Bauxite (1318-16-7) Physical and Chemical Properties
Bauxite
Principal aluminum ore used as feedstock for alumina production and a commodity mineral for industrial applications; procurement emphasizes grade, moisture and impurity profile for processing and handling.
| CAS Number | 1318-16-7 |
| Family | Aluminum ore / mineral dust |
| Typical Form | Granular or powdered solid |
| Common Grades | EP |
Bauxite is a heterogeneous ore and industrial mineral mixture dominated by hydrated aluminum oxides and oxyhydroxides; it belongs to the structural class of oxide/hydroxide mineral assemblages. Typical primary mineral phases are gibbsite, boehmite and diaspore, which are polymorphs or hydration states of aluminum oxides and hydroxides. These phases form layered and/or framework structures in which aluminum is coordinated by oxygen and hydroxide ligands; the ensemble behaves as an amphoteric oxide/hydroxide assemblage that exhibits limited aqueous solubility under neutral conditions but is chemically reactive under strongly acidic or strongly alkaline (caustic) process conditions used in industrial refining.
Key electronic and structural features are variable hydration, mixed-valence contributions from iron impurities in some deposits, and significant surface area and reactivity associated with microcrystalline and amorphous components. The material is generally nonvolatile, electrically insulating, and poorly soluble in water at ambient conditions; however, it is chemically attackable by concentrated caustic solutions (the basis of caustic leaching processes) and by strong acids or fluorides that dissolve alumina and siliceous impurities. As a mined material it occurs as friable rock or crust; dust formation and particle-size distribution control strongly influence inhalation exposure risk, handling and processing behavior.
Bauxite is the principal industrial source of processed alumina (\(\ce{Al2O3}\)) and, ultimately, metallic aluminum; it is refined commercially by caustic leaching (Bayer-type processing) to yield alumina, which is then reduced to aluminum metal by electrolytic processes. The material is also encountered in mining, bulk-material handling, and some petroleum-industry contexts such as hydraulic fracturing operations. Common commercial grades reported for this substance include: EP.
Overview and Composition
Qualitative Composition
Bauxite is not a single stoichiometric compound but a polymicritic mixture of hydrated aluminum oxides/oxyhydroxides together with gangue minerals. Typical constituent phases and chemical descriptions include: - Hydrated aluminum hydroxide/oxyhydroxide minerals: gibbsite (\(\ce{Al(OH)3}\)), boehmite and diaspore (both commonly represented by \(\ce{AlO(OH)}\)). - Alumina and related oxide component present as corundum-like material: \(\ce{Al2O3}\). - Associated impurities and gangue: siliceous material (amorphous and crystalline \(\ce{SiO2}\)), iron oxides (\(\ce{Fe2O3}\)) and minor titanium- and other metal-bearing oxides.
A computed, idealized stoichiometric representation present in some descriptor sets is \(\ce{Al2H2O4}\); this represents a small hydrated alumina unit rather than an industrial-grade bulk composition. Component compounds identified for the composition context include water (\(\ce{H2O}\)) and corundum-type alumina (\(\ce{Al2O3}\)). Reported impurity information includes the presence of 10–30% amorphous fused silica in some material streams; such siliceous content materially affects refining behavior and respiratory hazard potential.
Appearance and Typical Form
Bauxite is typically encountered as a dark-brown to reddish-brown, odorless, earthy to pisolitic rock or crust. Commercial material ranges from friable lumps to fine particulate powder depending on mining and comminution. It is commonly described as a solid bulk mineral; material safety documentation characterizes it as a dark brown odorless solid. Particle-size distribution in ore, screening and crushing operations leads to respirable dust fractions that are the principal occupational exposure concern.
Chemical Properties
Reactivity and Corrosive Behavior
The aluminum-containing phases in bauxite exhibit amphoteric oxide/hydroxide chemistry: they are relatively insoluble in water at ambient \(\mathrm{pH}\) but react under strongly alkaline conditions to form soluble aluminate species and under strongly acidic conditions to give dissolved aluminum ions and complex species. Industrial caustic leaching processes exploit solubility in concentrated sodium hydroxide to extract alumina. Strong acids and fluoride-containing reagents attack both alumina and siliceous gangue more aggressively; thermal dehydroxylation of hydroxide components produces transition toward alumina-like phases upon heating.
Bauxite is not generally classified as a corrosive liquid or gas; corrosivity as a bulk solid is not a principal attribute. However, dusts can carry reactive surfaces and trace acidic or alkaline residues that may influence corrosion of equipment or accelerate degradation of certain materials under processing conditions.
Computed molecular and structural descriptors (as reported) for an idealized hydrated alumina unit: - Molecular formula (computed descriptor): \(\ce{Al2H2O4}\) - Molecular weight: 119.977 \(\mathrm{g}\,\mathrm{mol}^{-1}\) - Exact mass / Monoisotopic mass: 119.958385 \(\mathrm{Da}\) - Topological polar surface area (TPSA): 44.4 - Hydrogen-bond donor count: 1 - Hydrogen-bond acceptor count: 4 - Rotatable bond count: 0 - Heavy atom count: 6 - Formal charge: 0 - Complexity: 34.2
Structural identifiers:
- SMILES: O.O=[Al]O[Al]=O
- InChI: InChI=1S/2Al.H2O.3O/h;;1H2;;;
- InChIKey: XXHQVTGCFGYKNL-UHFFFAOYSA-N
These descriptors reflect a small, idealized representation rather than the full mineralo‑chemical heterogeneity of commercial bauxite ores.
Compatibility and Incompatibilities
Bauxite and its component minerals are generally compatible with common construction materials under dry, ambient conditions, but compatibility is process-dependent: - Chemical incompatibilities: strong acids, concentrated alkalies and fluoride-containing reagents can attack the alumina and silicate components; hydrofluoric acid and strong mineral acids are particularly aggressive toward siliceous gangue and alumina phases. - Process incompatibilities: exposure to high-temperature oxidative environments or reducing atmospheres will change phase assemblages (dehydroxylation, sintering) and can influence material handling and kiln/calciner selection. - Materials-contact concerns: abrasive solid nature can cause mechanical wear on conveyors and crushers; entrained dust and fines can abrade seals and bearings.
No experimentally established numeric corrosivity thresholds or compatibility limits are provided in the current data context.
Usage and Safety
Industrial and Commercial Use Contexts
Bauxite is the principal raw material for industrial alumina production and, through downstream electrolytic reduction, metallic aluminum. Commercial refining employs caustic leaching of bauxite to dissolve alumina-bearing phases and separate gangue (Bayer-type processing), followed by calcination to produce technical alumina (\(\ce{Al2O3}\)). The aluminum industry encompasses mining, refining and smelting operations where bauxite is processed at large scale.
Other documented contexts include bulk-material handling and certain petroleum-industry applications such as use in hydraulic fracturing operations; its abrasive and mineralogical properties can also make it relevant in refractory, abrasives and proppant-related supply chains. In mining and refining, primary exposure risks arise from mechanical operations (breaking, blasting, excavation, crushing, loading) that generate airborne dust.
Hazards and Handling Considerations
Aggregate hazard classifications for bauxite indicate that, as a bulk ore, it is commonly reported as "Not Classified" under standard hazard criteria for pure materials; however, workplace hazards are dominated by airborne particulate exposure and material-specific impurities. Key safety considerations: - Respiratory hazard: inhalation of respirable bauxite dust can cause irritation of the respiratory tract; prolonged or repeated inhalation exposure to respirable dusts has the potential to cause lung injury. Siliceous content (reported 10–30% amorphous fused silica in some material streams) can increase respiratory hazard depending on particle size and crystallinity. - Eye and skin: dust may cause mechanical irritation to eyes and skin; moist or wet material can cause abrasive irritation. - Environmental and process hazards: bulk dust may present slip/settling issues and create housekeeping challenges; material may be abrasive to equipment.
Recommended handling controls and protective measures (class-level guidance): - Engineering controls: dust suppression, local exhaust ventilation at crushing and transfer points, enclosed conveyors and transfer systems, and routine housekeeping to minimize airborne dust. - Personal protective equipment (PPE): respiratory protection appropriate to measured airborne concentrations (e.g., particulate respirators), eye protection, and protective clothing to reduce skin contact with dust. - Storage: keep material dry and contained to limit dust generation and avoid water ingress that complicates handling. - Emergency and first-aid: treat dust contact with flushing of eyes and skin; for inhalation remove to fresh air and seek medical attention if symptoms persist.
For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and applicable local legislation.
