An Introduction to the Various Uses of Nitric Acid
Table of Contents
What you will learn
📋 What You'll Learn
This guide walks you through an introduction to the various uses of nitric acid with detailed instructions.
Nitric acid (HNO₃) ranks among the most important mineral acids produced worldwide. Historically known as aqua fortis ("strong water"), this powerful oxidizing acid has shaped civilizations for centuries — from medieval alchemists separating gold and silver, to modern engineers passivating stainless steel reactor vessels. This comprehensive guide explores the chemistry, industrial production, commercial grades, and dozens of real-world applications that make nitric acid indispensable across agriculture, metallurgy, chemical synthesis, defense, electronics, and beyond. Whether you are a seasoned chemical engineer, a laboratory researcher, or a procurement specialist sourcing the right concentration for your next project, the information here will serve as your definitive reference. For a broader overview of mineral acids, also see our Professional's Guide to Industrial Acids.
The Chemistry of Nitric Acid: A Dual-Threat Reagent
Nitric acid (HNO₃) is a strong, monobasic, mineral acid with a molar mass of 63.01 g/mol. In its pure, anhydrous state it is a colorless liquid with a sharp, acrid odor. Commercially, it is almost always encountered as an aqueous solution — typically between 40% and 70% concentration. Exposure to light and heat causes slow decomposition into water, nitrogen dioxide (NO₂), and oxygen, which gives aged or concentrated solutions a characteristic yellowish-brown tint.
Why Nitric Acid Stands Apart
What makes HNO₃ fundamentally different from other strong acids like hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) is its powerful oxidizing capability. The nitrate ion (NO₃⁻) readily accepts electrons from other substances. This dual nature — acting simultaneously as a strong acid and a strong oxidizer — unlocks reaction pathways that no other single mineral acid can achieve.
Physical & Chemical Properties at a Glance
For laboratory and process engineering work, having quick access to key physical constants is essential. The table below compares the properties of the most common commercial nitric acid concentrations:
| Property | ~42 Baumé / 67-70% ACS | ~65% Technical | ~40% Technical | 5-25% Dilute |
|---|---|---|---|---|
| Concentration (w/w) | 67-70% | ~65% | ~40% | 5-25% |
| Specific Gravity (20°C) | 1.40-1.42 | ~1.39 | ~1.25 | 1.03-1.15 |
| Baumé Degrees | ~42° Bé | ~40° Bé | ~30° Bé | 4-19° Bé |
| Boiling Point | ~121°C (azeotrope) | ~118°C | ~108°C | 100-106°C |
| Appearance | Colorless to pale yellow | Colorless to pale yellow | Colorless | Colorless |
| Oxidizing Strength | Very High | High | Moderate | Low-Moderate |
| Purity Grade | ACS Reagent Grade | Technical Grade | Technical Grade | Technical Grade |
| Key Applications | Trace-metal analysis, electronics, reagent prep | Fertilizers, large-scale synthesis | Pickling, cleaning, pH adjustment | Mild passivation, dilute cleaning |
| Alliance Chemical SKU | 70% ACS Grade | 65% Technical | 40% Technical | 5% Technical |
The 42 Baumé / 67-70% ACS grade represents the benchmark concentration for precision laboratory work. At this concentration, nitric acid forms a near-azeotrope with water (boiling at ~121 °C), making it stable and consistent for analytical procedures. Industrial users working in stainless steel passivation or chemical synthesis typically use the 65% technical grade for cost efficiency.
Industrial Production: The Ostwald Process
The vast majority of the world's 60+ million metric tons of annual nitric acid production relies on the Ostwald process, developed by German chemist Wilhelm Ostwald in the early 1900s. This remarkably efficient catalytic method converts ammonia (itself derived from the Haber-Bosch process) into nitric acid in three well-defined stages.
Catalytic Oxidation of Ammonia
Ammonia (NH₃) gas is mixed with filtered air (10:1 air-to-ammonia ratio) and passed over a platinum-rhodium catalyst gauze (typically 90% Pt, 10% Rh) at approximately 850°C. The catalyst oxidizes ammonia to nitric oxide (NO) with ~97% conversion efficiency. This exothermic reaction releases substantial heat, which is recovered to preheat incoming gas streams.
Oxidation of Nitric Oxide to Nitrogen Dioxide
The hot nitric oxide gas is cooled in a series of heat exchangers and reacted with excess atmospheric oxygen. This non-catalytic, homogeneous gas-phase reaction converts NO to nitrogen dioxide (NO₂), the brown gas responsible for the "red fuming" appearance of concentrated acid. Cooling favors the forward reaction, as higher temperatures drive equilibrium back toward NO.
Absorption in Water
The NO₂ gas enters large absorption columns (towers packed with inert media or sieve trays) where it reacts with water in a countercurrent flow to form nitric acid. Typical single-pass absorption yields 55-65% HNO₃. The concentration is then adjusted — either by further distillation to produce the standard industrial 65% grade, or by extractive distillation with a dehydrating agent (like concentrated sulfuric acid or magnesium nitrate) for 90%+ concentrations.
Major Industrial Applications of Nitric Acid
Nitric acid's unique combination of strong acidity and powerful oxidation makes it essential across an extraordinarily broad spectrum of industries. Below we examine each major application area in depth.
Agriculture & Fertilizers
~80% of global production goes to ammonium nitrate (NH₄NO₃) and calcium ammonium nitrate (CAN) fertilizers that feed billions.
Metallurgy & Refining
Dissolves base metals, passivates stainless steel, and separates precious metals through selective oxidation.
Chemical Synthesis
Nitration reactions produce explosives (TNT, RDX), polymers (Nylon 6,6 via adipic acid), and pharmaceutical intermediates.
Aerospace & Defense
Red fuming nitric acid (RFNA) serves as a hypergolic oxidizer for liquid rocket propellants and missile systems.
Electronics & Semiconductors
High-purity ACS grade etches copper traces, cleans silicon wafers, and prepares surfaces in PCB fabrication.
Laboratory & Research
Sample digestion for ICP-MS/ICP-OES trace metal analysis, acid-base titrations, and reagent preparation.
Agriculture: The Foundation of Modern Fertilizers
By far the largest consumer of nitric acid globally (approximately 80% of total production) is the fertilizer industry. The primary reaction is straightforward: nitric acid reacted with anhydrous ammonia produces ammonium nitrate (NH₄NO₃). This compound is exceptional as a fertilizer because it delivers nitrogen in two biologically available forms simultaneously — the ammonium cation (NH₄⁺) and the nitrate anion (NO₃⁻). Plants can immediately absorb nitrate nitrogen, while ammonium nitrogen provides a slower-release reserve. This dual-action mechanism makes ammonium nitrate one of the most efficient nitrogen fertilizers available, directly supporting the Green Revolution that has enabled global food production to keep pace with population growth.
Secondary agricultural applications include the production of calcium ammonium nitrate (CAN), potassium nitrate, and various micronutrient solutions where nitric acid serves as both the nitrogen source and the dissolving medium for calcium, magnesium, or trace metal oxides.
Metallurgy: Refining, Passivation & Surface Treatment
Nitric acid's oxidizing power makes it uniquely valuable in metallurgical applications:
- Precious Metal Refining (Inquartation & Parting): The classic "acid test" for gold relies on nitric acid. While HNO₃ cannot dissolve gold, it readily dissolves silver, copper, and base metal alloys, leaving purified gold behind. Gold refiners use a systematic process called inquartation — alloying gold with silver to a 1:3 ratio, then dissolving away the silver with nitric acid to recover 99.5%+ pure gold. For dissolving gold itself, a mixture of nitric and hydrochloric acid called aqua regia (3:1 HCl:HNO₃) is required.
- Stainless Steel Passivation: After welding, machining, or forming, free iron particles become embedded in stainless steel surfaces, creating sites vulnerable to corrosion. Nitric acid passivation (per ASTM A967 and AMS 2700) removes this free iron and promotes the formation of a uniform, protective chromium oxide layer. Typical passivation baths use 20-50% nitric acid at 120-150°F for 20-30 minutes. Learn more about why proper passivation matters for equipment longevity.
- Metal Etching & Pickling: In electronics manufacturing, dilute nitric acid etches precise patterns into copper-clad circuit boards. In steel production, mixed acid baths (HNO₃ + HF) pickle stainless steel to remove mill scale and oxide layers after hot rolling.
Chemical Synthesis & Nitration
Nitric acid is the fundamental reagent for nitration — the introduction of a nitro group (-NO₂) onto organic molecules. This single reaction type underpins entire sectors of the chemical industry:
- Explosives Manufacturing: Nitroglycerin, trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN) all begin with nitric acid nitration of organic precursors. Mixed acid (HNO₃ + H₂SO₄) is the classic nitrating mixture.
- Polymer Precursors: The synthesis of adipic acid — the key monomer for Nylon 6,6 production — uses nitric acid to oxidize cyclohexanol/cyclohexanone. Global adipic acid production exceeds 3 million tons annually, nearly all via nitric acid oxidation.
- Polyurethane Chemistry: Toluene diisocyanate (TDI), the primary feedstock for flexible polyurethane foams, is produced through dinitration of toluene followed by catalytic hydrogenation. The nitration step requires concentrated nitric acid with sulfuric acid as catalyst.
- Pharmaceutical Intermediates: Nitroaromatic compounds produced via nitric acid nitration serve as intermediates for analgesics, antibiotics, dyes, and agrochemicals. Controlled nitration with precise temperature and acid strength management is critical for selectivity.
Aerospace, Rocketry & Defense
In its most concentrated forms, nitric acid serves the aerospace and defense sectors:
- Red Fuming Nitric Acid (RFNA): Concentrated HNO₃ (>85%) containing dissolved NO₂ serves as a hypergolic oxidizer for liquid rocket propulsion. When combined with fuels such as unsymmetrical dimethylhydrazine (UDMH) or furfuryl alcohol, RFNA ignites on contact — eliminating the need for complex ignition systems. This property makes it invaluable for tactical missile systems where instant-start reliability is paramount.
- Inhibited Red Fuming Nitric Acid (IRFNA): Adding a small amount of HF (0.6-0.7%) to RFNA inhibits its corrosive attack on storage tanks, enabling long-term storage in aluminum and stainless steel containers.
Electronics & Semiconductor Manufacturing
The electronics industry demands the highest purity nitric acid available — typically ACS reagent grade or SEMI-grade with extremely low metallic impurities (parts-per-trillion levels). Applications include silicon wafer cleaning (RCA clean protocol), copper trace etching in PCB fabrication, and post-process residue removal from semiconductor devices. The acid's ability to dissolve metal contaminants without leaving ionic residues makes it indispensable in cleanroom environments.
Laboratory, Water Treatment & Specialty Uses
In analytical laboratories, nitric acid is the acid of choice for sample digestion prior to trace metal analysis by ICP-MS, ICP-OES, and atomic absorption spectroscopy. Its oxidizing nature completely destroys organic matrices, releasing metals into solution. Proper chemical storage in the lab is essential when handling concentrated grades. Additional specialty uses include water treatment (pH adjustment and denitrification), precious metal recovery in e-waste recycling, and as an analytical reagent in quality control laboratories across industries. For guidance on responsible end-of-life management, consult our guide on how to dispose of chemicals safely.
Application Guide by Industry: Concentrations & Dosages
Selecting the optimal nitric acid concentration is critical for efficacy, cost efficiency, and safety. The following comprehensive table maps specific applications to recommended concentrations and typical dosage parameters:
| Industry | Application | Concentration | Typical Dosage / Conditions | Grade Required |
|---|---|---|---|---|
| Agriculture | Ammonium nitrate production | 50-68% | Stoichiometric with NH₃, 170°C reactor | Technical |
| Agriculture | Fertigation (drip systems) | 53-55% | 0.5-2.0 L per 1000L water | Technical |
| Metallurgy | Stainless steel passivation | 20-50% | 120-150°F, 20-30 min immersion | Technical |
| Metallurgy | Precious metal refining | 50-70% | 3:1 mass ratio acid-to-alloy | Technical/ACS |
| Metallurgy | Steel pickling (w/ HF) | 8-15% HNO₃ + 1-3% HF | 140-160°F, 5-20 min | Technical |
| Chemical Synthesis | Nitration (TNT, RDX) | 68-70% (mixed acid) | 1:2-1:3 HNO₃:H₂SO₄ ratio | Technical |
| Chemical Synthesis | Adipic acid (Nylon) | 50-65% | Continuous oxidation, Cu/V catalyst | Technical |
| Electronics | Silicon wafer cleaning | 65-70% | RCA clean: HNO₃ dip, 5-10 min RT | ACS / SEMI |
| Electronics | PCB copper etching | 10-30% | Spray or immersion, 25-40°C | ACS |
| Laboratory | ICP-MS sample digestion | 65-70% | 5-10 mL per 0.5g sample, microwave 200°C | ACS Trace Metal |
| Water Treatment | pH adjustment | 5-25% | Metered dosing to target pH | Technical |
| Aerospace | RFNA rocket oxidizer | >85% + NO₂ | Stoichiometric w/ fuel (UDMH) | Mil-Spec |
Technical Comparison: Nitric Acid vs. Other Mineral Acids
Choosing the right mineral acid for your application requires understanding how HNO₃ differs from the other major industrial acids. This expanded comparison covers key chemical, physical, and practical differences. For deeper dives into each acid, explore our guides on hydrochloric acid applications, sulfuric acid concentrations, and phosphoric acid applications.
| Attribute | Nitric Acid (HNO₃) | Sulfuric Acid (H₂SO₄) | Hydrochloric Acid (HCl) | Phosphoric Acid (H₃PO₄) |
|---|---|---|---|---|
| Primary Chemical Function | Strong Oxidizing Agent | Strong Dehydrating Agent | Strong Non-Oxidizing Acid | Moderate Triprotic Acid |
| Molecular Weight | 63.01 g/mol | 98.08 g/mol | 36.46 g/mol | 98.00 g/mol |
| Volatility | High (fuming at RT) | Very low | Very high (fuming) | Non-volatile |
| Dissolves Copper? | Yes (readily) | Only when hot & concentrated | No reaction | No reaction |
| Dissolves Gold? | No (but aqua regia does) | No | No (but aqua regia does) | No |
| Passivates SS? | Yes (ASTM A967) | No | No (corrosive to SS) | No |
| Global Production | ~60M tons/yr | ~260M tons/yr | ~20M tons/yr | ~50M tons/yr |
| Top Industrial Use | Fertilizers (NH₄NO₃) | Fertilizers (phosphates) | Steel pickling | Fertilizers (DAP/MAP) |
| PPE Level | High (fumes toxic) | High (dehydration burns) | High (fumes corrosive) | Moderate |
| Storage Material | Glass, PTFE, HDPE | Steel, HDPE | HDPE, PVC-lined | SS 316, HDPE |
For operations using multiple mineral acids, our industrial solvents guide and chemical storage guide provide essential compatibility and segregation information.
Safety Protocols for Handling Nitric Acid
Nitric acid is classified as a Class 8 corrosive and a Class 5.1 oxidizer under DOT/IATA regulations. Its dual hazard profile demands rigorous safety protocols. Failure to follow proper procedures can result in severe chemical burns, toxic gas exposure, and potentially violent exothermic reactions. Always consult the Safety Data Sheet (SDS) before handling. For comprehensive PPE selection, see our guide on PPE for chemical safety, and for broader safety protocols, review our comprehensive chemical safety guide.
Mandatory Safety Protocols
- Respiratory Protection: Nitric acid fumes contain nitrogen oxides (NOx), which are acutely toxic and can cause delayed-onset pulmonary edema. A NIOSH-approved full-face respirator with acid gas (AG) cartridges or a supplied-air respirator is mandatory when handling open containers, during transfers, or in case of a spill. Engineering controls (fume hoods, local exhaust ventilation) should be the primary defense.
- Full PPE Required: Chemical-resistant gloves (neoprene, butyl rubber, or heavy nitrile — NOT latex), indirect-vent splash goggles, full-face shield, acid-resistant apron or full chemical suit. Double-gloving is recommended for concentrated grades.
- Ventilation: ALWAYS handle nitric acid inside a certified chemical fume hood or in a well-ventilated area with mechanical exhaust. Monitor ambient NOx levels with direct-reading instruments in enclosed work areas. OSHA PEL for HNO₃ is 2 ppm TWA and 4 ppm STEL.
- Storage Requirements: Store in a cool, dark, well-ventilated location in an acid-resistant secondary containment cabinet. Nitric acid is light-sensitive (UV causes decomposition). Store separately from organic materials, flammable liquids, bases, cyanides, carbides, metal powders, and reducing agents. Use glass, PTFE, or compatible HDPE containers only.
- Dangerous Incompatibilities: NEVER mix nitric acid with alcohols, acetone, acetic anhydride, turpentine, or other organic solvents — the resulting exothermic reactions can produce explosive compounds or violent detonations. Contact with metals generates toxic NOx gas. Contact with sulfides or cyanides releases toxic H₂S or HCN respectively.
- Spill Response: Evacuate the area, don appropriate PPE, contain with acid-compatible absorbent (vermiculite or dry sand — NOT sawdust), neutralize cautiously with sodium bicarbonate, and dispose per federal/state regulations. For guidance, see how to dispose of chemicals safely.
Environmental & Regulatory Considerations
Nitric acid and its production/use are subject to extensive environmental regulation. The Ostwald process generates NOx as a byproduct, and modern plants employ selective catalytic reduction (SCR) and extended absorption to minimize atmospheric emissions. Under the Clean Air Act, nitric acid plants are classified as major sources of NOx, requiring Best Available Control Technology (BACT) or Maximum Achievable Control Technology (MACT) standards.
From a sustainability perspective, the fertilizer industry is investing heavily in "green ammonia" produced from renewable hydrogen, which would make downstream nitric acid production carbon-neutral. Some manufacturers are also exploring electrochemical routes to produce nitric acid directly from nitrogen and water using renewable electricity, potentially bypassing the Haber-Bosch and Ostwald processes entirely. These developments align with broader green chemistry initiatives reshaping the chemical industry.
For end users, proper disposal of spent nitric acid solutions is essential. Waste containing nitric acid is classified as hazardous (EPA D002 corrosive waste) and must be neutralized and disposed of through licensed waste management facilities. Many industrial users implement closed-loop acid recovery systems that regenerate spent acid through distillation, reducing both waste and raw material costs.
Buyer's Guide: Selecting the Right Grade & Concentration
With so many available concentrations and purity levels, selecting the optimal nitric acid for your application can feel overwhelming. Here is a practical decision framework:
Choose ACS / Reagent Grade When:
- Performing trace-metal analysis (ICP-MS, ICP-OES, AAS)
- Working in semiconductor or electronics cleanroom environments
- Preparing standard solutions or analytical reagents
- Application requires certified purity with lot-specific COA
Choose Technical Grade When:
- Performing industrial-scale metal treatment, passivation, or pickling
- Manufacturing fertilizers, explosives, or polymer intermediates
- General pH adjustment in water treatment systems
- Cost efficiency is a priority and ultra-low impurities are not required
Concentration Selection:
- 67-70% — Maximum reactivity. Best for passivation, refining, synthesis, and analytical work.
- ~65% — The workhorse industrial concentration. Excellent balance of potency and handling safety.
- ~40% — Moderate strength. Ideal for pickling baths, cleaning, and applications where lower reactivity reduces risk.
- 5-25% — Dilute solutions for specialized cleaning, gentle passivation, or pH adjustment.
For industrial-scale procurement, Alliance Chemical offers flexible packaging from 500 mL laboratory bottles to 275-gallon totes with hazmat-compliant shipping throughout the continental United States. Our professional's guide to industrial acids provides additional context on acid selection across chemical families.
Source Laboratory & Industrial-Grade Nitric Acid
From ACS reagent-grade precision to bulk industrial supply, Alliance Chemical delivers the nitric acid concentrations you need with expert technical support, hazmat-compliant shipping, and competitive pricing.
Shop All Nitric Acid Request a Bulk QuoteFrequently Asked Questions
What is Nitric Acid and what is it used for?
The Chemistry of a Dual-Threat Acid Nitric Acid (HNO₃) is a highly corrosive mineral acid. In its pure, anhydrous form, it is a colorless liquid, but it is almost always used as an aqueous solution.
What safety precautions are needed when handling Nitric Acid?
The Chemistry of a Dual-Threat Acid Nitric Acid (HNO₃) is a highly corrosive mineral acid. This allows Nitric Acid to react with and dissolve metals that are non-reactive to other acids, such as copper and silver. Always consult the Safety Data Sheet (SDS) for complete handling and emergency information before use.
How is Nitric Acid used in industrial applications?
Nitric Acid is one of the most important and powerful mineral acids in modern chemistry and industry. Historically known as "aqua fortis" (strong water), its unique ability to act as both a strong acid and a potent oxidizing agent makes it an indispensable tool for applications ranging from fertilizer production to precious metal refining and rocket propulsion.
What grades or concentrations of Nitric Acid are available?
This definitive guide provides a technical exploration of its properties, applications, and critical safety considerations, equipping professionals with the knowledge to utilize it effectively. The concentration is then adjusted to meet commercial grades, typically ranging from a general-purpose 40% to the common industrial standard of 65-70%.
