Paper flotation

Moudgil and co-workers and Soto and Iwasaki have attributed the loss of selectivity to electrostatic forces encountered in the above mineral-collector systems. It was therefore, decided to modify the flotation behavior of apatite and dolomite by adding salts such as sodium chloride, in this paper, flotation results with dodecylamine hydrochloride collector are discussed. Flotation studies with sodium oleate collector have been discussed elsewhere. ... 

Cappelino et al. (1992) presented a very thorough study on the performance of centrifugal pumps with open impellers with emphasis on pulp and paper flotation circuits and deinking cells. High-consistency stock (12%) can have as much as 20-28% entrained air. 

Flotation tests were carried out in a Denver-type, 2-1 laboratory cell. The concentrations of the reagents were specified as solution concentrations. The procedure of waste paper flotation is described elsewhere [5]. For the filler flotation an aqueous dispersion with 0.2% filler in tap water (pH 8.5) was stirred with the respective collector for 10 min and then floated for 5 min. The floated fillers were subsequently filtered the filtrate was dried at 150°—180°C and weighed to determine the recovery. 

In some applications, such as the production of whipped cream, beer, meringue (-+food additives), foamed plastics, ->fire fighting foams, ore-(- mining chemicals) and waste paper-flotation (- paper additives), foamed concrete and - detergents, (controlled) foam formation is desired. Products enhancing this property are called foamers and are - surfactants or - water soluble polymers or mixtures of both. 

The examples in the preceding section, of the flotation of lead and copper ores by xanthates, was one in which chemical forces predominated in the adsorption of the collector. Flotation processes have been applied to a number of other minerals that are either ionic in type, such as potassium chloride, or are insoluble oxides such as quartz and iron oxide, or ink pigments [needed to be removed in waste paper processing [92]]. In the case of quartz, surfactants such as alkyl amines are used, and the situation is complicated by micelle formation (see next section), which can also occur in the adsorbed layer [93, 94]. 

Two main operational variables that differentiate the flotation of finely dispersed coUoids and precipitates in water treatment from the flotation of minerals is the need for quiescent pulp conditions (low turbulence) and the need for very fine bubble sizes in the former. This is accompHshed by the use of electroflotation and dissolved air flotation instead of mechanically generated bubbles which is common in mineral flotation practice. Electroflotation is a technique where fine gas bubbles (hydrogen and oxygen) are generated in the pulp by the appHcation of electricity to electrodes. These very fine bubbles are more suited to the flotation of very fine particles encountered in water treatment. Its industrial usage is not widespread. Dissolved air flotation is similar to vacuum flotation. Air-saturated slurries are subjected to vacuum for the generation of bubbles. The process finds limited appHcation in water treatment and in paper pulp effluent purification. The need to mn it batchwise renders it less versatile. 

After the resin is appHed to the paper, the wet treated web enters a drying oven where most of the solvent is evaporated off. Modem treaters, such as that shown in Figure 1, have air flotation ovens so that the web is never touched by hot conveyor bars that may cause streaks noticeable in the final product. 

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. 

Dispersion at temperatures of 90—110°C is a common final step io European mills processiog wax-coated old cormgated containers. Dispersion temperatures less than 90°C are reported to reduce wax particle size to improve pulp drainage properties on paper machines while improving paper strength (45). Dispersion has been used to reduce hot-melt adhesive, plastic coating, and asphalt particle size. These low density particles can then be removed from the pulp by flotation (46). 

Water Clarification. Process water that aeeds to be clarified comes from several differeat sources ia the recycling mill rejects from screeas and mechanical cleaners rejects from washers, thickeners, and flotation cells water that drains from the pulp as it is converted iato paper oa the paper machine (white water) and water from felt washers. These waters contain different dissolved chemicals and suspended soflds and are usually processed separately. 

The area of interest covered by this paper is limited to processes in which chemical conversion occurs, as in the processes noted above. Gas-liquid-particle processes in which a gaseous phase is created by the chemical reaction between a liquid and a solid (for example, the production of acetylene by the reaction between water and carbide) are excluded from the review. Also excluded are physical separation processes, such as flotation by gas-liquid-particle operation. Gas absorption in packed beds, another gas-liquid-particle operation, is not treated explicitly, although certain results for this operation must necessarily be referred to. 

A survey of applications was also done by Czichocki et al. [73], including such applications as inks and paints, paper, photography, plastics, emulsion polymerization, pharmaceuticals, flotation, corrosion inhibitors, lubricants, electroplating, electrophoresis, and catalysts for ethoxylation. 

Other plant-scale applications to pollution control include the flotation of suspended sewage particles by depressurizing so as to release dissolved air [Jenkins, Scherfig, and Eckhoff, Applications of Adsorptive Bubble Separation Techniques to Wastewater Treatment, in Lemlich (ed.). Adsorptive Bubble Separation Techniques, Academic, New York, 1972, chap. 14 and Richter, Internat. Chem. Eng, 16,614 (1976)]. Dissolved-air flotation is also employed in treating waste-water from pulp and paper mills [Coertze, Prog. Water TechnoL, 10, 449(1978) and Severeid, TAPPl 62(2), 61, 1979]. In addition, there is the flotation, with electrolytically released bubbles [Chambers and Cottrell, Chem. Eng, 83(16), 95 (1976)], of oily iron dust [Ellwood, Chem. Eng, 75(16), 82 (1968)] and of a variety of wastes from surface-treatment processes at the maintenance and overhaul base of an airline [Roth and Ferguson, Desalination, 23, 49 (1977)]. 

Krofta, M. and Wang, L.K., Pollution Abatement Using Advanced flotation Technology in the Paper and Pulp Industry, Powder and Bulk Solids Conference, Rosemont, Chicago, IL, May 1985. 

Flotation is also used in applications such as the separation of low-density solid particles (e.g. paper pulp) from water and oil droplets from oil-water mixtures. It is not necessary to add reagents if the particles are naturally hydrophobic, as is the case, for example, with oil-water mixtures, as the oil is naturally hydrophobic. 

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