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Policy No: 2017
Responsible Office: Safety & Environmental Compliance
Last Review Date: 02/09/2022
Next Required Review: 02/09/2027
Policy No: 2017
Responsible Office: Safety & Environmental Compliance
Last Review Date: 02/09/2022
Next Required Review: 02/09/2027

Aqua Regia

1. Purpose

This policy describes recommended procedures for the proper handling and disposal of Aqua Regia (CAS 8007-56

2. Applicability

These procedures shall be followed by Academic Affairs Division and USA Health employees and any
person who works with Aqua Regia.

3. Definitions

Aqua Regia: (Latin for “royal water”) also known as Nitrohydrochloric acid, is a corrosive, acidic, fuming
yellow liquid, prepared by slowly mixing one part concentrated nitric acid to three parts of concentrated
hydrochloric acid.

It is called “Aqua Regia” because it is one of the few acidic mixtures that can dissolve the “noble metals”
such as gold, platinum, silver, etc. It fumes and its yellow color is caused by the reaction of nitric acid
with hydrogen chloride to form nitrosyl chloride, chlorine and water – both chlorine and nitrosyl chloride
are yellow and volatile.

Aqua Regia is both an oxidizer and a corrosive material that will, over time, oxidize to form toxic gases
that are destructive to living tissue upon contact and may result in an explosion if not handled with extreme caution.

4. Policy Guidelines

4.1  Aqua Regia

Aqua Regia is commonly used to remove minor organic contaminants from glass or noble metal substrates in microfabrication and microelectronics labs. Some specific work practices which should be used are as follows:

4.1.1  Review the appropriate Safety Data Sheet before handling Aqua Regia. Consult with PI/senior lab investigator before using Aqua Regia for the first time.

4.1.2  When handling Aqua Regia always wear chemical-splash goggles, lab coat, closed-toe shoes and chemical- resistant gloves (18 mil neoprene, Silver Shield or any other gloves rated to protect against nitric and hydrochloric acid). A face shield and acid-resistant apron are recommended if working with a large volume
(>200 ml).

4.1.3  Always add nitric acid to the hydrochloric acid slowly.

4.1.4  Aqua Regia should only be used in a properly functioning chemical fume hood that contains NO organic material. The sash should remain down while all reactions are in progress.

4.1.5  Always use Pyrex glass containers. Aqua regia will dissolve some plastics and corrode/dissolve most metals.

4.1.6  Never prepare or manipulate Aqua Regia while alone.

4.1.7  Mix up only what is needed immediately, and then destroy any leftover material after each use. [See Neutralization and Dilution].

4.1.8  If glassware is left to soak, the container must be clearly labeled as “Aqua Regia – Extremely Corrosive”. A printed, legible note should be posted on the sash of the hood to identify the process occurring inside the hood.

4.1.9  Never add other acids or bases to Aqua Regia.

4.1.10  Never spray with water. This will result in a very exothermic heating of the mixture.

4.1.11  Dissolving metals or reacting organics in Aqua Regia releases toxic gases, so always work with it in a properly functioning fume hood.

4.1.12  Aqua Regia solution is very reactive and potentially explosive if reacting with some organics. It is very likely to become hot during a reaction, more than 100° Celsius (212° Fahrenheit). Leave the hot mixture in an open container in the hood until it is cool. Handle with care in an uncluttered hood.

4.1.13  Never store or leave Aqua Regia in a closed container. It will oxidize over time to form toxic
Nitrosyl chloride, Nitrogen dioxide, and Chlorine gases. This will pressurize the container and can lead to an explosion.

4.1.14  Aqua Regia quickly loses its effectiveness due to the oxidation of its reactive components. Mix fresh solution for each use.

4.2  In the event of an Exposure

Call 911 immediately. After any exposure to Aqua Regia, seek medical attention. If victims are taken to the hospital, send copies of SDSs for both Nitric and Hydrochloric Acid along with them.

4.2.1  Inhalation

Move the exposed person to fresh air at once. Perform artificial respiration if breathing has stopped. Keep the affected person calm, warm and at rest. When unconscious, loosen clothing and position in a secure recovery position. Get prompt medical attention.

4.2.2  Injection

NEVER MAKE AN UNCONSCIOUS PERSON VOMIT OR DRINK FLUIDS. Promptly get a conscious affected person to drink a large volume of water to dilute the swallowed chemical and wash out the mouth. DO NOT induce vomiting. Get medical attention immediately.

4.2.3  Skin

Promptly remove contaminated clothing, moving toward the closest safety shower and flush skin with tepid water for a minimum of 15 minutes. Get medical attention immediately if the skin shows signs of irritation.

4.2.4  Eyes

Move immediately toward the closest emergency eyewash and flush eyes with tepid water for a minimum of 15 minutes while lifting the eyelids. Get medical attention.

4.3  In the event of a Spill

4.3.1  Small spills of less than 200 ml of spent solution and no longer evolving gases, in a fume hood, can be cleaned up by lab personnel, who are aware of the hazards and have been trained in the proper cleanup procedure and have access to appropriate safety and clean up equipment. If you do not have appropriate equipment or training, contact the Safety & Environmental Compliance Department (460-7070).

4.3.2  Wear proper PPE.

4.3.3  Small spills (<200 ml of spent solution) can be soaked up with the appropriate HazMat absorbent pad (use one appropriate for Nitric Acid). Place all contaminated spill debris into a heavy-duty waste bag. Seal bag, attach filled out orange hazardous waste label.

4.3.4  Contact the Safety & Environmental Compliance Department (460-7070 or for pickup of waste materials.

4.3.5  If a reactive solution (a solution that is still evolving gases) is spilled in a fume hood, close the hood sash, inform all other lab personnel of the problem and evacuate the lab. Close door to the lab. From a safe location call USA Police (460-6312) or your facility’s security and 911 to activate the Mobile Fire- Rescue HazMat team. Contact Safety and Environment Compliance (460-7070).

4.3.6  If a reactive solution (a solution that is still evolving gases) spills outside of a fume hood,
evacuate the room immediately. Close the door to the lab. Evacuate the building by pulling the fire alarm. From a safe location, call USA Police (460-6312) or your facility’s security and 911 to activate Mobile Fire- Rescue HazMat team. Contact Safety & Environment Compliance (460-7070).

4.3.7 Once spilled materials have been cleaned up, decontaminate the area by washing with copious amounts of soap and water.

4.4  Disposal Procedures

Aqua Regia is considered hazardous by both the Alabama Department of Environmental Management and the federal EPA, due to its corrosive nature. It is restricted from sink disposal by both the University of South Alabama and Mobile Area Water and Sewer System until the solution has been neutralized and diluted to a pH greater than 6 and less than 11.

4.5  Neutralization Procedures

4.5.1  Place containers in secondary containment free from all organic chemicals and solvents.

4.5.2  Neutralization container should be a glass beaker and must never be more than 2/3 full, even after the dilution is complete.

4.5.3  Pour excess, spent waste Aqua Regia into a large quantity of ice (0.5kg of ice per 100 ml solution). Neutralize mixture using an aqueous basic solution, such as 1M or 10% sodium hydroxide (NaOH) or saturated sodium bicarbonate (NaHCO3) in water until pH is between 6 and 11. The neutralized solution may then be poured down the drain only with the permission of the Safety & Environmental Compliance Department.

4.5.4  If the neutralized solution contains heavy metals (e.g., gold, platinum, lead, chromium, etc.), the solution should be considered as hazardous waste and must be labeled and disposed of through Safety & Environmental Compliance (460-7070).

5. Procedures

Not Applicable.

6. Enforcement

The Principal Investigator (PI) is responsible for ensuring that all lab workers are aware of the hazards
associated with Aqua Regia and are trained in the proper handling and disposal methods. DO NOT use Aqua Regia unless it is absolutely necessary.

7. Related Documents

Not Applicable.