A Field Note On [Oxalic Acid]: specs, sourcing, and what buyers are really asking

If you work in textiles, metals care, or rare-earth processing, you already know the quiet power of Oxalic acid. It’s the kind of material that doesn’t shout—until it brightens a weathered oak panel or strips a heat exchanger of rust overnight. To be honest, it’s also one of those products where details matter: hydration state, purity, trace metals. A few ppm off and downstream lines complain.

What it is and why buyers care right now

Oxalic acid (dihydrate, CAS 6153-56-6; EC 205-634-3; formula H2C2O4·2H2O) is a white, transparent crystalline solid. Melting point ≈ 101–102°C, density ≈ 1.653 g/cm³. It dissolves easily in water and alcohol, and yes—it can sublimate around 100°C. Market-wise, two trends stand out: sustainability audits now push for REACH-registered sources, and process engineers keep asking for lower iron/chloride to protect stainless assets. Lead times? Still lumpy, but improving.

Typical product specs (dihydrate)

Process flow (industrial-grade)

Methods vary. Many producers carbonylate alcohols to diethyl oxalate, then hydrolyze; others employ carbohydrate oxidation routes. A simplified flow looks like this: raw materials selection → controlled reaction/oxidation → hydrolysis to Oxalic acid → crystallization of dihydrate → centrifuge → low-temp drying → screening → packaging (25 kg bag / 1000 kg big bag). QC checkpoints include purity by permanganate titration (per ACS methods), heavy metals by ICP-OES, chloride via IC, and Karl Fischer for water. Shelf life: ≈ 24 months sealed, cool and dry.

Applications and why they work

• Metal cleaning and passivation prep (per ASTM A380 guidance) — removes oxides/rust without excessive base metal attack.
• Textile & leather — bleaching, stain removal, and pH control in dyehouses.
• Wood restoration — deck/teak brightening; furniture refinishers swear by it.
• Rare-earth precipitation and mineral processing — reliable complexation behavior.
• Laboratory reagent and pharma intermediates — where low Fe and Cl really matter.

Feedback? Many customers say the “clean break” during crystallization correlates with fewer filter fines and more predictable dissolving times in CIP tanks. Sounds niche, but plant managers notice.

Vendor snapshot (real-world buying notes)

Customization and QA

Oxalic acid buyers commonly request: anti-caking treatments, milled grades for faster dissolution, and tighter Fe/Cl specs. Good suppliers provide COA + third-party test reports (ICP-OES, IC, KF) from ISO/IEC 17025 labs. UN 3261 (Class 8, PG III) handling applies; use corrosion-resistant packaging. Service life is best with lined big bags and humidity control.

Two quick case notes

• Textile dyehouse in Gujarat cut rework by 14% after switching to low-chloride Oxalic acid for stain removal prior to reactive dyeing.
• Food-equipment fabricator used a high-purity grade to prep welds before passivation; inspection per ASTM A380 showed cleaner surfaces and less flash rust.

Citations:
1) PubChem Compound Summary: Oxalic Acid (CID 971).
2) ECHA Substance Information: Oxalic acid.
3) ACS Reagent Chemicals, Oxalic Acid monograph.
4) NIOSH Pocket Guide to Chemical Hazards: Oxalic Acid.
5) ASTM A380 – Cleaning, Descaling, and Passivation of Stainless Steel.