Acid-dissolution of antigorite, chrysotile and lizardite for ex situ carbon capture and storage by mineralisation

Serpentine minerals serve as a Mg donor in carbon capture and storage by mineralisation (CCSM). The acid-treatment of nine comprehensively-examined serpentine polymorphs and polytypes, and the subsequent microanalysis of their post-test residues highlighted several aspects of great importance to the choice of the optimal feed material for CCSM. Compelling evidence for the non-uniformity of serpentine mineral performance was revealed, and the following order of increasing Mg extraction efficiency after three hours of acid-leaching was established: Al-bearing polygonal serpentine (<5%) <= Al-bearing lizardite 1T (approximate to 5%) < antigorite (24-29%) < well-ordered lizardite 2H(1) (approximate to 65%) <= Al-poor lizardite 1T (approximate to 68%) < chrysotile (approximate to 70%) < poorly-ordered lizardite 2H(1) (approximate to 80%) < nanotubular chrysotile (approximate to 85%). It was recognised that the Mg extraction efficiency of the minerals depended greatly on the intrinsic properties of crystal structure, chemistry and rock microtexture. On this basis, antigorite and Al-bearing well-ordered lizardite were rejected as potential feedstock material whereas any chrysotile, non-aluminous, widely spaced lizardite and/or disordered serpentine were recommended. The formation of peripheral siliceous layers, tens of microns thick, was not universal and depended greatly upon the intrinsic microtexture of the leached particles. This study provides the first comprehensive investigation of nine, carefully-selected serpentine minerals, covering most varieties and polytypes, under the same experimental conditions. We focused on material characterization and the identification of the intrinsic properties of the minerals that affect particle's reactivity. It can therefore serve as a generic basis for any acid-based CCSM pretreatment. (C) 2016 The Authors. Published by Elsevier B.V. All rights reserved.