The Navigator Company: Valorization of carbonate sludges

The Navigator Company recycles carbonate sludges, a waste product of their pulp processing and production stage. The sludges are partially fed into the lime kiln, to produce white liquor which, in turn, is used in the production of pulp.

The surplus of carbonate sludges is used as a raw-material to be incorporated in the production of Precipitated Calcium Carbonate (PCC), one of the main components of Navigator's wood free paper, reducing the overall consumption of fresh raw materials.

The PCC production takes place on site through a cooperation partner. The partnership and colocalization result in several win-win benefits: minimized sludge deposition in industrial landfills and reduced associated cost for Navigator; reduced mining of limestone (the fossil raw material equivalent) and the associated need for supplier management for the partner; and avoidance of transport cost and emissions associated with a traditional sludge disposal and PCC production chain for both sides of the partnership. 

Company in brief

The Navigator Company is an integrated forest producer, whose end products are pulp & paper, tissue and energy. Navigator is Portugal’s largest national added value generator, accounting for approximately 1% of GDP, and third-largest exporter.

As a forest-based industry, it promotes the transition to a low carbon and circular future across its value chain: processes use 90% of materials from renewable sources, return 80% of water to the environment and have a 80% waste recovery rate. Besides investing in R&D projects in the Circular Bioeconomy, the company is also establishing partnerships to further improve circularity.


Precipitated calcium carbonate (PCC) is an extremely versatile coating aid, filler and pigment that is employed in a wide variety of commercial products, including Navigator’s uncoated woodfree paper. It’s a refined natural form of limestone which can be produced using several techniques to selectively extract calcium from slag materials.

The carbonate sludges resulting from Navigator’s pulp manufacture, which are very rich in Calcium, are recycled and partially fed into the production process. As the feasibility of processing them in PCC mills to produce high quality PCC was demonstrated, it triggered the opportunity of replacing standard raw materials with a circularity approach.


The project is to use the surplus of carbonate sludges as a raw-material for the production of PCC. Since all PCC incorporated in Navigator’s paper is produced onsite through a cooperation partner (independent PCC Mill), this has all the ingredients for tremendous success.

Yet, lime sludge is still classified as processual waste and, according to Portuguese and EU Legislation, final users must have a specific license for its processing , representing some bureaucratic burden and clearly standing as a main barrier to expanding the initiative at scale.

Sustainability criteria

This initiative and partnership with onsite PCC mills is a good example of industrial symbiosis within the concept of circular economy. The main environmental outcomes consist in 1) minimizing sludge deposition in industrial landfills (a 30-40k ton reduction per year took place in one site), 2) reducing the mining of limestone (the fossil raw material equivalent); 3) reducing all direct and indirect GHG emissions related to the mentioned benefits.

Business case

Besides the environmental benefits resulting from this initiative, which contribute to the reduction of the overall consumption of fresh raw materials and to climate risk mitigation, other main business return refers to improved financial performance for both companies in the partnership: Navigator has reduced costs regarding waste management and PCC Mill company has cheaper raw material.

Such an initiative would also return extra benefits from advocacy of its positive outcomes and from “green” certification (tax breaks, …).

Next Steps

Navigator will engage in efforts to help declassify lime sludge as waste and make the transition to a by-product classification (secondary raw material), enabling it to be used in the production of PCC in all Navigator’s Paper Mills. The main goal is to expand the viable applications for this by-product and scale-up the pilot initiative and its benefits, which represent an interesting step forward in circularity.

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