Fine lime

When a kiln is used in conjunction with the Solvay process and the manufacture of soda ash, coke can be fired in the kiln along with limestone to give the larger percentages of carbon dioxide needed for efficient soda ash production. If a purer lime product is desired, the fine lime can be taken from area 4 in (Fig. 2). A less pure product is obtained from the bottom kiln section. Another kind of kiln is the rotating, nearly horizontal type. These can be as much as 12 ft in diameter and 450 ft long. Limestone enters one end. It is heated, rotated, and slowly moves at a slight decline to the other end of the kiln, where lime is obtained. 

If there are specific data germane to the assumption of dose-additivity (c.g.. if two compounds arc present at the same site and it is known that the combination is fine limes more toxic than the sum of the loxicilics for the two compounds), then tlie development of the hazard index should be modified accordingly. The reader can refer to the EPA (1986b) mi.xture guidelines for discussion of a hazard index equation llial incorporates quantitative interaction data. If data on chemical interactions are available, but arc not adequate to support a quantitative assessment, note the information in the assumptions being documented for the risk assessment. 

The coal had to have an adequate ash fusion temperature, preferably over 1200 °C and an acceptably low ash content. A high ash fusion temperature reduced the risk of crotching, caused by the ash fusing and bonding lumps of lime to each other and to the refractories. It also ensured that most of the ash did not adhere to the lime and could be removed by screening at (say) 6 mm. The ash-contaminated fine lime could be sold as a low-grade product. 

As explained above, fine lime may amount to 10 to 25 % of the output. It is, therefore, essential to find economic outlets for that product. 

As with most powders, fine quicklime may compact, leading to arching . Bunkers should, therefore, be fitted with aeration pads, vibrators or mechanical devices to break any hold-ups. Conversely, aerated fine lime flows readily and equipment to prevent flooding , such as rotary valves, should be fitted to silo discharges. 

Details of this process are still largely confidential. An early patent [20.14] described the hydration of reactive, fine lime (e.g., less than 6 mm) with water in the presence of an amine/glycol additive. Specified compounds were mono-, di- and tri-ethyleneglycols and mono-, di- and tri-ethanolamines, and mixtures thereof. Hydrates with surface areas of 46m /g were cited. 

Fine lime generally refers to screened products with a top size below 0.6 cm. 

In making these, a cask of fresh Smithfield lime, of the best quality, was taken, and the lumps broken into pieces of about the size of a pigeon s egg. These being carefully screened, in order to get rid of all dust and fine lime, and carefully intermixed, in order to obtain uniformity of quality throughout, were slaked by the affusion of water to the amount of one third the bulk of lime. When cold, the slaked lime was returned to the barrel, which was carefully headed and put in a dry place and on all occasions of withdrawing a portion of this lime for use, the cask was carefully re-headed. 

Standard methods are adopted to make chromite bricks. The bond material may be fine lime or hydrated MgO. Tar is added as a temporary bond material. Chromite bricks are arranged on top of magnesite bricks in the kiln. This is required to reduce the height of the chromite stack because green chromite bricks do not have sufficient strength. The firing temperature is 1450°C. 

Some limestones, more often the coarse crystalline types, can never be calcined successfully. Such stone tends to decrepitate during preheating or calcination into fine particles that interfere with this pyrochemical reaction. The adaptabiflty of a stone for calcination can only be ascertained with surety by empirical methods. Possibly the greatest influence on lime quaflty is the size gradation of limestone. Narrow gradations, such as... 

Pit and Quarry Maga fine, Cleveland, Ohio, numerous articles on production of limestone and lime. 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Formulated metal poHshes consist of fine abrasives similar to those involved in industrial buffing operations, ie, pumice, tripoH, kaolin, rouge and crocus iron oxides, and lime. Other ingredients include surfactants (qv), eg, sodium oleate [143-19-1] or sodium dodecylben2enesulfonate [25155-30-0], chelating agents (qv), eg, citric acid [77-92-9], and solvents, eg, alcohols or aUphatic hydrocarbons. 

Pre-liming. Lime slurry, 0.25% lime on juice (0.250 g of CaO/100 g juice), is added to bring the pH of the mixture into the alkaline range. Insoluble calcium salts are precipitated as finely dispersed coUoids. Calcium carbonate in the form of recycled first carbonation sludge is added to provide coUoid absorption and stabilization. Temperature may be cool (50°C) or hot (80°C) depending on the temperature of the next step, or occasionally on the type of diffusion equipment. Retention time is 15 to 30 min. 

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