Wet grinding

Wentworth process Weston cell Wet air oxidation Wet ball mill Wet-end additives Wet etching Wetfastness Wet grinding... 

For fine pulverization, both dry and wet processes are utilized, but increasingly the dry process is more popular because wet grinding ultimately requires drying and is much more energy intensive. A sensitive fan swirls the dust sizes into the air separator and permits coarse particles to recycle to the grinding mill or be rejected as tailings the fines are drawn into cyclones where the dust is collected. 

The coarse mica concentrate is either respiraled to produce a product with a grade suitable for use by wet grinding mica producers, or floated to further upgrade it for specialty high grade dry ground mica products. 

The general pieces of equipment used in grinding flake mica or mica concentrate into saleable mica products are hammer mills of various types, fluid energy mills, Chaser or Muller mills for wet grinding, and Raymond or WiUiams high side roUer mills. Another method is being developed, called a Duncan mill (f. M. Huber, Inc.), that is similar in many respects to an attrition mill. AH of these mills are used in conjunction with sieves, and all but some types of hammer mills incorporate air classifiers as a part of the circuit. 

Grinding is a continuous process. It may be either wet or dry, but wet grinding (at 50—80% soHds) is most common and requires less power per ton of material ground. Media consumption is significantly higher, however. Wet grinding is also the choice when subsequent processing is wet. In certain... 

Typically, ore bodies are relatively low in iron content. Iron minerals are finely divided in a gangue matrix. Wet grinding is usually required to Hberate the iron minerals, although some beach sands may have Hberated iron mineral values. Wet dmm separators are limited to the treatment of material <10 mm. The magnetic dmm separators appHed are usually related to the grinding circuit required to Hberate the iron mineral, and are typically designated by appHcation as cobbers, roughers, or finishers. 

The work index may be round experimentally from laboratoiy crushing and grinding tests or from commercial miU operations. Some rules of thumb for extrapolating the work index to conditions different from those measured are that for dry grinding the index must be increased by a factor of 1.34 over that measured in wet grinding for open-circuit operations another factor of 1.34 is required over that measured in closed circuit if the product size Xp is extrapolated below 70 [Lm, an additional correction factor is (10.3 + Xp)/l.l45X . Also for a jaw or gyratory crusher the work index may be estimated from... 

Dispersing Agents and Grinding Aids There is no doubt that grinding aids are helpful under some conditions. For example, surfactants make it possible to ball-mill magnesium in kerosine to 0.5- Im size [Fochtman, Bitten, and Katz, Ind. Png. Chem. Prod. Res. Dev., 2, 212-216 (1963)]. Without surfactants the size attainable was 3 [Lm, and of course the rate of grinding was very slow at sizes below this. Also, the water in wet grinding may be considered to act as an additive. 

In wet grinding there are several theories, which have been reviewed [Somasundaran and Liu, Ind. Png. Chem. Proce.ss Des. Dev., 11(3), 321 (1972) Snow, annual reviews, op. cit., 1970-1974. See also Rose, Ball and Tube Milling, Constable, London, 1958, pp. 245-249]. The Rehbinder theory (Rehbiuder, Schreiner, and i-... 

The net production in wet grinding in the Bond grindability test varies from 145 to 200 percent of that in diy grinding depending on mesh [Maxson, Cadena, and Bond, Trans. Am. Int. Min. Metall. Pet. Eng., 112, 130-145, 161 (1934)]. Ball mills have a large field of apph-cation for wet grinding in closed circuit with size classifiers, which also perform advantageously wet. 

FIG. 20-35 Drais wet-grinding and dispersing system (U.S, patent 3,957,210) Draiswerke Gmbh, [Stehr, International J, Mineral Processing, 431—... 

FIG. 20-43 Single -stage closed-circuit wet-grinding system, [Tomy, Pit Quarry Tehixiaiy-March 1.9,59),]... 

FIG. 20-45 Closed -circuit wet grinding with liquid-solid cyclone. [Tonty, Pit Quarry (Fehtuaty-March L95.9).]... 

FIG. 20-57 Autogenous mill circuit. Simphfied flow diagram of the Cleveland-Cliffs Iron Co. Empire iron-mine concentrator with two autogenous wet-grinding stages. To convert inches to centimeters, multiply hy 2.54 to convert feet to centimeters, multiply hy 30.5. 

In modern iustaUatious wet grinding is sometimes accomphshed in ball mills alone, operating with excess water in closed circuit with classifiers and hydroseparators. 

Figures 20-43 to 20-44 illustrate single-stage and two-stage closed-circuit wet-grinding systems. The circuits or Fig. 20-59 may also be used as a closed-circuit wet-grinding system incorporating a hquid-solid cyclone as the classifier.

Nassmahlen, n. wet grinding, wet milling, nassmechanisch, a. wet mechanical, wet-mill. Nass-metallurgie,/. hydrometallurgy. -mUhle,. f. wet mill, -probe, /. wet test. 

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