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Ash leaching

Valmet's ash leaching solutions offer solid performance for a wide range of ESP ash qualities.

The first systems from Valmet were delivered already in 2004, and Valmet has continued to develop the technology ever since.

Valmet Ash Treatment is a simple, robust process with excellent, long-term performance.

The ash leaching process

The ash leaching process begins with mixing the ESP ash with water. Non-process elements dissolve in the water, while the useful chemicals mostly remain as solid particles.

The solids are separated with a centrifuge and returned to the mill. The solution is rich in Chloride and Potassium and is sent to wastewater treatment.

Several strategies

An ash leaching plant can be operated in several ways. It can be set to either maximize the removal of non-process elements, or to maximize the recovery of useful chemicals.

When more water is added, more ash dissolves and more impurities are removed. But this also dissolves more of the useful chemicals. When less water is added, fewer impurities are removed, but more of the useful chemicals are recovered. 

The ratios can be adjusted to meet the current need in the mill.



Ash from modern recovery boilers contains high levels of carbonates. In theory, this is not much of an issue for an ash crystallizer, but because the carbonate level changes the solubility, the ash leaching process loses performance.

One solution is to lower the pH with sulfuric acid. This does however not not work for all mills. But Valmet’s two-stage ash leaching process – AshLeach Duo – offers good performance. This process offers many of the benefits of an ash leaching plant, with a performance that is close to that of a crystallizer.

Start and stop

Starting and stopping an ash leaching plant is relatively uncomplicated. This means that it is possible to run it only when it's needed.

Many mills use this to optimize their treatment of the ESP ash, and keep levels of unwnated chemicals at the desired, low target levels.


Our expertise is at your service

Our focus is to bring your performance forward utilizing our extensive experience and in-depth knowledge of pulp process technology. Get in touch with our experts through your local Valmet office, or the link below.