Selective flotation

Selective flotation is used in stock preparation systems for recovered paper processing. The objective is to remove contaminants from the suspension such as printing ink, stiddes, fillers, coating pigments, and binders. In selective flotation air is injected into the suspension generating bubbles that are mixed with the suspension. Such an air bubble may catch one or more particles. The particles 

In the past a large variety of flotation ceU designs were used. All cells have to ensure bubble generation, collision of the ink particles with the bubbles, transport of the ink-bubble aggregate to the suspension surface, and foam removal. 

Transport of particle-bubble aggregate to the suspension surface  

Foam discharge is done e. g. by free overflow over a weir, where a scraper may support the removal. In other designs the foam is discharged through sucking pipes by pressure difference, either by vacuum outside or pressure inside the cell. 

The cell body can be open but nowadays the cells are usually closed for environmental reasons. The closed cells can be pressurized or operate under a slight vacuum to avoid exhausts. One flotation line usually consists of several flotation steps where the accept stream of the preceding step is the inlet flow of the following one. The arrangement of these steps can also be different individual cells for each flotation step connected by pipes to a complete line, individual cell compartments which are aligned in a horizontal or vertical direction in one overall cell body, and column-like cells with internal recirculation are aU found. A special case is a vertical cydone-shaped cell where the ascent of the bubbles is mainly due to the centrifugal forces and is directed to the center. 

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Depressants are reagents that selectively prevent the reaction between a coUector and a mineral, thus preventing its flotation. For example, sodium cyanide [143-33-9] depresses sphalerite [12169-28-7] (zinc sulfide) and pyrite [1309-36-0] (iron sulfide) but not galena. It thus enhances selective flotation of the galena. 

On the basis of the function it performs, the flotation process can be divided into two categories (i) bulk and (ii) selective. The process is called bulk or collective flotation when it accomplishes the separation of several valuable components from the gangue minerals. In selective flotation, one valuable component is separated from several others. This selectivity could be accomplished by either using collectors selective with respect to a particular mineral or by differential flotation wherein two or more mineral concentrates are recovered consecutively from the same feed by using modifiers. 

Flotation. In many cases, contaminants adsorbed on the surface of clay particles, or contaminants occurring in soil as discriminate particles, have different surface properties to clean soil particles. By adding special chemical substances, the formation of a hydrophobic surface on the contaminated particles is possible. Pulp aeration results in the attachment of hydrophobic contaminated particles to the surface of the small bubbles that are formed. In this way, selective flotation of these particles is achieved. Contrary to the gravimetric separation methods, flotation offers the possibility to separate contaminated and noncontaminated particles of the same grain size and density but with different surface properties. 

Conox A process for beneficiating sulfide ores by selective flotation. Developed and offered by Lurgi. 

In flotation of gold-containing base metal ores, a number of modifiers normally used for selective flotation of copper lead, lead zinc and copper lead zinc have a negative effect on the floatability of gold. Such modifiers include ZnS04-7H20, S02, Na2S205 and cyanide when added in excessive amounts. 

The type of gangue minerals present, i.e. the selective flotation of cassiterite depends on the proper selection of depressant for certain gangue minerals. 

Strebzyn, V.G., Selective Flotation of Cassiterite in the Presence of Iron-Bearing Minerals, Obogasthenie Rud, No. 13, pp. 3-6, 1968. 

The treatment process and flotation properties of pyrochlore are very much dependent on the gangue composition of the ore. The selective flotation of pyrochlore from carbonatite ore is not possible since calcite and dolomite have similar flotation properties as pyrochlore. In addition, in the presence of carbonates, the stable pH required for flotation of pyrochlore (i.e. 5.0-5.5) cannot be maintained. 

Fatty acids and their variations were examined for selective flotation of zircon from Ta/Nb. No selectivity or zirconium flotation was achieved using fatty acids. 

From disseminated ores contained in mineral lenses, the recovery of bastnaesite and monazite is accomplished using flotation. The flotation properties of bastnaesite and monazite are similar to the gangue minerals contained in the bastnaesite and monazite, such as calcite, barite, apatite, tourmaline, pyrochlore and others, which represent difficulties in selective flotation. However, in recent years, significant progress has been made in the flotation of both monazite and bastnaesite [2,3]. 

In conclusion, it can be noted that the effect of pH on flotation of beach sand minerals is critical in selective flotation of monazite from other minerals. 

Method 2- It involves bulk flotation of rutile, ilmenite and zircon followed by selective flotation of mtile and ilmenite and depression of zircon. Figure 25.16 shows the flowsheet with type of reagent additions used in selective flotation of titanium from zircon. 

In flotation practice, the reducing environment produced in the grinding system may be useful for the interaction between galena and xanthate to form collector salt and not suitable for the formation of dixanthogen. It may promote the selective flotation separation of galena from pyrite. 

Tests have been done further on the separation of a Cu-Pb mixed concentration of ethyl xanthate flotation of copper-lead-iron sulphide ore by E- control modifying with H2O2. Test results are presented in Table 10.3. It indicates the possibility of selective flotation separations of copper-lead flotation concentration by control. The feed of copper-lead mixed concentrated assayed Cu 6.53% and Pb 62.38%. Using hydrogen peroxide as a potential modifier, a copper concentration with 24.19% Cu and recovery with 89% can be obtained after separation. 

Majima, H., 1969. How oxidation affects selective flotation of complex sulphide ores. Can. Met. (Quarterly), 8(3) 269-273... 

Xiong Daolin, Hu Yuehua, Qin Wenqing, Sun Wei, Liu Runqing, 2006. Selective flotation separation of marmatite from arsenopyrite by organic depressant PALA. Journal of Central South University, 37(4) 670 - 674 (in Chinese)... 

Zhang Qin, Hu Yuehua, Gu Guohua, Xu Jing, 2004b. Selective flotation separation of jamesonite from pyrrhotite by potassium cyanide. Journal of Central South University of Technology, 35(3) 372-375... 

This multi-step, one-pot process was taken further by integration of a third supported reagent for the sequential preparation of 3,5-diphenylpyrazole (Scheme 2.17). Following the previously established procedure, acetophenone was deprotonated and acylated to afford the 1,3-dicarbonyl species. This intermediate was easily separated from the spent polymers by filtration and passed without isolation into a suspension of the resin bound hydrazine salt (9), affording the desired pyrazole in 91% yield. In a subsequent publication, the authors reported that the depleted polymeric reagents from the first step of the conversion (i.e. (7) and (8)) were recovered and separated via a selective flotation procedure, enabhng them to... 

Frotliers are also added to stabilize the foam at the top of the chamber, so that the enriched mineral can be continuously scooped off. The selective flotation of a required mineral depends critically on surface properties and these can be carefully controlled using a wide range of additives. Throughout the world a large quantity (about 10 tons annually) of minerals are separated by this method. 

Examples of mixed post-consumer plastic waste by the combination of a three-stage sink-float method and selective flotation have been presented. The appropriate conditions, e.g., wetting agents, frother, depressant, and pH condition, are of importance (122). 

S. Pongstabodee, N. Kunachitpimol, and S. Damronglerd, Combination of three-stage sink-float method and selective flotation technique for separation of mixed post-consumer plastic waste, Waste Manage. (Oxford), 28(3) 475—483,2008. 

Step 6. Select flotation cell size from manufacturer s data for 3,000 bwpd. 

Chelating agents that can form insoluble, hydrophobic chelates on the surface of minerals are potential collectors for the selective flotation of minerals.3 4 As early as 1927, Vivian5 reported the use of cupferron, a well-known analytical reagent, as a collector for the flotation of cassiterite (Sn02). Since then, there have been a number of reports on the use of chelating agents in flotation. 

Figure 10.8 Illustration of a selective flotation process for the separation of heavy metal sulfides such as Cu-Mo, Cu-Ni, or Ni-Co-Cu, from unwanted gangue minerals, and from each other. From Leja [91]. Copyright 1982, Plenum Press.

Flotation has been used in removing oil and grease from wastewater. Selective flotation can be achieved by adding certain surfactants for the removal of metal ions, cyanides, fluorides, and carbonyl from hazardous wastes. 

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