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SNAP-tag technology: a useful tool to determine affinity constants and other functional parameters of novel antibody fragments
No full textAntibody derivatives, such as the single chain fragment variable (scFv), can be developed as diagnostic and therapeutic tools in cancer research, especially in the form of fusion proteins. Such derivatives are easier to produce and modify than monoclonal antibodies (mAbs) and achieve better tissue/tumor penetration. The genetic modification of scFvs is also much more straightforward than the challenging chemical modification of mAbs. Therefore, we constructed two scFvs derived from the approved monoclonal antibodies cetuximab (scFv2112) and panitumumab (scFv1711), both of which are specific for the epidermal growth factor receptor (EGFR), a well-characterized solid tumor antigen. Both scFvs were genetically fused to the SNAP-tag, an engineered version of the human DNA repair enzyme O6-alkylguanine DNA alkyltransferase that allows the covalent coupling of benzylguanine (BG)-modified substrates such as fluorescent dyes. The SNAP-tag achieves controllable and irreversible protein modification and is an important tool for experimental studies in vitro and in vivo. The affinity constant of a scFv is a key functional parameter, especially in the context of a fusion protein. Therefore, we developed a method to define the affinity constants of scFv-SNAP fusion proteins by surface plasmon resonance (SPR) spectroscopy. We could confirm that both scFvs retained their functionality after fusion to the SNAP-tag in a variety of procedures and assays, including ELISA, flow cytometry, and confocal microscopy. The experimental procedures described herein, and the new protocol for affinity determination by SPR spectroscopy, are suitable for the preclinical evaluation of diverse antibody formats and derivatives.National Research Foundation (South Africa
Neutral hydrogen and magnetic fields in M83 observed with the SKA Pathfinder KAT-7
No full textWe present new KAT-7 observations of the neutral hydrogen (HI) spectral line, and polarized radio continuum emission, in the grand design spiral M83. These observations provide a sensitive probe of the outer disk structure and kinematics, revealing a vast and massive neutral gas distribution that appears to be tightly coupled to the interaction of the galaxy with the environment. We present a new rotation curve extending out to a radius of 50 kpc. Based on our new HI dataset and comparison with multiwavelength data from the literature we consider the impact of mergers on the outer disk and discuss the evolution of M83. We also study the periphery of the HI distribution and reveal a sharp edge to the gaseous disk that is consistent with photoionization or ram pressure from the intergalactic medium (IGM). The radio continuum emission is not nearly as extended as the HI and is restricted to the main optical disk. Despite the relatively low angular resolution we are able to draw broad conclusions about the large-scale magnetic field topology. We show that the magnetic field of M83 is similar in form to other nearby star forming galaxies, and suggest that the disk-halo interface may host a large-scale regular magnetic fieldNational Research Foundation (South Africa
HI in Group Interactions: HCG 44
No full textExtending deep observations of the neutral atomic hydrogen (HI) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example and we have combined HI data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (N_HI < 2x10^18 cm^-2) to the neutral gas over a large field-of-view beyond the compact group itself. We find the giant HI tail north of HCG 44 contains 1.1x10^9 M_Sun of gas and extends 450 kpc from the compact group: twice as much mass and 33% further than previously detected. However, the additional gas is still unable to account for the known HI deficiency of HCG 44. The tail likely formed through a strong tidal interaction and HI clouds in the tail have survived for 1 Gyr or more after being stripped. This has important implications for understanding the survival of neutral clouds in the intragroup and circumgroup medium, and we discuss their survival in the context of simulations of cold gas in hot halos. HCG 44 is one of a growing number of galaxy groups found to have more extended HI in the intragroup and circumgroup medium than previously measured. Our results provide constraints for simulations on the properties of galaxy group halos, and reveal a glimpse of what will be seen by future powerful HI telescopes and surveysNational Research Foundation (South Africa
Between the church and the marketplace: how professional gospel musicians negotiate the tension between sacred and market contexts, with reference to the case of No Limits, a vocal music group from Soweto
No full textThe music industry as a sector of cultural industries provides an environment for musicians
to engage with the business of music. Churches, as religious and social environments,
provide a platform for musical activity and development for musicians. While the church has
provided musical development, the music industry has been looked to for sustaining musical
careers. Using the adaptation of the Landry value chain model, this research highlights
difficulties and successes that No Limits, a South African music group, has encountered in
pursuing a professional career in sacred and marketplace contexts. In turn, this has revealed
management and general administrative issues that independent musicians commonly face
in their pursuit of a professional career. The study observes how professional gospel
musicians handle the tension between the sacred and market contexts based on the
assumption that these contexts have varying operating systems and thus present a difficulty
for professional musicians seeking to operate in both contexts. The introductory chapter and
the literature review provide the background and context for the study, the relevant historical
information and the Seventh-day Adventist church context. A detailed narrative of the
development of No Limits is provided in the fourth chapter leading to the analysis presented
in the fifth chapter, which expands on specific moments and issues discussed in the
narrative within Charles Landry’s framework of a value chain. His model suggests an
integration of all the activities in the value chain in order to succeed in cultural pursuits.
These entail beginnings, production, circulation, delivery mechanisms and audience
reception (with feedback). No Limits was, therefore, analysed in terms of this model. Key
findings point to the difficulty associated with the professionalisation of the music occupation,
of seeking to be altruistic and sustainable at the same time. Also, that social and cultural
value of devotional content from the sacred context and the material economic demands
from the marketplace characterise the fundamental tensions for musicians pursuing
existence in these contexts. The Seventh-day Adventist church, in which No Limits was
incubated, provided the immediate context for this study and the data was collected through
an analysis of archives, discography and interviews with different individuals in the No Limits
value chain.National Research Foundatio
The preparation, characterization and phenylacetylene polymerization of novel palladacycles
No full textThis thesis describes the synthesis and characterization of novel cationic palladacycles derived
from various N-benzylidene-2,6-diisopropylaniline ligands and their use as catalysts in the
polymerization of phenylacetylene.
A series of N-benzylidene-2,6-diisopropylaniline ligands of general formula
(2-R-C6H3)CH=N-(2,6-iPr2-C6H3), (R = H (L1); R = Cl (L2); R = Br (L3); R = F (L4); R = OMe (L5))
were prepared by the Schiff-base condensation reaction of 2,6-diisopropylaniline with the respective
mono-substituted aldehyde in a 1:1 molar ratio. Reactions of ligands L1-L5 with (MeCN)2PdCl2 in a
1:1 molar ratio in the presence of NaOAc generated the dinuclear µ-Cl palladacycles (C1-C5) of the
type [PdCl(R-C6H3)CH=N-{2,6-(iPr)2-C6H3}]2 (R = H (C1), Cl (C2), Br (C3), F (C4), OMe (C5)). The
complexes were characterized by FT-IR-,
1H- and 13C{1H} NMR spectroscopy.
The mononuclear neutral palladacycles of the type [Pd(PR’3)Cl(R-C6H3)CH=N{2,6-iPr2-C6H3}Cl]
(PR’3 = PTA (C6-C10); PR’3 = PCy3 (C16-C20); PR’3 = PPh3 (C26-30)) were prepared by the cleavage
of the µ-Cl palladacycles C1-C5 with two molar equivalents of the respective phosphine ligand. These
complexes were fully characterized by FT-IR-,
1H-, 13C{1H}- and 31P{1H} NMR spectroscopy, ESI-MS
spectrometry as well as elemental analysis. Single crystal X-ray diffraction analysis of complexes C8,
C9, C18 and C30 confirmed that the geometry around the metal centre is slightly distorted square planar
and that the coordination of the phosphine ligand is trans relative to the imine moiety.
To generate the novel mononuclear cationic palladacycles, complexes C6-C10, C16-C20 and
C26-C30 were subjected to chloride abstraction by NaBAr4 (Ar4 = 3,5-bis(trifluoromethyl)phenyl) in
the presence of MeCN as coordinating solvent resulting in the cationic analogues with general formula
[Pd(MeCN)(PR’3)(R-C6H3)CH=N-{2,6-(iPr)2-C6H3}]+
[B(Ar)4]
-
(PR’3 = PTA (C11-C15); PR’3 = PCy3
(C21-C25); PR’3 = PPh3 (C31-35)) being isolated as air- and moisture-stable solids. These complexes
Stellenbosch University https://scholar.sun.ac.za
Abstract
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were characterized by FT-IR-,
1H-, 13C{1H}- and 31P{1H} NMR spectroscopy, ESI-MS spectrometry,
elemental analysis and in the case of complexes C15 and C25 by single crystal X-ray diffraction.
Spectroscopy data reveals that the coordination of the phosphine ligand to the metal centre remains
trans relative to the imine moiety after coordination of the acetonitrile ligand. From the crystal
structures of C15 and C25 it was observed that both complexes have a slightly distorted square planar
geometry around the metal centre with the plane of the 2,6-diisopropylaniline moiety almost
perpendicular to the plane of the endocycle ring.
The reactivity of the novel cationic palladacycle complexes (C11-C15, C21-C25, C31-C35)
towards phenylacetylene was evaluated. All complexes evaluated showed some degree of activity in
phenylacetylene polymerization, with conversions ranging from 56 % to 95 %. A mixture of both
cis-transoidal and trans-cisoidal polyphenylacetylene (PPA) were produced at room temperature with
moderate molecular weights while the trans-cisoidal PPA can selectively be produced when the
reactions are performed at slightly higher temperatures (60 °C). The nature of the ortho-substituent on
the cyclometallated-ring had a marked effect on the efficiency of the catalysts with the highest
conversion of 95 % being obtained for the complex with the most electron withdrawing substituent
(C14). Increasing the steric bulk of the auxiliary phosphine ligand leads to higher molecular weight
polyphenylacetylene being produced.National Research Foundatio
An economic perspective on school leadership and teachers' unions in South Africa
No full textThis dissertation considers two factors that are considered critical to disrupting an existing culture of
inefficiency in the production of learning in South Africa, namely school leadership and teachers’
unions.
This first part of the dissertation positions itself within a growing discourse in the economics
literature, and in local policy circles, on the importance of harnessing the role of school principals as a
route to educational progress. Using a unique dataset constructed by matching administrative datasets
in education, the study aims to provide greater specificity to our understanding of the labour market
for school principals in South Africa. Chapter two constructs a quantitative profile of this market with
implications for policy reforms in raising the calibre of school leadership. It identifies existing
inequalities in the distribution of qualified and experienced principals across poorer and wealthier
schools, gender disparities in principal positions, low levels of principal mobility across the public
education system and high tenure. Together, the evidence points to the need for policies aimed at
improving the initial match of principals to schools while developing incumbent principals over their
length of tenure. The findings highlight that improving the design and implementation of policies
guiding the appointment process for principals is a matter of urgency. A substantial and increasing
number of principal retirements are taking place across South African schools given a rising age
profile of school principals. Selection criteria need to be amended to identify relevant expertise and
skills, rather than relying on principal credentials as captured in payroll data which are shown to be
poor signals of principal quality.
While the rising number of principal retirements presents an opportunity to replace weaker principals
with better performing ones, this will be accompanied by various challenges including recruiting,
selecting and hiring suitable candidates. Moreover, it takes time for school principals to have their full
effect on school environments and initially, school performance may decline in response to a
leadership succession. Using a fixed effects estimation approach, chapter three suggests that principal
changes are indeed initially detrimental to school performance, especially in poorer schools. These
results are robust to using an alternative estimation strategy following the work of Heckman, Ichimura
and Todd (1997) to control for additional sources of estimation bias. The chapter also considers two
mechanisms through which school leadership changes may impact on school performance, namely
through rising promotion rates and teacher turnover.
After the discussion on school leadership, chapter four shifts its focus to measure teacher union
impacts on educational outcomes by investigating a disruption hypothesis that student learning is lost
as a direct consequence of teacher participation in strike action, particularly the intensive public sector strike of 2007. The study exploits heterogeneity that exists within schools in the level of teacher union
militancy to control for confounding factors that may bias estimates of strike effects. An acrosssubject
within-student analysis, following an approach by Kingdon and Teal (2010), suggests that
teacher strike participation negatively affects learning for students in the poorest three quarters of
schools in South Africa. However, the discussion reveals difficulties in isolating out, specifically,
unobserved teacher characteristics that may bias the observed strike effect. There is suggestive
evidence that the most marginalised students in rural areas, and those that are weaker academically,
are most at risk of learning losses as a result of teacher strikes. In this respect, industrial action has
implications for widening existing inequalities in student achievement across the South African
education system.National Research Foundatio
Novel streptomycete antimicrobial compounds: activity against pathogens from domestic rainwater harvesting systems
No full textDue to increased urbanisation, frequent droughts and poor water sources in rural communities,
the scarcity of water has become a major concern. Water is an essential part of life – in order to
meet the ever growing demand for water, it is imperative to search for alternative water
sources. Domestic rainwater harvesting (DRWH) is considered a potential source of water and is
commonly used in most parts of the world. However, the microbial quality of harvested
rainwater poses a serious health risk to the consumer. Pathogenic bacteria such as
Staphylococcus spp., Salmonella spp., Pseudomonas aeruginosa and Klebsiella spp., amongst
others, have been associated with rainwater harvesting systems and the poor quality of the
water is mainly attributed to faecal contamination caused by mammals, birds and reptiles.
Generally, these pathogenic strains are highly virulent and are often resistant to common
antimicrobials utilised for the treatment of diseases caused by these pathogens. An increase in
drug-resistant infectious diseases presents a significant challenge to antimicrobial therapies.
Urgent developments of novel antimicrobial agents are required to treat a wide spectrum of
targets which include bacteria, fungi, viruses and parasites.
Actinomycetes are a group of soil microorganisms known for the production of bio-active
compounds. Streptomyces pharetrae CZA14T is one such actinomycete which was first
described in 2005. Preliminary tests revealed that the strain has the ability to produce bioactive
compounds. Subsequently, the genome of CZA14T
was sequenced and submitted to an
online secondary metabolite prediction software, antiSMASH, to predict secondary metabolite
biosynthetic gene clusters (smBGCs) which then govern the expression of the compounds of
interest. Fifty-five smBGCs encoding for secondary metabolites of interest were predicted by
antiSMASH, of which, 23 were non-ribosomal peptide synthetases (NRPSs), seven were
lantipeptide/lassopeptides/bacteriocins, eight were polyketide synthases (PKSs) and the
remaining 17 biosynthetic gene clusters include genes for siderophores, terpenes,
butyrolactones, ectoines, melanin and genes labelled as “other”.
In the current study, previously identified optimal production media and fermentation
conditions for maximum antimicrobial production by CZA14T
were scaled-up from 0.5 L, 1 L and
2 L baffled flasks, to fermentation in a 3 L airlift reactor (ALR) and a 5 L continuous stirred tank
reactor (CSTR). Solvent extractions were performed on both the supernatant and mycelia to
test for extra- and intra-cellular production of bio-active compounds. Fermentation samples
Stellenbosch University https://scholar.sun.ac.za
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were also collected from the ALR at days 3, 6, 9 and 12, and used for molecular studies for
which RNA extraction was performed and cDNA was synthesised and sequenced. Using
molecular techniques, it was determined that CZA14T
possess the genes for the expression of a
Type-II PKS – curamycin A. Sequence information indicated that the Type II PKS involved in the
production of curamycin A was expressed under the fermentation conditions used in the ALR.
This Type-II PKS corresponded to the predicted Type-II PKS from contig 196, cluster 24 of the
CZA14T
genome.
Solvent extracts were analysed using Thin Layer Chromatography (TLC) and the inhibitory
efficacy of the crude and partially purified extracts were determined using filter disk diffusion
and bioautography assays against a range of ATCC clinical test strains and environmental DRWH
system isolates. Compounds separated by TLC showed bands with similar Rf
values when
visualised under UV light throughout all fermentation processes, but the focus of the study was
mostly on the extracts prepared from the fermentation in the ALR. Compounds produced by
CZA14T
exhibited a broad spectrum of bio-activity against all the test strains used in this study,
displaying both anti-bacterial and anti-fungal activity. Compounds produced by CZA14T in the
ALR displayed various chemical and physicochemical characteristics as determined by different
staining methods of the developed TLC plates and UV/Vis spectroscopy of the biologically active
compounds.
The crude compounds were partially purified using silica column chromatography and the
fractions collected were analysed by liquid chromatography-mass spectrometry (LC-MS).
Furthermore, the ALR fermentation broth was subjected to ammonium sulphate precipitation,
dialysis and organic solvent extraction. This yielded a set of bio-active compounds with activity
against various ATCC strains and DRWH system isolates. This sample was also subjected to LCMS
analyses and results showed the presence of a mass (1374.8 m/z) that corresponds to that
of curamycin A, which serves as additional confirmation that the smBGC that encodes for
curamycin A, is expressed under the fermentation conditions used in the ALR. Future studies
will focus on the purification and structural elucidation of the bio-active compounds produced
by CZA14T
, including curamycin A.National Research Foundatio
Synthesis of modified hydrocalumite: a novel katoite/portlandite precursor method
No full textA novel method of synthesising calcium/aluminium layered double hydroxides (LDHs) was developed, which makes use of a katoite/portlandite mixture as a precursor. The precursor mixture is synthesised by reacting CaO and Al(OH)3 in water. The synthesis has no expensive heating steps and does not produce any effluent, making the synthesis a ―green‖ method. (Van der Westhuizen, 2011) The purpose of this investigation was to launch an exploratory study on the effectiveness and limitations of the novel synthesis method when synthesising intercalated calcium/aluminium LDHs.
The novel synthesis method was compared to two traditional synthesis methods: co-precipitation and reconstruction. The novel synthesis method is equally as effective as the reconstruction method for the synthesis of organically modified Ca/Al LDHs. In most intercalations, the precursor method yielded more crystalline products than the reconstruction method. The co-precipitation method with nitrate salts was the least effective, since nitrate was more stable in the interlayer than the majority of the organic anions. For this reason, a Ca/Al-nitrate phase was the dominant crystalline species in these samples. Since the novel synthesis method produces organically modified LDHs of equal or higher quality than the traditional synthesis methods, it is a feasible method for producing LDHs. Since the method is also cheaper and more environmentally friendly than traditional synthesis methods, it is the preferential method for producing organically modified Ca/Al LDHs on a large scale.
When the precursor mixture was hydrated in a reaction vessel that was left open to air from 2 h to 24 h, at temperatures ranging from room temperature to 80 °C, the maximum conversion to hydrocalumite was 15 wt.%. This means that if the reactor is left open to air, there will only be 15 wt.% carbonate contamination from air in the form of hydrocalumite. If a sealed vessel is used, the conversion will be drastically less, since there is a negligible amount of carbon dioxide in the small volume of air trapped in the vessel. For this reason, it is not necessary to synthesise intercalated hydrocalumites in an inert atmosphere, unless 100 % purity is needed.
Chloride-intercalated Ca/Al LDHs form readily at temperatures from room temperature to 60 °C when aged for 2 h to 24 h. A maximum conversion of 64 wt.% occurs when the sample is aged for 12 h at 40 °C. In general, if the sample is aged for extended periods or at elevated temperatures, conversion decreases. A decrease in conversion is always accompanied by an increase in amorphous material, indicating that a more stable, amorphous phase forms if the LDH is aged for too long or at temperatures that are too high. Since no general trends could be found when intercalating chloride, further tests should be performed to determine what other factors influence the ability of the precursor to form an intercalated hydrocalumite.
In general, the conversion of the precursor to a benzoate-intercalated LDH increases with increasing reaction time and decreases with increasing temperature. Benzoate-intercalated LDH did not form at a temperature of 60 °C at any of the aging times tested, indicating that Ca/Al-benzoate is not stable at elevated temperatures. When the samples were aged for 24 h, there are two new primary peaks present on the XRD patterns. For this reason, there is either a new configuration of benzoate in the interlayer or a new crystalline symmetry present in the samples. As the temperature increased, a smaller d-spacing spacing was favoured.
Instead of using a katoite/portlandite mixture, a calcium source in the form of calcium oxide [CaO] or calcium hydroxide [Ca(OH)2] can be added to pure katoite prior to intercalating with an anion. Using an extra calcium source in combination with katoite, instead of the precursor mixture, renders similar results. The CaO converts rapidly to Ca(OH)2; therefore, both calcium sources are equally effective. Contrary to popular belief, an intercalated LDH material does not necessarily have to be synthesised at a high pH. All the weak acids with low solubility tested were able to intercalate at a pH as low as 5. This is not the case for soluble acids. Both strong and weak soluble acids tend to break down the layered material as soon as the pH drops below 10, as reported in literature. However, even for organic acids, it is recommended to keep the pH above 10, in order to maximise retention of layered material. The only benefit to intercalating organic acids at a lower pH is that the precursor and carbonate-intercalated LDH are broken down to a larger extent, making the final product purer.
When a katoite/portlandite precursor material is titrated with different acids, the top-down titration curves display two distinct plateaus for most acids. However, titrations with anthranilic acid shows only one distinct plateau, and titration with OH-substituted benzoic acid rings tend to exhibit an extra plateau. This is because the OH group dissociates at a high pH.
There are several factors affecting intercalation that have not been studied, which may have a large impact on the degree of intercalation. It is, therefore, recommended that the following factors also be investigated:
Mixing efficiency
Boiled vs. non-boiled water
Size of the anion
In order to determine the success of the intercalation experiments, the most important factor to test would be the properties of the intercalated LDH materials in their final applications.National Research Foundatio
Explicit academic vocabulary teaching of two grade 4 natural science and technology teachers in the North West province
No full textGrade 4 learners in South African English medium primary schools face many challenges.
They are confronted with various content-areas and the immense task to acquire the
academic vocabulary of each content-area. Domain-specific textbooks and content-area
lessons are filled with academic vocabulary crucial to the acquisition of conceptual
knowledge and understanding (Antonacci & O’Callaghan, 2011). This is exacerbated by the
fact that for many Grade 4 learners, English is also a Second Language (SL). Learners
need strong academic vocabulary knowledge in order to make sense of academic texts,
complete academic tasks or activities and achieve academic success (Antonacci &
O’Callaghan, 2011; Gardner, 2013; Marzano & Pickering, 2005; Nation, 2001; Snow, 2010).
Therefore, a need exists for the explicit teaching of academic vocabulary in the content-area
classroom, which includes the effective use of a number of language learning strategies
(Oxford, 2013).
Research has continually established that the scope of learners’ vocabulary knowledge
relates greatly to their reading comprehension, conceptual knowledge, school success and
success beyond the classroom (Gardner, 2013). Vocabulary learning, as well as vocabulary
teaching, is thus central to this study. Various components play a role in learning vocabulary,
such as, comprehensible input, the negotiation of meaning, noticing and awareness,
interaction, feedback and output (Mackey, Abbuhl & Gass, 2012). Research has found that
the use of learning strategies is very important for optimal word acquisition, but that these
strategies need to be explicitly taught (Oxford, 2013). There is an urgency to teach
vocabulary explicitly and effective instruction must include the use of various teaching
strategies. This study consequently looked at effective vocabulary teaching programmes
and possible examples of teaching strategies that could be used in the Grade 4 Natural
Sciences domain.
A qualitative case study research design was used in this study. Two Grade 4 Natural
Sciences and Technology teachers at two English medium primary schools in the North
West province were used in this study. Their lessons were observed over a period of four
weeks where the researcher made use of an observation matrix to establish whether the
teachers focused on the development of the learners’ academic vocabulary knowledge of
the Natural Sciences domain. Two sets of semi-structured interviews were conducted. The
interviews were tape-recorded and transcribed. Various documents were also analysed to ascertain what the beliefs and national goals are
in terms of academic vocabulary teaching. The data were analysed by means of content
analysis and by following the steps in Creswell’s (2009) qualitative data analysis process.
After analysing the data, it became clear that the policy document (South Africa. Department
of Education, 2011b) and Teacher’s Guide (Adatia, Barker, Clitheroe, Cohen, De Villiers,
Joannides, Van Zyl, Visagie, & Webb, 2013b) are not sufficient for teaching academic
vocabulary. Other problems were also discovered: the Learner’s Book (Adatia, Barker,
Clitheroe, Cohen, De Villiers, Joannides, Van Zyl, Visagie, & Webb, 2013a) does not focus
on the development of academic vocabulary; the teachers do not plan for the teaching of
academic vocabulary; there is a lack of explicit teaching of vocabulary; teachers lack the
motivation and responsibility to teach academic vocabulary, they are unaware of the types of
academic vocabulary and its importance for learning; they believe that the explicit teaching
of academic vocabulary is time consuming in an already full curriculum; they are unaware of
the national goals and guidelines as outlined in the policy document (SA. DoBE, 2013b);
they are not trained in Intermediate Phase teaching methodology; they lack personal
proficiency and struggle to effectively teach through the medium of English.
Both teachers could benefit from an intervention programme on the learning of academic
vocabulary and training in how to select academic vocabulary and how to teach vocabulary learning strategies.National Research Foundatio
Investigation of the effect of the reagent suite in froth flotation of a merensky ore
No full textThe mining industry is faced with a challenge to develop efficient and economically feasible processing routes owing to the depletion of high-grade ores, and the ever increasing demand for precious metals for a wide range of applications. The valuable minerals, PGMs (Platinum Group Minerals) and BMS (Base Metal Sulphides) in the ores are extracted through the aid of chemical reagents (activators, collectors, depressants, frothers, modifiers) which are added to the flotation circuits to facilitate the separation between these minerals and the undesired gangue minerals present in the ore. The process is made complex by many surface reactions taking place, the existence of secondary and interactive effects among the flotation reagents, as well as the surface liberation of the minerals. Owing to the stringent regulations around water usage, concentrator plants are left with no option but to recycle water within their operations. This practice leads to accumulation of pollutants, such as organics, flotation reagents residues, dissolved ions, etc., which will likely have an influence on the chemical environment of the process, and subsequently will bear an impact on the overall metallurgical performance of the concentrator. This makes the process even more intricate, making it difficult to account for the behaviour of the chemical reagents, as well as making it virtually impossible to precisely assess their individual contribution to the overall flotation performance. Hence it is of crucial importance to adopt a holistic approach when investigating the effects of the chemical parameters in a flotation process. This is a flotation chemistry study that adopted a two-level-four-factor (24) factorial experimental design to evaluate the simultaneous effects of the chemical parameters, with particular reference to collector, depressant, frother, and ionic strength of the synthetic plant water, as well as determining the possible interactive effects between the chosen parameters. This investigation was made possible by conducting batch flotation tests on a PGM-bearing ore from the Merensky reef of the Bushveld Igneous Complex. Sodium isobutyl xanthate (SIBX), a polysaccharide, namely guar gum, and a polyglycol ether, namely Dowfroth 250 were used as the collector, depressant and frother, respectively. These are the typical chemical reagents the dosages of which tailored in the PGM industry for the processing of the ores. The metallurgical performance indicators used were solids, water, copper and nickel recoveries as well as copper and nickel grades.National Research Foundatio