ऑक्सैलिक एसिड (Oxalic acid)

Oxalic acid is a white, crystalline organic acid. It is stronger than vinegar or citric acid, and its special trick is that it grabs iron and holds it in solution. That is why it lifts rust stains that soap and bleach cannot touch.

• Formula: C2H2O4 (sold mostly as the dihydrate, C2H2O4·2H2O)
• CAS number: 144-62-7 (anhydrous), 6153-56-6 (dihydrate)
• Molar mass: 90.03 g/mol anhydrous, 126.07 g/mol dihydrate
• Melting point: 101.5 °C for the dihydrate
• Solubility: about 95 g per litre of water at 20 °C, much more in hot water

It occurs naturally in small amounts in spinach, rhubarb and other plants, but the powder you buy is made industrially.

Azlok sells oxalic acid as a technical grade powder for cleaning, stain removal and workshop use, plus a ready-to-use spray.

See today's price per kg for current rates.

Home and cleaning

• Removing rust and iron stains from ceramic tiles, wash basins, toilets and concrete
• Removing yellow hard-water and rust marks from bathroom fittings
• Lifting rust spots from white cotton fabric

Wood and stone work

• Bleaching black water stains and iron stains on wood, especially oak and teak
• Restoring weathered grey wood on decks and doors
• Marble polishing in the stone trade

Lab and industry

• Standard for checking the strength of potassium permanganate and sodium hydroxide solutions
• Textile and leather processing, metal cleaning and rare earth processing

Rust stains on tiles or concrete:

1. Dissolve about 50 g of powder in 1 litre of warm water (roughly a 5% solution) in a plastic bucket.
2. Wearing gloves, apply with a sponge or old brush and leave for 10 to 15 minutes.
3. Scrub, then rinse thoroughly with clean water.
4. Repeat for stubborn stains rather than making the solution stronger.

Black water stains on wood:

1. Strip any polish or varnish first.
2. Dissolve about 50 to 60 g in 1 litre of hot water and brush it on the stain or the whole panel.
3. Let it dry; repeat if needed.
4. Neutralise with a solution of about 30 g sodium bicarbonate (baking soda) in 1 litre of water, then wipe with plain water and let the wood dry fully before finishing.

Test on a hidden spot first. Oxalic acid can dull polished marble, coloured grout and some glazed surfaces. Leave marble polishing to professionals.

• Oxalic acid is harmful if swallowed or absorbed through the skin. Wear rubber gloves and safety glasses every time.
• Avoid breathing the dust when you open the pack and mix it. Work in a ventilated area.
• Never mix with bleach (sodium hypochlorite). Acids and bleach release chlorine gas.
• Keep away from strong oxidisers such as potassium permanganate in storage, and from strong alkalis.
• Store in its sealed pack or a labelled plastic jar in a cool, dry place. Never keep it in food containers or the kitchen.
• Keep away from children and pets.
• Small leftover solution can be neutralised with baking soda until fizzing stops, then flushed with plenty of water.
• Wash hands and tools well after use.

If you have a single rust ring on a floor or a stained sink, the 200 g powder or the 200 ml spray is plenty. The spray suits quick touch-ups where you don't want to mix anything. For a whole bathroom, a balcony floor or a wood bleaching job, buy 450 g. Painters, polishers and maintenance teams usually prefer the 1 kg pack because they use it every week.

The powder stays good for years if kept dry. For 25 kg and above, send a bulk inquiry.