Barium Sulfate
Properties
| State | Solid (fine white powder) |
| Color | White |
| Solubility | Extremely insoluble in water (0.0024 g/L at 25°C) |
| Melting Point | 1580°C |
| Boiling Point | 1600°C (decomposes) |
About Barium Sulfate
Barium sulfate is the textbook insoluble salt — its Ksp of 1.1 × 10⁻¹⁰ is roughly four orders of magnitude smaller than the next least-soluble alkaline-earth sulfate (CaSO4 at Ksp = 4.9 × 10⁻⁵), and the disparity is what makes BaSO4 so useful in three otherwise unrelated applications. In medicine, the same insolubility that makes barium ions invisible to the GI tract makes barium sulfate the safe radiopaque contrast agent for upper-GI series and barium-enema imaging — patients drink or are given a thick suspension of BaSO4, and the heavy barium absorbs X-rays strongly enough to outline the gastrointestinal mucosa with millimeter resolution. Despite Ba²⁺ being a Group 1 muscle-channel toxin, essentially zero ions enter solution as the suspension passes through, so BaSO4 administration is safe at gram-level doses. In oilfield drilling, the same density (4.5 g/cm³) that makes BaSO4 X-ray opaque makes it the standard weighting agent for drilling muds — adding ground barite to the mud raises the column density to 1.4–2.4 g/cm³, which keeps high-pressure formation fluids contained until the wellhead seal is established. Around 80% of all mined barite goes into drilling mud. The third use, as the white pigment 'blanc fixe' in paints and paper coatings, takes advantage of BaSO4's high refractive index, complete chemical inertness, and resistance to weathering. In analytical chemistry, BaSO4 precipitation remains a standard gravimetric assay for sulfate determination at percent levels, even after instrumental ion chromatography has displaced it for trace work.
Where you'll encounter it
If you've ever undergone an upper-GI series or barium enema, the chalky white slurry you swallowed was a barium sulfate suspension stabilized with thickeners and sweeteners, dosed at 100–200 g of BaSO4 per study. The contrast image you saw on the radiology film was X-ray attenuation by Ba's K-edge at 37 keV. In the oil and gas industry, barite mining is a multibillion-dollar global market specifically because drilling muds need the density and chemical inertness — substitutes like hematite or galena exist but barite remains the standard. In a paint store, the white-pigment can labeled 'blanc fixe' or 'permanent white' contains BaSO4 as the active filler; it's used in artist's gesso primers and in some industrial paints because it doesn't yellow with age the way some other white pigments do.
Common Uses
- Radiopaque contrast suspension for upper-GI and barium-enema imaging
- Weighting agent in oilfield drilling mud (~80% of mined barite use)
- Blanc-fixe white pigment for paints, gesso, and paper coatings
- Inert filler in plastics and rubber for density and X-ray shielding
- Gravimetric standard for percent-level sulfate-anion determination
Safety Information
Practically inert because of insolubility — the medical-grade material is administered to patients orally and rectally with negligible systemic absorption, and the industrial-grade barite is non-hazardous in routine handling. The exception is dust inhalation in mining and grinding operations, where chronic exposure to fine BaSO4 dust (without other toxic contaminants) produces baritosis, a benign pneumoconiosis with characteristic chest-radiograph findings but no functional impairment. Standard industrial dust controls and N95 respiratory protection are sufficient.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.