Flotation Systems

Primary molybdenum ores at a relatively coarse grind go through an initial stage of flotation. At Climax Molybdenum, for example, the first separation is made at 35% + 100 mesh. The flotation system uses vapour oil as a promoter and pine oil as frother. A sulfonated coconut oil (syntax) is added to the system to emulsify the oil. 

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Contact angle is proportional to (ysv - 7sl), therefore addition of a surfactant that adsorbs at the solid-solution interface should decrease ysL d therefore increase the quantity above and make 6 smaller. Yet such addition in flotation systems increases 6. Discuss what is inconect or misleading about the opening statement. 

The 2eta potential and contact angle as well as flotation recovery correlate well in some flotation systems as shown in Figure 9 (20). 

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. 

Flotation. Tallow amines contain small amounts of short-chain compounds, eg, the octyl, lauryl, and myristyl (C ) groups. These amines usually produce enough froth for the flotation. Small quantities of specialized synthetic alcohols, eg, Dowfroth P, are frequentiy added to the flotation system to supplement the natural frothers. The quantities of the reagents used ia potash flotation plants are Hsted ia Table 5. 

In conventional chemical pulping systems, micronized talc is used for pitch control. The mechanism is not well understood, but talc does adsorb on the pitch and detackify it, preventing it from agglomerating and attaching on equipment. In de-inking talc is used both to enhance ink removal in conventional screening/centrifugation methods and as a carrier in flotation systems. 

Fig. 4. Schematic of a pressurized dissolved air flotation system, (a) Influent pressurization (b) recycle pressurization.

Flotation is a physical process involving relative interaction of three phases solid, water, and air. An understanding of the wettability of the solid surface, physical surface, and chemical phenomena by which the flotation reagents act and the mechanical factors that determine particle-bubble attachment and removal of particle-laden bubbles, is helpful in designing and operating flotation systems successfully. 

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

Air Flotation systems for separating oil and solids from wastewater include ... 

Air flotation is simply the production of microscopic air bubbles, which enhance the natural tendency of some materials to float by carrying wastewater contaminants to the surface of the tank for removal by mechanical skimming. Many commercially available units are packaged rectangular steel tank flotation systems shipped completely assembled and ready for simple piping and wiring on site. 

Figure 27. Continuous flotation system (Courtesy of Beckart Environmental, Inc., Kenosha, WI, email info beckart.com)...

The most common application of carbon adsorption in municipal water treatment is in the removal of taste and odor compounds. Figure 12 provides an example of a process flow diagram for a municipal water treatment plant. In this example water is pumped from the river into a flotation unit, which is used for the removal of suspended solids such as algae and particulate matter. Dissolved air is the injected under pressure into the basin. This action creates microbubbles which become attached to the suspended solids, causing them to float. This results in a layer of suspended solids on the surface of the water, which is removed using a mechanical skimming technique. Go back to Chapter 8 if you need to refresh your memory on air flotation systems. 

Figure 2.31 One way in which a number of flotation cells can be arranged into a flotation system.

A flotation machine must satisfy certain requirements which are listed in Table 2.9. All told, the components of a flotation system are the following ... 

This is relatively intricate and is best carried out with uniformly ripe coffee berries that are still firm. To achieve this uniformity the coffee berries are selectively handpicked. As soon as possible they are sorted further in a water-flotation system and sent directly to a pulping machine. Here the berries have the outermost skin and pulp removed and the mucilage layer is exposed. 

A modified reduction-flotation system (Figure 6.5) is very similar to the existing conventional reduction-precipitation system (Figure 6.4), except that a DAF clarifier [T-101F] is used for clarification15-57 instead of using a conventional sedimentation clarifier (Tank T-101, Figure 6.4). 

It should be noted that the chemical reactions of the conventional reduction-precipitation system (Figure 6.4) and the modified reduction-flotation system are identical. 

Comparatively, the modified reduction-flotation system will have lower annual total cost (amortized capital cost plus O M cost) and will require less space, because the flotation unit is very shallow in depth and thus can be elevated. It is expected, however, that the treatment efficiency of the modified system will be higher due to the fact that the DAF clarifier can separate not only the suspended solids but also organics such as oil and grease, detergent, and so on.57-58-61 Conventional sedimentation clarifiers can separate only insoluble suspended solids. 

Wang, L.K., Wang, P, and Clesceri, N.L., Development of a combined biological aeration and flotation system for groundwater decontamination, Proc. Industrial Waste Conference, Purdue University, West Lafayee, IN, 1993. 

Krofta, M. and Wang, L.K., Design of Dissolved Air Flotation systems for Industrial Pretreatment and Municipal Water and Wastewater Treatment, National Meeting of American Institute of Chemical Engineers, Houston, Texas, March 1983. 

Kinetics and Case Histories of Activated Sludge Secondary Flotation Systems... 

There are three common flotation system configurations (a) full-flow pressurization (b) partial flow pressurization without effluent recycle and (c) recycle flow pressurization, which have been graphically illustrated in Figures 27.8 through 27.10, respectively. 

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