Kaolin Samples Research Articles

Removal of Pb2+ from Aqueous Solution using Thach Khoan Kaolin from Phu Tho Province

Kaolin sample (mixture of halloysite and kaolinite) from Thach Khoan, Phu Tho province was studied to remove Pb2+ ions from an aqueous solution. The SEM-EDS and TEM analysis showed that in the kaolin sample, tubular halloysite and plate kaolinite minerals coexist, similar to the results from previous studies. The various treatment conditions such as contact time, solution pH, the adsorbent weight, and initial concentration of Pb2+ were examined and evaluated using batch adsorption experiments. The results showed that under experimental conditions of pH0 = 5.31 and a temperature of 25 °C, with 0.7 g of Thach Khoan kaolin material, the Pb2+ adsorption can reach equilibrium after about 50 minutes and efficiency reached 90.75%. The adsorption process follows the Langmuir adsorption isotherm model with the maximum monolayer adsorption capacity of 3.79 mg/g and follows the pseudo-second-order kinetic equation. This result indicated that unmodified Thach Khoan kaolin with a mixture of tabular halloysite and plate kaolinite minerals has a significant potential in removing heavy ions from aqueous solution.
 
 
 

Investigation of the Effect of Leachate on Permeability and Heavy Metal Removal in Soils Improved with Nano Additives

Soils with low permeability are widely used in solid waste landfills to prevent leakage of leachate into groundwater. By adding nanomaterials to clay soils, the permeability of the clay can be reduced as well as the retention of pollutants in the leachate. In this study, three different nanomaterials, iron oxide, aluminum oxide, and Oltu clay, were added to kaolin at two different rates (1% and 5%), and the effect of nanomaterials on permeability and heavy metal (iron, manganese, zinc, copper, and lead) removal rate was investigated. According to the experimental results, permeability decreased, and the heavy metal removal rate increased with increasing nanomaterial content in kaolin. With the addition of 5% iron oxide, 5% aluminum oxide, and 5% Oltu clay to kaolin, the average permeability decreased by 63%, 81%, and 96%, respectively. Iron (90–93%), manganese (47–75%), zinc (39–50%), copper (33–41%), and lead (36–49%) removal rates of nanomaterial-added kaolin samples were found to be higher than the removal rates of kaolin without nanomaterial addition. Oltu clay, which has the smallest size and high surface area, performed better than aluminum oxide and iron oxide in reducing the permeability of kaolin and retaining heavy metals.

Applying Saudi clay deposits for treatment of household water at the point-of-use

This research aims to beneficiate the clay deposits abundant in the Al Baha district to produce ceramic filters for “point-of-use” household water treatment technology to remove dissolved solids from water that is no longer valid for drinking purposes to meet the needs of the community through a safe household and industrial water supply after further treatment purposes. In addition, it helps to reduce the expenses of citizens earmarked to buy drinking water. A sample of laterite, clay, and kaolin from Al Baha district was thermally treated at 800 °C, acid treated with HCl, analyzed by XRD, FTIR, and SEM, and tested for treatment of household water. The temperature, pH, electrical conductivity (EC), and total dissolved solids (TDS) were measured. In the application step for point-of-use water treatment of household water, the treated materials were introduced in calcined kaolin filters and commercial polypropylene filters. Based on the results of household water treatment with raw and treated clay materials, the raw clay materials, has poor adsorption capacity. The thermal treatment of clay samples dehydrates the clay minerals into sintered aluminosilicates and enhances the conversion of poorly crystallized iron oxide to α-Fe2O3 without improving the adsorption capacity of clay materials. However, the acid treatment of the clay samples removes iron-bearing minerals leaving behind amorphous aluminosilicate matter characterized with improved adsorption capacity. It was concluded that the acid treatment of clay material by concentrated HCl acid completely leaches iron oxide phases and broke down and disintegrated the clay minerals into the amorphous matter with enhanced the adsorption capacity. The combination of selected acid-treated laterite, clay, and charcoal for the household water treatment filter at the point of use in the calcined kaolin filter and the polypropylene filter reduced the TDS content by 40–42%.

Leaching of Ibute-Nze kaolin iron-oxide impurity with oxalic acid process optimization of dissolution conditions using response surface methodology

The goal of this research was to remove iron oxide from Ibute-Nze kaolin by dissolving the clay mineral in an aqueous oxalic acid solution and optimizing the process. The chemical composition of the raw and modified clay was determined using x-ray fluorescence, and the morphology of the solid sample was determined using a scanning electron microscope. The best conditions for the oxalic acid leaching of iron-oxides impurity from Ibute-Nze kaolin were determined using response surface methodology based on Box-Behnken design. The studies were carried out within the following process parameter ranges: 40–90 leaching temperature; 0.075-0.355mm particle size; 1–6 mol/dm3 acid concentration; 0.02–0.12 g/cm3 kaolin sample to acid ratio and 30-240 min contact time. The characterization revealed that Ibute-Nze clay is kaolinitic in nature and calcination at 750 opens more pores for its leaching. According to the analysis of variance, a second-order polynomial regression equation provided the best fitting for the experimental data. The predicted and experimental response values were shown to be correlated (R2 = 0.9276) in the experimental runs. The following were found to be the best conditions for the leaching process variables: 83.2051 leaching temperature, 0.0827mm particle size, 3.6179mol/dm3 acid concentration; 0.0287g/cm3 kaolin to acid ratio and 217.932min reaction time. The chemical leaching process was 92.6035 per cent under these conditions, which made the clay good for industrial applications.

Thermal treatment of Kalabsha kaolin deposits, south of the Western Desert, Egypt: contribution to geopolymer production as green building materials

Kaolin samples were collected to study the mineralogical, texture, chemical composition, thermal behavior, and treatment and also the possibility to convert kaolinite mineral into metakaolin and use it as a natural pozzolanic and/or as geopolymer materials. Kaolinite is the main constituent of clay mineral, which related to many of the chemical weathering of parent rocks and complete leaching of alkali elements under warm, humid to semi-arid climatic conditions. However, quartz, anatase, and iron oxide are considered non-clay minerals. Cement substituted by metakaolin under different ratios in the concrete industry was carried out to enhance the physical and mechanical properties of the concrete. The best results are detected at 10% and 15% of cement replacement by metakaolin. Geopolymer production using Metakaolin (MK) was mixed with NaOH and Na2O-3SiO2 to replace the Portland cement in the concrete industry and the obtained results are suitable and match with the green building material concept.

Laboratory investigation of geogrout inclusion: the influence of the substitution ratio

Laboratory investigations using balloon tests were performed on normally consolidated kaolin samples to investigate their behaviour during and after the balloon expansion. The tests were carried out to simulate a soft soil improvement technique called CPR grouting (acronym for deep radial consolidation). The results allowed estimations of the parameters used in the design method, such as the consolidation potential, and evaluating the generation of pore pressures, injection pressures, post improvement deformation and optimised expanded volume. It was observed that the consolidation potential was extremely dependent on the substitution ratio. The tests satisfactorily reproduced the behaviour of the technique and represent a new device for geotechnical engineers, especially for those concerned with the improvement of soft soils.

Study of a Waste Kaolin as Raw Material for Mullite Ceramics and Mullite Refractories by Reaction Sintering.

A deposit of raw kaolin, located in West Andalusia (Spain), was studied in this work using a representative sample. The methods of characterization were X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size analysis by sieving and sedimentation, and thermal analysis. The ceramic properties were determined. A sample of commercial kaolin from Burela (Lugo, Spain), with applications in the ceramic industry, was used in some determinations for comparison purposes. The kaolin deposit has been produced by alteration of feldspar-rich rocks. This raw kaolin was applied as an additive in local manufactures of ceramics and refractories. However, there is not previous studies concerning its characteristics and firing properties. Thus, the meaning of this investigation was to conduct a scientific study on this subject and to evaluate the possibilities of application. The raw kaolin was washed for the beneficiation of the rock using water to increase the kaolinite content of the resultant material. The results indicated that the kaolinite content of the raw material was 20 wt % as determined by XRD, showing ~23 wt % of particles lower than 63 µm. The kaolinite content of the fraction lower than 63 µm was 50 wt %. Thus, an improvement of the kaolinite content of this raw kaolin was produced by wet separation. However, the kaolin was considered as a waste kaolin, with microcline, muscovite and quartz identified by XRD. Thermal analyses by Thermo-Dilatometry (TD), Differential Thermal Analysis (DTA) and Thermo-Gravimetry (TG) allowed observe kaolinite thermal decomposition, quartz phase transition and sintering effects. Pressed samples of this raw kaolin, the fraction lower than 63 µm obtained by water washing and the raw kaolin ground using a hammer mill were fired at several temperatures in the range 1000–1500 °C for 2 h. The ceramic properties of all these samples were determined and compared. The results showed the progressive linear firing shrinkage by sintering in these samples, with a maximum value of ~9% in the fraction lower than 63 µm. In general, water absorption capacity of the fired samples showed a decrease from ~18–20% at 1050 °C up to almost zero after firing at 1300 °C, followed by an increase of the experimental values. The open porosity was almost zero after firing at 1350 °C for 2 h and the bulk density reached a maximum value of 2.40 g/cm3 as observed in the ground raw kaolin sample. The XRD examination of fired samples indicated that they are composed by mullite, from kaolinite thermal decomposition, and quartz, present in the raw sample, as main crystalline phases besides a vitreous phase. Fully-densified or vitrified materials were obtained by firing at 1300–1350 °C for 2 h. In a second step of this research, it was examined the promising application of the previous study to increase the amount of mullite by incorporation of alumina (α-alumina) to this kaolin sample. Firing of mixtures, prepared using this kaolin and α-alumina under wet processing conditions, produced the increase of mullite in relative proportion by reaction sintering at temperatures higher than 1500 °C for 2 h. Consequently, a mullite refractory can be prepared using this kaolin. This processing of high-alumina refractories is favoured by a previous size separation, which increases the kaolinite content, or better a grinding treatment of the raw kaolin.

Extraction of TiO2 from kaolin deposits in the Central Region, Ghana: An alternative material for the formulation of climate-smart Portland cement

This paper is one of series of papers assessing the suitability of formulating titanium dioxide climate smart Portland cement in developing countries using locally available cementitious material like kaolin. In this paper, authors highlight extraction of titanium dioxide from kaolin deposits in the Central Region, Ghana using selective flocculation techniques and later used to formulate climate-smart cement. Titanium dioxide (TiO2) a photocatalytic ingredient which studies from developed countries have shown that when nano-sized of it is added to cement is able to reduce smog-forming air pollutants, keep surfaces of buildings clean and resist sulphate attack. However, developing countries with weak economies and low technologies are not able to utilize nano-size TiO2 in the formulation of climate-smart cement. It is within this context that this study was undertaken. About 450 g of 53 μm kaolin samples were treated with dispersing agents such as sodium polyacrylate and sodium silicate in excess amount so as to produce maximum deflocculation of the kaolinite particles. The percentage of titanium dioxide extracted ranges from 86.1% for kaolin samples from Saltpond to 91.8% for kaolin samples from Assin Foso respectively; which was later used to formulate climate-smart Portland cement. The ability of the formulated TiO2-ordinary Portland climate smart cement to degrade Rhodamine B dye was tested. Mortar pastes containing various percentages of TiO2-climate smart Portland cement with Rhodamine B dye were exposed to sunlight for 0, 24, 48, 72 and 96 h respectively. The test results indicate that addition of TiO2 extracted from kaolin and used to synthesize climate -smart ordinary Portland cement is able to degrade air pollutants from vehicular exhaust such as PAHs, and as such its use in the construction industry can improve the durability of buildings and for that matter the socio-economic development of the region as well as Ghana as a whole.

Modification of the Filler based on Kaolin and its Use in the Polymer Composites

Light mineral fillers are the natural inorganic materials of various compositions that have been used in a practical way since the beginning of the rubber industrial processing. Depending on the application, the natural kaolin is often modified by physical processes or by chemical processes (pillaring, adsorption, intercalation, functionalization, acid activation, etc.). It is important to modify kaolin due to improvement of its properties in order to adsorb the inorganic as well as organic molecules. In the introduced study, kaolin from Kaznějov deposit was modified by potassium acetate or dimethylsulphoxide and subsequently functionalized by accelerator dibenzothiazyldisulphide and its last modification was performed by silane treatment. Different techniques, such as the thermal (DTA) and spectral (FTIR) analysis were used to characterize modified kaolin samples. The main aim of the article is to observe the influence of modified kaolin forms on the physico-mechanical properties and structural changes of rubber mixtures. Combined with the carbon black, the given modified kaolin was mixed into a rubber blend in a particular ratio, which was5, 10, 24 phr. The effect of the modified kaolinite on the cure characteristics (minimum torque – ML, maximum torque – MH, optimal cure time – t90, scorch time ts2) and mechanical properties (tensile strength at break – TSb, elongation at break – Eb and hardness)in sulphur-cured rubber composites was investigated. In images from a scanning electron microscope (SEM), we observed the incorporation of modified forms of kaolin into the matrix of the rubber mixture.

Modelling the Effects of Nanomaterial Addition on the Permeability of the Compacted Clay Soil Using Machine Learning-Based Flow Resistance Analysis

Impermeable base layers that are made of materials with low permeability, such as clay soil, are necessary to prevent leachate in landfills from harming the environment. However, over time, the permeability of the clay soil changes. Therefore, to reduce and minimize the risk, the permeability-related characteristics of the base layers must be improved. Thus, this study aims to serve this purpose by experimentally investigating the effects of nanomaterial addition (aluminum oxide, iron oxide) into kaolin samples. The obtained samples are prepared by applying standard compaction, and the permeability of the soil sample is experimentally investigated by passing leachate from the reactors, in which these samples are placed. Therefore, Flow Resistance (FR) analysis is conducted and the obtained results show that the Al additives are more successful than the Fe additive in reducing leachate permeability. Besides, the concentration values of some polluting parameters (Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), and Total Phosphorus (TP)) at the inlet and outlet of the reactors are analyzed. Three different models (Artificial Neural Networks (ANN), Multiple Linear Regression (MLR), Support Vector Machine (SVM)) are applied to the data obtained from the experimental study. The results have shown that polluting parameters produce high FR regression similarity rates (>75%), TKN, TP, and COD features are highly correlated with the FR value (>60%) and the most successful method is found to be the SVM model.

Effects of kaolin characteristics on the mechanical properties of alkali-activated binders

The present study examines the potential use of six Kaolin samples collected from different deposits to produce calcined kaolin-based alkali-activated binders. The samples were initially characterized to assess their chemical compositions and reactivity through x-ray fluorescence (XRF), x-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and Chapelle-test. Mortar specimens were prepared for measuring the hydraulic activity as well as the compressive strength. The chemical analysis of the Kaolin showed a wide range of Al2O3 content (7.4–28.9 wt%), whereas the difference in the SiO2 was minor. Chapelle test results reflected the quality of the Kaolin used in this investigation, with values ranging from 350 to 700 mg/g. All Kaolin samples exhibited clay-based crystalline compounds that disappeared after calcination and converted to amorphous phases. A wide range of compressive strength values was obtained for the resultant alkali-activated binder (15–40 MPa) at 90 days. Direct correlations were found between calcined kaolin characteristics and the 90-days compressive strength of the alkali-activated binder. Kaolin samples with high pozzolanicity and higher Si/Al ratio were found to be more pronounced to produce alkali-activated binder with higher compressive strength values. Higher Fe and Al contents in the calcined Kaolin were found to lower the compressive strength of the alkali-activated binder.

Stabilization of Kaolin Clay Soil Reinforced with Single Encapsulated 20mm Diameter Bottom Ash Column

Ground improvement methods are used to reduce the weakness of soft clay, which is low strength and high compressibility. The stone column technique involves replacing any of the soil with crushed stone such as broken rocks or sand which is an efficient method of improving the strength parameters of soil. Bottom ash usage in materials of building will effectively decrease the buildup of the waste and hence protect the environment. This study is to determine the shear strength of kaolin soft clay reinforced with a 20 mm diameter single encapsulated bottom ash column with various lengths. The research will look into the physicomechanical qualities of the materials used, including subsoil and bottom ash. Three (3) batches of samples with each batch consists of five (5) samples were prepared by using compaction method. All kaolin samples with a diameter of 50mm and height of 100mm with single encapsulated bottom ash columns with various lengths which are 60mm, 80mm, and 100mm were tested under Unconfined Compression Test (UCT). The result illustrated that the strength of samples increases as the height and volume of encapsulated bottom ash column increases.

Sustainable ground improvement method using encapsulated polypropylene (PP) column reinforcement

This study investigates the effectiveness of encapsulated polypropylene (PP) column in enhancing the undrained shear strength of kaolin (soft clay). The usage of PP in treating problematic soil is a more sustainable and cost-effective alternative compared to other materials. The installation of granular column can be done by using vibro-replacement method. Several geotechnical tests to determine the properties of materials were conducted. The shear strength of treated kaolin sample was examined by using Unconfined Compression Test (UCT). There are seven (7) batches of soil sample in total which included a control sample, three (3) batches of 14 mm and three (3) batches of 20 mm diameter PP column. Different diameters of PP column were examined with 60 mm, 80 mm and 100 mm height, respectively with soil sample of 50 mm in diameter and 100 mm in height. The shear strength improvement of kaolin is 33.82%, 46.51%, and 49.88% when implanted with a PP column with a 7.84 area replacement ratio and 0.6, 0.8 and 1.0 penetration ratio. The soft soil treated using 16.00 area replacement ratio with 0.6, 0.8 and 1.0 penetration ratio has a shear strength increment of 25.22%, 33.39% and 37.59% respectively. In short, the shear strength improvement of the kaolin clay depends on the parameter of the PP column used to reinforce the sample.

Treatment of real industrial wastewater with high sulfate concentrations using modified Jordanian kaolin sorbent: batch and modelling studies

In the present study, BaCl2 modified Jordanian kaolin sorbent (obtained from Mahis, Jordan) was used to remove sulfate-contaminated industrial wastewater. The kaolin sample was pretreated to enhance its adsorption capacity and then characterized using X-Ray fluorescence (XRF) and Fourier Transform Infrared Spectroscopy (FTIR). Equilibrium isotherms for the adsorption parameters were carried out experimentally, and the adsorption data correlated very well with Freundlich and Temkin and Dubinin-Radushkevich models. Furthermore, the adsorption kinetics followed the pseudo-first-order and intraparticle diffusion models perfectly. The estimated value of the maximum adsorption capacity qm = 85.08 mg/g indicates that kaolin has a very high capacity to adsorb sulfate ions at studied parameters. The estimated value of the mean free energy (4.87 kJ/mol) is very low, confirming physical type adsorption. The study results established that modified Jordanian kaolin could serve as a safe and effective natural adsorbent for sulfate-contaminated industrial wastewater.

Chemical and Mineralogical Composition Analysis of Different Nigerian Metakaolins

In this work, four different metakaolin samples (C01, A6060, B6075, and C12090) were investigated to determine their constituent elements and the relative quantities of the oxide contents associated with each of the elements. Kaolin samples were collected from different sites at Okpella, a village in the Edo state of Nigeria, West Africa. The metakaolin was produced by calcination at 750℃, which was followed by the dealumination process. The prepared samples were characterized by Field Emission Scanning Electron Microscope (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Resonance (FTIR) spectroscopy, and X-ray diffraction (XRD) technique. Digital images were obtained and analyzed to determine the texture and porosity of the samples. FE-SEM images showed a slight difference in the morphology of the samples. Differing percentages of metal oxides were determined from the samples using EDS analysis. The major oxides present in all the samples were Silica (Silicon oxide) and Alumina (Aluminium dioxide). Aluminium was completely absent in C12090 but had a large percentage of silicon (36%).

PLATYMATCH – A particle-matching algorithm for the analysis of platy particle kinematics using X-ray Computed Tomography

Particle scale mechanisms influence the mechanical behaviour of geomaterials. A better understanding of soil micromechanics will help develop more accurate constitutive models and, by extension, safer and more economic geotechnical design. Sand-grained soils have been widely studied at the particle scale using X-ray Computed tomography and this has revealed important micromechanical behaviour of sands. Clays are least understood and studied at the particle scale. As technology rapidly progresses, to understand clay kinematics, a particle kinematic algorithm to match plate shaped (platy) particles will be required. Current algorithms developed for the matching of quartz and carbonate sand particles may not be suitable, since particle attributes that are strong discriminators of round particles may be less unique on platy particles, due to their extremely small c-axis and the reduced image resolution associated with their smaller size. This study presents, particle tracking of kaolin sample using mica markers and provides a platy soil particle matching algorithm for evaluating platy particle kinematics. After testing a range of alternative particle attributes, it was observed that a combination of particle major axis length, intermediate axis length, and perimeter was a good discriminant of the platy mica particles studied. On this basis, we developed PLATYMATCH, an optimised platy particle matching algorithm that considers a minimised combined normalised error of unique particle attributes within a defined search volume space. The algorithm was implemented such that particle attributes were compared in parallel, rather than sequentially, to avoid filtering out a potential particle match based on a single non-unique attribute. PLATYMATCH was then successfully validated using a compressed mica soil sample.

Sustainable Implementation of Recycled Tire-Derived Aggregate as a Lightweight Backfill for Retaining Walls

The study examined the use of recycled tire-derived aggregate (TDA) mixed with kaolin for retaining wall applications. The effects of the TDA content on the geotechnical properties of TDA-kaolin specimens such as the internal friction angle, maximum dry density (MDD), optimum moisture content (OMC) and saturated density (SD) were investigated. A total of 13 physical model tests were performed on a polymer concrete retaining wall using kaolin and TDA-kaolin mixtures as backfill material. Powdery, shredded, small-sized granular (1–4 mm) and large-sized granular (5–8 mm) TDA were mixed with kaolin at contents of 0%, 20%, 40%, and 60% by weight. The lateral wall displacement was measured on a fabricated steel strip footing close to the wall during loading. Lateral wall displacement also was simulated using finite element (FE) software (Optum G2). The results indicated that the addition of 60% TDA decreased the internal friction angle of the samples up to 8% compared to pure kaolin. In addition, the TDA particles caused the MDD of the TDA-kaolin samples to decrease up to 45%. The physical modeling results indicated that the kaolin samples mixed with 60% shredded TDA showed the highest elasticity in all tests at the failure moment of the footing.

Effects of Non-thermal Plasma Treatment on the Geopolymerization of Kaolin Clay

Kaolin samples obtained from Cameroon were used to produce geopolymer binders. Prior to its application, the raw kaolin samples were activated through the gliding arc plasma treatment using both spatial post-discharge and direct mode. A mixture of sodium hydroxide and silicate was used as the alkaline solution. In order to study the influence of the modifications generated by the gliding arc plasma treatment on the geopolymerization process, X-ray diffraction, thermogravimetric analysis, differential scanning calorimeter and Fourier transform infrared spectroscopy were carried out. In addition, scanning electron microscopy, nitrogen physisorption and compression tests analysis were also carried out on the resulting geopolymer samples to access their mechanical performance. The results showed that the geopolymerization process was not completed at the curing temperature of 90 °C. Plasma spatial post-discharge mode treated kaolin led to 20.48% increase in compressive strength when compared with the geopolymer prepared from raw kaolin.

Adsorptive capacity of spray-dried pH-treated bentonite and kaolin powders for ammonium removal

The effectiveness of ammonium (NH4+) adsorption was investigated, using spray-dried, pH-treated bentonite, and kaolin as adsorbents. Each powder's adsorption capacity towards NH4+ was examined after up to 120 min of sample exposure, and results were compared. The zeta potential values for bentonite samples were between −1.1 and −19.4 mV, while for kaolin samples, they were between −35.7 and −40.9 mV (pH range examined was 2–10). The adsorption isotherm for bentonite showed a fit with the Langmuir model. The pH 10-treated bentonite and as-received bentonite (dispersed as pH 10 in distilled water) showed the highest adsorption capacity towards NH4+. Meanwhile, for kaolin, the adsorption capacity was low and observed only at low NH4+ concentration (100 mg/L and 200 mg/L), with pH 10-treated kaolin showed the highest adsorption capacity.

Adsorption Behavior of Polyhydroxy‐Iron‐Modified Coal‐Bearing Kaolin for Fluoride Removal

AbstractAccording to previous research on polyhydroxy‐iron‐modified coal‐bearing kaolin for the removal of anionic dyes, we first performed a ball milling treatment and then modified the kaolin samples with polyhydroxy‐iron to prepare a high‐surface‐area adsorbent. This process not only increased the surface area up to 100 m2 g−1 while successfully avoiding high‐temperature calcination and acid treatment but also significantly increased the fluoride adsorption performance in terms of the removal rate, which reached 90 %. Compared with the removal rate of raw kaolin (11 %), that of polyhydroxy‐iron‐modified coal‐bearing kaolin (without ball milling) was ∼44 %. Various adsorption conditions that affect the adsorption capacity of the adsorbent were investigated, including the adsorption time, initial solution pH and initial fluoride concentration. The effect of the initial pH showed a wide (pH=6–8) application range. The adsorption kinetics of fluoride fit well with the pseudosecond‐order kinetic model, and the equilibrium data can be well described by the Freundlich adsorption model.