Oxalic Acid Dihydrate CAS:6153-56-6

Oxalic acid dihydrate (ethanedioic acid dihydrate, CAS 6153-56-6, C₂H₂O₄·2H₂O, MW 126.07) is a white crystalline powder that acts as a strong reducing and chelating agent. In its dihydrate form it is the oxalic acid most commonly traded for industrial use, supplied in industrial grade per GB/T 1626-2008 with an assay of ≥99.6% as dihydrate.

We supply it at a minimum order of 1 MT, in 25 kg / 50 kg bags or 500 kg / 1,000 kg FIBC, shipping from Qingdao, Shanghai or Tianjin within 7–14 days of confirmed order. Every batch leaves with a COA (batch number and dates included), backed by our ISO 9001 quality system. For evaluation, free samples (up to 500 g) are available; you pay freight only.

Oxalic acid dihydrate - also called ethanedioic acid dihydrate - is the hydrated crystalline form of oxalic acid, carrying two water molecules per molecule (C₂H₂O₄·2H₂O, MW 126.07). It appears as colorless-to-white crystals and dissolves readily in water (approximately 13–14 g per 100 mL water at 20 °C). Its defining chemistry is a strong reducing ability and the ability to chelate (bind) metal ions, which is what makes it effective for rust removal, stain removal and surface treatment.

Commercially, oxalic acid is most widely traded and used in its dihydrate form, because this form is stable under normal storage conditions. The anhydrous form (CAS 144-62-7) is the water-free version of the same compound - an alternative form we can discuss for processes that specifically require it. See the specifications table below for both CAS numbers.

Quick Specs at a Glance

COA - Actual Batch

Batch No. 20260128 · Manufacture Date: Jan 28, 2026 · Expiry Date: Jan 27, 2028

About GB/T 1626-2008 - this is China's national standard for industrial oxalic acid, setting specification limits for purity and the impurities listed above. The batch shown was tested to this standard and passes every item; results are given alongside the limits so you can compare directly. We keep the certificate for each batch on file; a copy is available on request.

Key Parameters - What They Mean

• Purity (assay as dihydrate) - drives yield and product quality in downstream synthesis; this batch passed at 99.99% against the 99.6% minimum.

• Sulphate - residual sulphate can interfere in metal surface treatment and downstream reactions; kept at ≤0.07%.

• Heavy Metals - relevant when oxalic acid is used in cleaning and detergent formulations with residual limits; ≤0.0005%.

• Ferrous (Fe) - iron content can cause yellowing or spotting in textile bleaching; the lower the better (≤0.0005%).

• Chloride - elevated chloride raises corrosion risk in metal treatment baths; ≤0.0005%.

• Residue on Ignition - a general measure of inorganic residues and overall purity; ≤0.01%.

• Calcium (Ca) - calcium can cause scaling in specific processes; ≤0.0005%.

Metal Cleaning & Surface Treatment

In metal working, oxalic acid removes rust, scale and tarnish by dissolving iron oxides - partly through its reducing action and partly by chelating ferric ions into soluble complexes. A typical treatment bath is a 5–10% aqueous solution applied at 40–60 °C, with contact time matched to the thickness of the deposit. It is widely used for pre-treatment of steel parts before plating or phosphating, and for cleaning stainless steel and heat exchanger surfaces. For concentration and dwell time specific to your substrate, contact us with your process details.

Stone & Marble Polishing & Restoration

For natural stone, oxalic acid is a trusted agent for removing iron stains, cement residues, efflorescence and water marks on marble, granite and travertine, and for restoring the polished surface. A common working solution is 100–200 g of oxalic acid per litre of warm water, applied with a polishing pad and then rinsed thoroughly. It is especially popular with marble restorers and stone-cleaning contractors - a strong market for our product in India and the Middle East. Always test on an inconspicuous area first, since acid treatment can etch calcareous stone if left too long.

Textile & Leather Processing

In textiles, oxalic acid is used as a mordant and bleaching assistant, and to remove iron-rust stains from fabrics without damaging the fibre. Dosing is commonly 0.5–2.0% on the weight of fabric (o.w.f.), depending on the substrate and treatment stage. In leather processing it helps neutralize and brighten tanned hides. Rinse thoroughly after treatment and validate the dose on a trial batch first.

Cleaning Products & Descaling

As a mild, highly water-soluble acid, oxalic acid is a common active ingredient in household and industrial cleaners - toilet bowl cleaners, rust-removing pastes and metal-polishing compounds. In descaling it removes limescale and rust deposits from radiators, boilers and heat exchangers. Formulators typically use it at 1–10% depending on the product type. We can supply in quantities that suit both formulation trials and production runs.

Pharmaceutical Intermediates

Oxalic acid is used as a synthetic intermediate and a purification or processing aid in pharmaceutical manufacturing - for example as an acidifying agent, a catalyst component, or a precipitating agent in certain isolation steps. Because industrial grade already meets GB/T 1626-2008 with tight heavy-metal limits, it serves most intermediate-stage applications. If your internal specification is stricter, send us your limits and we will confirm whether our current grade can meet them.

Wood Bleaching & Restoration

In wood restoration, oxalic acid removes iron and water stains from timber, returning faded or greyed wood to a clean, even tone before re-finishing. A 100–200 g/L solution in warm water is typically brushed onto the stained area, left briefly, then rinsed and neutralized. It is commonly used by flooring contractors and furniture restorers. As with stone, test on a hidden area and neutralize the residue before final finishing.

Standard Packaging Options

Shipments leave from Qingdao, Shanghai or Tianjin. MOQ is 1 MT for a trial order; free samples (up to 500 g) are available with the buyer covering freight. Oxalic acid is a Class 8 corrosive (UN 3261, Packing Group III), so all packaging and documentation comply with dangerous-goods requirements for sea freight

• MOQ: 1 MT for new customers - trial orders welcome.

• Custom packaging / OEM labelling on request.

• Payment terms: T/T, L/C, D/P, D/A, O/A. For repeat customers, terms can be adjusted based on the history of cooperation.

Tell us your specification or packaging requirement; we will confirm availability and reply with a firm quotation.

• Transport: UN 3261, Hazard Class 8, Packing Group III.

• Storage: cool, dry, well-ventilated area; keep packaging sealed to prevent moisture pick-up.

• Keep away from: oxidizing agents, alkalis and silver salts.

• Protective equipment: chemical-resistant gloves, safety goggles and a dust mask (a respirator for dusty working conditions).

• First aid - skin contact: remove contaminated clothing and rinse the skin with plenty of water. Eye contact: flush with clean water for at least 15 minutes and seek medical attention. Inhalation: move to fresh air; seek medical help if symptoms persist. Ingestion: do not induce vomiting - rinse the mouth and seek medical attention immediately.

• Shelf life: 24 months from production in sealed original packaging.

• The complete Safety Data Sheet (SDS) is available on request - contact our team.

• ISO 9001 certified quality management system.

• Products tested to GB/T 1626-2008; every batch is issued with a COA covering purity, sulphate, heavy metals, ferrous, chloride, residue on ignition and calcium - batch number, manufacture and expiry dates included.

• Third-party inspection by SGS, BV or Intertek can be arranged on request.

• Certificates are kept on file for every batch; a copy is available on request.

1. What is the difference between oxalic acid dihydrate and anhydrous?

Oxalic acid dihydrate (CAS 6153-56-6) carries two water molecules per molecule and is the form most commonly traded for industrial use, thanks to its stability under normal storage conditions. Anhydrous oxalic acid (CAS 144-62-7) is the water-free form of the same compound. We supply the dihydrate as our standard grade; if your process specifically calls for the anhydrous form, tell us and we will check feasibility.

2. What grades of oxalic acid do you supply?

We supply one industrial grade, tested to GB/T 1626-2008, with an assay of ≥99.6% as dihydrate. This is the grade suited to metal cleaning, stone and marble work, textiles, cleaning products, pharmaceutical intermediates and wood restoration. We do not carry food-grade oxalic acid.

3. What purity and standard is your industrial-grade oxalic acid?

Assay ≥99.6% as dihydrate, to Chinese national standard GB/T 1626-2008; the batch shown on this page tested at 99.99%. Impurity limits - sulphate ≤0.07%, heavy metals ≤0.0005%, ferrous ≤0.0005%, chloride ≤0.0005%, residue on ignition ≤0.01%, calcium ≤0.0005% - are listed in the COA table above.

4. Is oxalic acid hazardous? How is it classified for transport?

Yes. Oxalic acid is classified as a corrosive substance - UN 3261, Hazard Class 8, Packing Group III. Handle with care: avoid breathing dust and avoid contact with skin and eyes. For sea freight it ships in compliant packaging with the required dangerous-goods documentation. The complete Safety Data Sheet (SDS) is available on request.

5. How should oxalic acid be stored?

Store in sealed original packaging under dry conditions. The recommended shelf life is 24 months.

6. What is your MOQ? Can I get a sample first?

MOQ is 1 metric ton for a trial order. Yes - free samples of 500 g are available for evaluation; the buyer covers freight. Samples are drawn from the same batches as commercial production.

7. What packaging options do you offer for bulk orders?

25 kg or 50 kg woven bags with PE liners, and 500 kg or 1,000 kg FIBC jumbo bags. Custom packaging can be arranged on request. In 25 kg bags, one 20' container loads about 25 metric tons.

8. What is your lead time?

7–14 days from confirmed order, depending on quantity and packaging. We usually arrange shipment from major Chinese ports including Qingdao, Shanghai and Tianjin.

9. What documents do you provide with each shipment?

Each shipment includes a Certificate of Analysis (with batch number, manufacture and expiry dates), commercial invoice, packing list and bill of lading. If required by your quality department, independent inspection before shipment can also be coordinated.

10. How do you ensure consistent quality across batches?

Product is tested batch by batch to GB/T 1626-2008, and a COA covering all seven parameters is issued for each batch. Every certificate is kept on file, and we welcome third-party inspection before shipment if your QC requires it.

Send us your quantity, packaging and destination port. We will reply with a firm quotation.

Contact now

Hot Tags: Oxalic Acid Dihydrate CAS:6153-56-6, China Oxalic Acid Dihydrate CAS:6153-56-6 manufacturers, suppliers, factory, glutaraldehyde, potassium hydroxide 30, chlorinated acetic acids, dmso 99 9, 2 ethanoyloxy benzene carboxylic acid, pvc resin powder