Challenge: Intractable saline waste disposal

Intractable saline wastes are residual liquid and slurry streams with high dissolved ionic or suspended solid content, generated at the tail end of an industrial processing or hazardous waste treatment operation. These waste streams are considered intractable as they are no longer amenable to treatment, reuse or recycle, and due to their contaminant load, are often classified as hazardous and therefore regulated, therefore requiring solidification for stabilisation and encapsulation before disposal in purpose built monofills. Industries known to produce such waste in large volumes include mining/mineral processing, oil/gas, waste-to-energy, fertilisers, cement, and PFAS treatment operations. Key challenges with safe disposal of intractable saline waste which are currently facing strong public scrutiny include:

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• Regardless of the extent of waste stabilisation through solidification (using binders such as cement, fly ash, lime, or polymeric material) and efficiency of encapsulation using ponds lined with geotextiles, land disposal of intractable saline residue poses significant risks to the surrounding environment and water systems, due to the hygroscopic nature of salts, and the leakage of leachates generated from dissolution of encapsulated salt. This observation applies to both existing encapsulation and proposed microencapsulation methods for landfilling of intractable saline wastes.

• The proposed micro-encapsulation techniques using various binders mentioned above are invariably expensive, unsustainable, and are mostly based on establishing centralised disposal hubs to become economically feasible, and are therefore largely applicable to small-to-moderate volumes of waste, rather than for large volumes of intractable saline waste generated in industries such as mining and waste-to-energy operations.

• Full life cycle assessments (cradle-to-grave) published for projects proposing micro-encapsulation techniques invariably to point to their high carbon footprint largely due to embodied carbon in the binders.