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Arsenic and Aluminum ion Removal (3 replies)

9 months ago
Obergruppenfuhrer 9 months ago

Can anyone recommend for removal of arsenic and aluminum ion from the leachate collecting pond? I found some methods but i want to get benefit from your experiences.

John Koenig
9 months ago
John Koenig 9 months ago

We have used our Virotec technology on a number of rocks spoil heaps and tailings ponds to treat and remediate acid rock drainage resulting from past mining operations.

One particular project was at Gilt edge mine site in S. Dakota, USA where ViroMine media successfully treated heavy metal contaminants in acidic leachate and reduced As levels from 35mg/lt down to <0.01mg/lt and Al from 1200mg/lt to <0.05mg/lt.

Evaluation trials were conducted under US EPA controls and demonstrated effective permanent binding of As, Al and other heavy metals using this method.

9 months ago
Obergruppenfuhrer 9 months ago

I think your product bind with the Al and Asas a floc. According to my search, Al and As have reverse process. For example As(III) can be depressed as pH 10 and also As(V) at 10.5 . On the other hand the Al requires an ion exchange process with HCl addition or an cation exchange resin. How can your product realise the geochemical processes for these two impurities?

Dizzy Flores
9 months ago
Dizzy Flores 9 months ago
1 like by David

Maybe start from a fundamental level. Al is strongly pH-dependent and can be removed quantitatively (certainly to levels of environmental concern) by manipulating the pH. This is the standard basis for control of Al.

The management of As is a bit trickier, because with two oxidation states, different approaches may be needed, depending on the redox state. If your leachate pond is oxic, then the As will be present primarily as As(V). The standard water-treatment approach for As(V) is to sorb it to ferric oxyhydroxide, or something similar. This is where the basic chemistry of the Al comes back in: if the pond is toxic and also contains dissolved Fe [as Fe(III)], then raising the pH to remove the Al as Al(OH)3 will also precipitate Fe(OH)3, and the Fe(OH)3 (and probably also the Al(OH)3 at near-neutral pH), will sorb the As(v), and you are set to go to a settling/filtration steps and substantial improvements in your Al ad As concentrations. [There is nothing at a fundamental level different in this than in using the Virotek process - except that one is proprietary and the other is not.]

If the As is present as As(III), you have two possible routes: oxidize the system and follow the above, or consider a biological treatment process that will reduce the As, perhaps to a sulfide-producing level that precipitates the As as a sulfide mineral. Reduction by itself is not a pathway that will assist with your Al, so think about what you can accomplish that simplifies the overall problem most efficiently.

In any case (including proprietary additives), you are not violating conservation of mass - you are moving mass from the highly mobile aqueous phase to the relatively immobile solid phase. You must continue to manage the solids in some way that keeps the solids stable with respect to dissolution. Ordinarily this involves engineered sludge management, because you are quite correct that if you allow the system to evolve to another redox or acid-base state, then the work you did to remove Al and As from solution can be undone.

My experience is that it always is best to try to understand the underlying physico-chemical controls that can be expected to be important. Then one can understand what the basis for one specific approach or another may be, and have a good chance of selecting a technically sound and cost-effective solution. Sometimes that approach may be a proprietary one, or sometimes it is long-understood "conventional" technology. Of course you don't want to inadvertently interfere with a valid patent, but in any case you need to be able to tell your management why you have recommended the approach that you decide to put forward in terms of its technical value and show that you have done your due diligence on how best to execute the strategy that your believe is best.

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