Why get upset when someone disagrees with you or tells you do not understand?
Is it not your point of being here, to learn?
How will you ever learn when you are always arguing with those who are trying to help you learn.
If you believe you know more and disregard good instructions or advice you are restricting your ability to learn better.
why argue with those who have been studying this for many years, something you have only begun to learn yourself, or something you have not learned or completely understand yet?
Maybe they see something you do not, instead of blindly arguing, would it not be better to spend your time researching to see if they understand or can see something you cannot or do not see?
Just because you change the pH of your acid solutions does not mean you have removed all of the toxic metal salts, toxic metal salts can remain in a solution at almost any pH range.
Note at PH 7 many toxic metal ions still remain in the solution as even after you bring your solution to pH 7, metal ions such as silver, iron cadmium, chromium, zinc, nickel, lead, as well as any nitrate, chlorides sulfates or other salts of the acids used.
Although we can use pH adjustments in the process of treating our waste treatment to lower its toxicity to a somewhat less toxic level safer for the environment so that we can safely dispose of them. we remove these metals at different ranges of pH to get the most of these metals out of solution that we can.
This is why we bring our pH up above neutral 7, to where more of these toxic metal ions can be removed from the solution.
Say you have a mixed waste acid solution,.
We can cement precious metal values from the solution by using copper metal letting it settle decant the solution after removing values we can cement out the bulk of the copper ions from solution using iron metal (which will also help to reduce other metal ions to elemental form.
At this point, we still have many different toxic metal ions in solution.
Adjusting the pH to neutral pH7 will precipitate the iron ions as insoluble hydroxide along with some other metal ions,
The saltwater solution may look clear at this point because most of the metals ions that color the solution have been removed.
Do not fool yourself by the looks of this colorless water-like looking solution it will still hold many colorless toxic metal ions in solution.
bringing the pH to around pH10 will then precipitate more of the dangerous metal ions and we can remove these hydroxides.
After decanting we can then lower the pH back to pH7 by adding acid, here again, some more of the toxic metal salts will precipitate and can be removed.
Here we are left with a solution that is still not "Safe", but most of the major toxic metals have been removed from this saltwater solution of chlorides, nitrates, sulfates, or whatever other anions from the acids or chemicals used were, it is at least safe enough to dispose of.
The metal precipitates are still very dangerous and can be water-soluble.
I go a step further than what we normally recomend when discussing waste disposal
I roast my hydroxide salts to form less soluble oxides before disposal, I also evaporate my solutions to salts.
I normally find a use or reuse most of my byproducts so I can also minimize the amount of waste generated that needs to be treated.
My copper nitrate solutions I do not consider waste after silver removal, I consider it a valuable chemical reagent I can find many uses for such as in a recovery method, or make other useful reagents out of them like nitric acid...
