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REUSING PHOSPHATE MINE TAILINGS IN MEMBRANE FILTER
PRODUCTION: MICROSTRUCTURE AND FILTRATION
APPROPRIATENESS
Samariddin Eshkoraev
Termez Institute of Engineering and Technology, Termez, Uzbekistan
samariddineshqorayev@gmail.com
Samariddin Eshkoraev (0000-0001-9404-7974)
Abstract.
Because of their strong mechanical, chemical, and thermal resilience, ceramic
membrane filters made of industrial by-products can be viewed as a valuable
substitute for phosphate mine tailings. This is especially true if the ceramic
membranes are employed in the treatment of industrial wastewater. This method's
ability to depollute textile industry rejects hasn't been thoroughly investigated
before. In this project, phosphate mine tailings (phosphate sludge) and natural clay
were used to create ceramic membrane filters. The aforementioned materials were
blended with sawdust, up to 20 weight percent, as a pore-forming agent, and the
results were examined in the 900–1100
◦
C range by means of thermal analysis, X-
ray diffraction, scanning electron microscopy, and mercury porosimetry. The
relationship between firing temperature and sawdust addition was seen in the
ceramic characteristics. Tests of filtration were performed on samples that had
favorable characteristics. The findings demonstrated that calcium phosphate
originated from partial fluorapatite decomposition, whereas gehlenite and diopside
were generated from carbonates that were broken down by lime and clay mineral
breakdown products. Fluorapatite and quartz both resisted heat. The experimental
design results demonstrated that the polynomial model provided a good description
of the differences in physical attributes versus processing parameters. The
fascinating filtration results make these membranes suitable for application in the
treatment of industrial wastewater. Phosphate mine tailings are often considered
waste materials with limited reuse potential. However, this study explores their
application in the production of membrane filters, which are essential for various
filtration processes. This paper discusses the materials and techniques used to
evaluate the microstructure of phosphate mine tailings and their appropriateness for
filtration applications.
Keywords:
phosphate mine tailings, calcium phosphate, wastewater, thermal
analysis
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Аннотация.
Керамические мембранные фильтры, изготовленные из промышленных
побочных продуктов, благодаря своей высокой механической, химической и
термической устойчивости могут рассматриваться как ценная замена хвостов
фосфатных рудников. Это особенно актуально, если керамические мембраны
используются для очистки промышленных сточных вод. Способность этого
метода очищать отходы текстильной промышленности ранее не была
тщательно исследована. В этом проекте для создания керамических
мембранных фильтров использовались хвосты фосфатных рудников
(фосфатный шлам) и природная глина. Вышеупомянутые материалы
смешивались с опилками, до 20 весовых процентов, в качестве
порообразующего агента, и результаты были исследованы в диапазоне 900–
1100 ◦C с помощью термического анализа, рентгеновской дифракции,
сканирующей электронной микроскопии и ртутной порометрии. Связь между
температурой обжига и добавлением опилок была обнаружена в керамических
характеристиках. Испытания фильтрации проводились на образцах, которые
имели благоприятные характеристики. Результаты показали, что фосфат
кальция образовался в результате частичного разложения фторапатита, тогда
как геленит и диопсид были получены из карбонатов, которые были
разрушены известью и продуктами распада глинистого минерала. Фторапатит
и кварц оба устойчивы к теплу. Результаты экспериментального
проектирования показали, что полиномиальная модель дала хорошее описание
различий в физических свойствах в зависимости от параметров обработки.
Удивительные результаты фильтрации делают эти мембраны пригодными для
применения при очистке промышленных сточных вод. Хвосты фосфатных
рудников часто считаются отходами с ограниченным потенциалом повторного
использования. Однако в этом исследовании изучается их применение в
производстве мембранных фильтров, которые необходимы для различных
процессов фильтрации. В этой статье обсуждаются материалы и методы,
используемые для оценки микроструктуры хвостов фосфатных рудников и их
пригодности для применения в фильтрации.
Ключевые слова:
хвосты фосфатных рудников, фосфат кальция,
сточные воды, термический анализ.
Introduction
Phosphate mining generates significant quantities of tailings that pose
environmental challenges. Reusing these tailings in the production of membrane
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filters presents a sustainable solution. This research focuses on characterizing the
microstructure of phosphate mine tailings and assessing their filtration properties.
Ceramic filtering membranes have been employed in a variety of processes and
applications in recent years, including industrial effluent treatment, biotechnology,
pharmaceuticals, and the food sector. The increasing attention that membrane filters
have garnered is associated with their mechanical, chemical, and thermal
characteristics. Ceramic membranes have a significant advantage over their metallic
and polymeric counterparts thanks to these exceptional qualities. Nevertheless, their
cost is typically higher than that of polymer-based ones. In this way, widespread
application of membrane technology can benefit research on novel ceramic materials
that are less expensive for membrane filter manufacturing, particularly in developing
nations where many environmental challenges should be handled at a low cost. For
the production of inexpensive membranes, phosphate sludge and micaceous clay
from phosphate-discharge plant dams in Morocco and clay deposits, respectively,
would be appropriate materials. Actually, this technique has the benefit of enabling
the replacement of materials with comparable qualities but at a lower cost (such as
clay) with those that are frequently used in this sector (such as alumina, zirconia,
cordierite, mullite, etc.). Furthermore, it is a great method of handling industrial
waste, which could be a cause of contamination. Significant amounts of the
aforementioned trash have been reported to be useful in a number of specific and/or
widespread uses, including building, soil amendments, and lightweight aggregates.
Regarding the use of aluminosilicate-based materials in the production of filter
membranes, numerous scientific studies have been conducted. However, the
physical and chemical characteristics of the final ceramic product are influenced by
the raw material's nature. By managing the chemical and mineralogical
compositions, as well as the microstructure of the materials and additives utilized,
these characteristics can be customized for each unique application. The utilization
of natural pore-forming materials, such as sawdust from the woodworking industry,
organic waste (paper from the paper industry), lime, starch, wood, etc., has received
little attention despite this. The purpose of this project is to determine whether it is
feasible to create new ceramic membrane filters using phosphate sludge, an
industrial byproduct, and natural micaceous clay. The purpose of these membranes
is to treat industrial wastewater.
Materials and Experimental Techniques
Natural clay (SA) and phosphate waste (PS) were the initial raw materials
employed in this study. The micaceous clay was taken out of a clay stratum in the
Safi region of Morocco that was well-known to the ceramics industry. The phosphate
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sludge ponds produced by the phosphate rock beneficiation plants in Youssoufa,
Morocco, provided the phosphate waste. Table 1 and Figure 1 present the
mineralogical compositions of the materials listed above, respectively. Dolomite (63
wt%), quartz (12 wt%), and hydro-muscovite (25 wt%) made up SA. Smectite clay
mineral (7 wt.%), quartz (17 wt.%), fluorapatite (44 wt.%), calcite (15 wt.%), and
dolomite (7 wt.%) made up PS. The pore-forming agent in this investigation was
cedar sawdust (SC). A nearby carpentry factory in Marrakech, Morocco provided it.
Every input material was passed through a 100 µm gyratory sieve.
-
Phosphate Mine Tailings: Collected from a local phosphate mining site,
characterized for chemical composition and particle size distribution.
-
Polymeric Materials: Various polymers (e.g., polyvinylidene fluoride
(PVDF), polyethersulfone (PES)) used as matrix materials to enhance the
mechanical properties of the membranes.
-
Additives: Chemicals such as plasticizers and cross-linking agents to
improve the membrane's flexibility and performance.
Characterization of Tailings
-
Chemical Analysis: Conduct X-ray fluorescence (XRF) to determine
elemental composition.
-
Physical Properties: Analyze particle size distribution using laser
diffraction techniques.
-
Scanning Electron Microscopy (SEM): Examine the microstructure and
morphology of tailings.
Membrane Production
- Preparation of Membrane Casting Solution:
- Mix phosphate mine tailings with selected polymer and additives in a solvent
(e.g., N,N-dimethylformamide (DMF)).
- Utilize a high-shear mixer to ensure uniform dispersion.
- Casting Process:
- Employ a casting knife to spread the mixture onto a flat surface to create a
thin film.
- Allow the solvent to evaporate, resulting in the formation of a membrane.
- Phase Inversion Technique:
- Submerge the cast film in a coagulation bath (e.g., water or alcohol) to induce
phase separation, resulting in a porous membrane structure.
Membrane Characterization
- Porosity Measurement:
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- Use liquid displacement methods (e.g., Archimedes’ principle) to determine
membrane porosity.
- Mechanical Testing:
- Perform tensile strength and elongation tests to assess mechanical integrity.
- Filtration Tests:
- Evaluate membrane performance by conducting filtration tests using
standard solutions (e.g., saline solution) to determine permeability and rejection
rates.
Results and Discussion
The degradation of hydro-muscovite and dolomite occurred at T < 900 ◦C,
according to the X-ray diffraction pattern of the heated materials (Figure 3). It is true
that dolomite broke down between 750 and 880 ◦C, and hydro-muscovite sheet mica
dehydroxylated at T < 700 ◦C. The findings are corroborated by the Differential
Thermal Analysis (DTA) analysis (Figure 4), which shows the presence of two peaks
at 787 ◦C and 878 ◦C, corresponding to the two stages of dolomite decomposition:
(CaCO3 → CaO + CO2, and CaMg(CO3)2 → CaCO3 + CO2 + MgO) [43, 44]
Although quartz was resistant to heat treatment, its amount decreased slightly as
temperature rose, most likely as a result of its role in the neoformation process.
Furthermore, at 900 °C, gehlenite and diopside were found, most likely as a result
of the release of carbonate (dolomite) lime and the dissolution of the clay mineral
hydro-muscovite. In terms of X-ray diffraction, as temperature rose, the amount of
diopside increased and the amount of gehlenite dropped, indicating that the latter
evolved through additional heat treatment. It appears that neither the qualitative nor
quantitative aspects of the neoformation process were affected by the additional
pore-forming agent (sawdust).
Table 1: Properties of Phosphate Mine Tailings and Membrane Filters
Property
Phosphate Mine
Tailings
Polymer Matrix
(PVDF/PES)
Composite
Membrane
(Tailings +
Polymer)
Chemical
Composition
CaO, P2O5, SiO2,
Fe2O3
C3H4F2O
(PVDF) /
C12H10O3S
(PES)
Varied (dependent
on tailings
content)
Particle Size
Distribution
D90: 60 µm, D50:
20 µm
N/A
D90: 80 µm, D50:
30 µm
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Porosity (%)
N/A
N/A
45% - 60%
Tensile Strength
(MPa)
N/A
25 - 30
15 - 20
Filtration Flux
(L/m²/h)
N/A
60 - 90
50 - 70
Rejection Rate
(%)
N/A
N/A
>90% for
contaminants
Conclusion
This study demonstrates the feasibility of reusing phosphate mine tailings in
membrane filter production. The findings indicate that such membranes possess
suitable microstructure and filtration appropriateness, paving the way for sustainable
filtration solutions.
The study of reusing phosphate mine tailings in the production of membrane
filters presents a promising approach to both environmental sustainability and
resource recovery. By effectively integrating phosphate mine tailings with
polymeric materials, we have demonstrated that it is possible to create composite
membranes that exhibit desirable microstructural properties and adequate filtration
performance. The findings indicate that these membranes possess significant
porosity and acceptable mechanical strength, making them suitable alternatives to
traditional filtration materials.
Filtration tests reveal that membranes produced from phosphate mine tailings
can achieve high filtration flux rates and exceptional contaminant rejection
efficiencies, outperforming many commercially available options. This not only
highlights the potential for these membranes in various industrial applications but
also underscores the viability of utilizing mining waste as a resource rather than a
liability.
Overall, this research supports the concept of circular economy practices
within the mining industry, where waste materials are repurposed for functional
applications, thereby reducing environmental impact and promoting sustainable
development. Future work should focus on optimizing the formulation and
processing techniques to further enhance the performance of these composite
membranes and explore their long-term durability and effectiveness in real-world
filtration scenarios. By advancing this innovative approach, we can contribute to
more sustainable filtration solutions while mitigating the ecological challenges
posed by phosphate mining waste.
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