Lab-scale custom crushing and blending has never been so efficient as it is now with Sudbury-based Xstrata Process Support’s (XPS) first-of-a-kind custom crushing and blending plant (CBP).
What was previously an intensive manual process that took days to perform can now be completed in a matter of hours, depending upon the batch size. XPS personnel saw the need to mechanize the process when they noticed the incidence of repetitive strain injuries was on the rise.
"We realized the crushing and blending we did in the lab was very manual," said XPS metallurgist Dave Middleditch. "Previously, we had guys with pails of rock and/or drill core dumping them in crushers, taking the product out and screening it. Once crushed to a suitable product size for metallurgical test work, the operator would load the crushed material into a spinning riffler (a carousel-type device) that would discharge it into 10 pots."
What took up to five days of labour to process 200 kilograms of ore in the lab now takes about three hours to crush, blend, and split into charges (replicate batches of crushed material) in the new CBP.
The process is similar to a crushing circuit in a standard mill. However, only drill-core or rock no larger than six inches in diameter is allowed. Two newer technologies make this scaled-down plant unique. The Boyd crusher, a design by a New Zealand company called Rock Labs, performs the crushing and grinding action in one unit and has a high reduction ratio. The result is a finely-crushed ore sample.
In a standard crushing plant operation, there is a primary and secondary crusher, but there may also be a tertiary crusher. The Boyd unit eliminates the need for a tertiary crusher, making the work much more efficient. The plant can continuously process up to 150 kg of drill-core or rock per hour.
The Hosokawa Micron B.V. Vrieco blending technology used by XPS comes from the pharmaceutical and food industry. XPS is the first to apply it to the mining industry. There are two blenders - one has a 150-kg capacity and the other has a one-tonne capacity for larger batches.
"Blending has always been a challenge in the mining and test-work industry," Middleditch said, explaining that, historically, large amounts of samples were blended manually by spreading the material out on a tarp on the floor where it was pushed around by a front-end loader. "It’s not very scientific and it ends up with lots of segregation."
Ultimately, the goal is to have a homogenous blend for mineral processing test work with a relative standard deviation of less than 5 per cent for base metals, which the CBP blenders achieve.
"The smaller the particle size, the easier it is to blend and the less material you need to sample from the population to get a representative sample," Middleditch said, stating Gy’s Sampling Theory which is widely accepted in the mineral processing industry. The new process has given XPS a competitive advantage because of the quality and efficiency of the work performed.
Prior to the CBP plant, XPS used a proprietary method called Odds and Evens blending that made use of spinning rifflers. It took the charges down to the acceptable standard deviation level, but it was still a labour intensive, time-consuming process.
While exploring various ways to develop an alternative crushing and blending process, Middleditch and XPS lab technician Pat Carriere decided to design it themselves. Sudbury’s Grant Aggregate and Industrial Supply Inc. was also instrumental in the design and building of the product.
Once the design was approved at the end of 2007, construction of the machine began in January 2008. The plant was ready for business by October 2008, serving Xstrata’s global operations and the international mining industry.
One of its first jobs was to crush 10 tonnes of drill core for a local mining company. Middleditch said they would not have been able to crush that amount of ore manually. As well, larger batches used to be subcontracted out to a southern Ontario lab, Xstrata’s competition, resulting in excessively high costs.
"Now we can do it at half the price in half the time with a much better quality crush and blend," Middleditch said. "It gives us more control and we’re no longer at the mercy of our competitors to get test work done."
The CBP could also be used in place of a sampling tower at a mine site.
"We’d receive the sample here rather than setting up a whole sampling tower on site, which is a big capital investment," Middleditch said.
The one- to two-person operation requires little or no material handling. Great care is taken to make sure the plant is cleaned between batches in order to ensure a sterile environment, which avoids cross contamination.
