Investigating the fate of phosphorus in the chemical recovery cycle of kraft pulp mills

Maryam MousaviMaryam Mousavi (ChemE PhD student) supervised by Professor Niko DeMartini is working on the fate of phosphorus in the chemical recovery cycle of kraft pulp mills. As mills tighten water cycles and look to replace fossil fuel with biomass fuels, the buildup of non-process elements (NPEs), especially phosphorus, is a significant concern for the industry.

“In a kraft pulp mill, a high concentration of NPEs in the recovery cycle can cause numerous operational problems such as scaling, corrosion and a high dead load in the lime cycle. The main NPEs are phosphorus, magnesium, manganese, aluminum and silica,” explains Mousavi.

“In the lime cycle, phosphorus can accumulate because it can react with lime particles and form calcium-phosphate compounds that are partially insoluble in the recausticizng process. Therefore, the unreactive lime needs to be purged (for land filling) and fresh lime/lime rock needs to be purchased to keep the amount of reactive calcium oxide (CaO) in the lime at a desirable level depending on the targeted causticizing efficiency,” Mousavi elaborates.

Mousavi’s work will broadly clarify the fate of phosphorous in the lime cycle and provide needed information for evaluating the impact of different technologies for replacing fossil fuels with biomass fuels on NPEs in the recovery cycle, with an emphasis on phosphorous. Her research will generate new ideas about how to recover phosphorus from lime in a form that is useable. Additionally, it will help both industry and society to reach their environmental related goals, as biomass is a renewable energy resource that produces less GHG emissions compared to fossil fuels.

Mousavi’s project could not have happened without the support of the 22 companies from around the world that form the U of T Pulp & Paper Centre consortium. This summer, Mousavi will be heading to Finland through funding provided by the Johan Gadolin Scholarship and Mitacs Globalink Award to investigate the fate of phosphorus in the gasification of bark. She will be conducting this research at Abo Akademi. The initial phases of her research have already been published in the Technical Association of the Pulp & Paper Industry (TAPPI) Journal. It is Mousavi’s hope that her international collaborations will strengthen her ability to have her research industrially applied.