Article

Effects of organic acids on the dissolution of orthoclase at 80°C and pH 6

The University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063, USA
Chemical Geology 01/1996; DOI: 10.1016/S0009-2541(96)00044-7

ABSTRACT The dissolution of K-rich feldspar (orthoclase), quartz and Al(OH)3 was investigated at 80°C and pH 6 in buffered solutions of organic acids. Previous studies of the effects of organic acids (OA) on feldspar dissolution have typically been conducted in acidic, low-ionic strength solutions often under conditions which preclude isolation of effects of pH from those due to organic acids. Our experiments were conducted at constant pH, temperature, ionic strength, and buffer composition to allow direct comparison of experiments with and without OA. The dissolution experiments were conducted under closed-system conditions to: (1) determine the magnitude of mineral solubility enhancement by OA; (2) examine changes in reaction stoichiometry as equilibrium is approached; and (3) investigate the effects of OA on secondary mineral precipitation.The carboxylic acid species, oxalate and citrate, significantly enhanced the dissolution of orthoclase at pH 6. The concentrations of Si and Al in 10 m M oxalate and citrate solutions were nearly 3 times that in solutions of acetate buffer without oxalate or citrate. Aluminum was below the limit of detection ( < 0.007 mM) in the acetate buffer alone. Citrate increased the release of Si and Al from orthoclase more than did oxalate at the same concentration. Equilibrium modeling indicates that solutions with oxalate and citrate attained supersaturation with respect to gibbsite, kaolinite, and smectite, and saturation with respect to quartz. Nevertheless, orthoclase dissolution remained congruent with respect to Si and Al release.Separate experiments using pure quartz and Al(OH)3 suggest that a mechanism other than formation of Si-organic complexes may be involved in the OA-enhanced release of Si from orthoclase. The increase in dissolved silica was modest in 10 mM oxalate and 10 mM citrate solutions reacted with quartz, and did not increase with increasing OA concentration. The solubility of quartz was similar in solutions of oxalate and citrate. In contrast, Al(OH)3 dissolution was 50% greater in citrate than in oxalate, similar to the behavior of orthoclase. Citrate may be more effective in dissolving orthoclase than oxalate due to a stronger interaction between citrate and Al, rather than due to a synergistic effect of Al-citrate and Si-citrate complexes. These results have implications for the mass transport of Si and Al in diagenetic environments.

0 Bookmarks
 · 
312 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mineralogy, microbial ecology, and mineral weathering in the subsurface are an intimately linked biogeochemical system. Although bacteria have been implicated indirectly in the accelerated weathering of minerals, it is not clear if this interaction is simply the coincidental result of microbial metabolism, or if it represents a specific strategy offering the colonizing bacteria a competitive ecological advantage. Our studies provide evidence that silicate weathering by bacteria is sometimes driven by the nutrient requirements of the microbial consortium, and therefore depends on the trace nutrient content of each aquifer mineral. This occurrence was observed in reducing groundwaters where carbon is abundant but phosphate is scarce; here, even resistant feldspars are weathered rapidly. This suggests that the progression of mineral weathering may be influenced by a mineral's nutritional potential, with microorganisms destroying only beneficial minerals. The rock record, therefore, may contain a remnant mineralogy that reflects early microbial destruction of biologically valuable minerals, leaving a residuum of "useless" minerals, where "value" depends on the organism, its metabolic needs, and the diagenetic environment. Conversely, the subsurface distribution of microorganisms may, in part, be controlled by the mineralogy and by the ability of an organism to take advantage of mineral-bound nutrients.
    Geomicrobiology 01/2001; 18(1). · 1.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Most studies agree that the dissolution rate of aluminosilicates in the presence of oxalic and other simple carboxylic acids is faster than the rate with non-organic acid under the same pH. However, the mechanisms by which organic ligands enhance the dissolution of minerals are in debate. The main goal of this paper was to study the mechanism that controls the dissolution rate of kaolinite in the presence of oxalate under far from equilibrium conditions (−29
    Geochimica et Cosmochimica Acta 01/2006; 70(9):2191-2209. · 3.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: CO2 capture and storage (CCS) is an important strategy in combatting anthropogenic climate change. However, commercial application of the CCS technique is currently hampered by its high energy expenditure and costs. To overcome this issue, CO2 capture and utilization (CCU) is a promising CO2 disposal method. We, for the first time, developed a promising method to mineralize CO2 using earth-abundant potassium feldspar in order to effectively reduce CO2 emissions. Our experiments demonstrate that, after adding calcium chloride hexahydrate as an additive, the K-feldspar can be transformed to Ca-silicates at 800°C, which can easily mineralize CO2 to form stable calcium carbonate and recover soluble potassium. The conversion of this process reached 84.7%. With further study, the pretreatment temperature can be reduced to 250°C using hydrothermal method by adding the solution of triethanolamine (TEA). The highest conversion can be reached 40.1%. The process of simultaneous mineralization of CO2 and recovery of soluble potassium can be easily implemented in practice and may provide an economically feasible way to tackle global anthropogenic climate change.
    Chinese Science Bulletin 58(1). · 1.37 Impact Factor

Full-text

Download
8 Downloads