Flotation effectiveness

Dissolved Air Flotation Effective for WAS Relatively high power consumption... 

Comparison of experimental points with theoretical points is shown in Figure 10. Agreement is good at low pressure (i.e., p < lOOkPa), and may differ by as much as 10J at the higher pressures. This error is of the same order as that claimed by the existing, more empirical, models in the literature. A systematic agreement in shape is noted, and the actual error may be in the experimental data where "flotation" effects are serious for gravi-metic measurements at elevated pressures. 

In the matter of preferential treatment the flotation art has advanced very little. The oils make very little selective difference in the sulphides floated and various attempts to intensify the selective effect have not resulted in much advance. As the art stands today it is increasingly ineffective on material which is coarser than 40 mesh largely because of occluded gangue matter which weakens the flotation effect. The recovery on the very finest slime is also unsatisfactory. Any sulphide ore which has not been exposed to oxidation will float well on being ground to 40 mesh or finer and on those portions of it which will settle promptly in water. 

Other authors (7) reported that the Al-type floe is removed better in flotation than in sedimentation. Furthermore, the specific density of aluminum, which is lower than that of iron, is responsible for the better flotation effect. It appears that floe formation in the aluminum system does not provide sufficiently high sedimentation rates, although enough chemicals are available for solid-bubble enmeshment (i.e., good flotation). 

I.I. 0-p// diagram and flotation effect ofNu2S Na2S is a sulfidizing agent for copper, lead and zinc oxides and depressant for sulfide minerals. Na2S can be hydrolyzed and then dissociated in solution ... 

I. log C-pH diagram and flotation effect ofxanthates Xanthate hydrolyzes in solution to form xanthic acid, HX, and then dissociates ... 

Many of the industrial wastewaters amenable to clarification by flotation are colloidal in natme, for example, oil onulsions, pulp and paper wastes, and food processing. For the best results, such wastes must be coagulated prior to flotation. In fact, flotation is always the last step in the treatment. In order to aid the flotation effectivity, one uses surfactants. This leads to lower smface tension and foaming. The latter helps in retaining the particles in the foam under flotation. Further, the effectiveness of flotation is also dependent on what kind of gas is used to make the bubbles (e.g., air and CO2). This is related to the dipole characteristics of the gas (CO2 has a stronger dipole than Nj). 

Avoid a dissolved gas flotation effect. The produced water sample is depressurized as it passes through the choke valve... 

One way of avoiding droplet shear and gas flotation effects is to conduct an online sample measurement. This technique, however, requires specialized equipment, such as the Melvem Mastersizer, and is constrained in terms of the maximum pressure it can tolerate. Alternatively, a sample pressure cylinder (homh) can he used to avoid droplet shear and the gas flotation effect. Here, the sample is taken in a stainless steel cylinder with a needle valve and a ball valve and thus minimizes the shearing of droplets during sampling. 

The flotation of mica has been correlated to the adhesion force measured from surface force (SFA—see Section VI-4) experiments although, to these authors, it is clear that dynamic effects prevent an absolute comparison [69, 70],... 

Skin-care products Skin effect Skin flotation Skin infections Skin packaging Skin-So-Soft Skin stains Skiving... 

Fig. 1. Effect of particle size on the flotation recovery of a sulfide mineral. Mineral chalcocite [2112-20-9J, CU2S reagent potassium ethyl xanthate,...

Activators enhance the adsorption of collectors, eg, Ca " in the fatty acid flotation of siUcates at high pH or Cu " in the flotation of sphalerite, ZnS, by sulfohydryl collectors. Depressants, on the other hand, have the opposite effect they hinder the flotation of certain minerals, thus improving selectivity. For example, high pH as well as high sulfide ion concentrations can hinder the flotation of sulfide minerals such as galena (PbS) in the presence of xanthates (ROCSS ). Hence, for a given fixed collector concentration there is a fixed critical pH that defines the transition between flotation and no flotation. This is the basis of the Barsky relationship which can be expressed as [X ]j[OH ] = constant, where [A ] is the xanthate ion concentration in the pulp and [Oi/ ] is the hydroxyl ion concentration indicated by the pH. Similar relationships can be written for sulfide ion, cyanide, or thiocyanate, which act as typical depressants in sulfide flotation systems. 

The treatments used to recover nickel from its sulfide and lateritic ores differ considerably because of the differing physical characteristics of the two ore types. The sulfide ores, in which the nickel, iron, and copper occur in a physical mixture as distinct minerals, are amenable to initial concentration by mechanical methods, eg, flotation (qv) and magnetic separation (see SEPARATION,MAGNETIC). The lateritic ores are not susceptible to these physical processes of beneficiation, and chemical means must be used to extract the nickel. The nickel concentration processes that have been developed are not as effective for the lateritic ores as for the sulfide ores (see also Metallurgy, extractive Minerals recovery and processing). 

The majority of studies on the acute and chronic toxicity of phthalates to aquatic organisms show no toxic effects at concentrations 200—1000 times the water solubiUty. However, there are some studies iadicatiag higher toxicity which are beheved to be due to the flotation and entrapment effects outlined above. 

Scrubbing andDesliming. Sylvinite ores in North America contain 1—6 wt % water-insoluble clays. A significant portion of these clays is less than 0.002 mm in diameter. If not removed or controUed in some manner, clay bodies that are dispersed in the flotation solution, ie, brine saturated with KCl and NaCl, absorb the amine coUector, which is added to effect flotation separation, and the coUector is rendered ineffective. Clay is the most troublesome impurity encountered in the processing of sylvinite ore. 

Flotation. Flotation (qv) is used alone or in combination with washing and cleaning to deink office paper and mixtures of old newsprint and old magazines (26). An effective flotation process must fulfill four functions. (/) The process must efficiently entrain air. Air bubble diameter is about 1000 p.m. Typically air bubbles occupy 25—60% of the flotation cell volume. Increa sing the airRquid ratio in the flotation cell is said to improve ink removal efficiency (27). (2) Ink must attach to air bubbles. This is primarily a function of surfactant chemistry. Air bubbles must have sufficient residence time in the cell for ink attachment to occur. (3) There must be minimal trapping of cellulose fibers in the froth layer. This depends on both cell design and surfactant chemistry. (4) The froth layer must be separated from the pulp slurry before too many air bubbles coUapse and return ink particles to the pulp slurry. 

Biological processes are also being studied to investigate abiHty to remove sulfur species in order to remove potential contributors to acid rain (see Air pollution). These species include benzothiophene-type materials, which are the most difficult to remove chemically, as weU as pyritic material. The pyrite may be treated to enhance the abiHty of flotation processes to separate the mineral from the combustible parts of the coal. Genetic engineering (qv) techniques are being appHed to develop more effective species. 

Two types of floater aozzles are curreafly ia use and they are based on two different principles. The Bernoulli principle is used ia the airfoil flotatioa aozzles, ia which the air flows from the aozzle parallel to the web and the high velocities create a reduced pressure, which attracts the web while keeping the web from touching the nozzles. The Coanda effect is used to create a flotation nozzle when the air is focused and thus a pressure pad is created to support the web as shown ia Figure 19. 

CMC), reverses the effect that the surfactant has on contact angle at lower concentrations, and at or above the CMC there is no further lowering of surface tension. At the higher concentrations, the surfactant loses some of its beneficial effect on dewateriag, as shown ia Figure 5. The beneficial effects of surfactants on dewateriag are most pronounced ia cakes that have been partially deslimed or ia cakes of partially hydrophobic particles (eg, flotation concentrates) that are adsorbed onto each other. Surfactants at or above CMC have Httle practical effect on extremely fine cakes, where pores are small and the cake has no further opportunity to consoHdate. A number of filter cakes do not respond to surfactant addition at any level. 

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