Ni > Pb > Cd, and the concentrations in the tissues were found to follow the order: liver > gills > intestine > muscle. The results also indicated that there was no significant difference in the mean metal concentrations in the fish tissues of the samples investigated (p < 0.05). In conclusion, the fish from the dam are not excessively burdened with the metals investigated but should be monitored periodically.

Interference Effects of Excess Ca, Ba and Sr on Mg Absorbance During Flame Atomic Absorption Spectrometry: Characterization in Terms of a Simplified Collisional Rate Model

Group II elements constitute an environmentally important group of metals. Calcium ranks 5th in relative abundance in nature. It occurs in limestone, dolomite, gypsum and gypsiferous shale, from which it can leach into underground and surface waters. Calcium content of natural waters can range from zero to several hundred milligrams per liter, depending on the source and treatment of the water. Magnesium occurs in nature in close association with calcium. It ranks 8th in abundance among the elements, and is a common constituent of natural waters. As with calcium, concentrations of magnesium in natural water may vary from zero to several hundred milligrams per litre, depending on source and treatment of the water. Calcium and magnesium salts contribute to water hardness. Concentrations of Mg above 125 mg/L can have cathartic and diuretic effects on the water (APHA, 1992). Barium ranks 16th in relative abundance in nature, and occurs in trace amounts in natural waters. Strontium resembles calcium, and interferes in the determination of calcium by gravimetric and titrimetric methods. Although most portable water supplies contain little strontium, levels as high as 39 mg/L have been detected in well water (APHA, 1992). FAAS and ICP-AES are the preferred methods for determining Gp II elements including Mg. Signal enhancement and/or depression were reported previous when Gp II elements were determined by atomic absorption spectrometry in the presence of other Gp II elements as interferents by several authors (Zadgorska and Krasnobaeva, 1977; Czobik and Matousek, 1978; Kos’cielniak and Parczewski, 1982; Smith and Browner, 1984; Zaranyika and Chirenje, 1999). Our approach to the study of interelement effects in atomic spectrometry involves a technique of probing changes in the number densities of the excited and ground states. Experimental analyte line emission intensity (I) and line absorbance (A) signal ratios, I’/I and A’/A, respectively, where the prime denotes readings taken in the presence of the interferent, are determined and compared to theoretical values derived assuming steady state kinetics. The method was used to follow collisional processes on the excitation and

Interference Effects of Excess Lithium on the Emission Signal of the Calcium and Strontium Ionic Lines during Inductively Coupled Plasma Emission Spectrometry: Simulation in Terms of the Simplified Collisional Radiative Recombination Rate Model

ICP-AES Ca and Sr ion line signals were measured on 0-30 μg/mL Ca and Sr solutions, in the absence and presence of 1000 μg/mL Li as easily ionizable interferent, and the effect of the interferent on analyte calibration curve simulated using a simplified collisional radiative recombination rate model. Close agreement between experiment and theory was obtained for the full range of concentrations studied in the case of SrII, while the theoretical Ca ion line calibration curve exhibited close agreement below 10 μg/mL Ca concentration in the test solution, and a positive deviation of up to 18% from the experimental curve at higher Ca concentrations. The data obtained successfully demonstrates the potential of the simplified collisional radiative recombination rate model for simulating the effects of easily ionizable interferents on high ionization potential analytes.

Plasma Diagnostics through Kinetic Modelling: Characterization of Matrix Effects during ICP and Flame Atomic Spectrometry in terms of Collisional Radiative Recombination Activation Energy-A Review

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, ΔEa, 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 ΔEa values obtained are discussed.