This report describes the mineralogical characterisation and processing of several industrial

minerals collected by Dr DJ Morgan in October 1991 during a visit to Uganda (Visit report

WG/91/31R). The industrial minerals included raw materials (see Table 1) from African

Ceramics Ltd (Mutaka kaolin, feldspar and ball clay) and samples collected by the Geological

Survey and Mines Department Uganda (the remaining kaolin, talc and diatomite). The aim of

this study was to assess their quality for various applications, especially ceramic manufacture.

This work was carried out as part of the DDA/BGS project "Minerals for Development"

Mitchell, C.J.

English

NERC Open Research Archive

BRITISH GEOLOGICAL SURVEY TECHNICAL REPORT Mineralogy & Petrology Series REPORT NO. WG/92/11R MINERALOGICAL CHARACTERISATION AND PROCESSING OF SOME INDUSTRIAL MINERALS FROM UGANDA Date 10 April 1992 Classification Restricted Geographical index Uganda, Africa Subject index C J Mitchell Industrial minerals, mineral processing Bibliographic reference C J Mitchell (1992) Mineralogical characterisation and processing of some industrial minerals from Uganda British Geological Survey Technical Repon WG192111R ©NERC 1992 British Geological Survey, Keyworth, Nottingham NG12 5GG, UK                                                           This report has been generated from a scanned image of the document with any blank pages removed at the scanning stage.  Please be aware that the pagination and scales of diagrams or maps in the resulting report may not appear as in the original British Geological Survey Mineralogy and Petrology Report No. WG/92/11 Mineralogical characterisation and processing of some industrial minerals from Uganda C J Mitchell I. INTRODUCTION This report describes the mineralogical characterisation and processing of several industrial minerals collected by Dr DJ Morgan in October 1991 during a visit to Uganda (Visit report WG/91/31R). The industrial minerals included raw materials (see Table 1) from African Ceramics Ltd (Mutaka kaolin, feldspar and ball clay) and samples collected by the Geological Survey and Mines Department Uganda (the remaining kaolin, talc and diatomite). The aim of this study was to assess their quality for various applications, especially ceramic manufacture. This work was carried out as part of the DDA/BGS project "Minerals for Development". 2. SAMPLES Table I. Industrial minerals examined from Uganda· Samples Namasera kaolinite Mutaka kaolinite Koki kaolinite Kesinga 'talc' Kyamuhunga 'talc' Pakwach diatomite Mutaka feldspar Mukona ball clay Locality Entebbe SWUganda S of Mbirizi-Lyantonde road Kasesi District SWUganda NWUganda SWUganda Description Pinkish-brown, kaolitinised sandstone with fine sub-millimetre laminae and visible quartz, mica and iron oxide. A very white, friable kaolin-rich sandstone, containing large quartz crystals (up to several em in diameter). A finely laminated, pinkish-white mudstone, with a friable nature and powdezy surface. A dark greenish-brown, fme grained material with fine laminations and a soapy texture. A light green, fine grained material with a ·shiny lustre, soapy , texture and fme laminations. A very white, lightweight and fme grained material, with brittle fracture and a powdezy surface. A light brown, coarsely crystalline feldspar with a light brown dust coating. A homogeneous, brownish-grey clay with iron-oxide staining. 3. METHODS X-ray diffraction was used to detennine the mineralogy, using a Phillips PW 1700 X-ray diffractometer. Randomly oriented mounts were scanned over 3 - 50 °29 to determine bulk mineralogy and oriented clay fraction mounts were scanned over 1.5 - 30 ~9 to determine clay mineralogy. The traces were interpreted with reference to the JCPDS database. Thermogravimetric analysis (TO) was used to determine the quantitative mineralogy, specifically kaolinite. Major-element chemistry of the Mutaka feldspar was determined by X-ray fluorescence analysis of a fused glass disc using a Phillips PW 1480 X-ray fluorescence spectrophotometer. Particle-size distributions were determined by wet screening and/or X-ray sedigraph analysis. Brightness measurement was carried out by reflectance spectrophotometric analysis of unftred and fired material (2 hours at 1050°C), using a barium sulphate standard and values quoted are at 4700A. The Atterberg liquid and plastic limits of the Mukona ball clay were determined and the plasticity index was calculated from these. Scanning electron microscopy (SEM) was used to examine the surface texture of the Pakwach diatomite, using a Cambridge Stereoscan SEM. Wet processing of the kaolinite was carried out by attrition scrubbing and wet screening (2 mm to 63 ~m). Hydrocycloning was used to produce clay concentrates from the <63 ~m fractions. A small glass hydrocyclone, separating at approximately 10 ~m, produced an underflow (material mainly > 10 ~m) and an overflow (material mainly <10 ~m). The overflow products were examined by transmission electron microscopy (TEM) in order to study the kaolinite particle morphology and particle thickness was determined by metal shadowing. 4. RESULTS 4.1. Namasera kaolinite The Namasera kaolinite contains mainly quartz and kaolinite (18%) with trace amounts of mica and iron oxides. The clay fraction is mainly kaolinite and quartz, with a trace of mica (Table 2). The +63 ~m fractions contain mainly quartz, with the amount of mica and iron oxides increasing with decreasing particle size. The -63 ~m fraction contains 73% kaolinite at a recovery of 94% of that present in the original sample, with 51 % of the particles being <2 ~m in size. Due to a high proportion of iron oxide in the coarse silt, this fraction was further wet screened on 32 ~ and the -32 ~ fraction used as the hydrocyclone feed. The hydrocyclone feed has a high kaolinite content (77% ) and high recovery (88%), with 69% of the particles <1 0 ~ and 44% <2 J.1Ill in size. The underflow has a reduced kaolinite content (66%) but has a high recovery (58%) and a relatively coarse particle size, with only 29% < 2 ~ in size. The overflow has a high kaolinite content (82%), low recovery (31 %) and is very fme with 79% <2 J.1m in size (Table 3 and Figure 1). The overflow has a raw brightness of 50% and a fIred brightness of 66% (Table 5 and Figure 4). The TEM study of the overflow shows the kaolinite to consist of euhedral hexagonal plates, ranging from 0.1 - 1.25 J.1m in diameter (averaging 0.5 J.1m) and 0.01 - 0.14 ~ in thickness (averaging 0.04 J.1m), with an aspect ratio of 15.4. Figure 10 shows a typical assemblage of particles and Figure 11 shows a kaolinite plate with visible cleavage and metal shadow. 4.2. Mutaka kaolinite The Mutaka kaolinite contains mainly kaolinite (65%), with a small amount of K-feldspar, quartz and mica. The clay fraction contains mainly kaolinite, with a small amount of quartz and a trace of mica (Table 2). The +63 ~ fractions contain mainly quartz, feldspar, mica and iron oxides. The -63 J.1m fraction, which was used as the hydrocyclone feed, has a high kaolinite content (82%), a high recovery (93%) and contains 29% particles <2 J.1m in size. The hydrocyclone underflow has a reduced kaolinite content (79%), a high recovery (57%) and is relatively coarse with only 15% <2 J.1m. The overflow has a high kaolinite content (87%), a low recovery (35%) and 54% particles <2 ~ in size (Table 3 and Figure 2). The overflow has a raw brightness of 80% and a fIred brightness of 87% (Table 5 and Figure 5). TEM of the Mutaka kaolinite overflow shows mainly subhedral to rounded kaolinite plates and halloysitic rods. The kaolinite ranges from 0.05 - 1.18 J.1m in diameter (averaging 0.4 J.1m) and 0.01 -0.26 J.1m in thickness (averaging 0.09 J.1m). Aspect ratio averages at 5.6. Figures 12 and 13 show the typical assemblage of plates and rods. 4.3. Koki kaolinite The Koki kaolinite contains mainly quartz, with a small amount of kaolinite (16%), mica and plagioclase feldspar, with a trace of K-feldspar. The clay fraction is mainly quartz, with a small amount of kaolinite and mica, and a trace of feldspar (Table 2). The +63 J.1m fractions are mainly quartz, mica and feldspar. The -63J.1m fraction, which is used as the hydrocyclone feed, has a low kaolinite content (16%), a high recovery (99%) and is relatively coarse with only 21% <2 J.1m. The hydrocyclone underflow product has a very low kaolinite content (10%), high recovery (49%) and is relatively coarse with only 11 % <2 J.1m. The overflow has a low kaolinite content (23%), a high recovery (50%) and is relatively fine with 41 % particles <2 Jlm in size (Table 3 and Figure 3). The overflow has a raw brightness of 57% and a fired brightness of 66% (Table 5 and Figure 6). TEM of the Koki kaolinite overflow shows the kaolinite to consist of euhedral hexagonal plates, which range from 0.38 - 0.96 Jlm in diameter (averaging 0.63 Jlm) and 0.02 -0.1 ~m in thickness (averaging 0.06 Jlm), with an average aspect ratio of 12.9. Figures 14 and 15 show typical kaolinite crystals, with visible cleavage and metal shadows. 4.4. Kesinga and Kyamuhunga 'Talc' Both bulk and clay fractions of the Kesinga and Kyamuhunga 'talc' samples consist mainly of chlorite, with only a small amount of talc being identified (Table 2). 4.5. Pakwach diatomite The Pakwach diatomite contains mainly amorphous silica and kaolinite (39%), with a small amount of quartz and a trace of smectite. The clay fraction is mainly kaolinite, with a small amount of quartz and smectite and a trace of mica (Table 2). Under the scanning electron microscope the sample was seen to consist largely of diatoms with the appearance of segmented porous hollow tubes; and these have been tentatively identified as Melosira sp. This is a planktonic genus typical of a deep freshwater environment and preservation of whole diatoms, as in this sample, requires low energy pelagic sedimentation. The fine-grained matrix is kaolinite, as confirmed by energy dispersive analysis and it is present in about the proportion indicated by TO. Figure 8 shows a single diatom segment approximately 20 - 25 Jlm in diameter and about 10 Jlm long. Figure 9 shows single diatom segments and a chain of diatoms (about 100 Jlm long) in a matrix of rme-grained kaolinite. 4.6. Mutaka feldspar The Mutaka feldspar was wet screened on 1 mm and 63 Jlm sieves in order to remove the coating around the feldspar grains. The + Imm feldspar, which forms 92.8% of the sample, contains mainly K-feldspar and albite. This is confirmed by the chemistry, which indicates the presence of 64.82% Si02, 19.41 % A120 3, 0.53% F~03' 2.04% Na20 and 13.23% K20. The -lmm +63 Jlm fraction, which forms 3.8% of the sample, contains mainly K-feldspar and albite, with a small amount of kaolinite and quartz and a trace of mica. The -63 Jlm fraction, which forms 3.4% of the sample, contains mainly kaolinite (65%) and K-feldspar, with a small amount of albite and quartz and a trace of mica (Tables 2 and 4). 4.7. Mukona ball clay The Mukona ball clay contains mainly quartz and kaolinite (38%), with a small amount of albite and a trace of smectite. The clay fraction is mainly kaolinite and quartz, with a small amount of smectite and a trace of mica (Table 1). It contains 3.4% of particles +63 Jlm, 75.8% <10 Jlm and 44.9% <2 J,1m. The liquid limit is 30, the plastic limit 17 and the plasticity index 13. Raw brightness is 38% and the fIred brightness is 46% (fable 5 and Figure 7). 5. CONCLUSIONS AND DISCUSSION 5.1. Kaolinites The Namasera kaolinite can be upgraded to a product grading 82% kaolinite, with 79% particles <2 J,1m in size. However, the product has a poor colour that is not signifIcantly improved on fIring and is probably only useful for applications requiring low-brightness kaolin, such as agricultural pesticide carriers. The Mutaka kaolinite can be upgraded to a product grading 87% kaolinite, with 54% particles <2 J.1m in size and having high brightness (80% unfIred and 87% fIred). This kaolinite is worthy of further investigation for its potential use in paper and ceramics (and is in fact already being used as a ceramic raw material). The Koki kaolinite could not be appreciably upgraded, has a low clay content and poor colour, and is probably only of use for applications requiring low grade kaolin. 5.2. 'Talc' The Kesinga and Kyamuhunga 'talc' contain mainly chlorite and are probably only of potential use as low grade fIllers. 5.3. Pakwach diatomite The Pakwach diatomite is very white and contains a large proportion of diatoms in a kaolinite matrix. This is a very promising material worthy of further more detailed investigations. It is likely that both high-grade diatomite and kaolinite could be produced from the same material, by either air classifIcation or hydrocycloning. 5.4. Mutaka feldspar The Mutaka feldspar is an off-white K-feldspar, with a small amount of albite and low levels of impurities, such as F~O:J and Ti~. This material is already in use as a ceramic raw material. 5.S. Mukona ball clay The Mukona ball clay is a poor quality kaolinite, with low plasticity, high silt content and poor fired colour. This material is already in use as ceramic raw material. ---------Table 2. Mineralogy of some Ugandan industrial minerals Sample Mineralogy Namasera kaolinite Bulk Quartz ****, kaolinite 18%, mica *, iron oxides *. <2 J.1m Quartz ****, kaolinite ***, mica *. Mutaka kaolinite Bulk Kaolinite 65%, K-feldspar **, quartz **, mica *. <2 J.1m Kaolinite ****, quartz **, mica *. Koki kaolinite Bulk Quartz ****, kaolinite 20%, mica **, plagioclase **, K-feldspar *. <2 J.1m Quartz ****, kaolinite **, mica **, Plagioclase *, K-feldspar *. Kesinga talc Bulk Chlorite ****, talc **. <2 J.1m Chlorite ****, talc **. Kyamuhunga talc Bulk Chlorite ****, talc **. <2 J.1m Chlorite ****, talc **. Pakwach diatomite Bulk Amorphous silica ****, kaolinite 39%, quartz **, smectite *. <2 J.1m Kaolinite ****, quartz **, smectite **, mica *. Mutaka feldspar +1mm -1mm +63 J.1m -63 J.1m Mukona ball clay Bulk <2 J.1m K-feldspar ****, albite ***. K-feldspar ****, albite ***, kaolinite **, quartz **, mica *. Kaolinite 65 %, K-feldspar ***, albite **, quartz **, mica *. Quartz ***, kaolinite 38%, albite **, smectite *. Kaolinite ****, quartz ***, smectite **, mica *. Key: .... = >50 weight %, ••• = 20 - 50 wt %, •• = 7 - 20 wt % and • = <7 wt % Table 3. Ugandan kaolinite hydrocyclone separation Sample Namasera kaolinite Feed Underflow Overflow Mutaka kaolinite Feed Underflow Overflow Weight % of head 20.7 14.5 6.2 73.3 47.1 26.2 Koki kaolinite Feed 99.1 Underflow 68.4 Overflow 30.7 Kaolinite Wt% (77.2) 66.0 82.0 82.0 79.0 87.0 16.0 10.0 23.0 Recovery Wt% 88.8 58.0 30.8 92.5 57.4 35.1 99.1 48.8 50.3 Table 4. Chemical analysis of Mutaka feldspar, Uganda < 10 J..Lm < 2 J..Lm Wt% Wt% 69.4 43.5 57.5 28.5 97.0 78.5 65.0 29.0 48.5 15.0 97.0 54.0 65.5 20.5 51.5 11.0 96.5 40.5 64.82 0.01 19.41 0.53 0.009 0.09 0.06 2.04 13.23 0.13 0.39 100.72 Table 5. Brightness of kaolinites and ball clay, Uganda. Wavelength 4700 A 4900 A 0 0 Sample 5500 A 5800 A Namasera kaolinite overflow Raw 49.9 49.8 57.0 64.4 Fired 65.8 64.3 66.3 72.4 Mutaka kaolinite overflow Raw 80.2 81.7 84.7 86.6 Fired 87.1 86.5 81.0 89.9 Koki kaolinite overflow Raw 56.9 56.3 60.9 66.8 Fired 66.1 64.8 67.4 74.7 Mukona ball clay Raw 37.8 38.7 40.7 40.5 Fired 46.3 46.6 54.8 61.2 N.B. These figures are percentage reflectance values taken in comparison to a BaS04 standard using an EEL spectrophotometer over 4700 - 5800A. 80 60 <II .:: -1:11 -; 40 e :::I U 1 10 Diameter (Jlm) Hydrocyclone feed Underflow Overflow ---- - -100 Figure 1. Particle-size distributions of Namasera kaolinite hydrocyclone products <II .:: -1:11 -; 80 60 40 e 20 :::I U 1 10 Diameter (Jlm) Key • Hydrocyclone feed Underllow • Overflow 100 Figure 2. Particle-size distributions of Mutaka kaolinite hydrocyclone products I: = .c -41 .:: -= :; 80 60 40 e 20 = u 1 Key • • 10 Diameter (j.lm) Hydrocyclone feed Underflow Overflow 100 Figure 3. Particle-size distributions of Koki kaolinite bydrocyclone products 100 90 80 41 70 ~ Col I: • = : -Col 60 41 C 41 .. 50 a 41 ~ = 40 -I: 41 Col 30 .. 41 Key ,. 20 a Raw 10 • Fired 0 4600 4800 5000 5200 5400 5600 5800 6000 Wavelength (A) Figure 4. Spectral reflectance curves for Namasera kaolinite overflow product 100 90 ... : : :... """"i:I Q,I y = 80 CIS -Y Q,I C Q,I .. 70 Q,I ec CIS -= Q,I 60 y .. Q,I I:I.t Key 50 III Raw • Fired 40 4600 4800 5000 5200 5400 5600 5800 6000 Wavelength (A) Figure S. Spectral reflectance curves for Mutaka kaolinite overflow product 100 90 Q,I y = 80 CIS -Y Q,I ::::: c Q,I .. 70 Q,I : ec : CIS -= Q,I 60 y .. Q,I I:I.t Key 50 III Raw • Frred 40 4600 4800 5000 5200 5400 5600 5800 6000 Wavelength (A) Figure 6. Spectral reflectance curves for Koki kaolinite overflow product 100 90 80 ~ 70 y = til - ~ y 60 ~ c ~ .. 50 ~ • • =tl til 40 1:1 1:1 -1:1 1:1 = ~ y 30 .. ~ 1:1. 20 Key 1:1 Raw 10 • Fired 0 4600 4800 5000 5200 5400 5600 5800 6000 Wavelength (A) Figure 7. Spectral reflectance curves for Mukona ball clay Figure 8. SEM photomicrograph of a single diatom showing its porous tubular nature, Pakwach diatomite, Uganda. Figure 9. SEM photomicrograph of single diatoms and a chain of diatoms in a matrix of fine grained kaolinite, Pakwach diatomite, Uganda . Figure 10. TEM photomicrograph (Mag x 15,500) showing euhedral hexagonal plates and metal shadowing of Namasera kaolinite, Uganda . • Figure 11. TEM photomicrograph (Mag x 51,500) of a euhedral kaolinite crystal showing visible cleavage and metal shadow, Namasera kaolinite, Uganda. Figure 12. TEM photomicrograph (Mag x 31,000) showing subhedral hexagonal plates and halloysitic rods, Mutaka kaolinite, Uganda. Figure 13. TEM photomicrograph (Mag x 40,300) showing subhedral and rounded kaolinite plates and halloysitic rods, Mutaka kaolinite, Uganda. Figure 14. TEM photomicrograph (Mag x 40,300) showing euhedral hexagonal plates with visible cleavage and metal shadowing, Koki kaolinite, Uganda. Figure 15. TEM photomicrograph (Mag x 51,500) showing euhedral kaolinite plate, Koki kaolinite, Uganda. 

Mineralogical characterisation and processing of some industrial minerals from Uganda

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Mineralogical characterisation and processing of some industrial minerals from Uganda

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