Abstract
Exterra Technologies (formerly Exterra Carbon Solutions) is developing an integrated hydrometallurgical-pyrometallurgical process to valorize asbestos tailings from Québec’s historic asbestos mining operations by recovering mineral products while minimizing consumables through reagent recycling. In 2025, the hydrometallurgical circuit was piloted at SGS Lakefield, confirming stable operation of nitric acid leaching, impurity removal, and Ni-Co precipitation. Under optimized conditions, leaching extractions reached 92% Mg, 98% Ni, and 94% Co, with complete Fe/Al. The Ni-Co recovery circuit consistently achieved complete recovery of Ni and Co and produced concentrates assaying >25 wt.% Ni+Co. Leaching residues, characterized as having strong potential for SCM applications, were confirmed to be non-asbestos. Nitrate accountability was 99% with most nitrate reporting to the magnesium nitrate liquor product. The pyrometallurgical pilot program was conducted at Hazen Research (Golden, Colorado) to demonstrate Exterra’s ARC™ process for converting the magnesium nitrate liquor into high-purity MgO and regenerated nitric acid. The process includes a pyrolysis process to decompose nitrate salt, and a proprietary wet-scrubber system for NOx capture and nitric acid regeneration. Off gas from the pyrolysis process reached >150,000 ppm NOx (NO2:NO 45:1). The regeneration system achieved >99% NOx capture, reduced outlet NOx to <1,000 ppm, and produced nitric acid averaging 40 wt.% suitable for recycling, providing an engineering basis for process scale-up. Building on this success, Exterra plans to deploy the process at demonstration scale over the next 12-24 months, with a feed rate of 2.5 tonnes of serpentine tailings per day.