Papers by Hlanganani Tutu
Water SA, Oct 30, 2015
Acid mine drainage is generated when mining activities expose sulphidic rock to water and oxygen ... more Acid mine drainage is generated when mining activities expose sulphidic rock to water and oxygen leading to generation of sulphuric acid effluents rich in Fe, Al, SO 4 and Mn with minor concentrations of Zn, Cu, Mg, Ca, Pb depending on the geology of the rock hosting the minerals. These effluents must be collected and treated before release into surface water bodies. Mining companies are in constant search for cheaper, effective and efficient mine water treatment technologies. This study assessed the potential of applying magnesite as an initial remediation step in an integrated acid mine drainage (AMD) management system. Neutralization and metal attenuation was evaluated using batch laboratory experiments and simulations using geochemical modelling. Contact of AMD with cryptocrystalline magnesite for 60 min at 1 g: 100 mℓ S/L ratio led to an increase in pH, and a significant increase in metals attenuation. Sulphate concentration was reduced to ≈1 910 mg/ℓ. PH redox equilibrium (in C language) (PHREEQC) geochemical modelling results showed that metals precipitated out of solution to form complex mineral phases of oxy-hydroxysulphates, hydroxides, gypsum and dolomite. The results of this study showed that magnesite has potential to neutralize AMD, leading to the reduction of sulphate and precipitation of metals.
Water Science & Technology: Water Supply, Sep 24, 2016
Excess fluoride in drinking water is harmful to human health and therefore it needs to be removed... more Excess fluoride in drinking water is harmful to human health and therefore it needs to be removed from water before consumption. The potential of locally available mixed Mukondeni clay soils (MMCS) as a cheap adsorbent for the removal of fluoride from aqueous solution was investigated. Characterization of MMCS was done by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, Fourier transform infrared and Brunauer Emmett Teller. Cation exchange capacity and point of zero charge of the clays were determined using standard methods. Parameters optimized included: contact time, adsorbent dosage, initial fluoride concentration, pH and temperature. Optimization experiments were done in batch procedures. The results showed that the optimum conditions for the defluoridation of water using MMCS are 60 min, 1.5 g, 9 mg/L, 1.5/100 S/L ratios, pH of 2 and a temperature of 25 W C. The equilibrium isotherm regression parameter (R 2 ¼ 0.95) showed that the Freundlich isotherm gave a better fit than the Langmuir isotherm (R 2 ¼ 0.52) which indicates multilayer adsorption. Kinetic studies revealed that the adsorption followed pseudo second order kinetics. This study indicated that locally available MMCS are good in the defluoridation of groundwater but modification through blending with metal oxide modified clays can enhance their adsorption capacity.
Passive Remediation of Acid Mine Drainage
Contamination of fresh water resources by acidic and metalliferous effluents emanating from minin... more Contamination of fresh water resources by acidic and metalliferous effluents emanating from mining activities has rendered the environment unsuitable to foster life. Mine effluents from coal and gold mining are mainly acidic and contains elevated levels of toxic chemical species. Due to their toxic nature, this water need to be contained and treated prior discharge to the nearby environments.This book reports on the state of art technologies that were developed for remediation of acid mine drainage using cryptocrystalline magnesite, bentonite clay and mechanochemically synthesized cryptocrystalline magnesite-bentonite clay composite. Laboratory studies proved that the fabricated composite can neutralise acidity in mine effluent and attenuate elevated levels of chemical species. The obtained results were substantiated by PHREEQC geochemical modelling and it was pointed out that chemical species were precipitating as hydroxides, ferric hydroxides, oxyhydrosulphates and carbonates.
This paper evaluates the potential application of amorphous magnesite for remediation of Acid Min... more This paper evaluates the potential application of amorphous magnesite for remediation of Acid Mine Drainage (AMD). Magnesite was mixed with simulated AMD at specific S/L ratios and agitated in an orbital shaker and its capacity to remove metals and neutralize the acidity assessed over time. XRF analysis showed that magnesite contains MgO (88.54 %) as the major element. XRD revealed that magnesite is amorphous and contains periclase as major mineral phase. Results indicate that contact of AMD with magnesite leads to an increase in pH (pH≥10), and a reduction in EC, TDS and metal concentration to below DWAF guidelines. PHREEQC geochemical modeling predicted precipitation of Al, Fe, Mn, Mg bearing mineral phases could be responsible for attenuation of most metal species. However a high proportion of alkali and alkaline earth metals remained in the treated water which might require post treatment polishing.
remediation of acid mine drainage using cryptocrystalline magnesite: A batch experimental and geo... more remediation of acid mine drainage using cryptocrystalline magnesite: A batch experimental and geochemical modelling approach
Water Practice and Technology, 2017
The present study reports the optimum conditions for intercalating the Al3+ species to bentonite ... more The present study reports the optimum conditions for intercalating the Al3+ species to bentonite clay matrices and evaluate the potential of using Al3+-modified bentonite clay (Alum-Bent) for removal of oxyanionic species of As, B, Cr, Mo and Se from coal fly ash (FA) leachates. Removal of oxyanionic species was done in batch experimental procedures. Parameters optimized were: contact time, adsorbent dosage, concentration and pH. The adsorption affinity of Al3+-bentonite clay for oxyanionic species varied as follows: B ≈ Se > Mo > Cr ≈ As respectively. The adsorption data fitted better to Langmuir adsorption isotherm than Freundlich adsorption isotherm hence confirming mono-site adsorption. The adsorption kinetics fitted well pseudo-second-order kinetic model hence confirming chemisorption. The fact that most of the oxyanion were adsorbed at pH ≥ pHpzc indicated that both electrostatic and chemical interactions occurred with the clay surface and interlayers. The Al3+-modified ...
Fate of inorganic contaminants post treatment of acid mine drainage by cryptocrystalline magnesite: Complimenting experimental results with a geochemical model
Journal of Environmental Chemical Engineering, 2016
Abstract This study assessed the fate of inorganic contaminants post treatment of acid mine drain... more Abstract This study assessed the fate of inorganic contaminants post treatment of acid mine drainage by cryptocrystalline magnesite. To accomplish that, neutralization and metal attenuation were evaluated and complemented with simulations using geochemical modeling. Mineral phase formation and changes during the reaction of magnesite and AMD were also evaluated. The geochemical computer code PHREEQC and WATEQ4 database was used for geochemical modelling of the process water. Interaction of AMD with magnesite at an optimum solid: liquid ratio of 1:100 and contact time of 60 min led to an increase in pH, reaching a maximum pH of 10, resulting in significant precipitation of most metal species. Increase of pH in solution with contact time caused the removal of the metal ions mainly by precipitation, co-precipitation and adsorption. Sulphate concentration was lowered from 4640 down to 1910 mg/L. Fe was mainly removed as Fe(OH) 3 , goethite, and jarosite, Al as basaluminite, boehmite and jurbanite, Al(OH) 3 and as gibbsite and diaspore. Al and Fe precipitated as iron (oxy)-hydroxides and aluminium (oxy)-hydroxides. Mn precipitated as rhodochrosite and manganite. Ca was removed as gypsum. Sulphate was removed as gypsum, and Fe, Al hydroxyl sulphate minerals. Mg was removed as brucite and dolomite. Cryptocrystalline magnesite effectively neutralized AMD and attenuated concentration of inorganic species to within department of water affairs and sanitation (DWAS) water quality guidelines.
The Open Analytical Chemistry Journal, Jan 21, 2008
A review is given on the development of passive samplers for aquatic environments. Passive sample... more A review is given on the development of passive samplers for aquatic environments. Passive samplers that are simple and easy to use and with minimal consumption of organic solvents to desorb the analytes from the trapping media are focused. New developments in quality assurance procedures are highlighted.
Environmental Monitoring and Assessment, Feb 26, 2019
Phytoremediation is a cost-effective, ecofriendly technology for the removal of metals from pollu... more Phytoremediation is a cost-effective, ecofriendly technology for the removal of metals from polluted areas. In this study, six different plant species (Datura stramonium, Phragmites australis, Persicaria lapathifolia, Melilotus alba, Panicum coloratum, and Cyperus eragrostis) growing in a gold mine contaminated wetland were investigated as potential phytoremediators of mercury. The accumulation of total mercury and methylmercury in plant tissues was determined during the wet and dry seasons to establish the plants' variability in accumulation. The highest accumulation of total mercury was in the tissues of Phragmites australis with recorded concentrations of 806, 495, and 833 μg kg −1 in the roots, stem, and leaves, respectively, during the dry season. The lowest accumulation levels were recorded for Melilotus alba during both seasons. The highest amount of the methylmercury was found in Phragmites australis during the dry season with a value of 618 μg kg −1. The accumulation and biotransportation were not significantly different between the seasons for some plants. The results of this study indicated that plants growing in wetlands can be used for phytoremediation of mercury and suggest the choice of species for constructed wetlands.
Synthesis and characterization of a magnetic nanosorbent modified with Moringa oleifera leaf extracts for removal of nitroaromatic explosive compounds in water samples
Journal of environmental chemical engineering, Jun 1, 2019
Abstract In this work, magnetite nanoparticles functionalized with Moringa oleifera plant leaf ex... more Abstract In this work, magnetite nanoparticles functionalized with Moringa oleifera plant leaf extracts were synthesized and investigated as potential nanosorbents in the extraction of nitroaromatic explosive compounds from aqueous solution. The predicted maximum adsorption capacity towards the nitroaromatic explosive compounds was 282 μg g−1. Batch studies confirmed that the pseudo second order model explained the extent of the adsorption while the absorption mechanism followed the Langmuir model. The order of selectivity for the nitroaromatic explosive compounds studied was observed as follows: 2-nitrotoluene >3-nitrotoluene >4-nitrotoluene > nitrobenzene >2,6-dinitrotoluene >1,3-dinitrobenzene. The limits of detection ranged from 0.4 to 4.5 mg L−1. Even though the recovery values for the target analytes are relatively low (14–46%), the method has shown great potential and repeatability with an average RSD value of 2.33%. The Moringa oleifera functionalized magnetite nanoparticles are therefore a viable nanosorbent that can be used as a sorbent to effectively extract nitroaromatic explosive compounds from polluted water.
Chemosphere, Mar 1, 2021
Dairy farmers often keep almost all their newborn heifer calves despite the high cost of rearing.... more Dairy farmers often keep almost all their newborn heifer calves despite the high cost of rearing. By rearing all heifer calves, farmers have more security and retain flexibility to cope with the uncertainty in the availability of replacement heifers in time. This uncertainty is due to mortality or infertility during the rearing period and the variation in culling rate of lactating cows. The objective of this study is to provide insight in the economically optimal number of heifer calves to be reared as replacements. A herd-level stochastic simulation model was developed specific for this purpose with a herd of 100 dairy cows; the biological part of the model consisted of a dairy herd unit and rearing unit for replacement heifers. The dairy herd unit included variation in the number of culled dairy cows. The rearing unit incorporated variation in the number of heifers present in the herd by including uncertainty in mortality and variation in fertility. The dairy herd unit and rearing unit were linked by the number of replacement heifers and culled dairy cows. When not enough replacement heifers were available to replace culled dairy cows, the herd size was temporarily reduced, resulting in an additional cost for the empty slots. When the herd size reached 100 dairy cows, the available replacement heifers that were not needed were sold. It was assumed that no purchase of cows and calves occurred. The optimal percentage of 2-wk-old heifer calves to be retained was defined as the percentage of heifer calves that minimized the average net costs of rearing replacement heifers. In the default scenario, the optimal retention was 73% and the total net cost of rearing was estimated at €40,939 per herd per year. This total net cost was 6.5% lower than when all heifer calves were kept. An earlier first-calving age resulted in an optimal retention of 75%, and the net costs of rearing were €581 per herd per year lower than in the default scenario. For herds with a lower or higher culling rate of dairy cows (10 or 40% instead of 25% in the default scenario), it was optimal to retain 35 or 100% of the heifer calves per year. Herds that had a lower or higher cost of empty slots (€50 or €120 per month instead of €82 in the default scenario) had an optimal retention of 49 or 83% per year; the optimal retention percentage was dependent on farm and herd characteristics. For Dutch dairy farming conditions, it was not optimal to keep all heifer calves.
South African Journal of Botany, Mar 1, 2020
Moringa oleifera is an excellent source of bioactive compounds which exhibit nutritional and medi... more Moringa oleifera is an excellent source of bioactive compounds which exhibit nutritional and medicinal properties. Pressurized hot water extraction is known as a green, environmentally, faster and efficient extraction technique. However, it is facing a challenge with the degradation of thermolabile compounds at higher temperature. This research was performed to investigate the influence of extraction temperature, time and flow rate of pressurized hot water extraction in the recovery of Vitamin C and phenolic compounds from Moringa oleifera leaves. Response surface methodology (RSM) and artificial neural network (ANN) were used as estimates and predictive models with maximum responses. The optimal pressurized hot water extraction conditions were identified at: 91°C for temperature, 60 min for extraction time and 0.3 mL min −1 for flow rate, giving a predicted concentration of 3.92 ± 0.30, 4.74 ± 0.32 and 0.357 ± 0.19 g per 100 g of dry powder for kaempferol, quercetin and vitamin C, respectively. Evaluation of the two models through the statistical error parameters showed that ANN model gave a good predictive and estimation capabilities than RSM. Therefore, ANN can be recommended for use optimization method in the pressure hot water extraction.
Assessment of mobility of heavy metals in two soil types by use of column leaching experiments and chemometric evaluation of elution curves
International Journal of Environmental Analytical Chemistry, Jul 5, 2010
The objectives of this study were to evaluate the mobility of heavy metals (HMs) in two types of ... more The objectives of this study were to evaluate the mobility of heavy metals (HMs) in two types of soils (acidic forest soil and neutral agricultural soil) by leaching with calcium chloride solution in column experiments. The screening properties of neutral agricultural soil towards pollution by heavy metals (Ni, Cu, Zn and Cd) are approximately 10 times higher than those of
The Adsorption Properties of Agricultural and Forest Soils Towards Heavy Metal Ions (Ni, Cu, Zn, and Cd)
Soil and Sediment Contamination: An International Journal, Dec 23, 2010
Adsorption of Cu, Cd, Ni, and Zn in single and multi-metal solutions by agricultural and forest s... more Adsorption of Cu, Cd, Ni, and Zn in single and multi-metal solutions by agricultural and forest soils was investigated in batch sorption experiments. The results showed significant differences in sorption capacities of the studied soils. The selectivity order was as follows: agricultural soil≫ top forest soil > bottom forest soil. The adsorption sequence Cu > Zn > Ni > Cd
Critical parameters in a supported liquid membrane extraction technique for ionizable organic compounds with a stagnant acceptor phase
Journal of Chromatography A, Apr 1, 2010
The reviews cover important critical parameters that are often optimized in a supported liquid me... more The reviews cover important critical parameters that are often optimized in a supported liquid membrane extraction technique in both flat sheet and hollow fibre designs for ionizable organic molecules. Understanding of these parameters can enable one to predict the behavior of the compound before hand and thus reduce the number of optimization experiments. Moreover, less number of experiments can be also generated using statistical techniques which are now becoming more commonly used. Supported liquid membrane extraction optimal parameters such as the conditions of the pH of the acceptor and donor phases should easily be fixed from the pKa values of the compounds. Other parameters, including the polarity of the compound can help to predict the partitioning into the membrane and the behavior of the compound. The influence of parameters such as temperature on the mass transfer in supported liquid membrane depends on the design of the module, experimental design and type of mass transfer controlling the extraction process.
Molecules, Jun 2, 2021
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Membranes, Oct 29, 2020
In this article, a comprehensive review of applications of the hollow fibre-liquid phase microext... more In this article, a comprehensive review of applications of the hollow fibre-liquid phase microextraction (HF-LPME) for the isolation and pre-concentration of pharmaceuticals in water samples is presented. HF-LPME is simple, affordable, selective, and sensitive with high enrichment factors of up to 27,000-fold reported for pharmaceutical analysis. Both configurations (two-and three-phase extraction systems) of HF-LPME have been applied in the extraction of pharmaceuticals from water, with the three-phase system being more prominent. When compared to most common sample preparation techniques such as solid phase extraction, HF-LPME is a greener analytical chemistry process due to reduced solvent consumption, miniaturization, and the ability to automate. However, the automation comes at an added cost related to instrumental setup , but a reduced cost is associated with lower reagent consumption as well as shortened overall workload and time. Currently, many researchers are investigating ionic liquids and deep eutectic solvents as environmentally friendly chemicals that could lead to full classification of HF-LPME as a green analytical procedure.
Performance optimization of a membrane assisted passive sampler for monitoring of ionizable organic compounds in water
Journal of Environmental Monitoring, 2008
Journal of Chemistry
This work aimed at optimizing the QuEChERS method with PSA and then comparing it with Moringa Ole... more This work aimed at optimizing the QuEChERS method with PSA and then comparing it with Moringa Oleifera seed protein as a clean-up sorbent for the extraction of endocrine-disrupting chemicals. The response surface methodology approach was used in the optimization. A design of experiment (DoE) was used to investigate the effect of the sample mass (0.5–3 g), centrifuge speed (3400–4000 rpm) and time (5–20 min), the mass of N a C l and MgSO 4 1 − 3 g , and solvent extraction volume (5–10 mL). The analysis was done using GC-ECD and GC × GC TOFMS. The PSA method which was later replaced with Moringa Oleifera seed protein presented optimal values of 3 g of sample, 150 mg PSA, 4000 rpm for 6 min centrifuge conditions, including 2 g NaCl and 2 g MgSO 4 extracted in 10 mL methanol, respectively. Moringa Oleifera seed protein gave better selectivity, and the detection limits ranged between 0.16 and 1.77 μ g kg − 1 with RSD values ≤ 13.32 % , respectively. Moreover, recoveries were betwee...
Optimisation of semi-upscaled polymer inclusion membrane (PIMs) based device for passive remediation of metal ions in acid mine drainage (AMD)
Journal of Water Process Engineering
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Papers by Hlanganani Tutu