Could mining really be this easy? Cut the ore from the earth like a steady-handed surgeon, and then mend the wound with the salvaged skin of overburden and gangue. Surely we are not so lucky – we’ve forgotten the tailings – what to do about those pesky tailings?
“Paste those tailings!” cries an exuberant consultant from a continent down-under.
What could this mean? What is paste and why should I care? We’ll try to address those questions here.
Paste tailings are a variety of thickened tailings, so called due to their likeness to toothpaste, or tomato paste if you are among those who prefer food analogies (floc curds, soupy tailings, etc.). Though paste tailings will neither whiten your smile nor bulk your spaghetti sauce, this species of tailings works wonders on mine managers, satisfying an appetite for reclaim water and workable soil. Eli Robinsky first noted the benefits of thickened tailings at the Kidd Creek Mine in Timmins, Ontario back in the 1960s. The support for paste tailings has been growing ever since, though some tailings folks are still not comfortable with the term.
Paste tailings exhibit a pseudo-solid behaviour – that is, they are amicable and stay put most of the time, but may flow somewhat reluctantly given a push in the right direction (something like a junior engineer). For this reason, paste tailings and other forms of thickened tailings are said to stack under most conditions, an inspiring accomplishment for something once slime. A yield strength of 200 Pa is suggested by Richard Jewell and Andy Fourie as the lower bound for paste tailings, as described in their preeminent treatise, Paste and Thickened Tailings – A Guide (2006). Paste is an intriguing material, capable of supporting mine stopes long after the miners have moved on. Paste has an equally impressive talent of forming gently sloping, stable surface deposits – as functional as they are elegant.
Paste tailings are thick by nature – think of that toothpaste you used this morning (that you should have used this morning) – containing more solids than water, by weight. Where did all the water from the slurry go? Back to the plant, of course! In fact, it never left the plant. The mine manager sleeps well knowing that her process water has evaded exposure to the elements – the sun and the wind. She knows that once that water is out there, it’s hard to get back. The benefits of paste tailings have long been recognized in arid environs, though their application is broadly applicable beyond the deserts, too.
So what do I do with all this paste, née slime? As Robinsky proposed, we can put it back in the mine, or we can build great stable deposits of it on the surface. It all depends on your mining method, reclamation objectives, curiosity, and imagination.
Maybe that paste tailings stack would make an idyllic slope on which to grow shrubs and sweet clover – enough to bring the deer, bear, and birds back to the reclaimed mine? There is no right answer on what to do with the stuff, but rest assured there are many options available and experienced consultants willing to point you in the right direction.
Cut, paste, and click your way to a better understanding of paste technology at this link.
Why doesn’t everyone use paste? You need more thickeners and costly high maintenance PD pumps in the mill, if thickener breaks down the mill is down. If paste freezes in pipeline when pump breaks down good luck thawing the pipe. A tailings basin provides a good water storage buffer for excess water recycling. Paste requires more shifting of discharge points as it builds up so operating complexity. Large land area may be required as paste spreads out while conventional tailings can have a smaller footprint (but higher) and use coarse fraction for dam raises. Paste dam raises may require costly earthfill. One needs to look at the big picture and not only one side.
this is very informative sir