Sulfate uptake kinetics

Ingvorsen K. and Jorgensen B. B. (1984) Kinetics of sulfate uptake by freshwater and marine species of Desulfovibrio. Arch. Microbiol. 139, 61-66. 

Rees (1973 see p. 330) demonstrated that the overall isotope fractionation during bacterial sulfate reduction can be influenced by a change in the kinetics of sulfate uptake from first- to second-order due to saturation of enzymic activation, or permeation sites. The sulfate concentration at which the change in kinetics occurs is uncertain and indeed may not be the same for all organisms and all physiological conditions. Postgate (1951) found that the specific rate of Hj-linked sulfate reduction by washed cells of D. desul-furicans was independent of sulfate concentration between 1 and 100 mM. On the other hand, Harrison (1957) reported that with lactate as the electron donor, reduction was first-order with respect to sulfate below 10 mM sulfate but became independent of sulfate concentration above 10 mM. 

The first joint shipboard and airborne smdy related to the chemical compositiOTi and water-uptake behavior of particulates in ship emissions was conducted on emissions from a Post-Panamax class container ship off the central coast of California. The results showed that the majority of particles outside the ship plume did not show slow water uptake kinetics as compared to ammonium sulfate, but in-plume particles with critical supersaturation between 0.1% and 0.35% had slower uptake kinetics than ammonium sulfate [288]. 

Most authors continue to report complex uptake kinetics for sulfate (Anderson, 1980 Datko and Mudd, 1984a Deane-Drummond, 1987 Lass and Ullrich-Eberius, 1984 Nissen and Nissen, 1983) although Jones and Smith (1981) reported that the uptake mechanism of cultured tobacco cells exhibits monophasic kinetics with a of 20 nM. However, as discussed below, the measurements made in the latter study might reflect uptake of sulfate into the vacuole and incorporation into organic sulfur compounds rather than influx across the plasma membrane. Lass and Ullrich-Eberius (1984) reported that the uptake kinetics in Lemna can be described by two Michaelis-Menten terms... 

Ingvorsen, K., A. J. B. Zehnder and B.B. Jprgensen, 1984, Kinetics of sulfate and acetate uptake by Desulfobacter postgatei. Applied and Environmental Microbiology 47,403 -08. 

Calcium sulfate crystals were precipitated in a Continuous Mixed Suspension Mixed Product Removal (CMSMPR) crystallizer by mixing of calcium phosphate and sulfuric acid feed streams. The formed calcium sulfate hydrate (anhydrite, hemihydrate and dihydrate) mainly depends on the temperature and the solution composition. The uptake of cadmium and phosphate ions in these hydrates has been studied as a function of residence time and solution composition. In anhydrite, also the incorporation of other metal ions has been investigated. The uptake was found to be a function of both thermodynamics and kinetics. 

The level of impurity uptake can be considered to depend on the thermodynamics of the system as well as on the kinetics of crystal growth and incorporation of units in the growing crystal. The kinetics are mainly affected by the residence time which determines the supersaturation, by the stoichiometry (calcium over sulfate concentration ratio) and by growth retarding impurities. The thermodynamics are related to activity coefficients in the solution and the solid phase, complexation constants, solubility products and dimensions of the foreign ions compared to those of the ions of the host lattice [2,3,4]. 

The aim of this work is to study the incorporation of cadmium and phosphate in the three calcium sulfate modifications. The uptake of other metal ions in AH will also be described. Kinetic effects of operating conditions such as the residence time, sulfuric acid and phosphate concentration upon the phosphate and cadmium uptake has been investigated. In addition the influence of a growth retarding impurity, AIF3, on the cadmium and phosphate uptake will be given. 

In figure 6 the resulting Cd-concentration in the crystals is plotted versus the sulfate content of the solution. In 5.5 M phosphate solutions, K(Cd) seems to decrease from 0.02 to 0.5 M sulfate contents, while above 0.1 M sulfate K(Cd) increases. This tendency of higher uptake at higher sulfate concentrations has also been found for DH. The high K values at very low sulfate contents indicates a major influence of kinetics. 

The supersaturation is too low in all experiments to be measured accurately, but it seems reasonable to assume that the effect of residence time is imposed through the kinetics. Another observation is that the D-value for cadmium uptake in anhydrite is about ten times higher than in HH or DH. An explanation for this higher D seems to be related to the crystal structures of the calcium sulfates. Only the AH structure matches with an anhydrous CdSO phase, while no hemi- or dihydrate phase of CdS04 exists. 

For uptake proceeding by isomorphous substitution, the partition coefficient D depends on thermodynamic parameters such as ionic radius of the impurity ions and the phases of the calcium sulfate as well as on kinetics. 

The properties of formulations F31 and F were measured in ENSLIN equipment in order to compare the kinetics of water uptake and to study the dissolution profile, as shown in Figures 16-19. As observed in Figure 19, the dissolution of plant extract after 60 min is very slow when pH-modified (NA2C03) and sodium dodecyl sulfate (SDS) are not used (almost not change in color for formulation F). 

As previously discussed, Harrison and Thode (1958) invoked a two-step model to account for the range of isotopic fractionation encountered during sulfate reduction by D. desulfuricans. Rees (1973) developed a steady-state multi-step model for isotope fractionation during bacterial reduction. His approach differed from previous attempts in that he included the possibility of zero-order kinetics for describing the uptake of sulfate. His reaction scheme is basically of the form... 

---