Suitable metallic piping materials for reagents in a cyanidation gold plant

Dear all,

I've been tasked with reviewing the piping materials specification for a gold plant project that calls for HDPE pipe for the following substances, all at ambient temperature, though exposed to the sun in a tropical area:

- 20% w/v sodium cyanide solution
- 33% w/v hydrochloric acid solution
- 20% w/w sodium metabisulfite solution
- 20% w/v copper sulfate solution

In researching metallic alternatives for pipes, I've been considering PTFE-lined carbon steel pipe for the hydrochloric acid and 316L pipes for the rest, as the elution package already employs 316L equipment.

Does anyone have direct experience with these subtances and piping and can chime in?

Thanks.