Oxalic Acid for Around the Shop

Oxalic Acid

Oxalic acid is a white crystaline solid organic acid. It occurs naturally, in rhubarb, spinach, tea and many other plants. The commercial grade normally as the dihydrate. It is a rather strong acid as far as organic acids go being 3000 times stronger than acetic acid which is the acid in vinegar. It is very poisonous with 15 grams or a heaping teaspoon being the lethal dose.Oxalic acid is easily purchased online or can be had at hardware stores as wood bleach in a pinch. It is used by woodworkers, beekeepers, mariners and metal workers. One of its main uses is rust stain removal because oxalic acid is an excellent chelating agent that aggresively dissolves the iron oxide in rust.


Safety first

Although oxalic acid is safer to handle than nitric, sulfuric, or hydrofluoric acids, oxalic acid is still fairly strong and quite poisonous so proper
safety gear is important


Cleaning alloy wheels

Alloy rims cleaned with oxalic acid Alloy rims for cars and trucks can be a wonderful accent to the style of the vehicle. THe problem is with daily driving, especially in stop and go traffic, the iron composite break pads grind and grind putting a lot of dust on the wheels. Whats more is this iron dust is very hot from the friction and oxidizes to iron oxide. Still hot, they adhere to the aluminum/magnesium alloy in the wheels as a tough greyish black stain that cannot be removed with detergent or normal cleaning measures.What is needed is an aggresive acid or alkaline cleaner. Strong acid cleaners dissolve the iron oxides and some of the remaining iron thus allowing the break dust to be rinsed off with water. Alkaline cleaners work by partially dissolving some of the aluminum allot under the break dust leaving a fresh surface. The acid cleaners may contain, phosphoric, hydrofluoric, sulfuric, or hydrochoric acids or there mixtures. These acids are very dangerous to humans as they can several burn all tissue and may even discolor or destroy the alloy rims. Hydrofluoric acid is the worst as it can burn the skin and also poison you by attacking calcium in your body! A 50% solution of hydrofluoric acid solution spilled on the skin can kill you! Alkaline cleaners can be very dangerous also, a splash in the eyes can mean permanent blindness.

There is a safer option. That option is oxalic acid, although poisonous and somewhat irritating to skin, is much safer to use and handle. For cleaning automotive aloy wheels, a hot solution of 3 ounces crystals to 32 ounces of water will suffice. There is only minimal scrubbing involved and the break dust rinses away with a garden hose. Heavily deposited break dust may need two or more applications.

Also, on a somewhat related note, there seems to be a consensus that oxalic solutions will cleanup rusty chrome plated steel. I found an interesting thread in My Tractor forum about how to clean up rusty antique BMX bikes and such.

Removing rust stains from concrete

Concrete cleaned with oxalic acid Although muriatic or hydrchloric acid will perform this task, it is very corrosive and gives alot of poisonous and corrosive fumes. Furthermore, it actually dissolves some of the calcium from the concrete aggregate weakening it and promoting erosion. Clearly, a gently method is needed. Again it is oxalic acid to the rescue. The chemical action is a little different as instead of dissolving the calcium and the iron oxide stain, it only dissolves the iron oxide stain. It converts the red stain to a muddy green ferric oxalate complex after the oxalic acid is scrubbed into the wet concrete and absorbed. After 10 to 15 minutes, when the oxalic acid has had a chance to react, it is easily rinsed off leaving a perfectly white concrete that will look as good as it did the day it was poured.

Other Uses for oxalic acid

Oxalic still has other uses around the home or workshop. It is used to control pests by beekeepers and even to poilish marble. See the videos posted below for more information.

Reducing Gold Chloride solutions

If you are a gold refiner, then you are well aware of the process of dissolving scrap gold in aqua regia. Aqua regia is a mixture of Nitric and Hydrochloric acids that is used to dissolve precious metals like gold and platinum. When you have the golden solution of the chloride, it can easily be reduced to pure gold by reducing it with oxalic acid solution. See video below.


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