A customer in Virginia called us last year. He was expanding perlite for greenhouse mix. His product looked good most of the time, but every few batches he'd get complaints about black specks. Not a lot – maybe ten or fifteen dark grains per bag. But his buyers were big greenhouse operators. They didn't want any.
He tried everything. Screening didn't work because the dark pieces were the same size as good perlite. Hand picking at the bagging station? Two people with tweezers. You can imagine how that went.
The problem starts with the crude ore. Perlite comes from volcanic glass. But it's never pure. There are always darker parts – obsidian, iron-stained chunks, sometimes small black stones. These don't burn off in the expansion furnace. They just come out looking like burnt rice.
So he called us. We make optical sorters for minerals. Not just perlite – feldspar, quartz, barite, you name it. We told him we weren't sure if our machine could handle expanded perlite because it's so light and fluffy. Normal sorters are built for dense, heavy rock. Perlite floats around on the belt.
We spent a week on it. The first test was a disaster. The air jets blew the good perlite off the belt along with the bad stuff. We had to turn down the air pressure, slow the belt, and add a vacuum hood to hold the material down. After about forty adjustments, it worked. The machine pulled out the dark pieces and left the clean white perlite on the belt.
His raw expanded material had maybe 2-3% dark impurities. After one pass, it dropped to under 0.5%. That was good enough for his greenhouse customers. He bought the machine. That was fourteen months ago. He's shipped about 3,000 tons since then. No more complaints.
The machine we used is a standard model. Same one we sell for other minerals. But the perlite setup needs a lighter touch. We change the belt speed, the air nozzle timing, and the camera sensitivity. Nothing special. Just time spent watching the material go through.
We're Anhui Oursort in Hefei. If you're dealing with dark specks in your perlite – expanded or crude – send us a few kilos. We'll run it on our test machine and show you what comes out. No promises until you see the video.
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