Mine tailings recycling

[mickmac]

I have a lightweight mortar from Lead/Zinc tailings. The tailings had a high sulphate content that has been reduced to 0.28% water soluble sulphate and 1600ppm sulphate. If crushed, could this be used as a lightweight aggregate in concrete?

 

[SlideRuleEra]

I have a lightweight mortar from Lead/Zinc tailings.
If crushed...

Stop right there. Intentionally releasing residual lead into the environment... "Basic Information about Lead Air Pollution"

You will wind up in court... and likely loose.

 

[JedClampett]

I've got this question before on several "magic" ingredients. Lime sludge, other water and wastewater by-products. And my answer is the same; Manufacturers who make these materials (mortar, lightweight aggregate), have cheap sources of these materials already. Why are they going to introduce a new waste product that they have two track and will land them in court in the future? Unless your pay them to use it, they've got no interest and possibly not any interest even then.

 

[mickmac]

All toxins have been successfully bound and immobilized sufficiently. So much so that the formed product has been assessed under the Dutch Soil Quality Decree. It is suitable to be used beside water courses. This material if blended into a concrete would also be deemed inert for landfill purposes. I have used two different immobilizing additives that wrap up the toxic metals on a geological time scale. I think I'll continue in my quest!

 

[TigerGuy]

This actually sounds interesting. My wife worked for a pioneer in nano-technology some years back. They were doing all kinds of crazy stuff, but it worked.

It's not that we don't believe you, but we've all been fooled before. If your process and product work, and can be utilized in a cost-effective manner, I look forward to reading about it.

 

[mickmac]

I have been working on this for about 10 years on and off. I have recently revisited the process as the mine company is running out of space at the tailings dam. I've had the tailings briquetted with a low cement content (with additive) and at low moisture content. The pellets pass the drop test from 2m without breaking. UCS of 3.0MPa.
Below is the leachate test result. My question remains. If I want to make a lightweight aggregate, which will be used in a dry environment, surely a water soluble sulphate figure below 0.5% should suffice?

Max. Value Leaching value

mg/m2 mg/m2
Antimony 2.2 1.2
Arsenic 65.0 0.4
Barium 375.0 38.4
Cadmium 1.0 0.0
Chromium 30.0 0.2
Cobalt 15.0 0.6
Copper 25.0 0.4
Mercury 0.4 0.0
Lead 100.0 2.4
Molybdenum 36.0 0.2
Nickel 20.3 1.0
Selenium 1.2 0.1
Tin 12.5 0.6
Vanadium 80.0 0.4
Zinc 200.0 2.2
Fluoride 625.0 9.6
Bromide 168.0 7.7
Chloride 27,500 721
Sulphate 41,250 968

 

[SlideRuleEra]

mickmac - I apologize for my offensive statement. Now that a I understand you are working with stabilized mine tailings, I can appreciate what you are trying to accomplish.

In the early 1980's I was directly involved with design/construction/initial operation of facilities for my company's (electric utility) early adoption of large scale waste product commercialization:

Pulverized coal fly ash for use in concrete.

Pulverized coal bottom ash for use as aggregate of road beds & concrete.

Stabilized flu gas desulphurization (scrubber) sludge for environmentally responsible land fill.

In the late 1990's, same type work using scrubber sludge to produce a gypsum-equvalent product for wall board manufacture.​

If I may offer a (hopefully) constructive suggestion:

Refer to "stabilized mine tailing" to keep others from jumping to the conclusion (like I did) that your product releases lead.

Our projects took many years to convince regulators and the public that stabilized waste products are safe. Perhaps using wording such as "stabilized" will invite questions so that you can explain and educate.

 

[mickmac]

Absolutely no offence taken SlideRuleEra. I welcome all criticism. I'm glad you agree that it's difficult to convince the naysayers.
If you always do what you always did, you'll always get what you always got!

 

[SwinnyGG]

This is a tricky question.. I'm not sure anyone is going to be able to give you the simple yes/no you seem to be after.

There are other factors not discussed, and not evident in your test data, that affect the durability of concrete against sulfate attack. For example, C₃A content matters quite a bit in relation to the quantity of available sulfate reactant.

On the face of it, it sounds possible, but it sounds like you have research left to do.

 

[mickmac]

The modified/immobilized/stabilized tailings were cured saturated in mine water for two years prior to leachate testing. As I have alluded to before, the heavy metals, chlorides and sulphates have been locked up unable to leach.

Hydraulic backfill in this mine is problematic with constant breaches of cemented material in the stopes. Highly sulphidic.

I have also recorded an increase in UCS for a roller compacted concrete modified with one of my additives from 38MPa to 60MPa in a timespan from 28 days to one year.

As for C3A, I've been using a blend of 70/30 GGBS/OPC, so not just as relevant, I think.

 

[swazimatt]

Safety in Design is something all designers should consider. This takes into account all safety aspects of a design from investigation to construction and end of life decommissioning. While the leachates are locked up now, what will be the case when the item it is used in is decommissioned in 50 or 100years time?