Papers by Tholiso Ngulube
Dyes are growing to be a problematic class of pollutants to the environment. The disposal of dyes... more Dyes are growing to be a problematic class of pollutants to the environment. The disposal of dyes in water resources has bad aesthetic and health effects, hence the need to remove them from the environment. The need for treatment methods that are effective and low in price is rising hence a lot of research interest is being diverted towards adsorbents that are cheap, preferable naturally occurring materials like clays. In most reported dye adsorption studies, limited information on the relationship between characterization results with adsorbent performance on dye removal has been given. This review article seeks to report on the link between the adsorption characteristics of the clays and their adsorption capacities and to gather information on the modifications done on clays to improve their adsorption capacities. A critical analysis of the different mechanisms involved during the decolouration process and their application for dye removal has been discussed in detail in this up-to-date review. From a wide range of consulted literature review, it is evident that some clays have appreciable adsorption capacities on top of being widely available. It was also noted that several parameters like contact time, dosage, concentration, temperature and pH affect the removal of dyes. Furthermore, the application of clay minerals for decolourising water represents economic viable and locally available materials that can be used substantially for pollution control and management. Conclusions were also drawn and suggestions for future research perspectives are proposed.
Removal of heavy metals is very important with respect to environmental considerations. This stud... more Removal of heavy metals is very important with respect to environmental considerations. This study investigated the sorption of copper (Cu) and zinc (Zn) in single and binary aqueous systems onto laboratory prepared hydroxyapatite (HA) surfaces. Batch experiments were carried out using synthetic HA at 30°C. Parameters that influence the adsorption such as contact time, adsorbent dosage and pH of solution were investigated. The maximum adsorption was found at contact time of 12 and 9 h, HA dosage of 0.4 and 0.7 g/l and pH of 6 and 8 for Cu and Zn, respectively, in single system. Adsorption kinetics data were analyzed using the pseudofirst-, pseudosecondorder and intraparticle diffusion models. The results indicated that the adsorption kinetic data were best described by pseudosecond-order model. Langmuir and Freundlich isotherm models were applied to analyze adsorption data, and Langmuir isotherm was found to be applicable to this adsorption system, in terms of relatively high regression values. The removal capacity of HA was found to be 125 mg of Cu/g, 30.3 mg of Zn/g in single system and 50 mg of Cu/g, 15.16 mg of Zn/g in binary system. The results indicated that the HA used in this work proved to be effective material for removing Cu and Zn from aqueous solutions.
In the present study, the defluoridation capabilities and adsorption mechanisms of cryptocrystall... more In the present study, the defluoridation capabilities and adsorption mechanisms of cryptocrystalline magnesite were evaluated. All experiments were done by batch procedure. Conditions assessed include time, dosage, concentration, pH and the effects of competing ions. Optimum defluoridation conditions were observed to be 20 g/L magnesite, 2:100 solid:liquid ratio, 20 min of agitation and 60 mg/L fluoride concentration. Adsorption of fluoride by magnesite was observed to be independent of pH. Cryptocrystalline magnesite showed >99% efficiency for fluoride removal. Adsorption kinetics fitted better to a pseudo-second order than a pseudo-first-order thus confirming chemisorption. Adsorption data fitted better to a Langmuir than a Freundlich adsorption isotherm thus confirming monolayer adsorption. Cryptocrystalline magnesite successfully removed excess fluoride from aqueous solution to below Department of Water Affairs and Forestry water quality guidelines. As such, this material can be used for a point source defluoridation technique in rural areas and households in South Africa and other developing countries. Based on comparison studies, cryptocrystalline magnesite proved to have high adsorption capacity for fluoride removal and can be used as a substitute for conventional treatment methods.
A B S T R A C T Groundwater is the most appropriate and widely used source of drinking water for ... more A B S T R A C T Groundwater is the most appropriate and widely used source of drinking water for many rural communities in Sub-Saharan Africa. Studies reveal that in some of the boreholes, F − concentration may be way beyond the recommended limits for drinking water. This study evaluates the use of raw unprocessed bentonite clay and its Fe 3+-modified form for fluoride adsorption. A series of batch adsorption experiments were carried out to evaluate parameters that influence the adsorption process. Loading of Fe 3+ on bentonite was achieved by contacting the powdered clay with 80 ppm Fe 3+ solution for 15 min at S/L ratio of 2 g/100 ml. The raw unprocessed bentonite clay was observed to increase the pH of the F − solution as opposed to the Fe 3+-modified bentonite. Fe 3+ bentonite exhibited ≈100% F − removal as opposed to unprocessed bentonite <5% at initial concentration of 10 ppm F −. The Fe 3+-modified bentonite exhibited ≈100% F – removal over the pH range 2–10 decreasing at pH > 10, while the unprocessed raw bentonite clay showed release of F − over the same pH range. This is crucial for the application of this adsorbent, since defluoridation can be carried out at the normal pH of the groundwater with no adjustment unlike most other adsorbents. The Fe 3+-modified bentonite was effective in F − removal in high fluoride borehole water samples. The adsorption data fitted well to Langmuir adsorption model indicating a monolayer coverage of the adsorbent. The adsorption process was also observed to be favorable at room temperature. The results indicate that Fe 3+-modified bentonite has potential for application in groundwater defluoridation and more so as a candidate adsorbent for point of use water defluoridation systems for household use in rural areas in South Africa.
Al3+ -bentonite clay (Alum-bent) was prepared by ion exchange of base cations on the matrices of ... more Al3+ -bentonite clay (Alum-bent) was prepared by ion exchange of base cations on the matrices of bentonite clay. Intercalation of bentonite clay with Al3+ was performed in
batch experiments. Parameters optimized include time, dosage, and Al3+ concentration. Physicochemical characterization of raw and modified bentonite clay
was done by X-ray fluorescence, X-ray diffraction, energy dispersive X-ray spectrometry attached to scanning electron microscopy, Brunauer Emmett Teller analysis, cation exchange capacity (CEC) by ammonium acetate method, and pHpzc by solid addition method. Chemical constituents of water were determined by atomic absorption spectrometry (AAS), ion selective electrode (Crison 6955 Fluoride
selective electrode) and a Crison multimeter probe. For fluoride removal, the effect of contact time, adsorbent dosage, adsorbate concentration, and pH were evaluated in
batch procedures. The adsorption capacity of fluoride by modified bentonite clay was observed to be 5.7 mg g
¡1 at (26 +/- 2) C room temperature. Maximum adsorption of
fluoride was optimum at 30 min, 1 g of dosage, 60 mg L of adsorbate concentration, pH 2=12, and 1:100 solid/liquid (S/L) ratios. Kinetic studies revealed that fluoride adsorption fitted well to pseudo-second-order model than pseudo first order.
Adsorption data fitted well to both the Langmuir and Freundlich adsorption isotherms,
hence, confirming monolayer and multilayer adsorption. Alum-bent showed good stability in removing fluoride from ground water to below the prescribed limit as
stipulated by World Health Organization. As such, it can be concluded that Alum-bent is a potential defluoridation adsorbent which can be applied in fabrication of point of
use devices for defluoridation of fluoride-rich water in rural areas of South Africa and other developing countries. Based on that, this comparative study proves that Alumbent
is a promising adsorbent with a high adsorption capacity for fluoride and can be a substitute for conventional defluoridation methods.
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Papers by Tholiso Ngulube
batch experiments. Parameters optimized include time, dosage, and Al3+ concentration. Physicochemical characterization of raw and modified bentonite clay
was done by X-ray fluorescence, X-ray diffraction, energy dispersive X-ray spectrometry attached to scanning electron microscopy, Brunauer Emmett Teller analysis, cation exchange capacity (CEC) by ammonium acetate method, and pHpzc by solid addition method. Chemical constituents of water were determined by atomic absorption spectrometry (AAS), ion selective electrode (Crison 6955 Fluoride
selective electrode) and a Crison multimeter probe. For fluoride removal, the effect of contact time, adsorbent dosage, adsorbate concentration, and pH were evaluated in
batch procedures. The adsorption capacity of fluoride by modified bentonite clay was observed to be 5.7 mg g
¡1 at (26 +/- 2) C room temperature. Maximum adsorption of
fluoride was optimum at 30 min, 1 g of dosage, 60 mg L of adsorbate concentration, pH 2=12, and 1:100 solid/liquid (S/L) ratios. Kinetic studies revealed that fluoride adsorption fitted well to pseudo-second-order model than pseudo first order.
Adsorption data fitted well to both the Langmuir and Freundlich adsorption isotherms,
hence, confirming monolayer and multilayer adsorption. Alum-bent showed good stability in removing fluoride from ground water to below the prescribed limit as
stipulated by World Health Organization. As such, it can be concluded that Alum-bent is a potential defluoridation adsorbent which can be applied in fabrication of point of
use devices for defluoridation of fluoride-rich water in rural areas of South Africa and other developing countries. Based on that, this comparative study proves that Alumbent
is a promising adsorbent with a high adsorption capacity for fluoride and can be a substitute for conventional defluoridation methods.
batch experiments. Parameters optimized include time, dosage, and Al3+ concentration. Physicochemical characterization of raw and modified bentonite clay
was done by X-ray fluorescence, X-ray diffraction, energy dispersive X-ray spectrometry attached to scanning electron microscopy, Brunauer Emmett Teller analysis, cation exchange capacity (CEC) by ammonium acetate method, and pHpzc by solid addition method. Chemical constituents of water were determined by atomic absorption spectrometry (AAS), ion selective electrode (Crison 6955 Fluoride
selective electrode) and a Crison multimeter probe. For fluoride removal, the effect of contact time, adsorbent dosage, adsorbate concentration, and pH were evaluated in
batch procedures. The adsorption capacity of fluoride by modified bentonite clay was observed to be 5.7 mg g
¡1 at (26 +/- 2) C room temperature. Maximum adsorption of
fluoride was optimum at 30 min, 1 g of dosage, 60 mg L of adsorbate concentration, pH 2=12, and 1:100 solid/liquid (S/L) ratios. Kinetic studies revealed that fluoride adsorption fitted well to pseudo-second-order model than pseudo first order.
Adsorption data fitted well to both the Langmuir and Freundlich adsorption isotherms,
hence, confirming monolayer and multilayer adsorption. Alum-bent showed good stability in removing fluoride from ground water to below the prescribed limit as
stipulated by World Health Organization. As such, it can be concluded that Alum-bent is a potential defluoridation adsorbent which can be applied in fabrication of point of
use devices for defluoridation of fluoride-rich water in rural areas of South Africa and other developing countries. Based on that, this comparative study proves that Alumbent
is a promising adsorbent with a high adsorption capacity for fluoride and can be a substitute for conventional defluoridation methods.