Chemicals used in the Old Techniques demand a close monitoring on their disposal. If it's true, however, that quantities used by an amateur are minimum compared to those produced by industries or even by professional labs, on the other hand there is no reason in polluting freely and everyone should consider a proper way of disposing chemicals.
In some cases, there are chemicals that could interfere with the proper function of septic systems.
To effectively dispose washing waters and solutions different rules are to be followed with regards to the specific chemical.
Everyone must respect these principles, and accordingly organizing his work. It is preferable to keep all wastes in a large container so treatments can take place at one time.
To the latter, one must contact a chemical lab or a chromium plating facility to bring them all the residuals of the treatments.

In this paper we are giving instructions for some of the chemicals used in the Old Techniques processes, while others are to be treated differently and different procedures should be followed.

dichromate

oxalic acid and oxalates

ferricyanide

copper, lead and iron salts

Ammonium and potassium dichromate
These two chemicals are a danger to the environment, because they contain large amounts of hexavalent chromium
Chromium(VI) is highly soluble in water, with the exception of barium and lead salts. It must be reduced to its trivalent form to make it insoluble.
To do this one can simply add some sodium sulfite of thiosulfate (exhausted fixing bath are ok) and some hydrochloric acid to facilitate reaction. The color of the solution must shift from yellow-orange to greenish, confirming the conversion of Cr(VI) to Cr(III).
For each gram of potassium dichromate the following quantities are to be used:

1,3 g sodium sulfite anhydrous and 3,2 ml of hydrochloric acid at 37% w/w.

or

5,1 g sodium thiosulfate and 3,2 ml of hydrochloric acid at 37% w/w

For ammonium dichromate for each gram of the substance are necessary:

1,5 grams sodium sulfite anhydrous or 5,9 grams sodium thyosulfate

with the same amounts of hydrochloric acid.

Once Cr(VI) has been converted to Cr(III) this one must be converted in insoluble Chromium hydrate Cr(OH)₃.
To do this, add 0,9 gr of sodium hydrate (the one which is commonly available in hardware store is ok) diluted in some water for each gram of potassium dichromate. The dosage changes to 1 gram per each gram in case of ammonium dichromate. It is useful to regularly check the solution's pH with the indicator, which should become blue. Should it not become blue, slowly add more sodium hydrate until it does.
A flocculate, gray greenish precipitate will form, and let it sit down at least for a day. After this the clear solution above can be decanted (without tilting the container to avoid the precipitate to go into suspension) and discarded.
The mud-like substance on the bottom can be filtered out and disposed or left there for more to be added, for later disposing in larger quantities.
The final disposal of Chromium hydrate must be done with professional help, either a chemical lab or a chromium plating facility.




Oxalic acid and oxalates
Oxalic acid and oxalates are toxic and can compromise the functionality of a domestic septic system.
There are two methods of removing oxalates from a solution. The first one is precipitating it as calcium oxalate and filtering, and the second one is by oxidation with permanganate.

In the first case it is necessary to add a solution of calcium chloride (salt used on the roads for defrosting is ok, but be aware that it's not sodium chloride) by a ratio of at least 0,7 g of calcium chloride for each gram of potassium oxalate (0,9 in case of ammonium oxalate) mixing them thoroughly. A different approach is ok too: add some hydrochloric acid to a solution of calcium hydrate (lime) up until cloudiness vanishes. Use this solution to precipitate calcium oxalate.
After some time a white precipitate will form on the bottom of the container, which could adhere to the container's walls. After one day all the precipitate should be sitting on the bottom, and the liquid above can be decanted and discarded.
Again, the precipitate on the bottom can be filtered out or left there until a reasonable amount is collected to be taken to a lab for final disposal.
Another way to get rid of calcium oxalate is to burn it in a heater, because it decomposes in carbon dioxide and calcium oxide, both harmless.

Alternatively, add some drops of sulfuric acid to the solution containing oxalic acid or oxalate salts up until the indicator turns blue as stated above.
At this point one should add, continuously stirring, drop by drop a solution containing potassium permanganate. It oxides the oxalate to carbon dioxide becoming colorless manganese salt. At the beginning the reaction could be slow and the color may vanish only after minutes. This is why it is advisable to add the permanganate very slowly. At the end, when all the oxalate has been converted, no further reaction occurs and the solution will be colored in a stable pink.
Now it is necessary to eliminate the manganese. Slowly add a solution of sodium hydrate; a white precipitate will initially form which slowly will turn brown. Again, the clear liquid above can be decanted and discarded and the precipitate must be delivered to a chemical lab for final disposal.




Ferricyanide salts
Complex salts of iron and cyanide are stable, unless they are mixed with concentrated acids. This can lead to formation of gaseous cyanidric acid, which is lethal.
So using ferricyanide compounds is not dangerous. Those who may want to eliminate it will add some ferrous sulfate diluted in a little water. A deep blue precipitate will form because of the ferrous ferricyanide (turnbull blue, the same of cyanotipes) while the solution will lose its characteristic yellow color. The precipitate will be allowed to sit, then filtered and so on...




Copper, lead and iron salts
These metals are to be found in some toning baths, and are all insoluble in a moderately alkaline environment (lead may dissolve again otherwise). They can alternatively be precipitated as sulfides.
It is enough to add some calcium hydrate suspension to allow the hydrates compounds to precipitate. Those hydrates will be treated as above. It is advisable to stir the suspension well to favor the reaction with calcium hydrate which is only moderately soluble.
The calcium hydrate suspension is prepared by putting the calcium hydrate in water and stirring until the solution looks milky.

It is possible to check that there is no metal left by adding some drops of sodium sulfide to a sample of liquid taken from the surface (then not containing precipitate in suspension). If a black precipitate is formed it is necessary to add some more sulfide.