Sulphuric acid: Characteristics
Why battery makers pay a premium for clean acid
What this tab covers The physical and chemical properties that set its grade, price and uses, with the commercial grades and the standards that define them.Buyers care about strength, impurities and freezing point. Fertiliser and leach users take 93-98.5% technical acid. Battery, food and electronics users pay large premiums for low iron, heavy metals and chloride. Smelter acid can carry mercury, arsenic or colour, which limits it to leaching and fertiliser uses unless cleaned.
Properties that matter commercially
| Property | Value / specification | Why it matters | Source |
|---|---|---|---|
| Concentration | commercial grades 93-98.5% H2SO4; oleum 20-65% free SO3 | Higher strength cuts freight and suits sulphonation; 93% is used where low freezing point matters | Industry grades (indicative); IS 266 |
| Freezing point | 98% acid freezes at about 3 C; 93% acid at about -32 C (indicative) | Decides which grade can be stored and railed in cold climates | Physical data (indicative) |
| Density | about 1.84 g/cm3 at 98% | Heavy cargo; tanker and tank design | Physical data |
| Iron and heavy metals | technical acid typically under about 50 ppm Fe; electronic grade at parts per billion or lower (indicative) | Sets suitability for battery, food and semiconductor uses | Industry specifications (indicative) |
| Mercury and arsenic (smelter acid) | low-mercury grades often specified under about 1 ppm Hg (indicative) | Contaminants pass into fertiliser and food chains | Industry practice (indicative) |
Commercial grades
- Technical (93-98.5%) for fertiliser and leaching
- Oleum and 104.5% for sulphonation and caprolactam
- Battery grade for lead-acid electrolyte
- Food and reagent grades
- Electronic (semiconductor) grade, exempt from China's 2026 export ban