So just because someone else released toxic waste into the environment, its okay for you to do it? Just because its far away from people, its okay to release a toxic corrosive gas into the air? Would you be okay if I released a cylinder of chlorine gas up wind of you? Come on... that is a terrible stance to take, both ethically and professionally. As a refining community, we all have to take a higher moral standard considering the materials we work with.
I realize that that the amount of pollution that batch put into the air is nothing compared to what industry does, but that is not at the heart of what I am trying to tell you. What I am trying to tell you is your refiner (not you) has terrible practices and it will end up costing you in the long run. Let me just point out a couple examples.
First - That pot of acid is over open ground. If something happens (like the pot falls over, or gets dropped, boils over, runaway reaction etc...) there is nothing to catch the acid. Environmental concerns aside, you would lose THOUSANDS of dollars in gold from a simple mistake. I think just about everyone here can testify to the benefits of using a catch-pan form personal experience.
Second - That cloud of NOx... that's a pretty dense cloud of gas. If the wind changes or someone is not paying attention, just a sniff or two of that will probably send someone to the hospital. And there are simple ways of mitigating that like 4metals mentioned.
Third - I see no safety gear at all. The picture of the guys pouring 'liquid' could just be the addition of water and I am hoping they were using gloves and eye protection for the dangerous stuff.
These are all big red warning flags. Especially if someone is calling themselves a 'professional', because this kind of behavior is anything but.
One last thing that I should clarify what I meant... in my last post I said this should be done in a lab... I should have said in a controlled environment. Something as simple as a good work platform and basic safety gear. There are a couple guys here that built simple sheds in their back yards so they could have a dedicated space for refining. When you do that, you can control more aspects of your refining environment and make things safer, easier, and cleaner... all of which lead to better yields and more money. Not all of us have a dedicated lab, but those that take what they do seriously, do. Be weary of a 'professional' refiner who doesn't work in a controlled environment. Chances are they are not getting you the best yields on your material.