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Analysis of the biogas productivity from dry anaerobic digestion of organic fraction of municipal solid waste

- Matheri, Anthony Njuguna, Sethunya, Vuiswa Lucia, Belaid, Mohamed, Muzenda, Edison, Ntuli, Freeman

Atmospheric oxidative and non-oxidative leaching of Ni-Cu matte by acidified ferric chloride solution

- Sekhukhune, L.M., Ntuli, Freeman, Muzenda, Edison

Management and control of industrial effluents discharged to public sewers : a case study

- Ntuli, Freeman

  • Authors: Ntuli, Freeman
  • Date: 2012
  • Subjects: Biodegradability , Public sewers , Sewerage management , Industrial effluents
  • Type: Article
  • Identifier: uj:6048 , ISSN 2010-376X , http://hdl.handle.net/10210/10457
  • Description: An overview of the important aspects of managing and controlling industrial effluent discharges to public sewers namely sampling, characterization, quantification and legislative controls has been presented. The findings have been validated by means of a case study covering three industrial sectors namely, tanning, textile finishing and food processing industries. Industrial effluents discharges were found to be best monitored by systematic and automatic sampling and quantified using water meter readings corrected for evaporative and consumptive losses. Based on the treatment processes employed in the public owned treatment works and the chemical oxygen demand and biochemical oxygen demand levels obtained, the effluent from all the three industrial sectors studied were found to lie in the toxic zone. Thus, physico-chemical treatment of these effluents is required to bring them into the biodegradable zone...
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The effect of leaching time and ammonia concentration on the atmospheric leaching of copper

- Ntuli, Freeman, Muzenda, Edison, Ramatsa, Ishmael, Belaid, Mohamed, Kabuba, John

Temperature effect on volatile organic compounds – polydimethylsiloxane Interactions

- Muzenda, Edison, Ntuli, Freeman

  • Authors: Muzenda, Edison , Ntuli, Freeman
  • Date: 2011
  • Subjects: Waste gas streams , Volatile organic compounds , Polydimethysiloxane , Gas liquid chromatography
  • Type: Article
  • Identifier: uj:2179 , ISSN 2010-0221 , http://hdl.handle.net/10210/4559
  • Description: Temperature dependence of specific retention volumes (og V) of 13 volatile organic compounds (VOCs) of environmental importance between the gas and liquid stationary phase (polydimethysiloxane) (PDMS) were studied using the gas liquid chromatographic technique (GLC). Temperature was varied from 303.15K to 423.15K to allow transport calculations for different seasons. Four PDMS polymers with average molecular weight ranging from 760 to 13 000 were used as solvents. The results of this work confirm that PDMS is well suited for VOCs scrubbing from waste gas streams. Linear plots of log g V against T1 were obtained in all cases permitting predictions and interpolations to temperatures not studied here. Also dependable enthalpies and entropies of solute transfer from the mobile phase to the stationary phase can be calculated. The specific retention volumes reported in this work are in agreement with literature for similar systems. Efforts were taken to ensure the best possible accuracy and trace the possible sources of error. A gas liquid chromatographic system which secured a simple retention mechanism and showed reproducible solute retention over a long period of time was devised.
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The removal of Ni, Cu & Fe from a mixed metal system using sodium hypophosphite as a reducing agent

- Ngema, Promise Sethembiso, Ntuli, Freeman, Belaid, Mohamed

Municipal solid waste composition determination in the city of Johannesburg

- Ayeleru, Olusola Olaitan, Ntuli, Freeman, Mbohwa, Charles

An investigation into the effect of temperature on the leaching of copper-matte

- Muzenda, Edison, Ramatsa, I.M., Ntuli, Freeman, Belaid, Mohamed, Tshwabi, P.M.

  • Authors: Muzenda, Edison , Ramatsa, I.M. , Ntuli, Freeman , Belaid, Mohamed , Tshwabi, P.M.
  • Date: 2011
  • Subjects: Coppermatte leaching - Effect of temperature , Leaching - Effect of temperature
  • Type: Article
  • Identifier: uj:4703 , http://hdl.handle.net/10210/10944
  • Description: A study was carried out to determine the influence of the temperature and the reaction involved on the leaching of coppermatte. Copper (Cu) bearing matte from Impala Refinery (Pty) Ltd was used in the investigation. The experiments were conducted in a leaching cell submerged in a water bath, with ammonia concentrations (leaching solution) of 3.0M, temperature of 50°C, 60°C and 70°C, pH of 11 and for a time period of 130 minutes. Leaching tests indicated that Cu recovery increased in the temperature range 50°C - 60°C, however at a temperature of 70°C Cu recovery decreases because of cementation process as nickel displace copper. The shrinking core model was used to determine if the leaching process was diffusion controlled, or chemical controlled, or even mixed controlled. It was found that the leaching process could not be determined using the shrinking core model due to the cementation process of Cu. It was concluded that an increase in temperature results in an increase in the Cu recovery however the temperature should not be too high as cementation process increase with increasing temperature.
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Thermodynamics of Cu (II) adsorption onto South African clinoptilolite from synthetic solution by ion exchange process.

- Kabuba, John, Ntuli, Freeman, Muzenda, Edison, Mollagee, Mansoor

Performance of sodium mercaptobenzothiazole (NMBT) collector on the flotation of Black Mountain ore

- Ikotun, Adeshina G., Muzenda, Edison, Ntuli, Freeman, Belaid, Mohamed

  • Authors: Ikotun, Adeshina G. , Muzenda, Edison , Ntuli, Freeman , Belaid, Mohamed
  • Date: 2012
  • Subjects: Black Mountain ore , Copper metal , Sodium mercaptobenzothiazole
  • Type: Article
  • Identifier: uj:4689 , http://hdl.handle.net/10210/10478
  • Description: This paper investigated the performance of Sodium Mercaptobenzothiazole (NMBT) as a collector in the flotation of Black Mountain ore. The ore contains metals such as lead, copper and zinc and the associated minerals of economic importance are chalcopyrite, galena and sphalerite respectively, with traces of silver. The study evaluated the effectiveness of the collector and how pH affects the recovery of minerals in particular copper. The performance of the collector was influenced by mineral surface chemistry. The experimental test work was conducted at varying pH levels using Denver flotation cell in order to investigate the collector performance in a basic medium. The experiments were conducted at two different test runs of slightly basic solutions of pH 8.5 and 9.0. The results of both fresh ore and floated ore samples were analysed using XRF. Although Black mountain ore contains small quantities of copper as compared to other ores, a significant amount w recovered (±78% of the available copper in the ore), as an indication of the performance of NMBT.
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The effect of leaching time and ammonia concentration on the atmospheric leaching of copper

- Ntuli, Freeman, Muzenda, Edison, Ramatsa, Ishmael, Belaid, Mohamed, Kabuba, John

  • Authors: Ntuli, Freeman , Muzenda, Edison , Ramatsa, Ishmael , Belaid, Mohamed , Kabuba, John
  • Date: 2011
  • Subjects: Copper recovery , Leaching , Ammonia concentrations
  • Type: Article
  • Identifier: uj:5319 , ISSN 2010-4618 , http://hdl.handle.net/10210/8195
  • Description: The effects of ammonia concentration and leaching time were investigated to determine the optimum leaching conditions. The experiments were conducted in a leaching cell submerged in a water bath, with ammonia concentrations of 1.5 M, 2.0 M, 2.5 M and 3.0 M and varying leaching time from 0 to 300 min. Ni-Cu matte containing 23% by mass Cu was used in this experimental study. Increase in the concentration of the lixiviant was found to increase recovery when leaching for 130 minutes, with a recovery of 32.86% Cu using 3 M solution of ammonia. An increase in the leaching time resulted in more copper being leached for all lixiviant concentrations. However, leaching with 2 M ammonia solution gave a higher yield of copper compared to higher concentrations. This anomaly could be a result of cementation; Cu is displaced by Ni as Ni is a more electronegative metal than Cu .It was found that at higher concentrations more nickel was extracted.
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Thermal decomposition of sewage sludge under N2, Co2 and air : gas characterization and kinetic analysis

- Hernández, Ana Belén, Okonta, Felix, Ntuli, Freeman

  • Authors: Hernández, Ana Belén , Okonta, Felix , Ntuli, Freeman
  • Date: 2017
  • Subjects: Thermogravimetric analysis , Bioenergy , Waste treatment
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/246190 , uj:25515 , Citation: Hernández, A.B., Okonta, F. & Ntuli, F. 2017. Thermal decomposition of sewage sludge under N2, Co2 and air : gas characterization and kinetic analysis.
  • Description: Abstract: Thermochemical valorisation processes that allow energy to be recovered from sewage sludge, such as pyrolysis and gasification, have demonstrated great potential as convenient alternatives to conventional sewage sludge disposal technologies. Moreover, these processes may benefit from CO2 recycling. Today, the scaling up of these technologies requires an advanced knowledge of the reactivity of sewage sludge and the characteristics of the products, specific to the thermochemical process. In this study the behaviour of sewage sludge during thermochemical conversion, under different atmospheres (N2, CO2 and air), was studied, using TGA-FTIR, in order to understand the effects of different atmospheric gases on the kinetics of degradation and on the gaseous products. The different steps observed during the solid degradation were related with the production of different gaseous compounds. A higher oxidative degree of the atmosphere surrounding the sample resulted in higher reaction rates and a shift of the degradation mechanisms to lower temperatures, especially for the mechanisms taking place at temperatures above 400 C. Finally, a multiple first-order reaction model was proposed to compare the kinetic parameters obtained under different atmospheres. Overall, the highest activation energies were obtained for combustion.This work proves that CO2, an intermediate oxidative atmosphere between N2 and air, results in an intermediate behaviour (intermediate peaks in the derivative thermogravimetric curves and intermediateactivation energies) during the thermochemical decomposition of sewage sludge. Overall, it canbe concluded that the kinetics of these different processes require a different approach for their scaling up and specific consideration of their characteristic reaction temperatures and rates should be evaluated.
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Adsorption of Cu and Ni from AMD using activated bentonite

- Ntuli, Freeman, Falayi, Thabo, Molala, Panelope

Leaching kinetics on the removal of phosphorus from waste phosphogypsum by application of shrinking core model

- Mashifana, Tebogo, Ntuli, Freeman, Okonta, Felix

  • Authors: Mashifana, Tebogo , Ntuli, Freeman , Okonta, Felix
  • Date: 2018
  • Subjects: Phosphogypsum , Leaching , Kinetics
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/286415 , uj:30991 , Citation: Mashifana, T., Ntuli, F. & Okonta, F. 2018. Leaching kinetics on the removal of phosphorus from waste phosphogypsum by application of shrinking core model. South African Journal of Chemical Engineering, 27:1-6. https://doi.org/10.1016/j.sajce.2018.11.001
  • Description: Abstract: This study investigated the removal of phosphorus from waste phosphogypsum by using citric acid as a leaching reagent, evaluated the potential environmental effect of the final product produced and provide recommenda- tions for the application of developed products. A dissolution process was applied and three variables were studies namely, concentration, stirring speed and temperature. The results showed that Phosphorus can suc- cessfully be removed from waste phosphogypsum and the optimum leaching conditions were at the con- centration of 0.5 M and temperature of 40 °C, with no effect observed on varying the stirring speed. Shrinking core model (SCM) was used to determine the best fit for the experimental data. For the pore diffusion model (KD), all correlation coefficients yielded were above 0.9, illustrating a positively linear correlation of KD and leaching behavior for phosphorus. Pore diffusion proved to be the effective rate controlling mechanism for the removal of phosphorus from phosphogypsum. The analysis of moments of particle size distribution (PSD) also showed a reduction in particle size, indicating the dissolution of the solid particles. The application of Toxic Leaching Characteristic Procedure (TLCP) showed low concentrations on the effluent, indicating that the de- veloped product will not contaminate the environment through leaching. The obtained leachate concentrations were within the South African effluent discharge standards. The results also showed that dissolution had a significant contribution on the moments of particle size distribution, in terms of the volume, surface area and particles number. In respect to unconfined compressive strength the products developed can be used for load bearing and as backfill material.
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Kinetics study of ammonia removal from synthetic waste water

- Muzenda, Edison, Kabuba, John, Ntuli, Freeman, Mollagee, Mansoor

  • Authors: Muzenda, Edison , Kabuba, John , Ntuli, Freeman , Mollagee, Mansoor
  • Date: 2011
  • Subjects: Ammonium exchange , Langmuir isotherm , Clinoptilolite , Synthetic waste water
  • Type: Article
  • Identifier: uj:4698 , http://hdl.handle.net/10210/10933
  • Description: The aim of this study was to investigate ammonium exchange capacity of natural and activated clinoptilolite from Kwazulu-Natal Province, South Africa. X-ray fluorescence (XRF) analysis showed that the clinoptilolite contained exchangeable ions of sodium, potassium, calcium and magnesium. This analysis also confirmed that the zeolite sample had a high silicon composition compared to aluminium. Batch equilibrium studies were performed in an orbital shaker and the data fitted the Langmuir isotherm very well. The ammonium exchange capacity was found to increase with pH and temperature. Clinoptilolite functionalization with hydrochloric acid increased its ammonia uptake ability.
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Effect of pH on the recovery and grade of base metal sulphides (PGMs) by flotation

- Muzenda, Edison, Afolabi, Ayo S., Abdulkareem, Ambali S., Ntuli, Freeman

  • Authors: Muzenda, Edison , Afolabi, Ayo S. , Abdulkareem, Ambali S. , Ntuli, Freeman
  • Date: 2011
  • Subjects: Platinum Group Metals , Metal sulphides , Flotation
  • Type: Article
  • Identifier: uj:4713 , ISSN 2078-0966 , http://hdl.handle.net/10210/10959
  • Description: This study investigated the effect of pH on the recovery and grade of the Platinum Group Metals (PGMs) and base metal sulphides from the UG2 ore of the Bushveld Complex. This was achieved through running a series of test work in a Denver flotation cell at varying pH 6-11 at constant reagent dosage. The UG-2 reef is characterized by two predominant gangue phases i.e. chromite and silicate, that have significantly different physical and chemical properties. The test work was aimed at evaluating which pH gives best recoveries, and finding the effect of the chrome content in these recoveries. A pH of 9 gave the highest recovery compared to other pH ranges. However, the highest PGM grade was attained at a pH of 6 which is slightly acidic. Ideally this trend could be expected since the collectors (xanthates) are more stable in alkaline medium. The higher PGM recovery was also accompanied by higher chrome content as a result of their similar chemical properties.
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Characterisation of fruits and vegetables wastes in the city of Johannesburg

- Ayeleru, Olusola Olaitan, Ntuli, Freeman, Mbohwa, Charles

  • Authors: Ayeleru, Olusola Olaitan , Ntuli, Freeman , Mbohwa, Charles
  • Date: 2016
  • Subjects: Fruits , Johannesburg market , Vegetables
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://ujcontent.uj.ac.za8080/10210/388885 , http://hdl.handle.net/10210/214113 , uj:21237 , Citation: Ayeleru, O.O., Ntuli, F & Mbohwa, C. 2016. Characterisation of fruits and vegetables wastes in the city of Johannesburg.
  • Description: Abstract: Municipal solid waste (MSW) composition study is very important as a baseline to utilizing fresh fruit and vegetables (FFVs) wastes in waste to energy (WtE) project. The aim of this paper is to determine the composition of various waste components at the Johannesburg FFVs market. The study was conducted during the summer in 2015 to evaluate the various components of fruit and vegetable wastes (FVWs) generated at the market. This was done in order to evaluate the amount of FVWs that are generated daily at the market as a starting point for waste to energy (WtE) proposition for the City of Johannesburg (CoJ). Two international standards: ASTM D5231-92 - 2008 (American Standard Test Method) and UNEP/IETC -2009 (United Nations Environment Programme/International Environmental Technology Centre) were used as yardsticks for the procedure used. Samples were classified based on their colours; green (vegetables and fruits), blue/purple (vegetables and fruits), tan/brown (vegetables and fruits), yellow/orange (vegetables and fruits), red (vegetables and fruits) and other wastes which include corrugated boxes, metals, woods, plastic crates and other composite wastes. Samples were further classified into 135 classes in which some were not available due to seasonal variation and the samples were manually sorted by hands. From the results of the analysis, fruits constituted 55%, vegetables 38%, corrugated boxes and cartons 3%, metals, plastics, woods and other wastes all constituted 1% each.
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Examination of flotation reagents suitable for nickel concentrator plant

- Kabuba, John, Muzenda, Edison, Ntuli, Freeman

  • Authors: Kabuba, John , Muzenda, Edison , Ntuli, Freeman
  • Date: 2011
  • Subjects: Nickel concentrator plant , Flotation reagents - Evaluation , Frother , Magnetic separation
  • Type: Article
  • Identifier: uj:6249 , ISSN 2010-4618 , http://hdl.handle.net/10210/8193
  • Description: Examination of flotation reagents suitable for a nickel concentrator plant was investigated using nickel sulphide ore. A number of different new reagents were examined for the best suit for the nickel concentrator plant. It was found that more nickel was found on the magnetic particles, which were assumed to be mostly pyrrhotite. A dosage of 50 g/t was found to be a suitable dose for the collector Betacol 380 AC and gave the best results, however, it was found to be expensive. Betacol 380 AB was found to be suitable at a dose of 75% g/t. There was no flotation improvement when depressants were used in conjunction with Betacol 380 AC. An activator (copper sulphate) was found to improve the grade of copper, nickel and iron meaning it activated pentlandite. The ions improved the flotability of sulfides at the normal process pH after grinding in steel mill.
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Waste management, strategies and situation in South Africa : an overview

- Muzenda, Edison, Ntuli, Freeman, Pilusa, Tsietsi Jefrey

  • Authors: Muzenda, Edison , Ntuli, Freeman , Pilusa, Tsietsi Jefrey
  • Date: 2012
  • Subjects: Waste management - South Africa , Refuse disposal - South Africa
  • Type: Article
  • Identifier: uj:6044 , ISBN 2010-376X , http://hdl.handle.net/10210/10452
  • Description: This paper highlights some interesting facts on South African’s waste situation and management strategies, in particular the Integrated Waste Management. South Africa supports a waste hierarchy by promoting cleaner production, waste minimisation, reuse, recycling and waste treatment with disposal and remediation as the last preferred options in waste management. The drivers for waste management techniques are identified as increased demand for waste service provision; increased demand for waste minimisation; recycling and recovery; land use, physical and environmental limitations; and socio-economic and demographic factors. The South African government recognizes the importance of scientific research as outlined on the white paper on Integrated Pollution and Waste Management (IP and WM) (DEAT, 2000).
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The effect of poly(ethylene-alt-maleic anhydride) on the reduction crystallization behaviour of nickel powder

- Bodoza, T.F., Ntuli, Freeman, Chauke, D.F., Muzenda, Edison

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