Fine product

The three basic types of size reduction circuits used to produce a fine product ate shown in Eigure 1. The final stages of the grinding circuit are typically operated in closed circuit, at comparatively high circulating loads, so that the material has tittle chance of being broken a second time before it is removed from the circuit by a classifier. Rod mills are operated normally in an open circuit. 

Cry staUization at temperatures of about 40°C results in heavy nucleation and a fine product. At temperatures above 75°C, only cry stal growth occurs, giving rise to large, weU-cry staUized aggregates composed of hexagonal rods and prisms (Fig. 2a). 

Screening devices are used to make coarser separations that is, fine products having 95% passing ca 100-mm—50-p.m size. Dry-screening devices have a lower recommended size of ca 500 p.m. Wet-screening devices that produce 95% passing ca 500—50-p.m size are continually being improved. 

Pneumatic classification can be partitioned conveniently into coarse, ie, fine products above 95% < 100 pm intermediate, ie, fine products ranging between 95% < 100 and 30 pm and fine, ie, fine products below 95% < 30 pm. Pneumatic classification, like hydraulic classification, balances the force of gravity with drag forces (counter flow) in order to bring about a separation. 

Talc products are also characterized by their crystallinity or relative platiness. Mycrocrystalline talc products typical of Montana and AustraUa tend to have very fine natural grain sizes and thus are ea sily milled to very fine products of higher surface area (10—20 m /g). Macrocrystalline talc ores... 

The calcium carbonate industry is one of the most competitive of the industrial minerals industry. The market for fine products (97% <45 fim) is estimated to be between 5—9 million tons annually in the United States. The pricing is dependent on the grade which is determined by fineness, purity, and brightness it ranges from 30/kg for coarse materials to over 440/kg for some ultrafine coated or food grades (4). 

Three parameters define the performance of a classifier. These are cut size, shaipness of cut, and eapaeity. Cut size, X50, is the size at which 50 percent of the material goes into the coarse product and 50 percent into the fine. (This should not be confused with the cutoff size, a name sometimes given to the top size of the fine product .)... 

It has been suggested that the circulating load can be calculated by a material balance from size analyses of the feed, fine product, and coarse product of the classifier in a closed-circuit grinding system [Bond, Rock Prod., 41, 64 (January 1938)]. However, since size analyses are subject to error, it is better to use this information to check the size analyses (Vaillant, op. cit.). The appropriate equation is (Dahl, Classifier Test Manual, Portland Cem. Assoc. BuU. MRB-53, 1954)... 

Advantages of vibratoiy mills are (1) simple construction and low-capital cost, (2) veiy fine product size attainable with large reduction... 

Some mechanical air classifiers are designed so that the fine product must pass radially inward through rotor blades instead of spirally moving across them as with whizzer blades. Examples are the Mikron separator Hosokawa Micron Powder Systems Div.), Sturtevant Side Draft separator, and the Majac classifier shown attached to the Majac jet mill (Fig. 20-55). 

The fine product is carried in the air stream through the fan and discharge port and separated by a cyclone collec tor into a suitable container. 

Lime Lime used for agricultural purposes generally is ground in hammer mills. It includes burnt, hydrated, and raw limestone. When a fine product is desired, as in the building trade and for chemical manufacture, riug-roUer mills, ball mills, and certain types of hammer mills are used. 

Most gums and resins, natural or artificial, when used in the paint, varnish, or plastic industries, are not ground veiy fine, and hammer or cage mills will produce a suitable product. Typical performance of the di attrition mill is given in Table 20-25. Roll crusners will often give a sufficiently fine product. 

A heartfelt thanks goes to Butterworth Heinemann for their patience during the writing of this book, and to their fine production. A special thank you is extended to Laura Berendson and Tara Habhegger for their creative efforts throughout the production of this volume. 

Although the author has taken great care to ensure that the information presented in this volume is accurate, neither he nor the publisher will endorse or guarantee any designs based upon materials provided herein. The author wishes to thank Butterworth-Heinemann Publishers for their fine production of this volume. 

The volume has been organized as a desk reference and for use in training programs such as Employee Right-to-Know and OSHA 40-Hour Hazard Worker Training (29 CFR 1910.120). Special gratitude is extended to Noyes Publications for the fine production of this work. 

A heartfelt thanks is extended to Butterworth-Heinemann Publishers for their fine production of this volume, and in sharing my vision for this series, and to various companies cited throughout the book that contributed materials and their time... 

When Sommer tried to prepare the potassium salt of 3 the crystal-fine product obtained exploded with violence as he spread it upon a porous plate. The potassium salt was, however, isolated and analyzed by Browne and Hoel. It is anhydrous but very soluble in water. Several other salts have been prepared. The slightly soluble heavy-metal salts are very sensitive to shock and may explode violently even under water. 

The effect of pH on both clay swelling and fines production has been widely discussed(89-95). Little consensus is found in this literature. Suggested treatments range from application of fluoboric acid(96) to 15% KOH(92) solutions — both treatments are believed to create a protective silicate film that inhibits release of fines. Polyacrylate polymers can provide protection against swelling of smectite clays and shales(97-100). 

Fines production from untreated test sands and permeability damage observed in untreated cores indicated that the laboratory test flow rates were above the critical flow velocity required to initiate fines migration. 

Table V. Mineral Fines Production From Unconsolidated Test Columns...

Copolymer Treatment Fluid Mineral Fines Production... 

Table VII. Reduction of Mineral Fines Production Using NVP Copolymers...

Mineral Fines Production (% of untreated test column)... 

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