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Removal of salts and sulfates from solid waste
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Get them answered by the team at RHI Magnesita.
Background

RHI Magnesita is the leading global supplier of high-grade refractory products, systems and solutions which are critical for high-temperature processes in a wide range of industries. With a vertically integrated value chain, RHI Magnesita serves customers around the world, with around 15,000 employees in 47 production sites, 7 recycling facilities and more than 70 sales offices. 

 

To lead sustainable development in refractory industry, RHI Magnesita is working to optimize the use of raw materials in alignment with circular economy best practices. 

 

For this to be possible, in some cases it is necessary to pre-treat circular minerals (recycled refractory products returning from customer) in order to ensure the properties required for final application. This is the case, for example, of raw materials with high alkali content, which need to be removed before use. 

 

The recycling raw materials are, in fact, refractory bricks with varied chemical composition, but divided in two groups: magnesian (>75% MgO) and non-basic(>60%Al2O3). Other compounds include metal oxides such as SiO2, Fe2O3, CaO, among others. 

 

Alkalis occur in this matrix as Na/K salts and sulfates are also present. The content of these compounds can reach up to 3%. They come from the thermal processes in which refractory are used. In these environments, the alkalis are volatilized and infiltrate the bricks. Upon reaching the coldest parts of the refractories, the alkalis are reprecipitated in the form of salts. 

 

We are eager to partner with experts in refractories but also welcome collaborations with researchers and companies focused on adjacent spaces, such as ceramics, composites, construction, mineral processing, extractive metallurgy and mining.

What we're looking for

We are seeking technologies for the removal of alkalis present in post-consumer refractory bricks, with a particular focus on recovering the metal oxides MgO (magnesium oxide) and Al2O3 (aluminum oxide).

Solutions of interest include:
  • Washing
  • Leaching
  • Thermal treatment
Our must-have requirements are:
  • Removal of alkalis to the levels required for final application.
  • The solution cannot interfere with the properties of the refractory products (like refractoriness, mechanical stability, chemical stability, dimensional stability, thermal shock stability, among others).
Our nice-to-have's are:
  • Solutions at higher maturity stage are preferred, but lower maturity solutions are also welcome.
  • Competitive cost (or potential for competitive cost).
  • Applicable on a large scale for Industry (thousands of tons).
What's out of scope:
  • Solutions should not generate any component which is hazardous for health or environment
Acceptable technology readiness levels (TRL):
Levels 3-9
What we can offer you
Eligible partnership models:
Supply/purchase
Licensing
Co-development
Sponsored research
Benefits:
Sponsored Research
Funding is proposal-dependent, based on technology potential
Expertise
We offer the expertise of our team of scientists for collaboration and guidance during the development of the project.
Facilities and Services
Our research and development facilities are fully available for the project. Our R&D centers a count on modern equipment, technical expertise and partnership with leading technological partners.
Reviewers
TR
Tamara Ribeiro
Raw Materials & Minerals Technology Expert
JR
Juan Rosenzweig
Innovation Manager
Q&A with RHI Magnesita

The Q&A is now closed.

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Q.
Are these alkali compounds on the surface of the solid products, or are they "soaked in" to the product all the way through? One would require a washing effect, the other would need an extraction or leaching method.
3
A.
The alkalis are deposited in refractories by mechanisms like gas phase infiltration, that is, they are found inside the bricks. There is, however, a certain level of permeability that can favor washing processes.
TR
Tamara Ribeiro, Raw Materials & Minerals Technology Expert , RHI Magnesita
February 29, 2024
Is this response helpful?
0
0
Q.
Can you share more about what the recycled materials look like? (i.e., chemical composition, mineral composition, morphology, etc.)
1
A.
We are talking about refractory bricks, with varied chemical composition, but divided into two large groups: magnesian bricks (>75% MgO) and non-basic bricks (>60%Al2O3). Alkalis occur in this matrix as sodium and potassium salts and there is also the presence of sulfates. The content of these compounds is also variable but can reach up to 3%.
TR
Tamara Ribeiro, Raw Materials & Minerals Technology Expert , RHI Magnesita
February 29, 2024
Is this response helpful?
0
0
Q.
In reference to the "raw materials with a high alkali content, which need to be removed before use" section: For instance, are these alkali components different from the bulk mass of the refractory material, and how do they get there, are they formed during the use of the refractory material?
1
A.
Alkalis are not present in the original composition of refractories. They come from the thermal processes in which refractory linings are used. In these environments, the alkalis are volatilized and infiltrate the bricks. Upon reaching the coldest parts of the refractories, the alkalis are reprecipitated in the form of salts.
TR
Tamara Ribeiro, Raw Materials & Minerals Technology Expert , RHI Magnesita
February 29, 2024
Is this response helpful?
0
0
Q.
Can you link to literature or give general information as to the state of the art procedure that is currently used for removal of the alkali salts?
1
A.
The state of the art regarding alkalis removal are technologies related either to leaching or washing techniques.
TR
Tamara Ribeiro, Raw Materials & Minerals Technology Expert , RHI Magnesita
March 27, 2024
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0
0
Q.
What would be the targeted alkali content or refractoriness? What would be the maximum temperature for thermal treatment? And how many alkali-containing refractory phases (like NaAl11O17) are present?
1
A.
- Final alkaline content should be as low as possible. Less than 1.5% is desirable. - Refractory materials withstand high temperatures (above 1200oC). Therefore, the maximum temperature for thermal treatment will depend much more on the proposed solution than on the "decomposition" temperature of the materials to be treated. - The main alkali-containing phases are syngenite and sylvite, but other phases are possible.
TR
Tamara Ribeiro, Raw Materials & Minerals Technology Expert , RHI Magnesita
March 20, 2024
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