Careful consideration is required for the disposal of any hazardous chemical.
- Consult the Safety Data Sheet: The safety data sheet (SDS) for a chemical should be checked for the correct Personal Protective Equipment (PPE) to be worn and for any specific advice on disposal procedures.
- Chemical incompatibility: If storing waste as mixed waste, incompatible chemicals should not be placed in the same bottle. Information about the incompatibilities of a chemical can be found in the safety data sheet, Section 10: Stability and Reactivity. See the References for other sources of this information.
- Container type: A bottle or container of the same material as that in which the chemical is supplied is suitable for the storage of waste. Old chemical containers which are in good condition and have been thoroughly cleaned can be used for storing waste. Metal containers are generally not recommended for the storage of waste due to their reactivity and potential to corrode. Containers which have previously contained highly toxic waste should not be re-used, but should be disposed of via a licenced waste contractor.
- Local policies and guidelines: Disposal guidelines from your school jurisdiction, organisations such as your local council, water authority or the Environment Protection Authority (EPA) in your state/territory should also be considered.
The following options can be considered for disposing of laboratory chemical waste.
- Store as solid or liquid waste and arrange for collection by a licenced waste disposal contractor. This method of disposal applies to many organic liquids, heavy metal salts, and mercury waste as well as larger volumes of chemicals and any unknown chemicals.
- Recycle if safe and manageable. For example, copper sulfate or alum can be recovered by recrystallisation or evaporation of the solution. Crystals from class crystal-growing activities can be reused in the preparation of solutions.
- Landfill. Small quantities of non-hazardous solid chemicals such as sugars, or salts in which both the anion and cation are non-hazardous can be disposed of as general waste
- Wash to waste. Dilute solutions of small quantities of water-soluble, non-hazardous chemicals are accepted by most water authorities. These chemicals must be non-toxic to aquatic organisms. Unknown chemicals should never be put down the sink.
- Treat the waste to minimise the volume or reduce/eliminate the hazard, and dispose of the products accordingly. Consideration should be given as to whether this is economical in terms of the time and chemical resources required. Waste treatment methods include (i) neutralisation of acids or bases, (ii) evaporation of water from aqueous salt solutions, (iii) precipitation or displacement of metal ions from solution (iv) reduction of oxidising agents.
Segregation of chemical waste
All chemical waste requiring disposal by a licenced waste disposal contractor, should be collected into waste bottles which are correctly labelled, segregated from incompatible chemicals and stored securely.
Surplus, old or out of date chemicals are best kept in their original containers. Where chemical containers are degraded, these are best placed into secondary containment, which could be as simple as a strong zip lock plastic bag, if suitable.
Mixed waste: Ensure that only compatible chemicals are contained together. It is good practice to record what and how much of it you have put in the bottle, such as by attaching a label to the outside of the bottle on which to record each addition, or by keeping an electronic record (e.g. an Excel spreadsheet) which can be printed when compiling a waste manifest in preparation for waste collection.
Halogenated and non-halogenated solvents: These two categories of solvent are stored separately to avoid any chemical incompatibilities and hence, dangerous reactions. Also, depending on the waste contractor, the treatment methods they use may be less expensive for solvent in which there is no halogen component.
The following categories of waste can be stored as mixed waste:
- Organic liquid waste, non-halogenated
- Organic liquid waste, halogenated
- Aqueous waste; toxic inorganic substances, heavy metal mixtures
- Solid waste; toxic inorganic residues, heavy metal mixtures
- Aqueous waste, dilute acids
- Aqueous waste, dilute alkalis
The following waste can be stored separately:
- Lead residues
- Copper residues
- Nickel residues
- Chromium residues
- Zinc residues
- Silver residues
- Mercury residues
- Concentrated acid (a separate container for each acid)
- Note: Do not mix a concentrated acid with any other chemical.
Regarding the specific chemicals that you have mentioned:
- Small quantities can be diluted, neutralised and washed to waste.
Common reagents for the neutralisation of acids include dilute sodium hydroxide solution, or solutions of sodium bicarbonate or sodium carbonate or solid calcium carbonate. Carbonates have the advantage that neutralisation is indicated by the cessation of effervescence of carbon dioxide. The pH can be monitored with pH paper or indicator solution or a pH probe. Waste should be neutralised to within pH 6-8. The neutral solution can then be flushed down the sink with dilution.
- Large quantities should be stored in a suitably labelled container in secondary containment, or bunding, which is able contain the entire contents in the event of the container breaking.
- As noted above, concentrated acids should not be mixed with other chemicals
- Small quantities can be diluted to below 24% and washed to waste, as the alcohol is miscible with water.
- Large quantities should be stored as non-halogenated organic waste.
- Cobalt chloride, copper chloride, strontium chloride and lithium carbonate
- These chemicals are all toxic to either people and/or the environment and should therefore be disposed of by a licenced chemical waste disposal contractor.
- They can either be stored separately or with waste toxic inorganic substances.
- For pure chemicals, keep in their original containers if possible.
- Solutions can be evaporated in the fume cupboard and the salts stored as solids. If heating a solution to evaporate, in order to avoid decomposing the salt, heat only at low temperature in a fume cupboard and do not evaporate to dryness.
Assessing the risk and minimising waste
A risk assessment should be conducted prior to any activity using chemicals to identify all hazards and wastes produced. Science ASSIST has produced a one page risk assessment template for use, see ASSIST Risk Assessment Template.
It is good practice to minimise the chemical waste that is produced wherever possible. It can be instructive for students to assess the chemical waste produced as part of their laboratory activity. Suggestions for minimising chemical waste:
- purchase small quantities so as not to stockpile, and use chemicals only as required
- consider the use of microscale reactions and techniques in the classroom
- regularly dispose of old or out of date chemicals via licenced waste contractors; do not allow them to accumulate
Science ASSIST has answered similar related questions see:
Chemical disposal: disposal of potassium dichromate
Chemical Waste from Ester Prac: disposal of organic waste (esters)
chemistry: disposal of metal ions and sulfur species
Disposal of silver nitrate solid: disposal of silver nitrate solid
Mercury Spills: disposal of mercury
Mercury Thermometer: disposal of mercury thermometers
organic chemistry: disposal of organic waste (esters)
Organic waste: disposal of halogenated and non-halogenated organic waste
potassium permanganate: disposal of potassium nitrate
risk assessment: disposal of sodium thiosulfate and hydrochloric acid
SOP: Hazardous waste: General guidance of waste including chemical waste
Sulfur disposal: disposal of sulfur
waste chemical disposal: general information on chemical waste
More detailed information for each chemical in our List of recommended chemicals for science in Australian schools will be provided in the (future) Chemical Management Handbook.
Duffus, J. 2002. 'Heavy metals'—A meaningless term? (IUPAC Technical report) Pure Appl. Chem., Vol. 74: 793–807. http://publications.iupac.org/pac/2002/pdf/7405x0793.pdf
Pohanish, R.P., Greene, S.A. 2009. Wiley Guide to Chemical Incompatibilities, Third Edition, John Wiley and Sons Inc.
Queensland Department of Education Training and Employment. 2013, Guideline for Managing Risks with Chemicals in DETE Workplaces. Queensland DET website. https://education.qld.gov.au/health/pdfs/healthsafety/guideline-managing-chemicals.pdf (13 November 2013)
Urben, P., Bretherick, L. 2009. Bretherick’s Handbook of Reactive Chemical Hazards, Volumes 1 and 2, Seventh Edition, Elsevier Ltd.