Liming lime losses

Heavy soils, particularly clays, have a greater ability to retain calcium and magnesium ions than lighter, sandy soils. It is, therefore, common practice to apply limestone less frequently to heavy than to light soils. The frequency of application also depends on the rate of lime loss, which can only be determined by monitoring over successive years. 

When quicklime products are applied to the land, the first reaction is slaking. This produces finely divided calcium hydroxide and enables relatively coarse kibbled lime (a screened grade) to be used effectively. Some of the hydrated lime dissolves and produces a rapid increase in soil pH, within a week or two. The remainder of the lime carbonates, reacts relatively slowly, and keeps the pH in the required range for a prolonged period. The duration of that period depends on the rate of application, the nature of the soil and the rate of lime loss. 

Rotary kilns and, to a lesser extent, Fluo-SoHds kilns are used to calcine a wet precipitated calcium carbonate filter cake in the kraft or sulfate paper-pulp process (15). Lime is regenerated for use as a causticization reagent in recovering caustic soda for pulp digestion. Losses in lime recovery are replaced by purchased lime (see Paper Pulp). 

Caustic soda is removed from the carbonate—bicarbonate solution by treating with a slight excess of hard-burned quicklime (or slaked lime) at 85—90°C in a stirred reactor. The regenerated caustic soda is separated from the calcium carbonate precipitate (lime mud) by centrifuging or rotary vacuum filtration. The lime mud retains 30—35% Hquid and, to avoid loss of caustic soda, must be weU-washed on the filter or centrifuge. Finally, the recovered caustic solution is adjusted to the 10% level for recycle by the addition of 40% makeup caustic soda. 

Yields of propylene chlorohydrin range from 87—90% with dichloropropane yields of 6—9%. The dichloropropane is not only a yield loss but also represents a disposal problem as few uses are known for this material. Since almost all the propylene chlorohydrin is dehydrochlorinated to propylene oxide with lime or sodium hydroxide, none of the chlorine appears in the final product. Instead, it ends up as dilute calcium or sodium chloride solutions, which usually contain small amounts of propylene glycol and other organic compounds that can present significant disposal problems. 

Thermally efficient calcination of lime dolomite and clay can be carried out in a multicompartmeut fluidized bed (Fig. 17-27). Fuels are burned in a fluidized bed of the product to produce the required heat. Bunker C oil, natural gas, and coal are used in commercial units. Temperature control is accurate enough to permit production of hme of very high availability with close control of slaking characteristics. Also, half calcination or dolomite is an accepted practice. The requirement of large crystal size for the hmestoue limits apphcatiou. SmaU-sized crystals in the hmestoue result in low yields due to high dust losses. 

It has been reported that tetramethylene chlorohydrin undergoes loss of hydrogen chloride when distilled at pressures appreciably above 15 mm. If an oil pump is used for the distillation of the main fraction, it should be protected from hydrogen chloride by means of soda-lime towers. 

A formulation consisting of 2-acrylamido-2-methylpropane sulfonic acid, acrylamide, and itaconic acid has been proposed [676]. Such polymers are used as fluid loss control additives for aqueous drilling fluids and are advantageous when used with lime- or gypsum-based drilling muds containing soluble calcium ions. 

Although arsenic is not an essential plant nutrient, small yield increases have sometimes been observed at low soil arsenic levels, especially for tolerant crops such as potatoes, com, rye, and wheat (Woolson 1975). Arsenic phytotoxicity of soils is reduced with increasing lime, organic matter, iron, zinc, and phosphates (NRCC 1978). In most soil systems, the chemistry of As becomes the chemistry of arsenate the estimated half-time of arsenic in soils is about 6.5 years, although losses of 60% in 3 years and 67% in 7 years have been reported (Woolson 1975). Additional research is warranted on the role of arsenic in crop production, and in nutrition, with special reference to essentiality for aquatic and terrestrial wildlife. 

Salsigne A cyanide process for extracting gold from ores containing arsenic or antimony. Pre-treatment with a lime slurry reduces cyanide losses. 

---