Precipitation oleate

This test measures the minimum lime soap dispersant requirement (LSDR) (in g) which keeps 100 g of sodium oleate from precipitating in hard water (333 ppm CaC03). Although this is a convenient laboratory test, it bears little relation to an real in-use situation. 

Water that contains significant amounts of Ca2+ or Mg2+ is said to be hard. These ions cause soluble soaps such as sodium stearate, palmitate, and oleate to precipitate as insoluble scums, which are an unsightly nuisance as well as a waste of soap ... 

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. 

Precipitation of the catalyst from the reaction medium, followed by filtration, as in the cobalt-based hydroformylation process (see Section 5.4). Here cobalt is removed from the reaction products in the form of one of its salts or as the sodium salt of the active carbonyl catalyst. The aqueous salts can be recycled directly, but sometimes they are first converted into an oil-soluble long-chain carboxylic acid salt, such as the corresponding naphthenate, oleate, or 2-ethylhexanoate. 

Linstead and Whalley showed that urea complexes can be used for effective separation of straight- and branched-chain carboxylic esters. Swem s group used the method to advantage in working up autoxidized methyl oleate for isolation of long-chain hydroperoxides. These peroxides behave like branched-chain compounds because of the bulky peroxide group and remain in solution when nonperoxidic components of the mixture are precipitated as urea complexes. 

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 ... 

Precipitate flotation is applied in the analysis of natural waters. Trace ions in an aqueous solution are co-precipitated with colloidal metal hydroxide collectors and floated with the aid of a gas stream [94-96]. Tiny gas bubbles are trapped in the interstitial spaces and on the surfaces of the precipitates to give sufficient buoyancy. Surfactant ions having the charge opposite to the precipitate surfaces are used to make the surface hydrophobic. Another important role of the surfactants e.g., sodium oleate, sodium dodecylsulphate) is to form a stable froth layer to support the precipitate on the solution surface, which is important for complete separation of the precipitate. 

Trace amounts of phosphate can be co-precipitated with Al(OH)3, Fe(OH)3, or Be(OH)2 as collector [8-10]. Traces of phosphate, co-precipitated with Al(OH)3 at pH 8.5, have been floated with Na oleate, by passing a stream of nitrogen [11]. 

Precipitated from sodium oleate and concentrated Ca(NO3)2 solution. 

In order to prevent the close approach of the particles and thus their agglomeration, after the precipitation was completed (i.e., after the slurry had completely turned blac, the particles were coated in situ with ammonium oleate... 

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). 

Correlation of oleate adsorption and flotation maximum at about pH 7.5 for a variety of minerals and high abstraction (adsorption + surface precipitation) below this pH with the species distribution diagram (Fig. 4.9) suggests that the role of acid-soap dimer and precipitated oleic acid can be significant in controlling the adsorption and resultant flotation behavior. 

Floatabilities of francolite and dolomite using oleate as collector are shown in Figs. 4.28 and 4.29 as a function of oleate concentration and pH. It can be seen that the floatabilities of dolomite and francolite are quite similar with a sudden increase at an oleate concentration of 1.6 X 10 mol/1. Selective flotation of francolite from dolomite might be expected only above pH 9 or below pH 5. However, flotation of a binary mixture of dolomite and francolite (50 50) with 1.7 x 10 mol/1 oleate at pH 5.2 and 9.0 yielded poor separation. The loss of selectivity during flotation may be attributed to the interactions among the dissolved mineral species from minerals and oleate as well as the formation of oleate precipitates (Amankonah and Somasundaran, 1985). Depletion isotherms for labeled oleate on francolite and dolomite are shown in Fig. 4.30. Both francolite and dolomite show a two-region (II and III) linear isotherms with a break at a residual concentration of... 

At a concentration of >10 mol/1 (Region II), the slope of both curves increases significantly. This increased adsorption is attributed to possible precipitation of oleate on the mineral surface as well as in the bulk solution. The equation for both the isotherms is given below ... 

Relevant chemical equilibria responsible for the precipitation of Ca and Mg species with oleate are as follows (du Rietz, 1975 Leja, 1982) ... 

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 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 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. 

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