Production Ball mill process

The production rate of the ball mill process has been found to be proportional to the speed of the drum rotation. The energy needed for the production of 1 ton of lead oxide is fairly constant when the mill operates at between 55 and 90% of its critical rotation speed. The critical rotation speed is assumed to be the speed of drum rotation at which lead pieces stick to the drum walls under the action of centrifugal forces and do not rub against each other. 

After the above brief description of the two methods of leady oxide production the question arises logically as to which of the two processes is better. Table 5.1 compares the characteristics of the leady oxides produced by the Barton pot and ball mill processes [17]. 

The role of calcite and fluorite used in ball-milling process was proposed. When the minerals are mechanically crushed, the newborn solid surface is activated with the naked ionic species in situ generated. The naked carbonate and fluoride anions act as a strong base capable of deprotonating the active methylene compounds, with the consequent formation of a carbanion stabilized via the coordination with calcium cation, which combines with a carbonyl compound, eventually leading to the Knoevenagel product. 

Lead Oxide Characteristics of the Products of the Barton Pot and Ball Mill Processes... 

The raw ROM (run of mine) ore is reduced in size from boulders of up to 100 cm in diameter to about 0.5 cm using jaw cmshers as weU as cone, gyratory, or roU-type equipment. The cmshed product is further pulverized using rod mills and ball mills, bringing particle sizes to finer than about 65 mesh (230 p.m). These size reduction (qv) procedures are collectively known as comminution processes. Their primary objective is to generate mineral grains that are discrete and Hberated from one another (11). Liberation is essential for the exploitation of individual mineral properties in the separation process. At the same time, particles at such fine sizes can be more readily buoyed to the top of the flotation ceU by air bubbles that adhere to them. 

Another process, which also generates elemental sulfur as a by-product, has been patented by Envirotech Research Center in Salt Lake City (29). In the Electroslurry process, a ball mill finely grinds a chalcopyrite concentrate, which reacts with an acidic copper sulfate solution for iron removal. The Hquor is electrolyzed and the iron is oxidized to the ferric form. This latter step leaches copper from the copper sulfide for deposition on the cathode. Elemental sulfur is recovered at the same time. 

There is some beneficiation of talc by froth flotation (qv), practiced especially on ultramafic-type deposits. In this process (Fig. 2), talc is milled to its hberation size (—100 mesh (ca 0.15 mm)) using ball mills or ring-type roUer mills and then slurried at 10—30% in water. Flotation is done in conventional multistage float cells using methyl amyl alcohol as a frother. Typically two to four stages are required to upgrade the ore from 50—70% talc to 90—98%. The product is filtered and then flash-dried and milled to a final product. 

The oxide exiting either the Barton or ball mill reactor is conveyed by an air stream to separating equipment, ie, settling tank, cyclone, and baghouse, after which it is stored in large hoppers or dmmmed for use in paste mixing. Purity of the lead feed stock is extremely critical because minute quantities of some impurities can either accelerate or slow the oxidation reaction markedly. Detailed discussions of the oxide-making process and product are contained in references 55—57. 

Drum Separators Very coarse solids, up to 0.3 m (12 in), are often processed in a drum separator of the type shown in Fig. 19-32. This is similar to a ball-mill shell with hfters permanently attached to the wall. Medium and feed enter at one end, and the float product flows out through the discharge trunnion, while the sink is lifted by the rotation of the drum to a stationaiy launder, through which it is flushed out. Modifications of this type include division of the shell into two compartments, which permits simultaneous operation at two different piup densities resulting in various grades of products. The two-compartment revolving drum is illustrated in Fig. 19-32. 

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