Oxalic Acid: Product Uses and Usage Instructions

1. Product Overview

Oxalic acid (chemical formula: C₂H₂O₄), also known as ethanedioic acid, is a naturally occurring organic compound that appears as colorless crystals or white powder. It is highly hygroscopic and soluble in water, with strong chelating properties and acidic characteristics. This product is widely used in various industrial and daily scenarios, but it is corrosive and toxic, requiring strict compliance with safety operating procedures during use. Its CAS number is 144-62-7, and UN number is 3261.

2. Product Uses

2.1 Industrial Applications

• Metal Processing Industry: It is an efficient rust remover and metal cleaner. Oxalic acid can form water-soluble ferric iron complexes (ferrioxalate ions) with iron ions in rust, effectively dissolving rust and restoring the original state of metal surfaces. It is widely used in the restoration of antique metalware, machinery maintenance, and marine maintenance, as it can remove rust without damaging the metal matrix[superscript:5].

• Textile Industry: Used in dyeing and bleaching processes. It adjusts the pH value of the dye bath to ensure uniform penetration of dyes and strong bonding with fibers, thereby improving color fastness and brightness of fabrics. Fabrics treated with oxalic acid are more resistant to fading, which is favored by high-end textile brands.

• Wood Processing Industry: A high-performance wood bleaching agent. It can effectively remove tannin stains, watermarks, iron-based discoloration, and weathering marks on wood surfaces, rejuvenating aged or stained wood. It is widely used in furniture restoration, floor maintenance, and wood crafts processing, as it can gently lift stains without damaging wood fibers[superscript:7].

• Pharmaceutical and Chemical Industry: Serves as a key reagent in chemical synthesis, used in the production of APIs, antibiotics, and other pharmaceutical products. Its precise reactivity helps chemists construct complex molecular structures, ensuring the purity and effectiveness of products. It also participates in the esterification reaction to synthesize organic esters such as diethyl oxalate[superscript:6].

• Other Industries: Used in leather tanning and finishing to enhance the texture and durability of leather; used in stone cleaning and restoration to remove stains and discoloration on marble, limestone, and other stone surfaces (note: avoid using on acid-sensitive stones). It is also used in the production of catalysts, desiccants, and water treatment agents[superscript:3][superscript:5].

2.2 Daily Use (Low Concentration)

• Used as a household cleaner to remove rust stains on metal utensils, faucets, and kitchenware, as well as ink stains and mildew on white fabrics (use with caution to avoid damaging fabrics).

• Used in gardening to adjust soil pH, suitable for acid-loving plants such as azaleas and camellias (dilute to an appropriate concentration to avoid burning plant roots).

• Note: Concentrations above 10% are classified as regulated poisons in many regions (e.g., the UK), and private individuals need relevant licenses to purchase and use them. Daily use should choose low-concentration products (≤9.95%).

3. Usage Instructions

3.1 Preparation Before Use

1. Personal Protection: Wear appropriate protective equipment, including acid-resistant gloves, protective clothing, a face shield or safety goggles, and a particulate filter respirator (for dust or high-concentration operations). Avoid direct contact with skin, eyes, and respiratory tract. Do not eat, drink, or smoke during operation[superscript:4][superscript:8].

2. Work Environment: Operate in a well-ventilated area (avoid using ventilation for powder to prevent dust dispersion). Keep the work area clean and tidy, away from flammable, explosive, and alkaline substances (such as strong oxidants, sodium hypochlorite, and silver compounds) to avoid chemical reactions causing danger[superscript:4].

3. Solution Preparation: When preparing an aqueous solution, add oxalic acid powder to water slowly (do not add water to the powder to avoid splashing). Stir continuously until fully dissolved. The concentration should be adjusted according to the usage scenario:

1. Rust removal: 5%-10% concentration (for severe rust, the concentration can be appropriately increased, but not exceeding 10%).

2. Wood bleaching: 2%-5% concentration.

3. Household cleaning: 1%-2% concentration.

4. Soil adjustment: 0.1%-0.5% concentration.

3.2 Specific Operation Steps

3.2.1 Rust Removal (Metal Surfaces)

1. Clean the metal surface to remove loose debris, grease, and dirt.

2. Apply the prepared oxalic acid solution to the rusted area with a brush, or immerse small metal items in the solution.

3. Allow the solution to act for 10-20 minutes (adjust according to the severity of rust; do not let the solution stay on the metal surface for too long to avoid corrosion).

4. Scrub the loosened rust with a non-abrasive brush or cloth.

5. Rinse the metal surface thoroughly with clean water and dry it promptly to prevent flash rusting. For long-term protection, apply a protective coating (such as paint or anti-rust oil) after drying.

3.2.2 Wood Bleaching

1. Ensure the wood surface is clean, free of dirt, and existing finishes (sand the surface if necessary for heavily stained areas).

2. Apply the oxalic acid solution evenly to the wood surface with a brush or sponge.

3. Let the solution stand for 15-20 minutes, and check the bleaching effect regularly.

4. Rinse the treated area thoroughly with clean water to neutralize residual acid.

5. Allow the wood to dry completely (usually 24-48 hours) before applying finishes or sealants. For stubborn stains, a second application may be required; test on an inconspicuous area first to avoid damaging the wood[superscript:7].

3.2.3 Household Cleaning

1. Dip a cloth or brush into the dilute oxalic acid solution and wipe the stained area gently.

2. After cleaning, rinse the area thoroughly with clean water to avoid residual acid causing damage to the surface (especially for delicate surfaces such as ceramics and glass).

4. Safety Precautions

• Toxicity and Corrosion Warning: Oxalic acid is harmful if swallowed, causes severe skin burns and eye damage, and may cause respiratory irritation. The minimum lethal dose for humans is about 71 mg/kg, and ingestion of 5 grams can cause severe poisoning or even death. Repeated or prolonged skin contact can cause dermatitis and slow-healing ulcers[superscript:6][superscript:8].

• Emergency Treatment:

• Inhalation: Move to fresh air immediately, keep the respiratory tract unobstructed, let the patient rest in a semi-upright position, and seek medical attention promptly.

• Skin Contact: Remove contaminated clothing immediately, rinse the affected area with plenty of water for at least 15 minutes, and seek medical attention if burns occur.

• Eye Contact: Rinse with plenty of water immediately (remove contact lenses if easily possible) for at least 15 minutes, and seek medical attention immediately.

• Ingestion: Rinse the mouth immediately, do not induce vomiting, and seek medical attention immediately (gluconic acid calcium is an effective antidote).

• Storage Requirements: Store in a dry, cool, and well-closed container, away from strong oxidants, food, and feedstuffs. The storage temperature should not exceed 40℃, and it should be kept away from moisture, water, and direct sunlight. It should be packed in polypropylene woven bags lined with plastic bags. Do not transport with food and feedstuffs[superscript:6].

• Spill Disposal: Wear personal protective equipment, sweep the spilled substance into covered plastic containers (moisten first if it is powder to prevent dusting), and wash the remaining substance with plenty of water. Isolate the spill area and avoid the spilled solution entering water bodies to prevent environmental pollution[superscript:4][superscript:6].

• Other Notes: Keep out of reach of children and pets. Do not mix with other cleaning agents (especially alkaline agents) to avoid generating toxic gases. After use, clean the tools thoroughly and dispose of waste solution properly (neutralize with lime or soda ash before disposal)[superscript:4].

5. First-Aid Measures Summary

In case of any exposure to oxalic acid, prioritize stopping the exposure, rinsing with plenty of water (for skin and eyes), and seeking professional medical attention immediately. Do not take any self-treatment measures (such as inducing vomiting after ingestion) to avoid further harm.