What is Oxalic Acid?

Oxalic Acid is a dicarboxylic acid naturally produced by plants of the genus Oxalis, also known as wood-sorrels. Oxalic acid has many uses including in rust removal and other household cleaners, bleaching agents for wood pulp, and as a mordant in the dyeing process.

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Oxalic Acid the CAS Number 144-62-7.

The CAS Number is used to identify oxalic acid as an ingredient on safety data sheets (SDS) and other safety documentation. When looking for oxalic acid as an ingredient in cleaning products, bleaches, and mordants, look for the CAS Number within the composition table.

Notable Properties of Oxalic Acid

Pure oxalic acid is a white, odorless crystalline solid, typically found in powder form. Any color or odor comes from natural impurities or other ingredients within the oxalic-acid-based product.

What Makes Oxalic Acid Hazardous?

Oxalic acid is, as the name suggests, an acidic substance. It can cause irritation to the eyes, skin, and respiratory system. Symptoms of oxalic acid irritation include burning and redness of the skin and eyes, localized pain, and difficulty breathing. If ingested, oxalic acid can also cause kidney damage, in extreme cases leading to shock and convulsions.

Due to being a carbon-based substance, oxalic acid can also form combustible dusts and create a fire hazard.

Oxalic Acid Frequently Asked Questions

Is Oxalic Acid Organic?

Oxalic Acid is organic by the definition that it is a molecule with carbon-carbon bonds.

Since oxalic acid can be naturally derived from plants grown to the USDA certified organic standards, oxalic acid can also fall under that definition of organic.

Is Oxalic Acid Harmful to Humans? Is Oxalic Acid Toxic?

Oxalic acid can be harmful to humans. Per the Toxin and Toxin Target Database, oxalic acid is not metabolized by the body. However, oxalic acid will bond with metal ions, such as Ca2+, Fe2+, and Mg2+, forming a metal oxalate which is irritating to the digestive system and kidneys. A buildup of calcium oxalate can cause kidney stones, with either acute or chronic consumption having the potential to cause kidney damage.

As the mechanism of harm to the body system is not specific to the human body, oxalic acid can also be harmful to other animals that ingest it, including pets.

Is Oxalic Acid Harmful to Skin?

As an acid, oxalic acid is irritating to the skin. Prolonged contact, especially at higher concentrations, can cause chemical burns.

Will Oxalic Dissolve in Water? Is Oxalic Acid Soluble?

Oxalic acid is soluble in water, ethanol, and ether.

Does Oxalic Acid Remove Rust?

Oxalic acid is an ingredient in some rust removal products. This works by the oxalic acid and iron within the rust reacting, forming iron oxalate, which is water soluble and can be washed off the iron surface being cleaned.

6 Steps for Safety

Step 1: Read the Warnings

When working with a product for the first time, always read all the safety documents first. This includes safety data sheets, which should be provided by the manufacturer or importer of the oxalic acid powder. There may also be an OSHA chemical label, FDA cosmetics label, or a Consumer Protection label on the packaging of the oxalic acid powder product. These documents all contain important information on the hazards of the product and instructions on how to mitigate those hazards.

Different compositions in different products may cause additional hazards to be present beyond the properties of plain oxalic acid powder. Be sure to familiarize yourself with the differences between separate oxalic acid products.

Step 2: Prepare Your Workspace

Creating a safe workspace, sometimes referred to as engineering control, is a key component of working safely with any potentially hazardous substance.

Since the primary hazard of oxalic acid powder is the fine dust, both as an irritant and as a combustible dust, ventilation is important. Fans which would blow oxalic acid powder around should be avoided. Dust collectors and air filters which draw in and capture any stray oxalic acid powder are ideal.

Step 3: Gather Your PPE

For oxalic acid, you will need the following PPE.

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• Respiratory Protection
• A half-facepiece respirator with filters rated for protection against fine organic dust.
• A full-facepiece respirator can serve as both respiratory protection and eye protection.
• Eye Protection
• Safety goggles which create a seal around the eyes are needed to prevent any airborne oxalic acid from reaching the eyes.
• Open safety glasses, which do not have a sealing surface, will not work in preventing dust from reaching the eyes.
• Gloves
• Basic disposable gloves will prevent oxalic acid from touching the skin on the hands and causing irritation.
• Long Sleeves
• Long sleeves will prevent oxalic acid from touching the skin on the arms and causing irritation.
• Either a long-sleeved shirt, long-sleeved coat, or disposable sleeves will work.
• Launder any contaminated closing separately to prevent cross-contamination and inform anyone laundering the clothing of the presence of oxalic acid so they can take any necessary precautions.

Step 4: Clear Your Workspace

Having a clear workspace is an important part of safety. Clutter can cause accidents and can prevent you from noticing if something has spilled.

This is also a good time to double-check check any engineering controls, like a dust collector, are in proper working order and that no filters need to be changed out.

If you are working in a shared space, make sure anyone around you can also remain safe when you are working with oxalic acid. For those working at home, this can include family members and pets.

Step 5: Do The Work

If engineering controls and PPE are used properly, working with oxalic acid has minimal hazards.

If work cannot be completed in one sitting, be sure to properly seal any oxalic acid containers to prevent spills or accidental release when not in use.

Step 6: Clean Up

Dust generation should be avoided when cleaning up. Either a vacuum with a filter or a damp cleaning cloth can be used to pick up spilled or stray oxalic acid powder while preventing dust generation.

Be sure to dispose of any waste in accordance with local regulations, which can vary by State and county.

Further Reading

The National Library of Medicine has a PubChem article on Oxalic Acid as well as a HazardousSubstances Database Entry. The National Institute for Occupational Safety and Health (NIOSH) also has an Oxalic Acid pocket guide.

Check out the Safety Guide Series Hub for more safety guides.

Sources Cited

National Center for Biotechnology Information (). PubChem Compound Summary for CID 971, Oxalic Acid. Retrieved May 17, from https://pubchem.ncbi.nlm.nih.gov/compound/Oxalic-Acid.

National Center for Biotechnology Information (). PubChem Annotation Record for , OXALIC ACID, Source: Hazardous Substances Data Bank (HSDB). Retrieved February 12, from https://pubchem.ncbi.nlm.nih.gov.

National Institute for Occupational Safety and Health (, October 30). Oxalic acid. Cdc.gov. Retrieved May 17, , from https://www.cdc.gov/niosh/npg/npgd.html

Original Posting Date: May. 17,

Last Updated: Feb. 12,

Oxalic Acid Mixing Ratios and Tips - Updated March

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#1

Post by kamsquared » Sun Jan 05, 3:39 pm

Hey Rusty Bunchers!
The most common question we get on our Facebook forum and sometimes on this website for Beer Can Cleaning is how to use oxalic acid to remove rust from cans. Based on some recent posts, I am going to try to summarize the tips in this post.

If you have any comments for pros/cons/additions/corrections, please post them below and I will edit this top post as we go.

Where do I get oxalic acid?
You can buy oxalic acid online (Amazon) or at local stores. It is typically sold in crystal form in 2lb or 5lb bags and is sometimes called "wood bleach". Just look for the name "Oxalic Acid" in 99% purity. As of January , you can buy oxalic online for about $8/pound.

Does oxalic acid come in different strengths?
Oxalic acid itself DOES NOT come in different strengths. The types you can purchase online are noted as 99% pure.

Does oxalic acid have a shelf life?
The experience of the users polled is that, NO, oxalic acid DOES NOT have a known shelf life. It can sit for years - in powder form - with no affects.

What ratio of oxalic acid to water should I use?
There are many opinions on this but the general consensus is to use an oxalic acid to CAN ratio of about 1 tablespoon per can. This will typically be about 1/4 cup of oxalic per gallon of water, i.e. you can fit about 4 cans in a 1 gallon bucket.
There is a lot of discussion on various ratios depending on the amount of rust on the can, condition of the paint, etc. This is just a general starting point, you may find that you will add or reduce the amount of oxalic acid based on experience.

What temperature of water should I mix with the oxalic acid?
This is a little trickier.... Typically, you would use warm to hot water. However, hot water has a tendency to fade brighter paints like reds/bright blues or may take the paint off of some cans that have poor paint jobs, i.e. 70's pull tabs. Be careful and it's better to practice with just "warm" water.

How long should I soak cans in oxalic acid?
This will depend on the amount of rust on the can but a general rule of thumb is to do a first check after 15-20 minutes (check at least every 30 minutes thereafter). To really see how well they are doing, it is recommended to take the can out of the acid bath and clean them again under a warm water bath with dish soap and a toothbrush (just like your initial cleaning). This is another one that you will figure out as you gain experience.
Be careful not to "oversoak"!

Cleaning and Soaking TIPS!!

• Clean your cans thoroughly before using oxalic acid by using a good mix of warm water, dish soap, and tooth brush. This would include removing any mud or debris from the inside of the can. Any dirt, mud, etc will dilute the acid mix.

• Always add the acid to the water, per your high school chemistry teacher.

• Wear rubber gloves when handling the acid and/or the soaked cans.

• Soak cans outside or in a well ventilated area.

• Use just enough water to cover the cans you are treating....don't put 1 can in a 5 gallons of acid/water.

• Totally submerge the can by filling it with the oxalic acid mix as you sink it in the acid bath. It is obviously not necessary to clean the inside of the can but it's a lot easier than trying to hold the can down with some kind of weight.

• Practice soaking cans to gain experience by using cans that don't have value to you.....don't soak an Apache cone top as your first can!!

• Don't soak cans in direct sunlight as they will have a tendency to "green up".

Kamsquared
"I have your car towed all the way to your house and all you've got for me is *Lite* beer?"
Biff Tannen (Back To The Future)

Re: Oxalic Acid Mixing Ratios and Tips - Updated January

• Quote

#2

Post by Gravldo » Sat Jan 11, 3:03 pm

Contact us to discuss your requirements of Potassium Hydroxide Solution. Our experienced sales team can help you identify the options that best suit your needs.

Interesting as I was told that the soap would inhibit the oxalic acid but it seems everyone agrees with this recipe Shows Attended Lake Ozarks, Pat Taylor