Uses of Nitric Acid: An Australian Industry Guide
Nitric acid (HNO3) is one of the most useful industrial acids in Australia. At the common commercial strength of 68%, it is a strong mineral acid and also a powerful oxidiser. That combination lets it do jobs other acids cannot, such as passivating stainless steel. This guide covers the main uses of nitric acid, how it compares with other acids, and how to store and handle it safely. It also explains what to expect when you buy nitric acid in Australia.
What is nitric acid?
Nitric acid is a clear to pale yellow liquid with a sharp, suffocating odour. Commercial grades are usually about 68% w/w, which is close to the azeotrope (the strongest mix that can be made by simple distillation). Unlike hydrochloric or sulphuric acid, nitric acid oxidises many metals and organic materials as well as dissolving them. That oxidising power makes it valuable in metal finishing, laboratories and electronics, and it is also why it must be handled with extra care.
Main uses of nitric acid
1. Stainless steel passivation and metal pickling
Fabrication shops use dilute nitric acid to passivate stainless steel. The treatment removes free iron from the surface and helps the protective chromium oxide layer form again after welding or machining. Nitric acid is also used, often blended with other acids, to pickle steel and remove scale, oxides and heat tint.
2. Electronics and circuit boards
Nitric acid etches and cleans copper, nickel and other metals in printed circuit board and electronics manufacture, and is used in semiconductor wet processing.
3. Laboratory analysis and assay
Laboratories use nitric acid to digest samples before metals analysis (for example ICP and AAS), to prepare reagents, and in mining assay work. Mixed with hydrochloric acid, it forms aqua regia, which dissolves gold and platinum group metals in refining.
4. Water treatment and pH correction
Nitric acid can lower pH in process water, cooling water and some wastewater streams. It is also used to descale equipment such as heat exchangers. Because it adds nitrate, discharge limits for nitrogen should be considered before choosing it over other acids.
5. Hydroponics and fertigation
Growers use dilute nitric acid to bring irrigation water pH down (often to about 5.5 to 6.5) and supply nitrogen at the same time. It is normally diluted to a weak stock solution before a dosing pump injects it.
6. Food and dairy clean-in-place (CIP)
In CIP systems, an acid rinse often follows the alkaline (caustic) wash to remove mineral scale such as milkstone from stainless steel tanks and lines. Nitric acid based formulations are commonly used for this step.
7. Fertiliser and chemical manufacture
At industrial scale, nitric acid is the starting point for ammonium nitrate and other nitrogen fertilisers, and for nitration reactions used to make dyes, pharmaceuticals and polymer intermediates such as nylon precursors.
8. Jewellery and precious metals
Jewellers and refiners use nitric acid for acid testing and in refining processes.
Nitric acid vs other industrial acids
| Acid | Typical strength | Best suited to |
|---|---|---|
| Nitric acid | 68% | Passivation, metal etching, lab digestion, CIP acid rinse, fertigation |
| Sulphuric acid | 98% (also 50%) | Industrial processes, pH control, fertiliser and battery uses |
| Hydrochloric acid | 32% | Pool pH reduction, concrete etching, descaling |
| Phosphoric acid | 85% | Rust conversion, metal pretreatment, acid wash systems |
| Citric acid | Anhydrous powder | Milder descaling and cleaning |
For pool pH, hydrochloric acid is the usual choice, not nitric acid. Choose nitric acid when you need its oxidising action, for example passivation.
Safe handling and storage of nitric acid
Nitric acid 68% is classed as a dangerous good: UN 2031, Class 8 (Corrosive) with a Class 5.1 (Oxidising) subsidiary risk, Packing Group II. It causes severe burns, and its fumes, including nitrogen dioxide, are toxic to breathe. Always read the Safety Data Sheet before use (see our nitric acid safety data sheet guide).
- PPE: chemical splash goggles and a face shield, acid-resistant gloves, an acid-resistant apron and enclosed footwear. Use respiratory protection where fumes may build up.
- Ventilation: work outdoors, in a well-ventilated area or under local exhaust or a fume hood.
- Dilution: always add acid to water slowly, never water to acid, using HDPE, polypropylene or PVDF equipment.
- Incompatibles: keep away from organic materials and solvents (for example alcohols and acetone), reducing agents, alkalis, metals such as copper, zinc and mild steel, and combustible materials. Do not mix with hydrochloric acid except in a controlled aqua regia procedure; the mixture releases toxic chlorine and nitrosyl chloride gases.
- Storage: cool, dry, ventilated and out of direct sunlight, in the original container, separated from incompatible chemicals.
- Spill containment: store containers on a chemical bund and keep a spill kit on hand. Read our guide to chemical bunding requirements in Australia. Do not share a bund with alkalis, chlorine or organics.
Buying nitric acid in Australia
Nitric acid at 30% or higher is listed under the National Code of Practice for Chemicals of Security Concern. This is a voluntary code that asks suppliers to know their customers and report suspicious purchases. Legitimate business, trade and laboratory buyers are normally supplied without difficulty, but your supplier may ask about the intended use. Because nitric acid is a dangerous good, it travels with dangerous goods freight, and some regional deliveries need a freight quote.
Viva Blu supplies nitric acid 68% in 5 L and 20 L containers, dispatched from Brisbane with free pickup from our Windsor, QLD warehouse. For regular or larger volumes, call 0402 981 808.
Frequently asked questions
What is nitric acid mainly used for?
The main uses of nitric acid include stainless steel passivation and metal pickling, electronics etching, laboratory digestion and assay, pH correction in water treatment and fertigation, CIP acid rinses in food and dairy, and fertiliser and chemical manufacture.
What strength is commercial nitric acid?
The most common commercial grade is about 68% w/w, which is close to the azeotropic concentration. Viva Blu supplies nitric acid 68%.
Is nitric acid stronger than hydrochloric acid?
Both are strong acids, but nitric acid is also a strong oxidiser. That lets it passivate stainless steel and etch metals in ways hydrochloric acid cannot. For pool pH reduction, hydrochloric acid is the usual choice.
Do I need a licence to buy nitric acid in Australia?
Nitric acid at 30% or more is covered by the voluntary National Code of Practice for Chemicals of Security Concern, so suppliers may ask about your intended use. Licensing and storage obligations also depend on your state and quantities, so check with your state regulator.
How should nitric acid be stored?
Store it in its original container in a cool, dry, ventilated area away from sunlight, on a chemical bund, and separated from alkalis, organics, solvents, metals and combustible materials.