Used Photographic Fixer (With Impurities) Disposal: Safe Step-by-Step Guide

Always consult a manufacturer SDS. Read our Full Liability Disclaimer

Mixture: Complexes of Ag(S₂O₃)₂³⁻ and (NH₄)₂S₂O₃ or Na₂S₂O₃

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Hazard Level & Hazards:

When we create or update chemical disposal entries, our H-code hazard list is generous. We list hazards that may be just below regular cutoffs and would otherwise normally be unlisted. We do this to provide hobbyists a wider scope of safety risks that may still be relevant, despite normally being omitted. Our GHS icons, however, are congruent with typical legal labeling requirements of the respective chemical.

Medium
  • H319: Causes serious eye irritation
  • H410: Very toxic to aquatic life with long lasting effects
  • H411: Toxic to aquatic life with long lasting effects

Disposal Method

Never pour used fixer down the drain. While pure thiosulfate is mild, spent fixer contains dissolved silver. This is a regulated heavy metal that is highly toxic to microorganisms in septic systems and municipal water treatment plants.

  1. Silver Recovery (Optional) Use a silver magnet or a simple steel wool bucket (see Additional Tips) to precipitate the silver out of the solution. Once the silver is removed, the remaining liquid is significantly less hazardous, but some silver will remain.
  2. Collect the spent fixer in a clearly labeled HDPE container. Take it to your local HHW facility. Mention that it contains silver. Some facilities have specific protocols for precious metal recovery.
  3. Some commercial labs or university darkrooms accept used fixer for their own silver recovery systems.

Neutralizing Agent

Sodium Carbonate (Washing Soda) can be used to neutralize acidic fixers before disposal, but this doesn’t remove the silver

Storage Precautions

Store in a HDPE container in a cool, dark place. Label clearly as “WASTE: Spent Fixer (Contains Silver)”. Avoid extreme heat. Heat can cause the sulfur to precipitate out, creating a foul-smelling sludge.

Ideal Storage Container

HDPE. Review our chemical storage container guide for more information about container types and materials.

Other Names

Spent Hypo, Exhausted Fixer, Photographic Waste Solution

Additional Tips

  • You can recover nearly 99% of the silver in the fixer at home. Place a wad of fine steel wool in a plastic container and pour your spent fixer through it. The silver will trade places with the iron (a displacement reaction), leaving the silver as a black sludge at the bottom. You can eventually refine this sludge or sell it to a refiner.
  • Don’t guess if your fixer is spent. Use “Hypo Check” drops (Potassium Iodide). If a drop creates a cloudy white precipitate that doesn’t disappear when shaken, your fixer is saturated with silver and should be disposed of
  • If your fixer smells like rotten eggs (Hydrogen Sulfide), it has begun to sulfurize. By this point, it is useless for photography and should be processed for disposal immediately
  • To save money and ensure safety, use two fixer baths. Use “Fixer A” until it is nearly exhausted, then move to “Fixer B” for the final clear. When “Fixer A” is totally spent, promote “Fixer B” to the first position and mix a fresh “Fixer B.” This makes sure your film is always fully fixed while maximizing the silver concentration in the waste you eventually process.
  • Don’t trust the bottle’s capacity rating. Take a piece of undeveloped film leader, drop it into your used fixer, and time how long it takes to become transparent. If it takes more than double the time it took in fresh fixer, the solution is exhausted and ready for your silver recovery bucket
  • If you mix spent developer and spent fixer, the pH change can cause the silver to precipitate as a messy silt that is difficult to filter. Keep your waste separate until you are ready to perform a controlled recovery.

Silver Recovery Protocols

Incompatible Chemicals/Dangerous Combinations

  • Bleach (Sodium Hypochlorite) (NaClO) Toxic Gas - Mixing fixer with bleach can release toxic Chloramine and Sulfur Dioxide gases. Never mix photo chemicals with household cleaners.
  • Strong Acids (HCl, etc.) Harmful Gas - Adding strong acids to spent fixer will release Sulfur Dioxide (SO₂) gas, which is a severe respiratory irritant
  • Hydrogen Peroxide (H₂O₂) Oxidation/Heat - Can cause rapid oxidation and heat buildup
  • Ammonia (NH₃) (and Strong Bases) Explosive - While some fixers use ammonium thiosulfate, adding concentrated ammonia to spent fixer (which is rich in silver ions) can lead to the formation of Silver Nitride (Ag₃N) or fulminating silver. These are highly unstable, touch-sensitive explosive residues that can form on the crust of old bottles or in lab drains.
  • Potassium Permanganate (KMnO₄) (and Strong Oxidizers) Violent - Mixing these results in a violent redox reaction. The thiosulfate acts as a reducing agent, and the permanganate as a strong oxidizer. This can cause the mixture to rapidly heat up and burp corrosive liquid out of the container. Can release irritating sulfur oxide fumes.
  • Formaldehyde (HCHO) Toxic Gas - Sometimes found in old stabilizer baths. Mixing fixer directly with formaldehyde can trigger the release of toxic gases and create a sludge that is significantly harder to process for silver recovery

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