Direct carbonation of magnesium slag after salt lake lithium extraction for use as a cementitious material

Abstract

Carbonation of MgO and Mg(OH)₂ for the preparation of cementitious materials has attracted much attention due to the rapid strength gain and high CO₂ sequestration. This paper investigated the potential use of lithium extraction by-product magnesium slag from salt lake as MgO and Mg(OH)₂ sources to prepare construction material through carbonation. Calcium hydroxide and dipotassium hydrogen phosphate were used to promote the hardening and carbonation of magnesium slag. Properties of magnesium slag moulded by casting and compacting under 100 % CO₂ and 0.1 MPa pressure condition were compared and the phase changes were also analyzed. Results indicated that the cast moulding magnesium slag yielded uniform carbonation of the specimen, resulting in 1 h strength of 20 MPa. Compacted magnesium slag leads to the uneven carbonation but continuous strength development due to the internal moisture. Brucite in magnesium slag was the main reactant while hydromagnesite and amorphous hydrated magnesium carbonates were confirmed as the main carbonation products by combining XRD, FTIR, TGA analysis. In addition, K₂HPO₄ promoted the carbonation of Mg(OH)₂, leading to the uniform carbonation of specimens and increased 8 h strength to 49.4 MPa. This study builds foundation for use carbonation of Mg-based solid wastes as construction materials.