Ash2Salt

An unique process that recover clean commercial salts from fly ash

Background

Incineration is a common method for municipal solid waste treatment since it reduces the amount of waste, enables destruction of pathogens and organic contaminants, as well as possible recovery of energy in form of heat and/or electricity. Figure 1 visualize how fly ash is produced through incineration.

Even though incineration substantially reduces the waste’s volume and mass, bottom- and fly ash are produced in large quantities. The fly ash is captured in the incineration plant’s air pollution control and is often considered to be a hazardous waste when being disposed in a land fill. This is due to a high content of water-soluble chlorides and heavy metals in the fly ash. Because of its hazardous properties, it is expensive and problematic to manage.

Fly ash from Sweden is today mainly stored in special constructed land fills or on a discharged lime stone mine in Norway. The land fill and storing alternatives are not sustainable in a long-term perspective, but are temporary accepted because there is a lack of attractive alternatives.

The high chloride content of the ash makes it impossible (with current legislation) to land fill it without proper pre-management that avoids leaching of chlorides and stabilizes heavy metals. This pre-management is expensive and today only a few players can handle the fly ash. About 50% of Sweden’s produced fly ash is exported to Norway.

Solution

The Ash2Salt process is built upon two preceding steps. Fly ash is washed with water in the first step resulting in a washed ash (residual sand), and a leachate of mainly chloride salts and heavy metals that continues to step two.

In step two, sulphides are used to precipitate heavy metals from the leachate and the resulting chloride saturated liquid then continues to the Ash2Salt process. Ash2Salt process separates CaCl2 (aq), NaCl, and KCl by the use of a single evaporator. In addition, water extracted from the evaporator is recirculated to the initial washing step.

In a wash-plant for fly ash without the Ash2Salt process, following limitations exist:

  • The wash-plant must have permission to discharge large amounts of chloride effluents
  • The chloride content of the ash can vary depending on what the incineration plants burn resulting in different amounts of chloride effluent must be discharged.
  • A need for fresh water

The main advantages of having the Ash2Salt process are:

  • Enable washing of fly ash without a discharge of chlorides
  • High tolerance for variations of chloride content in the ash
  • Creates a source of income by producing pure commercial salts and ammonia
  • No need for fresh water since the Ash2Salt washes fly ash with land fill leachate and process water.

EasyMining’s patented Ash2Salt process is unique and can extract commercial salts from high chlorine containing fly ashes. After washing, the ash residue can be land filled without an exemption for high chloride contents. The Ash2Salt process can extract commercial grade:

  • Potassium chloride (KCl)
  • Sodium chloride (NaCl)
  • Calcium chloride (CaCl2)
  • Aqueous ammonia solution or ammonium sulfate