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It really depends on your local exact regulations, but this is from a hazard sheet for it:
SECTION 12 ECOLOGICAL INFORMATION
NO ACUTE TOXICITY BUT AVOID ENTRY INTO DRAINAGE SYSTEM. INORGANIC PREPARATION.
SECTION 13 DISPOSAL CONSIDERATIONS
ALWAYS DISPOSE OF ACCORDING TO LOCAL GOVERNMENT REGULATIONS.
NEUTRALISATION OF SPENT SOLUTION.
NEUTRALISE TO Ph of 8.5 – 9.0 SOLIDS WILL SEPARATE OUT. DECANT / FILTER THE LIQUID. SOLIDS MAY BE INCINERATED. BEFORE PUTTING LIQUID TO DRAIN NEUTRALISE TO Ph of 6.5 – 8.
Advice I have often seen for such materials is to neutralise and mix with casting plaster. Allow to set in a plastic bag and dispose of as solid. That way, nothing nasty can get in to the water system.
As I say, it really depends on your local regulations, so don't take anything I say as factual!
I don't know how to neutralise to pH 8.5 to 9 either, since neutral means pH 7 (I am a science and chemistry teacher...)
Can you check the pH of the solution - can you get pH paper ot tester (beer makers, garden centres and aquarium shops sell them)?
How much chemistry do you know? Here's a brief description, if you don't understand, ask again and I'll give you more details. If you do know, please don't be offended if I make it too simple...
pH 7 is neutral. Below that is acid, above is alkali. The further away from 7, the stronger the acid or alkali is (0 is most acid, 14 is most alkali)
If a solution is acid, adding enough sodium bicarbonate (baking soda) or chalk will make it neutral (it will fizz, just carbon dioxide). This is a good safe way to neutralise an acid.
If you want to move the pH above 7 you must add an alkali like sodium hydroxide (caustic soda), often sold for cleaning drains, or developing PCB's! Be careful with this, it attacks human flesh *very* nastily, worse than acid. Dissolve a teaspoon of sodium hydroxide in 500ml of water and add slowly, stirring and checking the pH until you reach what you want.
To move the pH down, you need to add acid, such as dilute hydrochloric acid or strong vinegar. Again, add slowly while stirring and checking the pH until you get where you want (probably neutral 7).
OK...
Personally, assuming the pH is above 7 (developer usually is), I would add plenty of white vinegar (it's usually cheaper than hydrochloric acid), then mix with the cheapest casting plaster you can find (don't use cement, it may react) in a strong plastic bag and let it set. Much easier.
Most countries also have a system for disposing of hazardous chemicals in an environmental acceptable manner. There may even be a monthly collection round or something for paint leftovers, waste engine oil, sulphated car batteries and other fun stuff. Worth checking and you sleep better at night.
Rick, isn't it so that tap water is slightly alkalic? Ph 8 or so?
Tap water can vary quite a lot, depending on its source and treatment.
Water that has spent any length of time travelling through rocks, rather than being stored in a reservoir will be slightly alkaline (yes, pH8 or thereabouts) due to the fact that most rocks contain things that neutralise acids, for instance chalk.
Water from rain or long-term reservoir storage without carbonate-rocks in the structure may be acidic (usually between 5 and 7), due to acid-rain (sulphuric and nitric acid) and dissolved carbon dioxide.
Treatments for killing bacteria often adjust the pH to around 7.
I did a field survey for precious metal exploration once, which involved measuring surface-water pH. Believe it or not, I frequently measured pH levels in streams in this area below pH 1 - really strong acid! This was an area where the soil was essentially old, thick peat. I didn't drink any! I did fall in a river though - and didn't dissolve.
A final point: consumer water filters (like Brita) tend to produce water that initially measures pH 5 - this can be neutralised to 7 by boiling since it is almost entirely due to dissolved carbon dioxide.
FoxyRick, your explanation was pitched just right - thank you so much! I did chemistry at school (not that you'd ever know!) and just about remembed enough to understand your post.
Thanks for the tip about vinegar, seems easy enough.
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if I make it too simple...