How discarded diatomite marls became a new source of wollastonite
The ceramic industry depends heavily on mineral raw materials that are often imported, energy-intensive, or both.
At the same time, many quarries accumulate large volumes of “waste” that quietly sit in tips and dumps.
What if part of that waste were not waste at all, but an untapped resource?
In our recent study, we tested exactly this idea: producing synthetic wollastonite (CaSiO₃) from diatomite-rich marls discarded in Spanish diatomite operations — and then using it directly in ceramic tile bodies.
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From quarry residue to industrial mineral
The starting material is deceptively simple.
A diatomaceous marl from waste tips near Hellín (Albacete) contains both:
• silica (from diatomite)
• calcium (from carbonate phases)
In other words, the exact chemistry needed to form wollastonite.
Instead of adding reagents, we simply calcined the raw waste at high temperature.
X-ray diffraction results show that:
• at 1000 °C → incomplete reaction, residual silica
• at 1050 °C → wollastonite becomes dominant
• at 1100 °C → similar phases but higher energy cost
The optimum condition was 1050 °C, where wollastonite forms efficiently without unnecessary firing.
So a quarry residue becomes a functional industrial mineral using only heat.
No chemical additives.
No complex synthesis routes.
Just thermal transformation.
Why wollastonite matters in ceramics
Wollastonite is widely used in ceramics because it:
• promotes liquid phase formation during sintering
• improves dimensional stability
• controls porosity
• enhances mechanical strength
• can lower firing temperatures
Spain imports natural wollastonite for these purposes.
Producing it locally from waste changes the equation.
Less transport.
Less extraction.
Lower cost.
Lower environmental footprint.
And potentially a circular supply chain.
Testing it in real tile bodies
The crucial question was not mineralogy, but performance.
We replaced calcium carbonate or natural wollastonite in white-ware tile formulations with the synthetic material.
The results were consistent:
• viable ceramic bodies
• adequate mechanical strength
• good whiteness
• controlled porosity
• and, most importantly, lower firing temperatures
Compared with the reference composition, the working temperature dropped by roughly 60 °C.
In industrial kilns, even small reductions in firing temperature mean significant energy savings and lower emissions.
For a sector that fires millions of square meters per year, this difference is not trivial.
It is structural.
Trade-offs and practical lessons
The method is not without challenges.
The synthetic powder showed:
• narrow particle size distribution
• relatively low specific surface
• soluble salts (Ca²⁺, SO₄²⁻)
These factors affected slurry deflocculation and compaction during processing.
In practice, this means:
• adjustments in deflocculants
• or washing/milling steps to remove salts
But these are manageable industrial optimizations, not fundamental barriers.
The core result remains: the material works.
A broader perspective
This study is not only about wollastonite.
It is about how we classify resources.
Mining and industrial sites often separate materials into “ore” and “waste”.
Yet chemistry does not respect those labels.
With minimal processing, a discard can become:
• a substitute for imported minerals
• a lower-energy feedstock
• a circular economy input
In this case, a marl heap becomes a ceramic raw material.
Not by adding complexity, but by recognizing value already present.
Sometimes sustainability is not about inventing new materials.
It is about looking again at the ones we already have.