Many points to comment on.
I thought long ago, that a big part of glossy advertising
was clay (someone mentioned kaolin, well that is a clay). There could easily be other components that are a problem.
I would have thought that when printers moved to soy based inks, that the reason to do so would be independent of black versus coloured. The lifetime of many of these print products is days at most. Having to use an ink that is colourfast for decades is not needed.
I've been looking for data on glossy and coloured print, and not finding it yet (and recent). I hope to find something soon.
Someone said sulfates are toxic. Sulfuric acid will hurt you, I don't think it is the sulfate that gets you. There may be some sulfates which are toxic.
There are metals and there are metals. I believe to the astronomy community
, anything with an atomic number higher than 2 is a metal. To me, a "heavy metal" is at least 4th row. Lead (Pb) is a dency, high atomic mass metal. Cadmium is up there. If you irradiate them with alpha particles (from a nuclear source), they will fluoresce X-rays and hence are rather easy to detect. Not all metal species are equivalent; big difference between hexavalent chromium and other valences of chromium.
Much of the biochar/bio-oil/bio-gas seems to be talking combustion methods to produce these things. I've thought about this, but I would much rather come at this from solar-thermal and just use destructive distillation with no oxygen input. The bio-oil fraction often is usable for asphalt. In specific instances, I think the bio-oil fraction may be considered similar to pitch; and possibly useful to make carbon
I don't think any old organic source should be subject to destructive distillation as a first process. Used motor oil is a good example, it needs to be processed in other ways first. But it may be that pyrolysis is the process to use at the end. In term of bio-char (which to me is very similar to activated charcoal), I don't want to produce bio-char which has "mobile" toxic species in it. If there is a way to produce bio-char which makes things like lead(Pb) less mobile, I would be less worrysome about lead(Pb). If your bio-char has 1ppm levels of the rare earths, uranium or thorium; I wouldn't worry about them (that is about the same as everywhere else on Earth).
But, if you have on your farm the ability to destructively distill "farm products"; what happens if you should get hit with a destruction order for all the chickens
on your farm? Using destructive distillation will probably get rid of whatever bird flu (or related) that caused the destruction order to be issued. It seems more likely for a monoculture farm to get hit with a destruction order; but it is possible that a permaculture
farm could get hit. Is anthrax more likely for a permaculture
There is lots of scrap iron/steel all over. A way to recycle that is to produce new cast iron
/steel. For someone on the farm, I think you should stay away from producing your own hot metal for structural purposes. If you want to make frames for park benches (and there isn't a bunch of radioactive cobalt in the melt - it has happened sometimes) and they don't need to be hot worked (forged, blacksmithed); I would consider using a high phosphorous iron alloy as a target. The iron pillars in India are a high phosphorus iron, and they have had phenomenal corrosion resistance over the centuries. Zinc tends to be volatile with respect to iron and steelmaking; I would have to look into lead(Pb), cadmium and others. But if you had some small amount of a vanadium compound on youyr farm, sticking it in an iron alloy with "high" phosphourus content would probably be okay.
There are ways of encapsulating materials in glass. And there are some glasses that melt at sufficiently low temperatures that things like zinc could be used there.
If you are going to dispose of things on the farm, you need to know where it is. You need latitude/longitude and depth. You probably should put it in a stainless steel container, and maybe there is some way to attach a conductor to it, so that you can locate it with RF similar to pipelines.
You can't (easily) cast deep things in epoxy, too much exotherm. But epoxy is a fairly inert material. Next step up for many things, is to encapsulate in glass. But for both, you then stick the "slug" into a stainless steel can.
Try to keep similar things in the can(s).
That's enough. Probably too long anyway.