A mathematical model of two-phase systems, such as clay suspensions, consists of a set of partial differential equations which reflect both the general laws of mechanics and the relations connecting the involved characteristics of the particular system under consideration. The latter equations are known as constitutive relations. The aim of this study was to find the constitutive relations for kaolin suspensions that are necessary when solving forward problems of fine sludge thickening processes. The task was to design and carry out experimental research of the given suspension and to find a convenient method of utilizing the results for the sake of getting the sought relationships. It follows from the applied mathematical theory of two-phase systems that the sought relationships are hydraulic conductivity of the suspension as a function of the solid-phase concentration and the dependence of the solid-phase concentration on the solid-phase stress. The first part of this study describes the experimental research. Since both the characteristics are difficult to measure, it was necessary to analyze the suspension's characteristics and their measurability. Subsequently, the process of the suspension preparation and the method of laboratory measurements were determined. The following sections present...

Microcalorimetric measurements and contact angle measurements were conducted to study the surface chemistry of powdered minerals. The contact angle measurements were conducted on both flat and powdered talc samples, and the results were used to determine the surface free energy components using Van Oss-Chaudhury-Good (OCG) equation. It was found that the surface hydrophobicity of talc increases with decreasing particle size. At the same time, both the Lifshitz-van der Waals (gSLW) and the Lewis acid-base (gSAB) components (and, hence, the total surface free energy (gS)) decrease with decreasing particle size. The increase in the surface hydrophobicity and the decrease in surface free energy (gS) can be attributed to preferential breakage of the mineral along the basal plane, resulting in the exposure of more basal plane surfaces to the aqueous phase. Heats of immersion measurements were conducted using a flow microcalorimeter on a number of powdered talc samples. The results were then used to calculate the contact angles using a rigorous thermodynamic relation. The measured heat of immersion values in water and calculated contact angles showed that the surface hydrophobicity of talc samples increase with decreasing particle size, which agrees with the direct contact angle measurements. A relationship between advancing water contact angle qa, and the heat of immersion (-DHi) and surface free energies was established. It was found that the value of -DHi decrease as qa increases. The microcalorimetric and direct contact angle measurements showed that acid-base interactions play a crucial role in the interaction between talc and liquid. Using the Van Oss-Chaudhury-Good's surface free energy components model, various talc powders were characterized in terms of their acidic and basic properties. It was found that the magnitude of the Lewis electron donor, gS-, and the Lewis electron acceptor, gS+, components of surface free energy is directly related to the particle size. The gS- of talc surface increased with decreasing particle size, while the gS+ slightly decreased. It was also found that the Lewis electron-donor component on talc surface is much higher than the Lewis electron-acceptor component, suggesting that the basal surface of talc is basic. The heats of adsorption of butanol on various talc samples from n-heptane solution were also determined using a flow microcalorimeter. The heats of adsorption values were used to estimate % hydrophilicity and hydrophobicity and the areal ratios of the various talc samples. In addition, contact angle and heat of butanol adsorption measurements were conducted on a run-of-mine talc sample that has been ground to two different particle size fractions, i.e., d50=12.5 mm and d50=3.0 mm, respectively. The results were used to estimate the surface free energy components at the basal and edge surfaces of talc. It was found that the total surface free energy (gS) at the basal plane surface of talc is much lower than the total surface free energy at the edge surface. The results suggest also that the basal surface of talc is monopolar basic, while the edge surface is monopolar acidic. The results explain why the basicity of talc surface increases with decreasing particle size as shown in the contact angle and microcalorimetric measurements. Furthermore, the effects of the surface free energies of solids during separation from each other by flotation and selective flocculation were studied. In the present work, a kaolin clay sample from east Georgia was used for the beneficiation tests. First, the crude kaolin was subjected to flotation and selective flocculation experiments to remove discoloring impurities (i.e., anatase (TiO2) and iron oxides) and produce high-brightness clay with GE brightness higher than 90%. The results showed that a clay product with +90% brightness could be obtained with recoveries (or yields) higher than 80% using selective flocculation technique. It was also found that a proper control of surface hydrophobicity of anatase is crucially important for a successful flotation and selective flocculation process. Heats of immersion, heats of adsorption and contact angle measurements were conducted on pure anatase surface to determine the changes in the surface free energies as a function of the surfactant dosage (e.g. hydroxamate) used for the surface treatment. The results showed that the magnitude of the contact angle and, hence, the surface free energy and its components on anatase surface varies significantly with the amount of surfactant used for the surface treatment. / Ph. D.

The objective of my work was to develop HDPE clay nanocomposites for packaging with superior barrier (gas and water) properties by economical processing technique. This work also represents a comparative study of thermoplastic nanocomposites for packaging based on linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon12. In this study properties and processing of a series of linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon 12 nanocomposites based on Na-MMT clay and two different aspect ratio grades of kaolinite clay are discussed.

Food packaging should ensure the safety and quality of food, minimize spoilage and provide an easy way of storing and handling it. Barrier coatings are generally used to meet the demands placed on fibre-based food packages, as these have the ability to regulate the amount of gases that can enter them. Some gases are detrimental to food quality: oxygen, for example, initiates lipid oxidation in fatty foods. Using both experimental data and computer modelling, this thesis explains some aspects of how the structure of barrier coatings influences the mass transport of oxygen with the aim of obtaining essential knowledge that can be used to optimize the performance of barriers. Barrier coatings are produced from polyvinyl alcohol and kaolin blends that are coated onto a polymeric support. The chemical and physical structures of these barriers were characterized according to their influence on permeability in various climates. At a low concentration of kaolin, the crystallinity of polyvinyl alcohol decreased; in the thinner films, the kaolin particles were orientated in the basal plane of the barrier coating. The experimental results indicated a complex interplay between the polymer and the filler with respect to permeability. A computer model for permeability incorporating theories for the filled polymeric layer to include the polymer crystallinity, addition of filler, filler aspect ratio and surrounding moisture was developed. The model shows that mass transport was affected by the aspect ratio of the clay in combination with the clay concentration, as well as the polymer crystallinity. The combined model agreed with the experiments, showing that it is possible to combine different theories into one model that can be used to predict the mass transport. Four barrier coatings: polyethylene, ethylene vinyl alcohol + kaolin, latex + kaolin and starch were evaluated using the parameters of greenhouse gas emissions and product costs. After the production of the barrier material, the coating process and the end-of-life handling scenarios were analysed, it emerged that starch had the lowest environmental impact and latex + kaolin had the highest. / Food packaging is required to secure the safety and quality of food, as well as minimize spoilage and simplify handling. Barrier coatings are generally used to meet the demands placed on fibre-based food packages, as these have the ability to regulate the amount of gases that can enter them. Some gases are detrimental to food quality: oxygen, for example, initiates lipid oxidation in fatty foods. This thesis focuses on the mass transport of oxygen in order to gain deeper knowledge of, and thereby optimise, the performance of barrier coatings. This experimental study, together with computer modelling, characterized the structure of barrier materials with respect to the mass transport process. The performance of the barriers was evaluated based on the parameters of environmental impact and product costs. As the long-term aim is to use non-petroleum-based barrier coatings for packaging, these should be evaluated by assessing the properties of the material in question, its functionality and its environmental impact to provide more insight into which materials are desirable as well as to develop technology. The results from this study indicate that several parameters (the orientation, concentration and aspect ratio of the clay and the polymer crystallinity) influence the properties of a barrier. Using this knowledge, researchers and food packaging engineers can work toward improving and customising renewable barriers. / VIPP

MENVSC / Department of Ecology and Resource Management / Some boreholes in South Africa which serve as a source of drinking water for rural communities are reported to have high fluoride concentration, much above the WHO guideline of 1.5 mg/L. This study aimed at activating aluminosilicate clay soil mechanochemically, modifying aluminosilicate clay soil with Al-oxide and fabricating porous ceramic granules using Al-oxide modified mechanochemically activated aluminosilicate clay soil/ mechanochemically activated clay soil/ corn starch and evaluating their performances in defluoridation of groundwater. The raw clay materials were mechanochemically activated for 5, 10, 15 and 30 minutes for physicochemical transformation of the solid aggregate. The morphology of the samples showed the honeycomb structure. The surface area analyses of samples using Brunauer–Emmett–Teller (BET) gave the highest surface area of 50.5228 m2/g at 30 min activation time. Hence, the optimum activation time was 30 min. The Fourier Transform Infrared (FT-IR) analysis showed increase in the absorbance of FT-IR by Si-O-H groups at 510 cm-1 with increasing milling time. This is evidence that more surface Si-O-H groups were available at higher particle surface area that would be necessary to interact with fluoride. X-ray diffraction (XRD) analyses revealed that, at 30 minutes milling time, the peak broadening is intensified whereas the reflection peak intensities decreased. The X-ray fluorescence spectrometry (XRF) results for 30 minutes milling time showed that silica and alumina were the highest components in the clay soil. Using the activated clay in batch defluoridation of fluoride-spiked water, a maximum fluoride removal of 41% was achieved at a pHe of 2.41. The initial fluoride concentration was 9 mg/L while the sorbent dosage was 0.6 g/100 mL and the contact time being 30 minutes. The adsorption data fitted to both Langmuir and Freundlich isotherms. The adsorption data fitted only the pseudo-second-order kinetic, showing chemisorption. Optimization of Al3+ concentration for modification was carried out by modifying the mechanochemical activated aluminosilicate clay soil with different concentrations of Al3+ from which the optimum modification was achieved with 1.5 M. Characterisation studies on the Al-oxide modified mechanochemically activated aluminosilicate clay soil by SEM, BET, FT-IR, XRD and XRF, analyses were carried out to determine the resultant changes in physicochemical properties of the adsorbent owing to modification. The SEM image of Al-oxide modified mechanochemically activated clay soil showed many small pores and honey-comb structure on the surface of different images. The BET surface area and the BDH adsorption cumulative area of the Al-oxide modified mechanochemically activated v aluminosilicate clay soil were more than double those for the raw clay soil. There was also an increase in pore volume of the Al-oxide modified mechanochemically activated aluminosilicate clay soil. The FT-IR spectra showed that there was increase in the absorbance by the Si-OH, H-O-H, Al-O-H and Si-O-Al. The equilibrium pH of solution was higher than the point-of-zero charge (pHpzc) implying that fluoride removal occurred at solution pH > pHpzc where the net surface charge of the mechanochemically activated clay aluminosilicate soil was negative.The efficiency of 1.5 M Al-oxide modified aluminosilicate clay soil to remove fluoride from water was studied and found to be 96.5 % at pHe 6.86, contact time of 30 minutes and dosage of 0.3 g/100 mL for 10 mg/L fluoride solution at 200 rpm shaking speed. The result shows that Al-oxide modified mechanochemically activated aluminosilicate clay soil is effective for defluoridation. The adsorption data fitted to both Langmuir and Freundlich isotherms. The adsorption data fitted only the pseudo-second-order kinetic, showing chemisorption. Al-oxide modified mechanochemically activated aluminosilicate clay soil was tested for fluoride removal on field water and the percentage fluoride removal was 96.5 % at the dosage of 0.6 g/100 mL with the pHe of 6.48. The optimum Al-oxide modified mechanochemically activated aluminosilicate clay soil/ mechanochemically activated clay soil/ corn starch mixing ratio for fabrication of porous ceramic granules was determined by varying ratios and temperature. The optimum ratio found was 20:5:1.The porous ceramic granules were characterised using SEM, BET, FT-IR, XRD and XRF. SEM analysis showed that the porous ceramic granules have the porous structure of the organic foam template. The porous ceramic granule showed an increase in pore surface area and volume as compared to mechanochemically activated aluminosilicate clay soil. The FT-IR showed the presence of a strong broad bending and stretching vibrations band at about 993 cm-1 which shows the presence of Si–O–Si bonds. Mineralogical characterisation showed the presence of quartz, albite, horneblende and microcline as the main minerals of the calcined porous ceramic granules. The major oxides of the porous ceramic granules as shown by XRF analysis were SiO2, Al2O3, MnO and Na2O. The porous ceramic granules reduced the concentrations of fluoride in the water from 10 to 3.31 mg/L. The optimum adsorption capacity was 0.6648 mg/g at a pHe of 6.32 and the percentage fluoride removal was 66.9 % at an adsorbent dosage of 1.0063 g/100 mL and a temperature of 600 ⁰C. The porous ceramic granules were tested for fluoride removal on field water and the percentage fluoride removal was 45.4 % at the dosage of 1.0009 g/100 mL with the pHe of 7.87. Mechanochemically activated aluminosilicate clay soil showed higher adsorption capacity at acidic pH, therefore it is recommended that future work should focus on improving their adsorption capacity at wider range of pH. The porous ceramic granules can also be evaluated in column dynamic flow experiments.

PhD (Environmental Sciences) / Department of Ecology and Resource Management / The presence of arsenic in groundwater has drawn worldwide attention from researchers and public health officials due to its effects on human health such as, cancer, skin thickening, neurological disorders, muscular weakness, loss of appetite and nausea. World Health Organisation (WHO) has set the limit of 10 μg/L for arsenic in drinking water in trying to reduce the effects of arsenic. This was further adopted by South African National Standard (SANS). The present study aims at evaluating arsenic concentration in selected groundwater sources around Greater Giyani Municipality in Limpopo Province and further synthesize clay based adsorbents for arsenic removal using Fe3+ and Mn2+ oxides and hexadecylammonium bromide (HDTMA-Br) cationic surfactant as modifying agents. The first section of the work presented the hydrogeochemical characteristics of groundwater in the Greater Giyani Municipality. The results showed that the pH of the samples ranges from neutral to weakly alkaline. The dominance of major anionic and cationic species was found to be in the order: HCO3 ->Cl->SO4 2->NO3 - and Na+>Mg2+>Ca2+>K+>Si4+, respectively. Hydrogeochemical facies identified in the study area include CaHCO3 (90%) and mixed CaNaHCO3 (10%) which shows the dominance of water-rock interaction. About 60% of the tested samples contains arsenic concentration above 10 μg/L as recommended by SANS and WHO. Concentration of arsenic was found to be ranging between 0.1 to 172.53 μg/L with the average of 32.21 μg/L. In the second part of this work, arsenic removal efficiency of locally available smectite rich and kaolin clay was evaluated. Results showed that the percentage As(V) removal by kaolin clay was optimum at pH 2 while the percentage As(III) removal was greater than 60% at pH 2 to 12. For smectite rich clay soils, the percentage of As(III) and As(V) removal was found to be optimum at pH between 6 and 8. The adsorption isotherm data for As(III) and As(V) removal by both clays fitted better to Freundlich isotherm. Adsorption of both species of arsenic onto the clay mineral occurred via electrostatic attraction and ion exchange mechanisms. Both clay soils could be regenerated twice using Na2CO3 as a regenerant. Kaolin clay showed a better performance and was selected for further modification. In the third section of this work, Fe-Mn bimetal oxide modified kaolin clay was successfully synthesized by precipitating Fe3+ and Mn2+ metal oxides to the interlayer surface of kaolin clay. Modification of kaolin clay increased the surface area from 19.2 m2/g to 29.8 m2/g and further v decreased the pore diameter from 9.54 to 8.5 nm. The adsorption data fitted to the pseudo second order of reaction kinetics indicating that adsorption of As(III) and As(V) occurred via chemisorption. The adsorption isotherm data was described by Langmuir isotherm models showing a maximum As(III) and As(V) adsorption capacities of 2.16 and 1.56 mg/g, respectively at a temperature of 289 K. Synthesized adsorbent was successfully reused for 6 adsorptiondesorption cycles using K2SO4 as a regenerant. Column experiments showed that maximum breakthrough volume of ≈2 L could be treated after 6 hours using 5 g adsorbent dosage. Furthermore, the concentration of Fe and Mn were within the WHO permissible limit. In the fourth part of the work kaolin clay was functionalized with hexadecyltrimethylamonium bromide (HDTMA-Br) cationic surfactant and its application in arsenic removal from groundwater was investigated. The results revealed that adsorption of As(III) and As(V) is optimum at pH range 4-8. The maximum As(III) and As(V) adsorption capacities were found 2.33 and 2.88 mg/g, respectively after 60 min contact time. Pseudo first order model of reaction kinetics described the adsorption data for As(V) better while pseudo second order model described As(III) adsorption data. The adsorption isotherm data for As(III) and As(V) fitted well to Langmuir model indicating that adsorption of both species occurred on a mono-layered surface. Adsorption thermodynamics model revealed that adsorption of As(III) and As(V) was spontaneous and exothermic. The As(III)/As(V) adsorption mechanism was ascribed to electrostatic attraction and ion exchange. The regeneration study showed that synthesized adsorbent can be used for up to 5 times. In the firth part of the work inorgano-organo modified kaolin clay was successfully synthesized through intercalation of Fe3+ and Mn2+ metal oxides and HDTMA-Br surfactant onto the interlayers of the clay mineral. The batch experiments showed that As(III) removal was optimum at pH range of 4-6, while the As(V) removal was optimum at pH range 4-8. The adsorption data for both species of arsenic showed a better fit to pseudo second order of reaction kinetics which suggest that the dominant mechanism of adsorption was chemisorption. The isotherm studies showed better fit to Langmuir isotherm model as compared to Freundlich model. The maximum adsorption capacity As(III) and As(V) at room temperature as determined by Langmuir model were found to be 7.99 mg/g and 7.32 mg/g, respectively. The thermodynamic studies for sorption of As(III) and As(V) showed negative value of ΔGᴼ and ΔHᴼ indicating that adsorption process occurred spontaneously and is exothermic in nature. The regeneration study showed that the vi inorgano-organo modified kaolin clay can be reused for up 7 adsorption-regeneration cycles using 0.01 M HCl as a regenerant. Thomas kinetic model and Yoon-Nelson model showed that the rate of adsorption increases with increasing flow rate and initial concentration and decreases with increasing of the bed mass. In conclusions, adsorbents synthesized from this work showed a better performance as compared to other adsorbents available in the literature. Among the synthesized adsorbents, inorgano-organo modified clay showed highest adsorption capacity as compared to surfactant functionalized and Fe-Mn bimetal oxides modified kaolin clay. However, all adsorbents were recommended for use in arsenic remediation from groundwater. The following recommendations were made following the findings from this study: 1) routine monitoring of arsenic in groundwater of Greater Giyani Municipality, 2) evaluating the possible link between arsenic exposure and arsenic related diseases within Giyani in order to find the extent of the problem in order to establish the population at risk, 3) The toxicity assessment for HDTMA-Br modified kaolin clay should be carried out, 4) Materials developed in the present study should be modeled and tested at the point of use for arsenic removal, and lastly, 5) this study further encourage the development of other arsenic removal materials that can be used at household level. / NRF

PhDENV / Department of Ecology and Resource Management / Kaolin dominated soils are common in the tropical and subtropical regions. People depend on kaolin-rich soils for agricultural production of food and fiber. The most popular of all South African soils is the Hutton form which accounts for the marvelous redness of the landscape across the Country. The apedal (structureless) soils in the group are characterised by a relatively low CEC (< 11 cmolc kg-1) reflecting oxidic mineralogy with predominantly kaolinitic assemblage. The geochemical and mineralogical composition of soil kaolin has significant implications on soil fertility, geochemical exploration and engineering properties. Despite the dominance of kaolin in these soils, little is known of their properties in the medium. The nature of kaolin minerals in soils varies with parent material, degree of weathering and pedogenic environment. Most studies conducted in South Africa on kaolins are limited to reference kaolins with little or no publication on soil kaolins, hence, this study. This research involved the evaluation of mineralogical and geochemical characteristics of oxidic soils and soil kaolins developed from four (4) selected parent rocks which were basalt, granite, arkosic sandstone, and gneiss. Soils developed from quartzite were selected as control. Representative soil samples collected from profiles developed from the different parent rocks were analysed for physico-chemical, mineralogical, and geochemical data. The mineralogical and geochemical data obtained by x-ray diffractometry (XRD), x-ray fluorescence (XRF), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) were used in unraveling the influence of the provenance and degree of weathering on the soil characteristics. The mineralogical and geochemical data for soil kaolins were determined through XRD, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and differential scanning calorimetry, XRF, and LA-ICPMS to establish their mineralogical and geochemical properties with respect to their parent rocks. Comparison between the soil kaolins and selected reference kaolins were also conducted. The phosphorus (P) sorption data acquired photometrically were employed to evaluate the relationship between the P sorption capacities of the soils and soil kaolins. The influence of soil properties on the fertility of the soils were assessed based on the physico-chemical (pH, particle size distribution, and electrical conductivity (EC)) and chemical (organic matter (OM) content, cation exchange capacity (CEC), available P, exchangeable cations (Ca, K, Mg, Na, and Al), and P sorption) data. The mineralogical and geochemical data for the parent rocks were obtained by XRD, optical microscopy, XRF, and LA-ICPMS. Multivariate statistical analyses were also conducted. Results showed that the dominant colour in the studied bulk soils was dusky red (31 %) followed by brown (23 %), reddish brown, yellowish red, and yellowish brown (23 %) as well as strong brown, dark brown, reddish grey, very dark greyish brown, and dark red. Soil textures were clayey to sandy loamy with OM contents between 0.41 and 4.76 %. The pH, EC, CEC, exchangeable cations, and available P values generally ranged from 5.22 to 8.38, 10.25 to 114.40 μS/cm, 2.93 to 18.30 cmol/kg, 0.03 to 13.92 cmol/kg, and <0.01 to 54.99 mg/kg, respectively. Kaolinite and quartz were the dominant phases for soils developed from basalt whereas, quartz and plagioclase were the dominant mineral phases in soils developed from granite, arkosic sandstone, and gneiss, respectively. Other minerals present in the soils were microcline, muscovite, hematite, goethite, montmorrillonite, anatase, gibbsite, chlorite, and actinolite. Geochemical compositions of the bulk soils show relative enrichment of Fe2O3, TiO2, CaO, K2O, MgO, MnO, and Na2O (except for CaO, K2O, MgO, MnO, and Na2O in soils developed from basalt). Chemical index of alteration (CIA), chemical index of weathering (CIW), and plagioclase index of alteration (PIA) values varied between 54.92 and 99.81 % which suggest low to high degree of chemical weathering. The ACN-K and A-CNK-FM diagrams for the different soils also support these observations. Trace elements were generally enriched in soils developed from basalt and gneiss (except for Rb, Sr, and Ba in soils developed from basalt), but were depleted in soils developed from granite and arkosic sandstone (except for Cr and Ta). The principal factors responsible for the mineralogical and geochemical characteristics of the soils were the parent rocks and degree of weathering. In the soil kaolins, the dominant clay mineral was kaolinite accounting for 23 to 85 wt % followed by montmorrillonite, chlorite, and gibbsite. The non-clay minerals like quartz, plagioclase, muscovite, microcline, anatase, goethite, hematite, and actinolite accounted for the remaining percentages. The soil kaolins were characterised by thin platy kaolinite particles with partially to poorly-ordered structural order. The platy kaolinite crystals have their longest dimension sizes between 0.06 and 0.25 μm. The dehydroxylation temperatures for the studied soil kaolins ranged from 425 to 475 ˚C. The SiO2/Al2O3 ratio was lowest in soil kaolins developed from basalt and higher in soils developed from granite, arkosic sandstone, and gneiss which is consistent with their mineralogy since the former have more kaolinite. Higher Fe2O3 and CEC values were obtained relative to reference kaolins which could be attributed to the presence of more structural iron in the soil kaolins as well as their smaller crystal sizes. The presence of weatherable and accessory minerals accounted for the enrichment of Co, Ni, Cu, Zn, and Pb in the soil kaolins. The kaolinite in the soils were formed by leaching and desilication of the primary minerals in the parent rocks under suboxic conditions. H-type P adsorption isotherms obtained for both the soils and soil kaolins indicated their high affinity for phosphorus by chemisorption. The average maximum P adsorption values were in decreasing order of soils developed from basalt > granite > arkosic sandstone > quartzite (control) > gneiss, respectively whereas, for soil kaolins is basalt > granite > quartzite (control) > arkosic sandstone > gneiss, respectively. Relative to other soils developed from different parent rocks, soils developed from basalt (with more clay content) had higher capacity and buffer power for P adsorption. The standard P requirements for the soils ranged from 7.78 to 92.91 mgP/kg and were classified as low based on the Langmuir model. Significant correlation between the P adsorption parameters for the soils and soil kaolins indicated that the later could be taken as a good predictor for P sorption dynamics in the soils. Electrical conductivity of the soils were taken to be negligible in interfering with plant growth. The available P values were generally below the critical level of 12 – 15 mg/kg for soils developed from basalt, gneiss, and quartzite (control) but higher in soils developed from granite and arkosic sandstone. All the soil evaluation factor (SEF) average values estimated were greater than five indicating that they are not of poor soil fertility. The correlation results between the soil properties and P sorption parameters suggest that several variables can influence the P sorption dynamics of the soil. Regression analyses further indicated that CEC, pH, OM, and clay content in the soils account for 99 % bounding P energy variation whereas, Fe2O3 accounts for 76 % P sorption maximum variation in the soils. In addition, variations in Fe2O3 and sand contents in the soils account for 96 % and 95 % maximum buffering capacity and external P requirement (EPR) variations, respectively. Models to advance the interplay between the various soil properties and P sorption parameters in the soils were developed. Mineralogical and geochemical characteristics of the soils were principally controlled by the parent rocks and degree of weathering. The soil kaolins displayed significant differences relative to reference kaolins. Langmuir model is most suited for describing P sorption in soils and soil kaolins developed from different parent rocks within the studied area. P sorption parameters for the soils can readily be obtained from the P sorption parameters of the kaolins present in them. EPR obtained and models for predicting P sorption parameters from selected soil properties developed for the various soils will improve the efficiency of routine P fertilizer applications. Iron oxide (Fe2O3) played the most crucial role in explaining the P sorption dynamics of the soils. The major contributions from this study have been: better understanding of the influence of parent rock characteristics and degree of weathering on the soil characteristics, the nature of soil kaolins and its influence on soil properties as well as P sorption dynamics in soils have been better established, and improvement of the understanding on the relationship between soil properties and P sorption dynamics in the soils. / NRF