Martijn,
I am glad you’re going to do the needed research, it is important for your safety and others around you.
This study is so very important, and your willingness to do the work is also important, Your willingness to do the study will give you a better understanding of the dangers involved and how to try and avoid many of them, it can also help you get a better understand the chemistry of recovery and refining.
This study can even help you to live long enough to enjoy some of the gold you get from doing this type of work
NOx is a term used to describe many gases of nitric acid, and its reactions, and the many different combinations of nitrogen and oxygen compounds.
We normally breath nitrogen with some oxygen, but when these two gases combine in different ways than air they can become extremely dangerous to breath, and form deadly pollutants, some are water soluble, and with moisture in the air can create acidic air or acid rains, or even form acids in your lungs.
Some can be scrubbed fairly easily in the proper scrubber, others are very hard to convert to a compound that can be trapped or neutralized in a scrubber, or be broken down to a safer form.
Some are not water-soluble until the pick up another oxygen, some we can see, some we cannot, some we may smell, and some we may not.
In recovery and refining we deal with several different acids, and many different chemical reactions that create many different gases and compounds, we also create many different very toxic compounds with our waste.
It is hard for me to express how extremely dangerous this work can be, we are working with dangerous acids and bases, and metals which can become very toxic in compounds, the chemical reactions can be complex, there are so many different dangers involved in the chemistry and work of recovery and refining of metals.
We do so many very dangerous chemical reactions, and produce many different toxic substances, and deadly gases and compounds as byproducts, even some of the reactions performed in the work of recovery and refining is almost making some possible flammable, or even explosive reactions, which can become extremely dangerous if not done right, or responsibly, to minimize these dangers as much as possible.
Study is the only way you will learn how truly dangerous this work or chemistry really is, and how to do it as safely as possible without harming yourself or others.
The more you study about it, the more you will begin to see these dangers, some are so complex we may not even be able to learn them all with one lifetime of study, that is if we can live even one full lifetime doing this type of work, and do not shorten it when trying to get a little gold.