Monday, 14 March 2016

Membrane technology to recover metals and reuse mine wastewater

Membrane technology has become widely used in various industries in recent years, but has been slow to be adopted in the ever conservative mining industry. One of the main advantages of membrane technology is that it works without the addition of chemicals and with relatively low energy use.
Membranes are used more and more often for the creation of process water from groundwater, surface water or wastewater, and they are now competitive with conventional techniques. The membrane separation process is based on the presence of semi-permeable membranes, the principle being quite simple: the membrane acts as a very specific filter that will let water flow through, while it catches suspended solids and all other salts and ions, creating a concentrated stream and a pure water stream. There are various methods to enable substances to penetrate a membrane. Examples of these methods are the applications of high pressure, the maintenance of a concentration gradient on both sides of the membrane and the introduction of an electric potential.
We are therefore delighted to introduce a new company to the MEI fold, Genesys International, who will be sponsoring Sustainable Minerals '16 in Falmouth in June. Genesys is an industry leader in the development and manufacture of speciality antiscalant and cleaning chemicals for Reverse Osmosis (RO), Nano-Filtration (NF) and Ultra-Filtration (UF) membrane systems.
In the past 5 years there has been a dramatic increase in the number of RO, NF, UF Membrane systems used in mining, and in a paper at the conference, Stephen Chesters will identify over 300 mines with potential to use RO/NF/UF membrane technology. There are sixty-one operational membrane plants and fifty-one of these have been commissioned in the last ten years, 65% of which are in gold and copper mines. In precious metal mines, waste water can be concentrated using membrane plant so additional metals can be recovered from barren liquor. Acid mine drainage (AMD) is increasingly treated and then reused or sent off site as a potable supply to the surrounding communities.
Membrane plants can suffer from rapid fouling and calcium sulphate (gypsum) scale. The reasons for this will be explored and new techniques for preventing sulphate scale and to clean fouled membranes will be introduced. Genesys has recently launched a new and innovative method for RO membrane cleaning incorporating micro-bubbles and effervescent reagents to enhance deposit removal. The company is looking to grow its business in the mining industry and is currently working on a number of research projects and is keen to form alliances to service the mining industry world-wide.
 
Twitter @barrywills

7 comments:

  1. This has got a huge potential and very bright future! All mines, struggling for improving grinding efficiency (from SAG or BALL mills) can optimize their process, production, power consumption and achieve higher recovery.

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  2. How does not compare economical with precipitation technologies?

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  3. It's good to add new technology which is more eco friendly and less energy intensive.

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  4. While membranes are typically a more expensive option than precipitation, the two can be complementary. A recent acid mine drainage installation uses a high density sludge (HDS) circuit to capture the majority of heavy metals, but roughly 2,000 mg/l sulfates remain in solution. (Actual dissolved sulfates depends on a number of other factors.) Ultra-Filtration and nano-filtration can capture sulfate ions and reach approximately 10 mg/l; far below regulatory requirements. However, flushing the membranes produces a high-sulfate stream that must then be treated in a smaller HDS flowsheet. Waste from that smaller HDS goes back to the main HDS precipitation circuit while the ~2,000 mg/l effluent (but low volumetric flow) is blended with the effluent of the nano-filters for a final stream that meets regulatory requirements.

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  5. Excellent. Once again, engineering learns from biology, where partially permeable membranes (e.g. cell membranes) are at the order of the day - and have been for 2 billion years.

    Many thanks, Barry, for this posting.

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  6. It would be great if some technical details are also given; at this stage we need not bother much about cost of membrane but should know what is technically feasible with reference to recovery of values and water.
    Rao,T.C.

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  7. There is an increasing adoption of membrane technology for metals extraction and AMD clean up and often both. The paper at the Sustainable Minerals conference will address technical aspects, real case studies and problems encountered and innovations to improve operation of membrane plant. The very stressed mine water quality has historically caused rapid fouling and scaling of membranes. Improvements in antiscalants, membrane cleaning techniques and operator confidence has resulted in more widespread use. An RO plant will typically concentrate up feed water four times (75% recovery) giving a concentrated stream which could now be a pregnant liquor and a pure water stream suitable for process use. The cost benefit analysis is individual for each plant. The attached presentation from a membrane manufacturer gives a useful overview.
    http://www.aiche.org/sites/default/files/docs/conferences/event/c.1_young_suschem_final.pdf

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