Proceedings of the 10th World Congress on Mechanical, Chemical, and Material Engineering (MCM'24)
Barcelona, Spain - August 22-24, 2024
Paper No. MMME 116
DOI: 10.11159/mmme24.116

Pre-treatment of a Hydrocarbon Contaminated Platinum group Minerals
Mine Sludge using a Non-ionic Surfactant
Sonwabile Chintsiza, Willie Nheta

Mineral Processing and Technology Research Centre, Department of Metallurgy, University of Johannesburg
Doornfontein Campus, P.O Box 17911, Johannesburg, 2028, South Africa
sonwabilechintsiza@gmail.com; wnheta@uj.ac.za
Abstract - In South Africa, the Merensky, Upper Group 2 (UG-2), and Platreef are the three primary platinum group mineral (PGM)
reefs found in the Bushveld Igneous Complex (BIC). PGM output is now mostly sourced from Platreef and UG-2 reefs. Most of thePGM mines have become highly mechanised, leading to the production of mine sludge contaminated with hydrocarbons. This study
investigated the removal of the hydrocarbons using a non-ionic surfactant in preparation for the flotation process. The contaminatedmine sludge was characterised for hydrocarbon content, mineralogical and elemental composition. Response Surface MethodologyBox-Behnken (RSM-BBD) design of experiments was used to design the washing experimental runs. The results revealed that thesample contained 9.32g/t of total four elements (Pt, Pd, Rh and Au) with most of the PGMs found in the sulphide form. Chromite andquartz are the common gangue minerals that were found in the sample. Fourier transform infrared spectroscopy showed that there werehydrocarbons present in the sample. The washing experiments showed that Triston-100 (TX-100) can be used to remove hydrocarbons
from the contaminated PGMs mine sludge. The optimum washing conditions with a hydrocarbon removal efficiency of 91.86% were
found to be 12.25 g/kg surfactant concentration, 150 minutes of washing time and a pH of 12.
Keywords: Bushveld Igneous Complex, Mine sludge, Non-ionic surfactant, Flotation, Upper Group 2

1. Introduction

Platinum, palladium, rhodium, ruthenium, iridium and osmium are all members of the platinum-group elements(PGEs). PGEs are some of the rarest metals on the planet; nowadays, the usual PGE concentration in mined ores isbetween 5 and 15 ppm. These metals exist in nature and have similar physical and chemical characteristics [1]. Around
75% and 50% of the world's platinum and palladium deposits respectively, are found in the Merensky, UG-2 and Platreefof the BIC [2]. Drilling and blasting techniques have been used for a very long time to mine these reefs. There are two
types of mining: open-cast and underground mining [3].
In South Africa's more recent mines, mechanised mining is a common mining technique because of the depth of themines. Machinery that runs "off track" or without tracks is used in the process. Due to its ability to deliver the necessary
high-power output, diesel is the fuel that is most frequently utilised for such heavy-duty equipment used in industrial areas,
including transportation, mining and construction [3]. Due to the size of such equipment, pipe failure might result in oilleakages, contaminating the mine sludge that is formed from the dust and spray water. The mine sludge is then collected,piled up, and then stored. This contaminated mine sludge needs to be remediated before processing through sulphide froth
flotation because the contaminant will cause low platinum group minerals (PGMs) recovery if not removed [4]. Surfactants
are used in the washing of hydrocarbon-contaminated ore to remove these pollutants, which presents difficulties when it
comes to flotation [5].
The aim of this project is to remediate the hydrocarbons from the PGMs mine sludge using a non-ionic surfactant. The
effect of pH, washing time and surfactant concentration on hydrocarbon removal efficiency was investigated based on theResponse Surface Methodology (RSM).

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2. Materials and Methods

2.1. Materials
A PGMs mine sludge sample contaminated with hydrocarbons was sourced from one of the UG2 ore processing
plants in the Limpopo province, South Africa. The non-ionic surfactant Triston 10 (TX-100), chemically known as
Polyethylene Glycol Octyl Phenyl Ether, was supplied by Merck, South Africa. H2SO4 and NaOH, which were used as pH
regulators, were also supplied by Merck, South Africa. All reagents were of analytical research (AR) grade.
2.2. Mineralogical and surface morphology characterization of the hydrocarbon contaminated PGM minesludgeTo determine the chemical composition of the PGMs mine sludge sample, Rigaku ZSX Primus X-ray fluorescence(XRF) equipment was used. To determine the mineral composition of the PGM mine sludge sample, Rigaku Ultima V Xray diffraction (XRD) equipment was used, where X-rays are generated in a cathode ray tube by heating a filament toproduce electrons, accelerating the electrons by applying a voltage of 20 to 45 Kv and bombarding the CuKα radiation
target material with electrons. To show how liberated the particles are in the PGMs mine sludge, TESCAN Vega 3XMU
scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) equipment was used. The sample
was degreased prior to being put on top of the mould to increase adherence during the preparation for the scanning electron
microscopy analysis. To determine the presence of hydrocarbon functional groups present in the PGM mine sludge sample,
Fourier transform infrared spectroscopy (FTIR) equipment was used.
2.3. Mine sludge washing experiments
1kg of the PGM mine sludge was used for each experimental run. Firstly, 5L of H2O was poured into a 10L bucket andthe pH was then adjusted according to the design of experiment table (Table 1) using the pH regulators and conditioned for
5 minutes. After conditioning, a measured amount of the surfactant was added into the 5L bucket and pH adjusted once
again while conditioning the mixture for another 5 minutes. After the conditioning time, 1kg of the sample was thenpoured into the conditioned pulp and Triston-100 (TX-100) surfactant was also added. Washing time was then measuredaccording to (RSM-BBD) design of experiments. After washing, the remaining solid sample was separated from thesolution using filtration process. The resulting sample was then taken for FTIR analysis to determine the presence ofhydrocarbons in the sample after washing. After the FTIR analysis, the formula (1) below was used to calculate thehydrocarbon percent removal (%R) of hydrocarbons:%𝑹𝑹 =𝑪𝑪𝒐𝒐 −𝑪𝑪
𝑪𝑪𝒐𝒐× 𝟏𝟏𝟏𝟏𝟏𝟏(1)

Where Co and C were the contaminant concentrations before and after washing detected in the washed sample,respectively.
2.4. Design of washing experiments
For the design of washing experiments, the (RSM-BBD)was used to optimize the remediation of the hydrocarbons
from the PGM mine sludge [6]. The factors investigated were the pH of the slurry, concentration of the surfactant and thewashing time. 15 experiments were conducted as shown in Table 1.

Table 1: The designed experiments using Box Behnken Design.

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Triston-100 (TX-100) Surfactant
Concentration (g/kg)
Experiment No.

Washing Time (min)

pH

B1150

1215

B290

815

B330

825

B490

1225

B530

1215

B6150

415

B790

815B890

45B990

125

B1090

815

B1190

425

B12150825

B1330

85B14150

85B1530415

3. Results and Discussion

3.1. Chemical Composition of the PGM mine sludge
To determine the chemical composition of the PGMs mine sludge sample as received, the XRF was used and theresults are represented in Table 2. Based on Table 2, the PGMs mine sludge contained mainly 24.77% of iron,followed by 12.12% of silicon and lastly 8.43% of chromium. The mine sludge contained base metals such as Fe, Ni,Cu, Co and Zn which indicates that sulphides can be found in the sample. The presence of chromium in the minesludge sample might also indicate the presence of chromium spinels in the sample. The sample did not have any toxic
elements in it that might make it radioactive, so it safe to handle the sample. The elemental composition of the minesludge proved that it originated from UG2 ore.
Table 2: XRF results of the as- received sample of the PGMs mine sludge.

ElementNa

Mg

AlSiPS

ClK

Ca

Ti

Element % Wt

0.12

4.03

4.27

12.12

0.03

0.27

0.32

0.34

5.51

0.51

Element
Element % Wt

V
0.13

Cr
8.43

Mn
0.21

Fe24.77

Ni
0.41

Cu
0.08

Zn
0.14

Sr
0.03

Zr0.01

Co
0.03

O
38.24

The sample was analysed for (Pt, Pd, Rh and Au) using nickel sulphide fire assaying and the results revealed thatthe sample contained 5.68, 2.95, 0.6 and 0.09g/t respectively, giving a total of 9.32g/t. This indicates that the sample isof very high grade and it is worthy processing it.

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3.2. Mineralogical Phases of the PGMs mine sludge
The phases present in the PGMs mine sludge were determined using the XRD (Fig. 1). It shows that the samples
contain sulphides like sphalerite, covellite, chalcopyrite and cubanite. Quartz and chromite were also detected as some ofthe main gangue minerals present in the sample. These results may partially confirm that this sample is of UG-2 origin.
Generally, PGMs are associated with base metal sulphide minerals, chromite and silicate matrices in UG-2 ore.

DI
AH

700

Intensity (cps)

600

E
D500

D
A

400300

C
B

DA

A
C
GBF
BC
GD

A = Anorthite
B = Chromite
C = Iron Dichromate(III)D = Diopside
E = Quartz
F = Sphalerite
G = Covellite
H =Chalcopyrite
I = Cubanite

20010000204060802-Theta (deg)Fig.1: XRD spectra of the PGMs mine sludge.

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3.3. Surface Morphology of the PGMs mine sludge sample
The surface morphology of the PGMs mine sludge was determined using the SEM-EDX equipment as shown in Fig.
2 and Table 3, respectively. The results show that the sample contains minerals like chromite, chalcopyrite, covellite,anorthite and cubanite. These results agree with the XRD spectra (Fig. 1) in terms of the minerals present in the sample.
The content of the SEM-EDX analysis differs from that of the XRF because the SEM-EDX analysis only focuses on one
spot as compared to XRF that focuses on the entire sample being analysed. Fig. 2(A and B) show the major phases thatcontain the valuable and the gangue minerals. Figure 2B shows that the PGMs are found in mineral phases of diameter
5.98 µm. The most probable phases found at spectrum 1 (Fig 2C) are: chromite, anorthite, cubanite, chalcopyrite andPGMs sulphide minerals whilst those found at spectrum 2 (Fig 2D) are: Chromite, anorthite, covellite and chalcopyrite.
This shows that PGMs are found associated with base metal sulphides as well as within chromite matrix. The Fig. 2C show
the presence of platinum (Pt), palladium (Pd) and iridium (Ir) at a concentration of 0.16, 0.02 and 0.27% respectively. Thisconfirms the presence of PGMs in the sample. The phase containing PGMs is well liberated and there is no need to mill thesample further. However, the phase is very fine and this will give challenges in the flotation stage.

Fig. 2: SEM-EDS images of the PGMs mine sludge

Elements
Spectrum 1
Spectrum 2
Elements
Spectrum 1O
46.20
41.95
Pt0.16

Table 3: Chemical composition of the PGMs mine sludge (EDS).

Cr0.31
10.09
Ca0.31

Ag
0.16
Ti-Mg
16.66
11.98
V-Al
0.34
4.66
Fe
6.19

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Si
28.67
18.91
Mn
0.20

Pd
0.02
Cu
0.13

Os
0.51
-

Ir
0.27

Spectrum 2-

0.17

0.16

0.18

11.90

-0.04

3.4. Functional groups present in the PGM mine sludge sample
To determine the presence of hydrocarbons in the PGMs mine sludge, FTIR was used and the results are shown onFig. 3. The FTIR method used to characterise the solid sample was the KBr method which introduced alcohols (O-Hbonds) in the sample and its peaks are from the range of 3000-3700cm-1 [7]. The general range of the wavenumber ofhydrocarbons (C-H bond) is 2850-3000cm-1. As shown on Fig. 3, hydrocarbons (C-H bond) are present in the PGMs minesludge sample. Therefore, this confirms that the PGMs mine sludge sample is contaminated with hydrocarbons.

Fig. 3: FTIR results of the PGM mine sludge.

3.5. Washing experiment results

The efficiency of the washing experiments was calculated following equation 1 and the results are shownin Table 4. The average hydrocarbon concentration (Co) in the as-received sample of the PGMs mines sludge wasfound to be 58.3ppm. B1 showed the highest hydrocarbon removal efficiency with 91.86%, followed by B4,with 79.87 %. The lowest hydrocarbon removal efficiency was achieved at B10, with 50.20%.
Table 4: Concentrations of the hydrocarbons in PGM mine sludge after washing experiments and the calculated hydrocarbon removal
percent in the sample.

Experiment No.

Hydrocarbon concentration after washing (ppm)

Hydrocarbon removal (%)

B1

4.75

91.86

B2

22.67

61.12

B3

24.91

57.28

B4

11.74

79.87

B513,.05

77.63

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B6

16.17

72.28

B7

24.89

57.32

B8

12.91

77.87

B9

27.60

52.68

B10

29.04

50.20

B11

12.72

78.20

B12

24.43

58.11

B13

22.63

61.19

B14

28.86

50.51

B15

15.70

73.08

4. Conclusion

Hydrocarbon contaminated PGMs mine sludge has great potential as a source of PGMs. The mine sludge contains
a high grade of PGEs. Most of the PGM are associated with base metals, chromite and silica. The FTIR results haveshown that the hydrocarbons were presents in the sample at the wavenumber of is 2850-3000cm-1 of the sample. TheSEM-EDX results revealed that the sample is fully liberated and no further milling is required. However, the grain
sizes are too fine (D- 5.98) and they will be difficult to process using froth flotation. An optimum hydrocarbon
removal of 91.86% was achieved under optimum washing conditions of a pH of 12, Triston- 100 (TX-100) dosage of15g/kg and washing time of 150 minutes. Further studies on the application of other non-ionic surfactants and theflotation behaviour of the washed mine sludge are recommended.

Acknowledgements

The authors would want to thank the University of Johannesburg and the National Research Foundation of South
Africa [Grant number 132291] for the financial support of this project.

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