Precipitation magnesium oleate

Prepare a little magnesium oleate by treating a solution of sodium oleate with magnesium sulfate. Carefully wash the precipitate free from soluble impurities and dry at about 110°. Suspend 1 g. of the dry salt in 100 cc. of benzene and provide the flask with a reflux condenser. Boil until solution is obtained. Possibly the product is a colloidal dispersion rather than a very perfect solution. It has been found that a very little sodium oleate mixed with the magnesium oleate rendered the emulsions more permanent. 

According to the above reactions, removal of carbonate groups from the mineral surface should result in the reduction of the intensity of carbonate peak as shown in Fig. 4.33. On the other hand, adsorption and surface precipitation of oleate can take place on the dolomite surface leading also to similar reductions. A new peak at 1351 cm when the oleate concentration reaches about 10 mol/1 can be clearly seen in Fig. 4.33b and the intensity of this peak increases with the increase in the oleate concentration, where precipitation of calcium and magnesium oleates is likely to occur both on the particle surface and in the bulk. The peak heights of both the carbonate and the oleate (7co and 7oi) in the spectra were measured. Bulk precipitation using a common tangent baseline method (Willis et al., 1987) and the ratio Ico/Ioh is plotted in Fig. 4.34. This plot also... 

It can be seen that magnesium addition to calcium oleate solution or vice versa does shift the transmission curve to lower oleate concentrations, indicating co-precipitation of calcium and magnesium oleates due to synergistic effects. Overlapping of both the curves in Fig. 4.36 is also in line with the behavior of the dolomite and francolite systems in microflotation and dissolution experiments. Simultaneous measurements of dissolved species in the supernatant of the precipitated solutions (Fig. 4.37) showed Ca and Mg levels to remain almost constant until solubility products of their oleate are reached (2 x 10 " mol/1... 

At intermediate concentrations (10 to 2 x 10 mol/1. Region II), the solubility Umit of calcium and magnesium oleates may exceed in the interfacial region but not in the bulk solution. Then, surface precipitation of oleate on the mineral particles occurs leading to an increase in oleate depletion and a decrease in the levels of dissolved calcium and magnesium species. The hydrocarbon tails of the oleate molecules would be oriented towards the bulk making the mineral surface hydrophobic. 

At higher concentrations (>2.0 x 10 mol/1. Region III), the slope of the isotherm is higher and a sharp decrease in concentrations of dissolved species takes place. This suggests that oleate depletion and bulk precipitation of calcium and magnesium oleates predominates in this region. 

The most important characteristic of hard water is its reaction with soap. If distilled or soft water be shaken with a solution of soap a lather or foam is formed immediately. If, however, a dilute solution of soap be added drop by drop to some hard water in a bottle which is stoppered and shaken after each addition, it will be found that no lather is formed at first. The water, at the same time, assumes a turbidity owing to the formation of an insoluble precipitate. Finally, after sufficient soap has been added, a lather will appear. Soaps are sodium salts of fatty acids of high molecular weight, such as sodium oleate CuHggCOONa. The salts of sodium are soluble in water, but those of calcium and magnesium are not and, in hard water, the ions of these elements displace the sodium, giving precipitates of their insoluble fatty acid salts ... 

At low concentrations (<10 mol/1. Region I), oleate species adsorb individually on the mineral possibly due to electrostatic interactions. In this range, no precipitation of dissolved calcium and magnesium species with oleate occurs. 

SDS in the formation of a stable supporting foam layer. With only sodium oleate, a stable foam layer is not formed on the solution surface, probably due to the reaction of an excess of sodium oleate with magnesium ions in seawater. With only SDS, most of the precipitate does not float. 

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