Fine grinding, effect

Many hours are therefore required to effect virtually complete removal of moisture. The actual time depends on the nature of the material, the temperature, and the particle size. The time may, of course, be shortened by fine grinding to reduce the particle size and by operating at a high temperature. There are, however, practical limitations to this procedure. 

The Griffin mill is similar to the pendulum mill, other than it employs only one grinding head and the separation of the product is effected using a screen mesh fitted around the grinding chamber. A product fineness from 8 to 240 mesh at an output from 0.15 to 1.5 kg/s may be obtained. These mills are widely used for dry fine grinding in many industries and are noted for their simplicity and reliability. 

Prior to conducting the sorption experiment, the coal extract (200 mg) was first placed in a Wig-L-Bug capsule and ground for 1 minute under nitrogen. This grinding effectively reduces the extract to a fine powder, which is then used for the sorption experiment. Approximately 50-70 mg of the extract was then placed on the sample pan and the hangdown tube was replaced. The sample was maintained at 30.00 0.02 C by means of a constant temperature bath which surrounded the hangdown tube. 

The particle size of metallic silicon also has a noticeable effect on the chemical activity of contact mass in case of coarse grinding, the reactivity of powder is lower than required in case of fine grinding the reactivity rises sharply, and the heat has to be intensively diverted from the reaction zone. 

Coarse grinding of the raw materials with crushers, pan grinders, hammer mills or cross beater mills is often carried out by the raw material suppliers. Thus in ceramic manufacture only fine grinding is required, for which wet grinding in ball mills, in which greater communition effects are realized than in dry mills, is satisfactory. 

Effect of Physical Condition.—The increased exposure of surface due to fine grinding will be discussed later but two interesting phenomena should be mentioned here. (1) When the finest portion of a suitable crushed soluble material is added to a saturated solution of the same it will often dissolve to cause super-saturation which effect could never be gotten by contact with the coarser particles. (2) The rate of dissolution for different faces of the same crystal usually varies. These facts point to the necessity of making tests on the actual material to be treated when considering a leaching problem. 

The removal of both mineral matter and sulfur species to very low values would provide premium solid fuels and possibly new chemical feedstocks. Several techniques are being explored to achieve these goals. The mineral matter in a physically cleaned coal can be further reduced by the solubilization of the aluminosilicate minerals. This can technically be accomplished with the use of alkaline and then acid treatments. A variety of studies are under way to define the conditions required for effective removal of the mineral matter and establish the amount of sulfur reduction that can be accomplished. Others involve the use of fine grinding to liberate the coal from the mineral matter. Then an agglomerant is used to separate the coal matter from the aqueous phase containing suspended mineral matter. A new approach uses microwave energy to selectively decompose the clays into species that can be solubilized and removed. Still another technique involves treatment with carbon dioxide to reduce the particle size and permit the liberation of the mineral matter. Over the next few years these will be studied further and it is hoped that coal will become available in a form with less of these interesting, but not entirely desirable mineral species. 

One of the major problems with these kind of products is the effect of particle size. In order to minimise grind size effects in ground coffees of different roasts. Little and MacKiimey (1956) standardised on a very fine grind with maximum hghtness value. Seakins (1971) tackled the problem by another means and developed a method to measure the colour of casein by immersing it in a liquid of similar refractive index. Reflectance measurement of dry sample preparations resulted in poor separation of colour grades because reflectance increased as particle size decreased. However, when transmittance values were measured on the liquid suspension, the colour grades were clearly differentiated. 

Fertilizer of very low water solubility generally must be ground to small particle size to ensure sufficiently rapid dissolution in the soil and utilization by plants. For example, the effectiveness of raw phosphate rock generally increases with fine grinding down to a particle diameter of about 150 pm below that, little further benefit has been established [12]. Other materials of low solubility that require relatively fine grinding include basic slag, limestone, dolomite, dicalcium phosphate, and fused phosphates [13,141. Micronutrient or secondary... 

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