As the pulp processes are increasingly closed, the importance of following how and if the composition of the sludge changes to ensure that the separation works fully increases. Separation of green liquor sludge from green liquor acts as the kidney of the chemical pulping processes.
When analyzing metals in green liquor with green liquor sludge, it is important to know how the customer wants the samples analyzed. What we need to know before analysis is whether the sample should be analyzed on a shaken sample (with green liquor sludge) or whether it is the metals in the green liquor (sedimented sample) that are of interest. When analyzing green liquor, the sample is peroxide treated and analyzed using standard addition technology with ICP-OES.
With the green liquor sludge that is sedimented or filtered out during the sludge separation, many metal compounds disappear from the recycling process, which otherwise cause a lot of problems in the lime cycle. The green liquor must be sufficiently clean and free of green liquor sludge for the subsequent causticization.
With an increasing degree of closure in the pulp process, the levels of process-disrupting metals increase and thus the risk of problems. For example, increments can form in pipes and heat exchangers that reduce their efficiency and filters can also be adversely affected.
With our analyzes of green liquor and sludge, it is easy to keep track of the process-disrupting metals and solve problems that arise later in the process but which have their cause in the separation of green liquor sludge. It is important to keep track of not least aluminum and magnesium in the lye cycle. Therefore, the sludge separation must work and not let sludge through with the green liquor.
The sludge is separated from the green liquor and then the fractions are treated separately. The treated fractions are then pooled and analyzed with ICP-OES. The result shows the constituent metals and their contents.