Precipitation calcium oleate

On the basis of the IR data, the general consensus is that when minerals exhibit 100% flotability, several types of chemisorbed oleate as well as precipitated calcium oleate are present at the surface, in agreement with the initial hypothesis of Peck [425]. However, there is controversy concerning the assignment of the adsorption bands of adsorbed oleate and, hence, the structure of surface species. It stems from the strong dependence of the oleate-calcium coordination on the deposition and precipitation conditions-an effect well known for L monolayers and LB films of alkanoates [426]. The amount of oleate adsorbed on a fluorite slab, as measured by IR spectroscopy, is quite different than that for fine fluorite particles [412]. For the slab, there exists an adsorption saturation point, but for fine particles, the amount of adsorbed oleate increases with concentration, although the concentration dependence of the amount of oleate in the... 

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. 

Figure 10.40 (16) illustrates the adsorption of different amounts oleate on to calcite at a natural pH of 9.6, plus the corresponding zeta potential data as a function of pH. Adsorption at pH 9.6, when the surfactant and surface are similarly charged, takes place due to the interaction of the surfactant with the calcium species on the surface. The sharp increase in the adsorption above 3 X 10 mol/1 was attributed to possible precipitation of calcium oleate, since, with calcium present at a concentration of 1.5 x 10 mol/1, the solubility limit is exceeded for calcium oleate above 5 x 10 mol/1 of oleate. Corresponding measurements at constant ionic strength reveal little change in the zeta potential below concentrations of 10 mol/l of oleate. Adsorption on calcite at these concentration levels and at pH values below the lEP (pH 8.2) can therefore be considered due to electrostatic attraction between the negative oleate ions and the positive surface sites. 

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 ... 

In mineral-reagent systems, surface precipitation has been proposed as another mechanism for chemisorption. The solubility product for precipitation and the activities of the species at the solid-liquid interface determine the surface precipitation process. Under appropriate electrochemical conditions, the activity of certain species can be higher in the interfacial region than that in the bulk solution and such a redistribution can lead to many reactions. For example, the sharp increase in adsorption of the calcium species on silica around pH 11 has been shown to be due to surface precipitation (Somasundaran and Anan-thapadmanabhan, 1985 Xiao, 1990). Similar correlations have been obtained for cobalt-silica, alumina-dodecylsulfonate, calcite/apatite/dolomite-fatty acid, francolite-oleate and tenorite-salicylaldoxime systems. The chemical state of the surfactant in the solution can also affect adsorption (Somasundaran and Ananthapadmanabhan, 1985). 

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. 

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. 

Anionic Surfactants Early studies by Savins [1967] showed that sodium oleate soaps with potassium hydroxide and potassium chloride in aqueous solution had good DR effectiveness. Increasing the concentration of KCl from 5% to 10% gave better drag reduction results. Unfortunately, the soaps precipitate and are ineffective as DRAs in the presence of calcium ions, which are present in most aqueous systems. Solutions of anionic surfactants such as SDS and SDBS are not drag reducing. Little research on anionics as DRAs has been carried out. 

Fig. 1. Calorimeter heating scans of various lipidsr Stearic acid. (B) Cholesterol oleate. (C) A calcium precipitate of cardiolipin.

Foam films stabilized by anionic surfactants can be destroyed by the addition of an oppositely charged inorganic species or near-stoichiomeric concentrations of metallic ions to form insoluble salts. For example, fatty acids and their derivatives (tall oil, stearate, etc.) can be precipitated by the addition of calcium, aluminium and zinc salts (forming insoluble salts of the acids). There have been several attempts to relate the defoaming action to the solubility product of the particles. A typical series of results for metal oleates are shown in Figure 8.4. The influence of hydrophobic calcium fatty acid soaps on foaming, and quantification of the data in terms of the solubility product of the calcium and sodium fatty acids have also been reported. Cationic surfactants added to foam stabilized by anionic surfactants could also destroy the foam. Unfortunately, due to the formation of solid contaminants and the adverse consumption of chemicals, precipitation antifoamers are used infrequently in industry. 

A curious feature of these experiments concerns a decrease in the antifoam effect as the solutions aged over a few days. This occurred despite a concomitant increase in turbidity associated with increase in particle size of the precipitate. The effect was apparent with both surfactants and is exemplified in Figure 4.67b for the alcohol ethoxylate. More or less total elimination of the antifoam effect is seen after about 2 days of aging. We are therefore forced to conclude that the observed antifoam effect concerns some process of interaction between calcium and oleate ions... 

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