"Dewatering of tailings is very much in focus now. Getting the water out of the tailings is one of the key avenues to ensuring a reliable TSF design post-discharge, and certainly there has been a lot of focus on that with the TSF failures in recent years," according to Matt Treinen, Director at Paterson & Cooke. Matt sat down for an interview for Mining Journal and Mining Magazine's 2021 Tailings Program.

Paterson & Cooke is a global leader in high-level consulting and engineering of tailings solutions, including slurry systems. Treinen said the firm provides services for greenfield projects, where it helps clients understand what technology makes sense for the project, as well as at existing operations, where it helps troubleshoot how to improve their tailings systems.

It is important to look at new greenfield projects with a holistic "10,000 ft view" where you can assess the site location, dewatering requirements and overall tailings objective to select the best available tailings technology. Filtered tailings are in vogue right now but their potentially high cost means they are not always the best fit at every site.

It is important to understand, he said, that "every incremental step you make in the dewatering process, it becomes more difficult to dewater and by nature more expensive to dewater."

That assessment often requires a "one-foot view" where materials are tested at one of Paterson & Cooke's labs around the world, he said.

"Most of our offices have labs adjacent to the office so the engineers can get out to the lab, see how the material behaves, understand the dewatering behavior, and look at alternate technologies … to optimize the overall system."

"As the project advances into the next stages we certainly can get involved in the full engineering and design of a particular dewatering system, whether that's a thickener operation or a filtered tailings operation," he said. That is more of a 1,000 ft view.

Lastly we get involved at a "100  foot view" (about the size of many thickeners) where the firm assesses how to make improvements at existing sites.

"Maybe there (have been) ore changes, or variations in properties and they're not getting the dewatering that they need. How can we optimise that? Maybe it's retrofitting, thickener technology, maybe that's looking at the slurry pump selection, maybe the (tailings) pipeline size is no longer appropriate and they're getting excessive wear." he said.

Paterson & Cooke has implemented a number of systems globally, ranging from tailings slurry pipeline systems for conventional tailings facilities, and all the way through to implementation of various dewatering technologies.

Dewatering technologies begin with something as basic as a cyclone or screen to pull some of the water out, all the way through thickening and advanced tailings filter presses.

"We've been involved in quite a lot of cyclone sand systems design and implementation in the southwest United States and South America where they use that cyclone material for dam construction. We've completed countless numbers of thickener audits to help improve thickener operations, anywhere from conventional thickeners to high-rate and paste thickeners, to troubleshoot and get them back to operating where they should be operating."

They have also seen a huge interest in filtered tailings over the last few years. We're in the process of implementing a filtered tailings system in Mexico, a fairly small scale operation where they're filtering the tailings and then depositing it into a mined-out pit," he said.

"We also implemented a paste backfill system at the same site a couple of years ago, (so) they can also put a huge amount of the tailings back underground".

"Similarly we're also working on a filtered tailings plant for a power plant operator here in the United States, maybe a non-conventional, but similar, filtered tailings application."

In some cases, thickened tailings is being used as a stepping stone to filtered tailings.

"We assisted with a filtered tailings design in Canada a couple years ago where the plan was to take incremental steps: they've gone from conventional tailings, moving to thickened tailings and then working to close out those tailings storage facilities. They could get comfortable with the thickening operation before implementing filtered tailings in the next year or two."