Sebete Mabaleha’s journey started at the National University of Lesotho (NUL), took him to the University of Cape Town (UCT) for his master’s in Chemical Engineering, and now he’s doing a PhD in Chemical Engineering at the University of Adelaide in Australia. But before all that, when he was still a student at NUL, he had a clever idea: what if the piles of waste stone lying around in places like Lekokoaneng could be cleaned and turned into high quality sand to make high-performance concrete, the kind used in big dams, long bridges and high-rise buildings?

Turns out, he was right.

“We looked at this waste that no one cared about,” Sebete says, “and thought—what if it’s not waste at all?”

Sebete began a full-on research project. Later, he worked with a team of other NUL and University of Johannesburg (UJ) scientists as seen in his just published beautiful piece of work in the journal: Particulate Science and Technology; see the link: https://www.tandfonline.com/doi/full/10.1080/02726351.2025.2528131

His goal? To purify sandstone waste and test if it could be used to make manufactured sand, also called MS—a substitute for river sand, which is getting harder and more expensive to find in Lesotho.

Let’s talk about the stone.

It’s called Clarens Formation Sandstone, or, if we think local, Lekokoaneng Sandstone.

You’ll find it across the country, but it’s named after Lekokoaneng village near TY, where it’s mined the most. It’s creamy white, smooth, and easy to carve—which is why it’s used to make tombstones, walls, and decorative pieces.

But here’s something cool—this sandstone was formed about 200 million years ago, when the land we now call Lesotho was still part of the supercontinent Pangaea. Wind blew fine desert sand into massive dunes. Over time, layers of volcanic lava buried and pressed it, turning it into the stone we see today. So yes, Sebete was working with rock that’s older than the Maloti Mountains!

When stonecutters carve blocks from the sandstone, they leave behind a huge amount of leftovers—broken bits, fine dust, and chunks no one uses. These just pile up and create a mess. But what if that mess could become something useful?

Sebete and his team crushed the sandstone waste into powder and studied it in the lab. They used equipment like:

• XRF (X-ray fluorescence) to find out what elements were inside

• SEM-EDS (scanning electron microscopy with energy-dispersive X-rays) to look closely at the shape and surface of the sand particles

What they found was impressive.

The sandstone was made up of about 75% quartz, the mineral that makes great construction sand. The rest included feldspar, clay, and a bit of iron—nothing too serious if handled right.

“Quartz is what gives concrete mortar its strength,” he explained. “And this stone had a lot of it.”

The improve the quartz, it had to be cleaned from other substances. So, the next step was purification.

Sebete tried four different ways to clean the sand:

• Washing with room temperature water (WRT)

• Washing with boiling water (NBW)

• Attrition (ATT)—scrubbing the sand using friction in water

• Washing with sulphuric acid (CSA)

Attrition came out on top. It cleaned the sand best, removing the fine dusty coating that weakens concrete.

The real test came when they used the purified sand to make mortar blocks and compared their strength with that of blocks made from regular river sand.

The result?

The blocks made with manufactured sand were more than twice as strong as the river sand ones.

Yes, twice.

“People assume river sand is always better,” Sebete said. “But our sand was cleaner, more compact, and just made better mortar.”

And there was more good news. The sandstone waste produced up to 84% usable sand, and it had almost no organic content, meaning fewer impurities that interfere with cement hardening.

So what does this all mean?

It means that instead of mining more river sand or importing materials, Lesotho could use its own sandstone waste to make strong, clean construction sand. That’s cheaper, smarter, and better for the environment.

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