Hardcoat anodizing dust toxicity

A. Unless you do a dichromate seal of these hard anodized components, I think you are right in considering the dust to be aluminum oxide. And I doubt that aluminum oxide is much of an ingestion hazard since so much of the earth is made of aluminum oxide, and aluminum salts are widely used in water treatment.

However, there are those who feel that asbestosis, silicosis, and similar lung diseases are related not so much to the chemical nature of the contaminant as to the particle size. I have no qualifications to be able to comment on that, but I would be concerned that the exposure limits shown on the MSDS you are referring to may not necessarily accurately represent the possible hazards of the particular particle size your grinding process generates. So I think you are right to be trying to investigate whether there is anything special about your case. I don't know of any research on it, but maybe one of our readers does.

But our lungs are not the best filter for any sort of dust. It doesn't matter what you are sanding or what is causing dusting, you should be wearing a particulate mask when particulates of anything are being generated.

A. Michael,

What Ted says seems 100% right to me ... but 'perception' of dusts gets people worried, often quite unnecessarily.

May I suggest a simple mild steel RECYCLE system. Why Recycle? Because heating 'air' in wintertime costs $$$.

You have 3 options. 1. A mass transfer scrubber design but that is bulky, expensive and tends to plug up. 2) a refined blade type horizontal mist eliminator 3) A 'dump box'.... this consists of, say, a cheap round, deep(Moulded Polyethylene?)tank with a loose lid and 3 outlets. The first outlet in an incomer duct using, say, 2,500 to 3,000 FPM design. This enters the tank from the top OR is a 90 degree bend facing down. The second outlet is the outgoing duct and larger, say 2,000 FPM design and this is ABOVE and dead opposite to the first one. And in between the two is a deflector plate in the middle that forces the air stream downwards. The third outlet is nothing more than a largish drain outlet.

In this manner the bulk of the grindings will drop down to the bottom of the tank.

To refine the process, the outgoing duct should protrude into the tank by an inch or so. Then get some Jaycloth and put it over the end. Ideally you could have a moulded Cap with a loose fitting so that it will hold the Jaycloth, via a screw, in situ.... this outlet duct has to be near the top of the tank...

Now if you wanted to knock out particles to 12 microns, you'd use a good eliminator ... but that costs $$$, induces a higher (max. 1") pressure drop, then you'd need a bottom tank, a pump and a few minor controls in order to constantly spray the beast. ... I have over 3 million CFM of these in service but I don't think that this is warranted in your case.

I hope that this is of some help to you.

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

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A. The smell is a sulfur oxide such as SO₂. The Surface Treatment and Finishing of Aluminum and Its Alloys by S. Wernick, R. Pinner, P.G. Sheasby ⇨
mentions that the anodic film may incorporate as much as 15% sulphate anion, SO₄(-2). Heating via grinding decomposes the sulphate. The heat of grinding may also locally activate the transformation of the gamma-alumina to alpha-alumina, releasing an additional 22 kJ/mol of heat. Get MSDSs for aluminum sulphate (anhydrous) and aluminum oxide powder.

Wet grinding will minimize the heating, smell and dust.

A. Hi again Mike,

You mention smell ... but you don't say a thing about ventilation!

Ideally, you, as you know, should have a hood/hoodlet as close as possible to the odor source. Maybe you have this and everything is to Hoyle but you still get a smell.

Maybe, too, it is one of those smells which are highly odiferous ... in which case perhaps you should consider an 'additive' as there are Companies specializing in 'masking' such as Oderchem, here in Canada.

From a dust capture viewpoint (and I'm not trying to sell you a Rolls Royce) perhaps consider the rough capture data (but that needs fine honing) that I previously mentioned.

And, ah, if the dust is really problematical, I recall once (Cincinnati-Millicron) where one of my vaunted eliminators initially failed and a white powder, which ESCAPED from the mass transfer scrubber (!) passed through. But success was achieved using a wetting agent, TSP [trisodium phosphate ⇦this on eBay or Amazon [affil links] ] ... and then the initial scrubber failed or burnt down and the TSP idea bore real fruit! Another application was removing dry cedar dusts of low micron size which was escaping from a cyclone ... this being a carcinogenic material ... and where a huge jump in efficiency was achieved using air atomizing nozzles to wet out those mini particles.

Food for thought ... hope it helps !

JET DC-650BK Dust Collector
30-Micron Bag Filter, 650 CFM, 1 HP, 1Ph 115/230V


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A. USEPA released a study on airborne dusts and how it affected primarily people with asthma, late last year. This is not associated with the dust problems that followed 9-11 either, altho that would also give you a pause for thought.

For my nickel, I think that you need a point exhaust system such as those sold for welding exhaust. Something as simple as one of those dual bag filter systems sold by several firms aimed at woodwork shops would go a long way to reducing the particle count and would diffuse the smell considerably. Plain old dryer exhaust flex pipe would probably work at the pickup point. It will help and it will also make everyone "feel" better.