A feasibility study to recover antimony

Matthew Bisset, Ryan Bovencamp, Yianni Georgoulas, Egor Kolyada and Linghan Wei

Community Partner: Skeena Gold and Silver
Degree:
- Bachelor of Applied Science
Program:
- Mining Engineering
Campus: Vancouver

Our project

Skeena Gold and Silver is in the midst of developing their Eskay Creek project – which had operated as an underground mine from 1994-2008 – as an open-pit mine in northwestern BC. During their feasibility studies they identified up to 28,000 tonnes of contained antimony (the element, Sb) in their gold-silver ore in the life-of-mine plan, with the antimony primarily occurring as stibnite (the mineral).

Antimony is a critical mineral used in alloy hardening and fireproofing, as well as in applications for electronics and semiconductors. There are currently no operating mines in North America that produce an antimony concentrate, causing the supply to be largely reliant on imports from Asia. Skeena asked us to investigate the potential of creating a separate antimony concentrate within their planned circuit that would not negatively impact the existing mine economics.

Skeena Gold and Silver

Our design solution

Our goal was to design a process that would recover antimony before the ore enters the primary precious‑metals flotation circuit. We evaluated multiple reagent schemes and ultimately focused on performing a kerosene pre‑float, because kerosene enhances stibnite’s natural hydrophobicity. Literature confirms that stibnite floats readily under these conditions, and kerosene can selectively promote antimony recovery.

We designed a full antimony flotation circuit that includes four flotation stages (or banks), followed by concentrate dewatering equipment.

The technical challenges we faced

We spent many hours in the lab evaluating different reagent schemes, and every test seemed to reveal a new challenge. For example, our initial assumption was that the antimony ore would be more hydrophobic than it actually was, so our early recoveries were disappointing.

We embarked on a cycle of trial and error to try and get the best results possible.

We also observed that arsenic minerals floated readily. Although we initially thought this might be a problem as arsenic has historically been considered a penalty element, it is now sought after in some markets as a potential value source.

Another challenge was that our data was based on monthly production flows. Analysing the block model and pit design using Deswik showed that antimony grade fluctuations were muted at the monthly scale, and that a finer schedule (weekly or daily) or strategic stockpiling could improve circuit utilization and lead to increased overall antimony production.

Deswik

What’s next for our project

When we compared our kerosene circuit alongside Skeena’s two most promising internal testwork circuits, we identified that one of Skeena’s approaches had the strongest technical and economic benefits. Although the overall antimony recovery from our kerosene approach is too low to be economically competitive, it does affirm the underlying assumption that stibnite can be floated ahead of the precious metals circuit.

What we’re most proud of

We’re proud that we took this project from an initial concept all the way to a complete circuit design and economic model. As mining engineering students, it was exciting to work on something at the scale of hundreds of millions of dollars. We mixed samples, ran flotation tests, interpreted metallurgical data, designed equipment layouts and built a full economic model with sensitivity analyses.

We also grew significantly both as individuals and as a team. This project allowed us to gain new experience in areas – for example, some of us had more metallurgical experience from co-op positions but were able to gain new skills in economic analysis.

We all became more well-rounded over the course of this project. We also gained insight into how engineering decisions are made on large‑scale projects and what it’s like to work with a client — including meeting with our project sponsors at Skeena’s downtown Vancouver office.