KAOLINITE

Kaolinite is the principal crystalline mineral in many kaolin deposits, but Kaolinite and kaolin are not strictly interchangeable terms.
Kaolinite identifies the 1:1 layered aluminosilicate Al2Si2O5(OH)4, whereas kaolin is a natural clay raw material that can also contain quartz, mica, feldspar, titanium minerals, iron minerals and other clay phases.
Softness, platelet morphology, whiteness, low abrasiveness, low ion-exchange capacity and predictable thermal conversion give Kaolinite commercial value in paper, ceramics, coatings, polymers, catalysts and activated construction materials.

CHEMICAL IDENTITY AND COMMON NAMES

Kaolinite belongs to the kaolinite subgroup of the kaolinite–serpentine mineral group.
The name describes a specific mineral species with a defined layer structure rather than every white clay or aluminium silicate.
Kaolin and china clay are industrial rock or clay terms for materials composed predominantly of Kaolinite, together with deposit-dependent accessory minerals.

Dickite and nacrite share the ideal chemical composition of Kaolinite but have different layer-stacking arrangements.
Halloysite has a related 1:1 aluminosilicate layer chemistry but commonly displays tubular morphology and can contain interlayer water.
These minerals therefore require separate mineralogical identification even when bulk chemical analyses appear similar.

Synonyms and Common Names: Kaolinite, Natural Kaolinite, Kaolinite (Al2(OH)4(Si2O5)), Aluminium hydroxide silicate, Aluminum hydroxide silicate, Aluminium silicate hydroxide, Aluminum silicate hydroxide, Aluminiumhydroxidesilicate, Aluminumhydroxidesilicate, Dialuminium disilicon pentaoxide tetrahydroxide, Dialuminum disilicon pentaoxide tetrahydroxide, Aluminium hydroxide dioxodisiloxane-1,3-bis(olate) (2/4/1), Kln

TECHNICAL IDENTIFICATION

CAS Number: 1318-74-7
EC / EINECS Number: 215-286-4
Molecular Formula: Al2Si2O5(OH)4
Alternative Formula Notation: Al2H4O9Si2
Oxide Formula Notation: Al2O3·2SiO2·2H2O
Molar Mass: 258.16 g/mol
Mineral Class: Dioctahedral 1:1 phyllosilicate
Mineral Group: Kaolinite–serpentine group
IMA Mineral Symbol: Kln
Crystal System: Triclinic
Space Group: P1
Ideal Al2O3 Content: Approximately 39.50% by mass
Ideal SiO2 Content: Approximately 46.55% by mass
Theoretical Dehydroxylation Mass Loss: Approximately 13.96% by mass

MINERAL STRUCTURE AND FUNCTIONAL BEHAVIOUR

Each Kaolinite layer combines one sheet of silicon–oxygen tetrahedra with one sheet of aluminium–oxygen and hydroxyl octahedra.
The paired tetrahedral and octahedral sheets form an electrically near-neutral layer approximately 0.72 nm thick.
Hydrogen bonding joins adjacent layers and limits the entry of water and exchangeable ions between them.

This compact 1:1 arrangement explains why Kaolinite has low swelling, low shrink–swell capacity and substantially lower cation-exchange capacity than smectite clays.
Kaolinite develops useful plasticity when mixed with water, yet it does not form the strongly swelling gels associated with bentonite.
Dispersion behaviour depends mainly on particle size, platelet stacking, edge charge, pH, soluble salts and the type of dispersant rather than on interlayer expansion.

Microscopic Kaolinite particles commonly occur as pseudohexagonal plates and stacked booklets.
Platelet geometry provides surface coverage, barrier effects, smoothness and reinforcement, while the mineral’s low hardness limits abrasion of processing equipment and finished surfaces.
Surface hydroxyl groups support hydrogen bonding and allow silane, fatty-acid and other surface treatments to improve compatibility with organic matrices.

PHYSICAL AND CHEMICAL PROPERTIES

Physical State: Crystalline mineral solid
Commercial Appearance: Fine white, off-white, cream, pale yellow, grey or lightly tinted powder and clay
Odour: Odourless when dry
Crystal Habit: Microscopic pseudohexagonal platelets, stacks and compact earthy aggregates
Mohs Hardness: 2.0–2.5
True Density: Approximately 2.60–2.68 g/cm³
Streak: White
Lustre: Pearly on cleavage surfaces and dull to earthy in fine aggregates
Cleavage: Perfect basal cleavage on {001}
Refractive-Index Range: Approximately 1.553–1.570
Water Solubility: Insoluble
Volatility: Nonvolatile
Vapour Pressure: Negligible
Combustibility: Noncombustible
Flash Point: Not applicable
Cation-Exchange Capacity: Approximately 3–15 meq/100 g
Swelling Behaviour: Low and non-expanding under ordinary aqueous conditions
Thermal Behaviour: Dehydroxylates and transforms before conventional melting

Ideal Kaolinite is white, while iron oxides, titanium minerals, organic matter and other impurities introduce cream, yellow, grey, brown or red tones.
Brightness and fired colour are consequently more useful commercial selection parameters than a general colour description.
True density is a mineral property, whereas bulk density depends on milling, agglomeration, moisture, aeration and compaction.

Kaolinite is resistant to water and many dilute chemical environments at ambient temperature.
Strong acids and concentrated alkalis can attack the aluminosilicate lattice, particularly at elevated temperature.
The mineral surface is hydrophilic before modification and can adsorb water, polar molecules and ions at external faces and particle edges.

THERMAL TRANSFORMATION AND ACTIVATION

Heating removes free and adsorbed moisture first without changing the Kaolinite lattice.
Dehydroxylation begins at approximately 400 °C and normally progresses through the 450–700 °C range as structural hydroxyl groups leave as water.
The reaction disrupts long-range crystallinity and converts Kaolinite into metakaolin, an amorphous and substantially more reactive aluminosilicate.

Al2Si2O5(OH)4 → Al2Si2O7 + 2 H2O

Calcination temperature, residence time, heating rate, particle size, water-vapour pressure and structural disorder determine the degree of dehydroxylation.
Controlled activation commonly targets a highly dehydroxylated but non-recrystallised material for pozzolanic and alkali-activated applications.
Excessive thermal treatment reduces this reactivity as spinel-like phases, mullite and crystalline silica phases develop at higher temperatures.

Ceramic firing intentionally uses these transformations differently.
Metakaolin formation, sintering, vitrification and eventual mullite development contribute to fired strength, dimensional change, whiteness and thermal resistance.
Iron, titanium, alkali metals, particle packing and accompanying quartz strongly influence the firing window and final ceramic appearance.

PRODUCTION AND COMMERCIAL FORMS

Most commercial Kaolinite originates from primary residual deposits formed by weathering or hydrothermal alteration of feldspar-rich rocks and from secondary sedimentary deposits created after transport and redeposition.
Primary deposits commonly require removal of coarse quartz, mica and incompletely altered rock, while sedimentary deposits can provide very fine particle populations with different colour and impurity profiles.

Dry processing uses selective mining, crushing, drying, pulverising and air classification to obtain economical mineral fillers and ceramic feedstocks.
Wet beneficiation begins by blunging the clay with water and dispersant, followed by degritting and particle classification with screening, hydrocyclones or centrifuges.
Magnetic separation, flotation, selective flocculation and chemical bleaching can reduce iron- and titanium-bearing colour bodies and improve brightness.

The refined slurry is dewatered by filtration or centrifugation and then supplied as filter cake, spray-dried granules, dried powder or concentrated slurry.
Delamination separates stacked booklets into thinner platelets for coating and reinforcement functions.
Milling controls top-cut and residue, while surface treatment changes compatibility with rubber, plastics, sealants and other organic systems.

Commercial forms include hydrous powder, delaminated platelets, ultrafine grades, high-brightness grades, low-abrasion coating grades, ceramic grades, surface-treated fillers and calcined derivatives.
Hydrous material retains the crystalline Kaolinite structure and structural hydroxyl groups.
Calcined kaolin and metakaolin are manufactured from Kaolinite but no longer retain the original crystalline mineral phase.

APPLICATIONS AND INDUSTRIES

Paper coating and filling

Kaolinite functions as both a mineral filler within the fibre network and a coating pigment on paper and paperboard surfaces.
Fine, bright platelets fill surface irregularities and improve smoothness, opacity, print definition, ink holdout and coating uniformity.
Coating grades place particular emphasis on particle-size distribution, platelet aspect ratio, slurry viscosity, brightness, abrasiveness and low coarse residue.

Hydrous Kaolinite supports gloss and smoothness in coated papers, while calcined derivatives provide greater light scattering, opacity and bulk in selected formulations.
Stable high-solids dispersion is essential because excessive viscosity restricts coating speed and produces uneven application.

Ceramics and whitewares

Kaolinite supplies both silica and alumina to porcelain, sanitaryware, tableware, electrical porcelain, tiles and glazes.
Before firing, fine Kaolinite contributes workability, suspension stability, green strength and controlled drying behaviour.
During firing, dehydroxylation and subsequent reactions develop glassy phases and mullite that influence strength, translucency, dimensional stability and heat resistance.

Ceramic selection focuses on mineralogical purity, particle size, plasticity, casting rate, deflocculant demand, drying shrinkage, fired shrinkage and fired colour.
Low iron and titanium are especially important for white bodies, while soluble salts and carbonaceous matter can create firing defects.

Refractories and glass fibre

Kaolinite-rich feedstocks provide a balanced source of alumina and silica for refractory shapes, kiln furniture, ceramic fibre and glass-fibre production.
Calcination and high-temperature firing convert the raw mineral into thermally stable phases, with mullite formation supporting refractoriness and mechanical stability.
Low iron, low alkali content and controlled quartz are important where colour, electrical properties or high-temperature performance are critical.

Paints, inks and surface coatings

Fine Kaolinite extends primary pigments, adjusts sheen and contributes to suspension, film smoothness, hardness and scrub resistance.
Platelets improve coverage and barrier pathways, while calcined derivatives increase opacity through internal void structure and enhanced light scattering.
Oil absorption, brightness, particle top-cut, dispersion viscosity and compatibility with aqueous or solvent-borne binders guide grade selection.

Rubber and polymer compounds

Kaolinite reinforces natural and synthetic rubber, increasing stiffness, hardness, dimensional control and abrasion resistance in footwear, cable compounds, hoses and moulded goods.
Fine high-surface-area grades provide stronger reinforcement, whereas coarser soft-clay grades provide economical extension and processing control.

In thermoplastics and thermosets, Kaolinite functions as a mineral filler that can improve rigidity, dimensional stability, surface finish, electrical insulation and gas-barrier performance.
Calcination reduces structural hydroxyl content, and surface treatment improves wetting and adhesion in nonpolar polymer matrices.
Moisture, particle size, dispersion and treatment chemistry influence compound viscosity, mechanical properties and appearance.

Adhesives and sealants

Kaolinite contributes body, sag control, solids adjustment, reinforcement and shrinkage management in adhesives, mastics, caulks and sealants.
Platelet alignment can increase barrier performance and help control flow without introducing the extreme thixotropy of highly swelling clays.
Surface-treated grades are selected when moisture resistance and compatibility with hydrophobic binders are required.

Cementitious binders and geopolymers

Raw crystalline Kaolinite has limited pozzolanic reactivity, but controlled calcination produces reactive metakaolin for cement and alkali-activated binders.
Metakaolin reacts with calcium hydroxide in Portland-cement systems and supplies reactive alumina and silica to geopolymer networks.
Kaolinite content, calcination degree, amorphous content, fineness and residual quartz determine activation efficiency and binder performance.

Catalysts, molecular sieves and adsorbents

Kaolinite supplies aluminium and silicon for the manufacture of zeolites, molecular sieves, catalyst matrices and ceramic catalyst supports.
Thermal activation, acid treatment or alkaline conversion opens the original structure and creates more reactive or porous materials.
Modified Kaolinite also serves in specialised adsorption systems for pigments, organic molecules and dissolved ions, although unmodified Kaolinite has lower exchange capacity than swelling clays.

Pharmaceutical, cosmetic and personal-care uses

Purified Kaolinite is incorporated into powders, masks, creams, poultices and selected pharmaceutical formulations as an absorbent, bulking agent, opacifier, texture modifier and mineral excipient.
Fine particle size gives a smooth skin feel, while external surfaces adsorb oils and moisture without strong interlayer swelling.
These grades require controlled mineral identity, microbial quality, elemental impurities, crystalline silica, colour, odour and particle size.

Agricultural formulations

Processed Kaolinite acts as a mineral carrier, diluent and anticaking component in fertiliser and crop-protection formulations.
Specially engineered particle-film grades form a light-coloured physical coating on plant surfaces that can reduce heat loading and interfere with insect contact or recognition.
Agricultural performance depends on particle size, dispersibility, adhesion, coverage, wash-off behaviour and formulation compatibility.

GRADE SELECTION AND COMMERCIAL PERFORMANCE

Kaolinite is purchased by mineralogical composition and functional performance rather than by molecular assay alone.
An industrial grade can contain associated quartz, mica, feldspar, anatase, iron oxides and other clay minerals even when Kaolinite is the dominant phase.
X-ray diffraction establishes the mineral phases, while chemical analysis alone cannot distinguish minerals having similar elemental compositions.

High-brightness coating grades require low colour-bearing impurities, fine controlled particle size, good high-solids rheology and low abrasion.
Ceramic grades are differentiated by fired colour, plasticity, casting behaviour, shrinkage, strength and fluxing impurities.
Polymer and rubber grades are selected by reinforcement level, moisture, particle top-cut, surface treatment and dispersion in the chosen matrix.

Metakaolin feedstocks require high Kaolinite content and a calcination profile that maximises dehydroxylation and amorphisation without excessive recrystallisation.
Pharmaceutical and personal-care grades add tighter controls for trace elements, microbial content, mineral contaminants and sensory properties.
Research grades may emphasise high mineral purity, crystallinity, reference diffraction behaviour or specified surface area.

DISPERSION, FORMULATION AND PROCESS CONTROL

Kaolinite powder should be incorporated under controlled dust extraction and dispersed with mixing energy appropriate to the agglomerate strength.
Adding a compatible dispersant to the liquid phase before the mineral can improve wetting and reduce the formation of persistent lumps in aqueous slurries.
High shear separates soft agglomerates, but excessive milling can alter platelet aspect ratio and increase equipment-derived contamination.

Slurry rheology responds to solids content, pH, dissolved salts, platelet edges and dispersant dosage.
Over-dispersion can change water demand and downstream retention, while under-dispersion produces high viscosity, sediment or surface defects.
Paper, paint and ceramic processes therefore evaluate viscosity under the shear conditions relevant to pumping, coating, casting or spraying.

Dry polymer compounding requires low moisture and effective distributive mixing to prevent platelet agglomeration.
Surface-treated Kaolinite should be matched to the polymer polarity, coupling system and processing temperature.
Ceramic bodies require controlled water addition, de-airing, drying rate and firing profile to manage cracking, warpage and shrinkage.

QUALITY, SPECIFICATIONS AND DOCUMENTATION

Mineralogical analysis by X-ray diffraction quantifies Kaolinite and identifies quartz, mica, feldspar, smectite, illite, anatase, rutile and other crystalline phases.
X-ray fluorescence or elemental analysis measures SiO2, Al2O3, Fe2O3, TiO2, alkali metals and other inorganic constituents.
Thermogravimetric analysis and loss on ignition provide information about adsorbed moisture, structural hydroxyl content, carbonates and organic matter.

Particle-size distribution, percentage below selected micrometre limits, coarse residue, specific surface area, oil absorption, bulk density and moisture describe physical performance.
Brightness, whiteness, yellowness and fired colour are central for paper, coating, polymer and ceramic applications.
Slurry pH, viscosity, sedimentation, dispersant demand and abrasion are important for wet-processing grades.

Application-focused testing can include ceramic casting rate, drying and firing shrinkage, fired strength, water absorption, polymer reinforcement, rubber hardness or pozzolanic activity.
Crystalline-silica content receives separate attention because quartz can affect both abrasion and respirable-dust classification.
Trace metals and microbiological testing support selection for pharmaceutical, cosmetic and other high-purity uses.

A Certificate of Analysis records batch-controlled chemical, mineralogical and physical parameters.
A Technical Data Sheet explains grade form, performance characteristics and recommended application areas, while a Safety Data Sheet covers hazards, exposure controls and emergency measures.
Detailed procurement files can also include particle-size curves, brightness data, X-ray diffraction results, chemical analysis and application-specific test reports.

SAFETY AND ENVIRONMENTAL CONSIDERATIONS

Kaolinite is noncombustible, nonvolatile and stable during ordinary storage.
The main occupational concern is inhalation of fine airborne dust generated during transfer, milling, mixing and cleanup.
Short-term dust exposure can irritate the eyes, nose, throat and respiratory tract, while prolonged heavy respirable exposure can cause chronic lung effects, including kaolinosis and pulmonary fibrosis.

Natural Kaolinite grades can contain quartz or other forms of crystalline silica.
Enclosed conveying, local exhaust ventilation, filtered dust collection and suitable respiratory protection limit exposure to both Kaolinite and associated respirable minerals.
Safety controls should reflect the measured respirable fraction and crystalline-silica content of the handled grade.

Kaolinite is a persistent inorganic mineral and does not biodegrade.
Spills can create slippery surfaces, visible turbidity and sediment loading in water, even though the mineral has low water solubility.
Containment of powder, slurry and wash water prevents unnecessary release to drains, soil and surface water.

FIRST AID

Inhalation: Move the exposed person to fresh air and obtain medical attention if coughing, breathing discomfort or other respiratory symptoms persist.
Skin Contact: Wash with soap and water and remove contaminated clothing.
Eye Contact: Rinse cautiously with clean water for at least 15 minutes, remove contact lenses when easy to do and obtain medical attention if irritation continues.
Ingestion: Rinse the mouth and obtain medical advice if a significant quantity has been swallowed or discomfort develops.
Note to Physicians: Treatment is symptomatic and supportive, with attention to respiratory irritation after substantial dust exposure.

HANDLING AND STORAGE

Handling: Use closed transfer or local exhaust ventilation, minimise drop distances and prevent airborne dust formation.
Ventilation: Provide extraction at bag opening, charging, milling, blending and packing points.
Storage: Keep containers tightly closed in a cool, dry and well-ventilated location protected from moisture and contamination.
Incompatibilities: Strong acids and concentrated alkalis can attack Kaolinite, particularly under heated process conditions.
Spill Control: Recover powder with a filtered industrial vacuum or careful damp collection and avoid dry sweeping or compressed air.

PACKAGING AND PROCUREMENT CONSIDERATIONS

Kaolinite is commonly supplied in moisture-resistant bags, lined bulk bags, drums, filter cake, spray-dried granules or concentrated slurry, depending on grade and process scale.
Fine high-brightness, surface-treated and high-purity powders benefit from sealed packaging that protects particle condition and prevents cross-contamination.
Slurry procurement additionally considers solids content, dispersant system, viscosity, preservation and transport stability.

A precise purchasing request identifies the intended paper, ceramic, coating, rubber, polymer, adhesive, construction, catalyst, cosmetic, pharmaceutical or agricultural use.
Critical parameters can include Kaolinite content, accessory minerals, SiO2 and Al2O3, Fe2O3, TiO2, quartz, brightness, fired colour, particle-size distribution, residue, moisture, pH, viscosity, oil absorption, surface treatment and packaging form.
Selecting these parameters around the actual process produces more useful procurement criteria than a generic purity description.

Ataman Kimya supports Kaolinite procurement with attention to mineralogical composition, particle engineering, brightness, rheology, thermal behaviour, application grade, documentation and packaging.
For Kaolinite specifications, grade selection, technical documentation, packaging options and supply inquiries, contact Ataman Kimya at +90 216 577 10 10 or info@atamankimya.com.