Quartz dissolution associated with magnesium silicate hydrate cement precipitation

Abstract

Abstract. Quartz has been replaced by magnesium silicate hydrate cement at the Feragen ultramafic body in south-east Norway. This occurs in deformed and recrystallized quartz grains deposited as glacial till covering part of the ultramafic body. Where the ultramafic body is exposed, weathering leads to high-pH (∼ 10), Mg-rich fluids. The dissolution rate of the quartz is about 3 orders of magnitude higher than experimentally derived rate equations suggest under the prevailing conditions. Quartz dissolution and cement precipitation start at intergranular grain boundaries that act as fluid pathways through the recrystallized quartz. Etch pits are also extensively present at the quartz surfaces as a result of preferential dissolution at dislocation sites. Transmission electron microscopy revealed an amorphous silica layer with a thickness of 100–200 nm around weathered quartz grains. We suggest that the amorphous silica is a product of interface-coupled dissolution–precipitation and that the amorphous silica subsequently reacts with the Mg-rich, high-pH bulk fluid to precipitate magnesium silicate hydrate cement, allowing for further quartz dissolution and locally a complete replacement of quartz by cement. The cement is the natural equivalent of magnesium silicate hydrate cement (M-S-H), which is currently of interest for nuclear waste encapsulation and for environmentally friendly building cement, but it has not yet been developed for commercial use. This study provides new insights that could potentially contribute to the further development of M-S-H cement.

Formation of natural Magnesium Silica Hydrate(M-S-H) and Magnesium Alumina Silica Hydrate(M-A-S-H) cement

“…In this paper we give additional information of the Feragen M-S-H cement described by de Ruiter and Austrheim [11] and de Ruiter et al [22]. In addition, we describe a second occurrence from Leka, Norway, reported in a master thesis by Hu [23], where M-S-H grade into M-A-S-H cement in the presence of plagioclase.…”

“…The FUC was extensively mined for chromite, starting in 1824 and terminated in 1939. The mine tailing and locally the mines shafts are coated with hydrocarbonates (4,22). The carbonation of the mine tailings starts ca.…”

“…The carbonation of the mine tailings starts ca. 10 cm below the surface and is particularly well developed on the down facing side of rock fragments in the tailing [22]. On the surface at both FUC and LOC hydrocarbonates only form under overhangs.…”

“…De Ruiter and Austrheim [11] focused on the similarity in structure and composition of the naturally formed Mgsilicate cement and human-made M-S-H (magnesium silicate hydrate) cement [19][20][21]. De Ruiter et al [22] elaborated on the reaction between the high pH fluid and quartz and highlighted the importance of deformation to enhance dissolution rates of quartz and documented by TEM work that the quartz at the contact with cement developed a μm thick amorphous zone.…”

Spontaneous hierarchical surface engineering of minerals through coupled dissolution‐precipitation chemistry

“…[21,22] This dissolution rate is relatively high compared to other common minerals, which range from ≈10 −6 (e.g., calcite) to ≈10 −13 (e.g., quartz). [23][24][25] The high dissolution rate of calcium silicate allows for efficient dissolution-precipitation processes, making it suitable as a model mineral for exploring surface engineering through dissolution-precipitation chemistry. Additionally, calcium silicate is the primary component of ordinary Portland cement, the most consumed man-made materials (≈4 Gt per year) responsible for ≈7% of total CO 2 emission.…”