Geochemical and mineralogical impacts of H2SO4 on clays between pH 5.0 and −3.0

Investigation of acidic dissolution of mixed clays between pH 1.0 and −3.0 using Si and Al X-ray absorption near edge structure

“…Through a series of long-term (14-365 d) batch experiments, Shaw and Hendry (2009) investigated the impact of H 2 SO 4 solutions between pH 5.0 and À3.0 on three mixed clays with different phyllosilicate ratios (montmorillonite, illite, and kaolinite) typically used as liner materials in mine settings. They found that dissolved Al concentrations increase substantially between pH 1.0 and À3.0 to peak values of 2.3 Â 10 À2 mol L À1 g À1 , while Si values increase to a peak of 1.2 Â 10 À3 mol L À1 g À1 at pH 0.0 and then decrease between pH 0.0 and À3.0.…”

“…The authors indicate that peak Al and Si concentrations represent mobilization of between 40 and 60% of total Al from the Kc, Km, and BK solid phases. Furthermore, through X-ray diffraction (XRD) analyses Shaw and Hendry (2009) demonstrate; (i) the loss of montmorillonite crystal structure at pH 6 1.0; (ii) a considerable decreases in illite and kaolinite peak intensities at pH 6 1.0; (iii) precipitation of amorphous silica (a-SiO 2 ) at pH 6 0.0, and (iv) precipitation of anhydrite and possibly aluminite (Al 2 [SO 4 ][OH] 4 Á7H 2 O) at pH 6 À1.0. Previous acidic dissolution studies of phyllosilicates conducted at pH 6 1.0 indicate that Al-octahedral layers preferentially dissolve, while the associated Si-tetrahedral layers remain relatively unaffected (Mendioroz et al, 1987;Pesquera et al, 1992;Gates et al, 2002;Belver et al, 2002;Komadel, 2003;Tyagi et al, 2006).…”

Dissolution kinetics of soil clays in sulfuric acid solutions: Ionic strength and temperature effects

“…A decrease in dissolution rate of a polymineralic natural clay sample with an increase in pH (from pH 1 to 5) in batch dissolution experiments was also reported by Shaw and Hendry (2009). The dissolution of minerals occurs at the mineral surface and is initiated by proton adsorption at the mineral-aqueous interface.…”

“…A similar effect of solution ionic strength on the initial cation release has been observed in an earlier study on montmorillonite dissolution, over the same ionic strength and pH conditions (Bibi et al, 2011b). Similarly, in a batch experiment study conducted by Shaw and Hendry (2009) on polymineralic samples containing illite, kaolinite, smectite and quartz, a greater Si release compared to Al was observed at pH 3 and 5 in H 2 SO 4 solutions. Despite the presence of considerable amounts of quartz, the difference in initial Al and Si concentrations was attributed to inhibited Al release from the dissolution of phyllosilicates.…”

“…Considerable efforts have been devoted to study the dissolution mechanisms of individual phyllosilicates under laboratory conditions (Amram and Ganor, 2005;Bibi et al, 2011c;Brandt et al, 2003;Cama and Ganor, 2006;Cama et al, 2002;Golubev et al, 2006;Kalinowski and Schweda, 2007;Kohler et al, 2003;Lawson et al, 2007;Metz et al, 2005b;Oelkers et al, 2008;Yang and Steefel, 2008;Zysset and Schindler, 1996). Only limited research has been done on the acid dissolution of natural clay samples or phyllosilicates isolated from soils (Jurjovec et al, 2002;Salmon and Malmstrom, 2006;Shaw and Hendry, 2009), particularly with a focus on comparing the neutralisation potential of different mineral groups such as carbonates, oxide minerals and phyllosilicates. To our knowledge there is no published research on the dissolution of natural soil clays such as those encountered in IASS under highly-saline and acidic conditions.…”