Finally having had several weeks without rain, I could get round to burning my ever larger pile of wood waste,
I have just had a large bonfire, about 5 cu m of material ... consisting of a mix of sawn wood - pallets, offcuts, etc. some conifer trimmings, old roots, and a few pieces of OSB board. About 10% of the wood was tanalised timber.
No plastic or laminates etc.
All reduced down to a barrow full of ash ... now the big question is do I dump this, compost this, or add it to garden.
The Tanalised content being the issue - but the batten off-cuts had to go somewhere.
I THINK that there are copper and arsenic salts that will remain in the ash. But in small quantities.
These are more fungicides, than plant poisons.Most planst sem to cope pretty well with metals in slat form, in lowsih concentrations.
Ash itseklf is of course fairly alkaline, and loaded with I think potassium slats, so tehetr si a chance youy can dry out roots and kill plants with too much of it.
But apart from that, wood ash is a reasonable addition to soil in small quantities. Not nearly as good as chipped wood itself mind.
Wood ash is a strong single nutrient plant food. In small amounts it feeds, in large amounts it kills everything. So an effective way to clear weeded ground.
It does depend on the temperature but ash from cca treated timber can but up to 10% of the mass as copper, chrome arsenic compounds in the ratio 2:2:1.
There's a tannery that makes chrome leather where the offcuts are gasified and chrome recovered from the char.
Char that is still not considered activated carbon can still be effective at grabbing heavy metals the Forestry commission have trialled char in soils adjacent to water containing mine tailings and it has adsorbed sufficient metal to be within the realms of commercial ore concentrations.
As temperatures get higher then there's more chance of metallic compounds being volatilised, I think the chrome changes from a trivalent state to a hexavalent one as it volatilises and this can be nasty to breathe in.
There are reports of arsenic poisoning from burning coal in China which points to products of combustion ending up in the air.
Personally I wouldn't burn CCA treated wood but would burn creosoted stuff, in either case I'd bin the ash,
I'm not a chemist and it may be a trivial amount (IIRC the typical dose of cca salts was 5kg in 400kg of wood but it was concentrated in edges and surfaces) but I'd want to avoid long term effects on my garden.
Long time ago there was a geologist here, John Schmitt, who was better qualified to answer, I don't know what happened to him.
I have just created 3 new raised beds, filled with sifted soil (been using a power sifter for some weeks) - had 36 ton of top soil ... about 25% of it got sifted out as stone, weed and compacted clay. So the beds have this new soil ... no plants yet.... so adding the ash may be a good thing ? I could add it to the compost bins ... and let it have 6 months in there first ?
Although maybe adding it to the raised beds, and letting it over winter may do soil some good then ?
In small quantities yes. we do the same here.used as a mulch,it CAN destroy plants. Which is a possible use actually.
It wont rot. So no point. uzse it as a sprinkled top dressing for fruit and veg, dig it n, or just pile it up somewhere till it sprouts weeds, Then you know itys OK!
Normally ash is excellent finely spread over lawns, etc. However, the metal content from the tanilised wood is a disaster, so you can't use this. It probably won't much harm grass, but if someone decides to put a vegetable patch there, many vegetables are excellent at extracting heavy metals from the soil and they end up concentraced in the food, which is really bad news. The metals will stay in the ground for decades, so you need to consider whoever moves in after you, even if you never intend to grow food. (This is why there are now restrictions on where you can use tanalised timber, roofing battens being one of the few I believe.)
So, you should treat as waste just as for waste tanalised timber, as the burning will not have got rid of tanalising metals - actually it really concentrates them.
stick the end in the bonfire, then pull it out when its on fire and sniff it- if there's horrible stinky smoke then its some kind of chemical so take it out of the fire and hide it.
Hicksons celcure was green, celbronze was tan, they were both cca waterborne preservatives. I expect other manufacturers offered similar colours.
Nowadays the name remains but chromium and arsenic aren't used other than in specific building use.
Plainly timber arising from renovations, offcuts and old fencing will reamin a disposal problem for some time. As far as I can see the only approved route outside of licensed incineration is recycling for industrial board making.
OTOH burning is reasonably OK, if the products remain at ground level, and gradually seep back to whence they came. Namely the ground, in reasonably dilute concentrations.
There is actually huge case for centralised domestic waste burners, whose combustion products are scrubbed with water spray, the resulting soups being a source of interesting chemicals, and whose slag is probably mineral rich enough to be reprocessed for metals, at least.
That may have been the case once when there were 1/3 the population in England and very few industrial products to burn but nowadays groundwater pollution is a big issue. It was the reason for much of the move away from landfill rather than lack of holes in the ground.
For 20 years I worked on an estate where the grand house had 1700 gallon water tanks filled by a hydraulic ram running off spring water. They had to move to mains water in around 1980 because the spring had become contaminated by heavy metals, thought to emanate from a public car park 700 metres away on higher ground where stolen cars were regularly torched.
The point is that the ecosystem is robust enough to take some injuries but when 50 million people dump on it ...
This is a different, and controversial subject, but yes it does seem that the rules on waste, separating weee, recycling batteries etc are aimed at making it easier to clean the flue gases from waste incinerators.
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