Effect of organic ligands and heterotrophic bacteria on wollastonite dissolution kinetics

Abstract

Wollastonite (CaSiO 3 ) dissolution rates were measured at 25°C in 0.01 M NaCl using a mixed-flow reactor as a function of pH (5 to 12) and concentration of forty organic ligands. Mostly stoichiometric dissolution was observed at these conditions. For seven ligands (acetate, citrate, EDTA, catechol, glutamic acid, 2,4dihydroxybenzoic acid, glucuronic acid), batch adsorption experiments and electrokinetic measurements performed as a function of pH and ligand concentration confirmed the interaction of ligands with >CaOH 2 ؉ sites and allowed quantification of their adsorption constants. The effect of investigated ligands on wollastonite dissolution rate was modeled within the framework of the surface coordination approach taking into account the adsorption of ligands on dissolution-active sites and the molecular structure of the surface complexes they form. A positive correlation between surface adsorption constant and the stability constant of the corresponding reaction in homogeneous solution was observed. At neutral and weakly alkaline pH, the following total dissolved concentrations of ligands are necessary to double the rate of wollastonite dissolution: EDTA (10 ؊4 M), phosphate (1.5 ⅐ 10 ؊4 M), catechol (3 ⅐ 10 ؊4 M), 8-hydroxyquinoline, gallic acid or adipate (5 ⅐ 10 ؊4 M), 3,4-DHBA (7 ⅐ 10 ؊4 M), PO 3 ؊ (7.5 ⅐ 10 ؊4 M), glutamate (0.002 M), citrate (0.003 M), malate or 2,4-DHBA (0.004 M), phthalate or succinate (0.005 M), tartrate (0.006 M), thioglycolate (0.008 M), aspartame (0.01 M), gluconate, ascorbate (> 0.01 M), malonate, diglycolate or lactate at pH 8.4 (0.02 M), formate or fumarate (0.05 M), oxalate (>0.05 M), bicarbonate (0.075 M), lactate at pH 5.6 (0.1 M), acetate (> 0.1 M), salicylate (0.15 M), humic acids (> 54 mg/L of dissolved organic carbon, DOC), gum xanthan (1.5-2.0 g/L). Sorbitol, mannitol, glucose, glucosamine, saccharose, fulvic acids and silica at pH ϳ 7 exhibit weakly inhibiting or no effect up to concentration of 0.1 M. The presence of the following ligands leads to a decrease of dissolution rates by a factor of 2: silica at pH 10.7 (2 ⅐ 10 ؊4 M), glucuronic acid (0.001 M), algae exudates (30 mg/L DOC), mannit (0.02 M), urea (>0.05 M), pectin (>15 g/L), alginic acid (> 2 g/L).Overall, results of this study demonstrate that high concentrations (0.001-0.01 M) of organic ligands, whether they are originated from organic matter, enzymatic degradation or bacterial metabolic activity, are necessary to appreciably enhance wollastonite dissolution. This is further corroborated by batch experiments on live and dead cultures of soil bacteria Pseudomonas aureofaciens interaction with wollastonite. The release rates of both Ca and Si are only weakly affected by the presence of live or dead bacterial cells in inert electrolyte solution and in nutrient media: there is only ϳ20 percent-increase of dissolution rate in experiments with live cultures compared to dead cultures. However, the reproducibility of rate measurements in ligand-free solutions at 7 < pH < 8 achieves ؎ 30 percent. Therefore, the...

Mineral CO2 sequestration by environmental biotechnological processes

“…1.4b) or the free cations in the aqueous solution ( Fig. 4c) (Pokrovsky et al, 2009;Ullman et al, 1996). In addition to the illustrated mechanisms, direct bacterial effects such as biofilm growth can also potentially improve the dissolution process via chelation by metabolites or oxidation-reduction reactions (Bennett et al, 2001;Castanier et al, 1999;Frey et al, 2010;Rogers & Bennett, 2004;Uroz et al, 2009).…”

“…However, the high costs and intensive energy needs associated with such chemical or physical treatments of silicate minerals have been mentioned as the main drawbacks for application of these methods (Gerdemann et al, 2007;Huijgen et al, 2003;Renforth et al, 2011;Sipilä et al, 2008). Therefore, recently, the application of biological processes as a more cost-efficient method for enhancing the dissolution of alkaline silicates has been investigated (Bennett et al, 2001;Pokrovsky et al, 2009;Rawlings et al, 2003;Ullman et al, 1996;Welch & Ullman, 1993;Wogelius & Walther, 1991). Microbial processes can primarily increase the dissolution rate of silicate minerals by modifying the environmental conditions such as pH reduction by e.g.…”

“…Biological processes occurring in the fermentation process are able to improve the weathering (dissolution) of silicate minerals by various means: change in solution pH, pCO 2 , ionic strength and production of exometabolites like organic ligands. In addition, direct bacterial effects such as biofilm growth can also potentially improve the dissolution process (Castanier et al, 1999;Pokrovsky et al, 2009;Salek et al, 2013c). While the effect of pCO 2 and ionic strength on silicate dissolution rate is well characterized, particularly for Mg and Fe silicates such as olivine (Golubev et al, 2005;Rimstidt & Dove, 1986), the effects of organic ligands on Ca silicates such as wollastonite have been hardly studied and the studies performed were at neutral and weakly alkaline pH (Pokrovsky et al, 2009).…”

“…In addition, direct bacterial effects such as biofilm growth can also potentially improve the dissolution process (Castanier et al, 1999;Pokrovsky et al, 2009;Salek et al, 2013c). While the effect of pCO 2 and ionic strength on silicate dissolution rate is well characterized, particularly for Mg and Fe silicates such as olivine (Golubev et al, 2005;Rimstidt & Dove, 1986), the effects of organic ligands on Ca silicates such as wollastonite have been hardly studied and the studies performed were at neutral and weakly alkaline pH (Pokrovsky et al, 2009). The organic ligands are known to enhance the dissolution rate by two key mechanisms: adsorption of ligands to >CaOH 2 + and >CaOH° sites on the mineral surface and complexation with the free Ca ion in the aqueous solution.…”

“…A study performed by Huijgen et al, 2007 showed that the sequestration cost could be reduced from 102 to 77 euro/ton CO 2 -avoided, by using steel slag instead of wollastonite. Recently, the application of biological processes as a cost-efficient method for enhancing the dissolution of silicates and precipitation of carbonates have also been investigated (Bennett et al, 2001;Pokrovsky et al, 2009;Ullman et al, 1996;Uroz et al, 2009;Welch & Ullman, 1993). The following section (1.3) elaborates on the application of biological processes for the mineral carbonation of CO 2 .…”