Not in a similar industry, but I don't think you can avoid the position that some of the items you're using definitely are chemical hazards. I know I wouldn't want to consume excessive quantities of H2SO4 or NaOH
I suspect you'll need to implement some sort of verification testing regime as part of your prerequisite program, assuming your HACCP study doesn't lead to the conclusion that one or more of the controls is a CCP.
As for safe limits, I'm not very familiar with the Brazilian regulatory system for foodstuffs but it's possible these have been established or considered within that?
Alternatively, one would hope that regulations and/or risk assessment from other regulatory bodies may have enough credibility to be useful in this scenario.
The EU is the system with which I'm most familiar but equivalents for at least some of it will exist in other regions, but as a starting point:
The limits for some metals are included within the appendix to Regulation (EC) 1881/2006 and subsequent amendments - available here in multiple languages: https://eur-lex.euro...ELEX:32006R1881
Some of these substances are permitted additives within the EU, so maximum limits can be seen in the EFSA additives database here: https://webgate.ec.e...es.pagination=1
For those without specific limits, and indeed this is potentially useful in general, the European Food Safety Authority publishes all of its risk assessment and these can be found fairly easily through Google. For example a search for "EFSA risk assessment H2SO4" finds the page for the most recent risk assessment, and links to the full document: https://www.efsa.eur...ournal/pub/5868
It may also be worth looking to see if their is either a national or international trade body for your specific sector, as some of these provide far more detailed guidance on a range of contaminants/hazards that go beyond the scope of regulatory limits, and can also provide general useful advice on such things.