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Coal Mining Water Treatment"The impacted waters from both active and decommissioned coal mines vary greatly, depending on the age of the workings, the age of the associated soil heaps and many other factors, including the local geology."
Coal waste water treatment process

Coal Waste Water Treatment Processes

Some of these waters can be strongly acidic and can contain high levels of dissolved salts and heavy metals. Others can have a near neutral pH with lower concentrations of heavy metals but with a higher hardness and higher concentrations of silica and sometimes phosphates.

Miwatek is able to design and construct coal mine water treatment plants that can recover high quality drinking water from all of these different coal impacted waters and which are able to accommodate the quality and the quantity variations that typically occur over time and season by season.

A typical water treatment process for coal impacted water would include:
  1. A first stage where all the ultra-fine coal and suspended solids, if present, are removed from the feed water using the appropriate technology for the water quality that is to be treated. Sometimes, this stage can be achieved as part of the following stage.
  2. A heavy metals, silica, phosphate and hardness removal stage using a chemical precipitation process.
    • Where components within the impacted water have sufficient potential for the creation of reusable by-product(s), then the chemistry can be arranged so as to optimize their reuse potential. This often requires the use of caustic soda as the principal reagent.
    • By using caustic within this stage, most of the risks associated with scale formation within the subsequent RO stage(s) can also be eliminated.
  3. The product from the chemical precipitation stage would then go through a clarification process followed by pH adjustment, ultra-filtration and reverse osmosis stages, so as to create the product water.
    • The selection of the chemical pre-treatment and the specific selection of the UF and RO equipment are the key to ensuring that this water reliably complies with the particular requirements of the Client.
  4. The remaining brine would then be reacted, using proprietary process technology, to produce gypsum and a weak caustic solution. This solution would be a suitable reagent for the initial chemical precipitation stage and is usually able to supply the whole of that reagent requirement.
    • The use of this solution makes the reagent cost for the chemical precipitation stage essentially the same as if a combination of lime and limestone had been used directly.
    • For those impacted waters where the sodium and the chloride concentrations do not exceed the reuse or discharge criteria for the recovered water, the process arrangement and control strategies that have been developed and honed within Miwatek are able to utilize all of the brine within the overall treatment process.
    • Where the sodium and/or the chloride concentrations exceed the reuse or discharge criteria, an appropriate portion of the brine would be put through further concentration steps so as to recover the maximum proportion of reusable water.
    • Normally, the Miwatek process would be able to achieve 100% recovery of the impacted water, making the mine site into a Zero Liquid Discharge (ZLD) facility.
Additional process steps would be added if and when they are needed. These could include:
  • FOG removal (fuels oils and greases)
  • Uranium or other radio nuclide removal using ion exchange technology
  • Ion exchange modules to remove nitrates, etc.
  • Sludge de-watering as needed to suit the residue reuse or the local disposal arrangements.
  • Recovery of reusable salts from any excess brine.
The installed process would provide a cost effective, practical and reliable solution. In addition, it would be designed to suit the analysis of the impacted water and the expected variability over time of both the analysis and the flow. The design would also take into account the whole life cycle cost, including the disposal options for the precipitation residues and for any brine that cannot be recycled within the process. The Miwatek process is modular, making feed water flow and quality changes easy to manage. In most cases the modules can be integrated with existing infrastructure.