[liviug]

Hello. I am new into chemistry and I'm trying to be as conscious as possible about release of waste products into trash or sewage.

I am currently working on purifying some agriculture-grade copper sulfate by crystallization. The crystals are then washed with cold distilled water and, because the crystals form on the bottom, as well as touching each other, potentially trapping impurities between them I'm planning to do a double run of the process. My first question is:
1. is that really necessary and how can I ensure I generate sulfate that is as clean as possible?
This process results in small quantities of copper sulfate on glassware and gloves which I wash by spraying with a solution of sodium bicarbonate The waste water then drips into a container where I gather the resulting copper carbonate, separate the liquid then dry the carbonate. Although I aim to gather as much carbonate as possible, there will be some left on glassware which I wash off with a commercially available descaling product containing 9% phosphoric acid and trace sulfamic acid. I am currently assuming this is safe to wash down the drain. So question 2:
2. Are trace amounts of copper phosphate harmful to pour down drain? What about trace amounts of copper carbonate? What is a better way of making the substances safe enough for easy disposal? Are there any "safe" copper compounds? Is copper II oxide a safer form? Should I electrolize it into pure copper for environmental reasons?
A third issue I'm facing is knowing what substances I'm actually looking at. In theory the reaction of copper sulfate with sodium bicarbonate should result in highly insoluble copper carbonate falling out of solution. However, after filtering the carbonate, the resulting clear solution theoretically containing just sodium sulfate slowly fades back to a teal color over the course of a few hours and becomes cloudy again. This in my mind hints to some other soluble copper compounds being present in equilibrium with the carbonate which dissolve after the carbonate is removed?
3. Am I wrong about that asumption?
The substances I'm using are:
* dirty copper sulfate from anti-fungal plant treatment which contains small flakes of copper, which hints at the process it was produced with
* food grade sodium bicarbonate

[Borek]

2. Are trace amounts of copper phosphate harmful to pour down drain?

Potentially. Which usually means they are heavily regulated.

Please check with your local water/sewage company, they should be able to to guide you.

[TheodorCurtius]

This might also be relevant: 
https://www.ehow.com/how_8413286_treat-roots-sewer-copper-sulfate.html

Seriously though, many copper salts can be recycled by adding some hydrochloric acid and reducing the copper(II) back to copper metal using iron metal. Not sure if this will work for all copper salts, but I'd guess so...

[liviug]

2. Are trace amounts of copper phosphate harmful to pour down drain?

Potentially. Which usually means they are heavily regulated.

Please check with your local water/sewage company, they should be able to to guide you.

I wrote them today. I'll keep you posted. But as a general rule, insoluble salts are better than soluble ones, right?

[liviug]

This might also be relevant: 
https://www.ehow.com/how_8413286_treat-roots-sewer-copper-sulfate.html

Seriously though, many copper salts can be recycled by adding some hydrochloric acid and reducing the copper(II) back to copper metal using iron metal. Not sure if this will work for all copper salts, but I'd guess so...

The link is very interesting. I will not be releasing large quantities of copper sulfate in the sewer until I get an answer from my sewage company but nevertheless, it's interesting some people can and do that.
About reducing the copper salts, I will definitely give it a try. I got a similar suggestion from chatGPT a while back, but I had forgotten about that. I guess I should stop washing my copper sulfate glassware with sodium bicarbonate.

Many thanks. Very useful advice.