Multistep concentration of lizardite/antigorite from chrysotile mine tailings – case of the Carey Mine site in East-Broughton (Québec)

Abstract

Abstract Revalorization of mining residues is of central concerns to the mining industry and the environment. Specifically, environmental management of residual products from the exploitation of chrysotile in the Thetford Mines region is one of the government concerns in Quebec and Canada. This work uses mining wastes in a second resource generation for production of magnesium from cheap and health-friendly mineral sources; the goal being to produce chrysotile-depleted pre-concentrates for a use as precursors in the leach off extraction of magnesium. The concentration of lizardite/antigorite from chrysotile containing serpentine rock mine tailings originating from the Carey Mine site in East-Broughton (Québec) was carried out using a suite of hydrocyclone, settling/decantation and magnetic separations. Four size classes of the mining residue, namely (−3150,+1580), (−1580, +600), (−600, +300) and (−300, +150) μm, were tested with an aim to reduce the level of objectionable asbestos fibers to allow access to the safer Mg-bearing minerals contained in the mine waste sources. The asbestos fibers clean-up consisted of subjecting the sieved fractions to two hydrocyclone steps, six settling/decantation steps and two magnetic separation steps. The best results were achieved when the hydrocyclone separators led to Mg recovery of 85% (±4) for the coarsest size fraction size. Both hydrocyclone underflow streams underwent settling/decantation separations. The settling tests lasted 30 min and led to Mg recoveries of 82.5% (±1.8) of Mg in the ultimate concentrate. SEM characterizations revealed that it was possible to reduce substantially the amount of chrysotile fibers to render the coarse-sized fraction in the mining waste usable while significantly lowering the health risk of the fibers. A two-step magnetic separation was applied to the final settling/decantation underflow to remove magnetic minerals such as magnetite from the lizardite/antigorite concentrate. The final quasi-non-magnetic chrysotile-depleted lizardite/antigorite concentrate allowed sample recovery of 62.5% (±0.9) wt. of Mg. These preliminary results are intended as a first compulsory step in support of viable restoration and sustainable development scenarios for the Thetford Mines mining sites as second-breath sources for valuable magnesium.