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  • Sometimes green saves green – by accident

Photonics Spectra
Aug 2012
Michael Naselaris and Zachary Hobbs - Sydor Optics

Environmentally friendly solutions can have a positive financial impact. In this case study, recycling polishing slurry is shown to be good for the environment and the bottom line.

Just because a project is green doesn’t mean it started out that way. Our story begins with the price explosion of rare earths, namely cerium oxide, which started in September 2010 as a result of the newly imposed Chinese export quota restricting availability. Cerium oxide is used by optical component manufacturers around the world in very fine abrasive slurry to polish optics.

This export quota resulted in frequent price increases over a six-month period – with constant uncertainties about the delivery of product. Companies were given two days’ notice before arrival of the material in the US. China supplies more than 95 percent of the world’s rare earths, so the quota meant that prices increased about 600 percent over a short period.

Optics cannot be manufactured without cerium oxide. Many optics companies in the US and around the globe started worrying about the availability of the material and started to purchase as much as possible in advance for inventory. Some suppliers were putting their customers on allocation based on annual purchases. Our company was lucky; as a large consumer of this material, we had options to make larger purchases when it was available, thereby avoiding any downtime. We went so far as to purchase material by the ton.

Cerium oxide is a vital ingredient in the optics polishing process. As availability declines, recycling this rare earth can help optical component manufacturers save money. Photos taken by Managing Editor Laura S. Marshall at Sydor Optics.

Still, we use approximately 750 kg per month, and with restricted availability, we started looking at alternate suppliers, hoping to purchase even more, but achieved minimal success. By accident, we met Mark Mayton of Flint Creek Resources, a local chemical engineer who was consulting with a local company making a cerium additive for diesel fuel. The necessity for continuous product warranted investigating the option of recycling or reusing the spent cerium oxide. Our thoughts were on reducing costs and ensuring constant supply, but we welcomed the byproducts of recycling such as reduced waste stream.

Particles do not break down significantly during the polishing process, making them a strong candidate for recycling. Over time, polishing slurry becomes filled with glass swarf, along with trace amounts of polishing pad material and tooling material. Removing these contaminants allows for easy reuse of the cerium oxide particles.

We started the process by collecting what we easily could off the machines. The spent slurry was allowed to settle for about a week, and then the concentrated solids were removed for separation of cerium from glass swarf and other contaminants. Once separated, the cerium was remixed with dispersion and suspension additives, and the recycled slurry was returned in reusable containers at a concentration of 50 percent solids.

Although our savings initially were minimal, we needed to overcome some of the challenges of collecting more of our spent cerium oxide. We originally captured about 15 percent for recycling, but now we are above 40 percent – with efforts in place to increase this to 80 percent. We examined other methods of collecting even more used slurry, such as scraping the slurry trough in the polishing machines, where polishing slurry tends to settle. We evaluated the amount lost in drag-out, when parts and tooling are removed from the machine after processing. We also discovered better solutions for collecting more slurry from the machine cleaning process at end-of-day shutdown.

Now that we are more conscientious about what enters the waste stream, the recycling process has resulted in considerably less waste, lower cost and no noticeable difference in performance with regard to stock removal, surface roughness or polishing times. With the reduced waste came a reduction in charges for added municipal water treatment of our waste stream. Our goals now are to reduce discharge to drain to as close to zero as possible while improving recycling efficiency to greater than 80 percent.

So far, thanks to this recycling process, we have seen a 10 percent cost savings per month; recycled slurry currently makes up 20 percent of the slurry used in our polishing operations, and 50 percent of our polishing operations now use recycled slurry. Since we started this process, back in early 2011, we have been contacted by about a half-dozen other companies in the US and Europe that either wanted to recycle our slurry for us or buy it outright.

Our initial results were published and presented in March at the Center for Advanced Materials Processing (Clarkson University)/Center for Advanced Ceramic Technology (Alfred University) First Joint Spring Symposium in Rochester, N.Y.

Meet the authors

Michael Naselaris is general manager at Sydor Optics; email: Zachary Hobbs is a process engineer at Sydor; email: For more information about Flint Creek Resources, contact Mark Mayton at

cerium oxide
A polishing material that has a quicker polishing action than rouge (ferric oxide) and that is cleaner to handle.
The optical process, following grinding, that puts a highly finished, smooth and apparently amorphous surface on a lens or a mirror.
The name of the mixture of liquid and grinding or polishing compounds used in processing optical materials.
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