Understanding the acid dissolution of Serpentinites (Tailings and waste rock) for use in indirect mineral carbonation

Abstract

Solid carbonates can be formed by indirect mineral carbonation using the pH swing method for CO2 storage. It occurs at low temperatures and pressures in four stages: acid dissolution, purification, carbonation, and recovery. Although acid dissolution requires short reaction time that favors the extraction of reactive metals, lack of knowledge about the effects of temperature, acid concentration and particle size on metal extraction reveals that it is a critical stage of indirect mineral carbonation. In order to employ mining waste for indirect mineral carbonation, acid dissolution of serpentinites, tailings (SERP-GO) and waste rock (SERP-MG) were investigated, and their performances were compared. A Taguchi experiment design was used to assess the parameters that influence the acid dissolution process. Hydrochloric acid was used in acid dissolution for Mg and Fe extraction from both, SERP-GO and SERP-MG, and the process parameters (temperature, acid concentration, particle size and excess acid) were evaluated for 2 h of reaction. According to signal-to-noise ratio analysis of the Taguchi method, the optimized condition for Mg extraction of both samples was at 70 °C, 4 M HCl, 69 μm and twice the excess acid. The results indicated that of Mg and Fe extraction from de samples was more efficient for SERP-GO (71% and 85%) than SERP-MG (33% and 31%). Based on these findings, it was possible to have a better understanding of the factors affecting the dissolution of serpentinite tailings, to develop a more effective process for the use of mining waste in the indirect mineral carbonation process.