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Reverse Osmosis (12 replies)

Carl Jenkins
9 months ago
Carl Jenkins 9 months ago

Under what conditions is really a feasible option for reverse osmosis plant, to treat Acid rock drainage?

Alan Carter
9 months ago
Alan Carter 9 months ago

There are far more cost effective methods for neutralizing and removing/precipitating metals from leachate streams. So the logical answer would be that using RO to treat acid leachate would only be feasible when the water produced can be sold to recover cost - but don't forget to subtract the cost of treating the brine generated from RO.

9 months ago
Obersturmbann 9 months ago

It would be better to use a traditional or high density sludge liming treatment system, and only install RO to treat high sulphate/TDS after lime precipitation of metals.

Dizzy Flores
9 months ago
Dizzy Flores 9 months ago

It depends on what you mean by "feasible." Assuming that one has reasonable infrastructure (power, roads, water supply, engineering support...), ultra-filtration (including RO - the membranes have to be chemically compatible with the solution to be treated) is certainly technically feasible. The Ashkelon plant in Israel uses RO, and it is the largest desalination plant in the world. Small, portable units, capable of being powered by solar units, are standard issue to modern military units some operating in extremely remote and infrastructure-poor regions.

Whether it is cost-effective is a different question. Firstly, one has to determine what the "effect" is that must be achieved. If one has only to neutralize the solution and control trace metals, then no one would choose RO, because lime addition would always be cheaper and would meet the defined "effect." But lime treatment/HDS cannot control the [SO4] below gypsum saturation in the resulting chemistry, and if [SO4] must be low, then it will not achieve the "effect" and so, although cheaper is not "cost-effective." Waters high in Se would also be problematic by alkaline addition, but bio-treatment might be cost-competitive with RO.

All water-treatment methods have to address the management of waste streams - RO has brine, but lime-treatment has gypsum sludge. The laws of thermodynamics, eh? The costs of waste management in ARD control - by any treatment technology - can be very substantial and may pose special technical challenges that can affect decisions in alternatives analyses. 

Tony Verdeschi
9 months ago
Tony Verdeschi 9 months ago

We are using electro-coagulation to great effect/low cost and will go on an industrial scale trial early next year at global coal mining group.

9 months ago
Hauptsturm 9 months ago

Does anyone have reasonably up-to-date figures for the treatment of AMD using RO?

Basic Capex and Opex pre- and post-HDS would be informative.

Ace Levy
9 months ago
Ace Levy 9 months ago

I view reverse osmosis as an option of last resort. While it is effective in reducing total dissolved solids it is both expensive and if not buffered the final product can actually act as a solvent when returned to the environment due to the lack of mineralization in the solution.

Dizzy Flores
9 months ago
Dizzy Flores 9 months ago

Here is a link to a published report on the large-scale RO treatment system operated by the Bingham Canyon Mine (Utah, USA) for dealing with the sulphate plume (SO4 500 - 1500 mg/l) in the Zone A Plume of the Southwest Jordan Valley. The remedial program delivers 3500 acre-feet per year (4.32E+06 m^3/a: 5-year rolling average) of treated water to the local water-supply agency.


Note the emphasis in the article on the site-specific detail of the plume chemistry in terms of RO performance, and therefore cost.

9 months ago
Obergruppenfuhrer 9 months ago

If you are in need of treatment efficiency which exceeds that provided by HDS, I would think that ion exchange would be more attractive than RO for mining applications. Here in Ontario, Canada we do have some mines that are successfully using full time IE in scenarios where the receiver has very little assimilative capacity.

Helena Russell
9 months ago
Helena Russell 9 months ago

RO is a good choice for treating the water after AMD is pre-neutralised. Otherwise, the spending will be a jaw-down one. I visit some mining sites where Zn is enriching in AMD water even after neutralisation due to its high solubility. If regulator requires the AMD after treatment should be a drinkable one, you will have no choice but applying RO.

Dizzy Flores
9 months ago
Dizzy Flores 9 months ago

If you want to use RO as a polishing module to meet discharge (e.g. for SO4, one of the oxyanions that is not controlled by your alkaline addition), our experience is that you

•must clarify and probably pre-filter to remove fine-grained gypsum or other colloids that would foul the membranes, and

•Depending on the total chemistry, you may find that inflow [SO4] has to be below ca.

1500 mg/L in order to avoid excessive gypsum precipitation with adverse impacts of membrane life. Note in the Bingham Canyon example above that they use RO only on the portion of the plume that is < 1500 mg/L SO4 and is neutral pH. They handle large flow volumes, but it is a big plant with significant CapEx and OpEx, especially when calculated out to 40 years.

If one had a small discharge - say seepage form a small audit that does not spike too heavily in flow of low pH, but also low metals and sulphate, then many things are possible that simply are non-starters for large flows with high SO4/low pH solutions.

Courses for horses...

9 months ago
Gruppen 9 months ago

Another alternative not mentioned previously in this forum is hydrotalcite-based precipitation using the Virtual Curtain technology developed by CSIRO, Australia's national science agency. Rapid, in-situ or pump and treat, substantially less sludge generated than lime and potential to re-mine the precipitate given the high concentration factor.

Bill Fraser
9 months ago
Bill Fraser 9 months ago

When we talk about treatment of mine water, RO is simply a unit operation that concentrates contaminated water - not so much a "water treatment" process in its own right. Pre-treatment of mine water and the additional processing or disposal of brine are usually the costly and difficult part of a treatment system that includes RO. In fact, RO racks are relative inexpensive.

If the only goal is to concentrate the mine water then it is appropriate to limit the discussion to pre-treatment and RO. Otherwise, it is quite meaningless to discuss performance of a RO unit without also discussing pre-treatment and processing or management of residuals in the same breath. I find it more useful to think of RO as nothing more than the unit operation that concentrates the contaminated mine water.

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