Magnesium solubility data

Clay minerals are present in almost all surface-water and ground-water systems, and in many instances may be controlling the concentration of aluminum, silica, iron, magnesium, or other cations in solution. The thermodynamic data necessary to evaluate the state of reaction (saturation) are not available for some clay minerals, and for those minerals with published values, the data are in disagreement by as much as 10 kilocalories per mole for the same clay mineral. A critical review of the available data for kaolinite and sepiolite, incorporating both the most recent thermodynamic data for the components in the reaction schemes and a more complete computation for the solubility data, yields the values of -907.7 +1.3 and 1105.6 +0.4 kilocalories per mole for the free energy of formation of kaolinite and sepiolite, respectively. 

Solubility data Saturated magnesium sulfate solutions at 110 F and 50 F contain 32 wt% MgS04 and 23 wi% MgS04, respectively. 

The key to the partitioning of thorium in the described conceptual flow sheet is the solubility in cadmium-magnesium. Experimental data associated with this problem have been obtained. The weight percent thorium in solution was determined by taking samples of the equilibrated liquid at varying temperatures and alloy compositions. The samples were analyzed for thorium, magnesium, and cadmium using atomic absorption spectroscopy and the results are estimated to have a relative accuracy of 3%. 

The primary solubility data and the calculation of the solubility products, defined in the usual way, are presented. This presentation contains some unexpected results. The total solubility of the metal ion and selenite are approximately equal in water and in the inert salt solutions for the magnesium and manganese selenites. This is the expected result for a simple dissolution reaction. For calcium selenite, the metal ion concentration was about 100 times greater than the total selenite concentration whereas for zinc selenite the opposite was found. There is no comment in the paper on these results, which contradict the equilibrium reactions used in the paper to define the reported solubility products for calcium and zinc selenite. The review also noted that the calculation of the magnesium and selenite activities from the total concentrations introduces activity coefficients between 0.1 to 0.01 at moderate ionic strengths. Thus the values of these coefficients appear unreasonably small. On the whole, the activity coefficient corrections introduced appear to vary in an erratic way between the various systems studied. 

Table 3.1-2 Solubility data and intermetaUic phases in binary magnesium alloys [1.4]...

Data on the solubihty of magnesium hydroxide in water are not all in agreement, but the solubihty is extremely low. The extent of Mg(OH)2 solubihty is 10 mg/L, which is about 1/100 the solubihty of Ca(OH)2. In concentrated solutions of NH Cl and NH CO, the solubihty of Mg(OH)2 is markedly increased, but in no instance does its solubihty equal that of MgCO in water heavily permeated with CO2. Dolomitic hydrates are slightly less soluble than high calcium hydrates, but much nearer the latter in value than Mg(OH)2, because the presence of MgO and Mg(OH)2 does not impede the dissolution of its Ca(OH)2 constituent. 

Sohnes, D. and Rieger. A. Solubilities of magnesium sulfite hydrates, J. Chem. Eng. Data, 39(1) 161-162,1994. 

Three approaches have been used in attempting to account for the buffer behavior of milk in terms of the properties of its components. These are calculation, fractionation, and titration of artificial mixtures. Whittier (1933A.B) derived equations for dB/dpH in calcium phosphate and calcium citrate solutions, taking into account available data on dissociation constants and solubility products. Presumably this approach could be extended to calculate the entire buffer curve. It demands precise knowledge of the dissociation constants of the several buffers, the dissociation of the calcium and magnesium complexes, and the solubility products of the calcium and magnesium phosphates under the conditions of a titration of milk. 

In order to broaden the data base of the limestone DA process and to evaluate the impacts of closed-loop operation, a series of pilot plant tests was conducted under the sponsorship of U.S. Environmental Protection Agency s (EPA) Industrial Environmental Research Laboratory in Research Triangle Park, NC (IERL-RTP). The testing concentrated on evaluating the effects of magnesium and chloride ions since appreciable accumulations of soluble salts containing these two species are expected in a limestone DA system under closed-loop operating conditions. 

The goal of this research was to improve activity coefficient prediction, and hence, equilibrium calculations in flue gas desulfurization (FGD) processes of both low and high ionic strength. A data base and methods were developed to use the local composition model by Chen et al. (MIT/Aspen Technology). The model was used to predict solubilities in various multicomponent systems for gypsum, magnesium sulfite, calcium sulfite, calcium carbonate, and magnesium carbonate SCU vapor pressure over sulfite/ bisulfite solutions and, C02 vapor pressure over car-bonate/bicarbonate solutions. 

Some pertinent data for the elements are given in Table 4-1. Beryllium has unique chemical behavior with a predominantly covalent chemistry, although it forms an aqua ion [Be(H20)4]2+. Magnesium has a chemistry intermediate between that of Be and the heavier elements, but it does not stand in as close relationship with the predominantly ionic heavier members as might have been expected from the similarity of Na, K, Rb, and Cs. It has considerable tendency to covalent bond formation, consistent with the high charge/radius ratio. For instance, like beryllium, its hydroxide can be precipitated from aqueous solutions, whereas hydroxides of the other elements are all moderately soluble, and it readily forms bonds to carbon. 

A variety of studies have used in vitro biodurability tests to the determine dissolution rate of various silicate minerals in simulated lung and lysosomal fluids (Hume and Rimstidt, 1992 van Oss et al., 1999 Jurinski and Rimstidt, 2001 Werner et al., 1995). Most in vitro studies of mineral solubility analyze changes over time in solution chemistry for a limited number of constituents such as aqueous silica, magnesium, and iron. With this information, coupled with analytical data on the composition of the fibers after being leached, dissolution rates can be... 

---