Reagents and Chemicals

Rheology of Polymer Solutions

Viscosity measurement represents one of the simplest experimental techniques for characterizing polymers. In general, the viscosity of a polymer solution depends on the molecular weight of the polymer and on the configuration of the molecules. For essentially linear polymers such as the polyacrylamide flocculants, coiling of the molecule in response to changes in its environment leads to changes in viscosity which can be evaluated in terms of an effective radius of gyration.

For flexible molecules which form random coils in solution it can be shown that the radius of gyration (Rg), defined as the root-mean-square distance of the elements of the chain from its center of gravity, can be calculated from viscosity data using the following relation:

[n] = 14.7∅Rg/M………………………………………………(1)

where M is the molecular weight of the polymer, ∅ is Flory’s universal constant (2.1×10)21) and [n] is the intrinsic viscosity of the solution defined by:

intrinsic-velocity-flocculation

in which n is the viscosity of a polymer solution of concentration C and η0 is the viscosity of the pure solvent.

It should be emphasized that the application of Equation 1 to aqueous solutions of polymer flocculants is approximate at best since it is by no means clear that ….Read more

Downdraft Tables

downdraft tablesAs well as metal working, welding or cutting, downdraft tables are also used for human dissection tables although rim exhausts are usually used for this purpose. For manual shoe repair and during application of artificial fingernails, downdraft tables are the only type of exhaust possible.

Larger versions are used for sanding, grinding, polishing, and welding. Since welding generates large amounts of heat together with the contaminants, a downdraft table, although handy, is not suited for this use. There could be problems with grinding, since the contaminants are generated with a high velocity in different directions and a downdraft table is only suited for capturing contaminants with low velocity and a temperature equal to or lower than room temperature. A partial solution to this is to surround the table on three sides with walls (0.2 to 0.5 m high) to deflect the generated contaminants and to diminish the amount of air pulled in from the sides.

Very large downdraft rabies have been used for sources such as electrocutting and welding of large steel sheets.

air flow of downdraft tableModification to processes can also indirectly reduce pollutant emissions. ….Read more

How to Transport Lime

Lime is transported in large volumes by the three common surface modes, i.e., barge, railroad, and truck.

Barge Transportation

Barges used in lime transportation have a capacity up to 1,500 tons and 1,400 ton loadings are very typical. The hulls of the barges are double skinned and constructed with water-tight sections. This type of barge design protects the lime in the cargo compartment in the event the outer steel surface of the hull is punctured or ripped open. The water-tight sectional design virtually insures that the barge will not sink if the outer hull surface is ruptured.

The lime is protected by barge covers. These barge covers may be rolled aside or lifted off during loading or unloading. Once the covers are closed they are weather-tight and protect the lime from rain, wind, and other adverse weather conditions.

Loading and unloading can only be done when there is no rain. Loading and unloading systems must also effectively control dust emmissions. Loading is accomplished by spouts and chutes that lower into the barge, vacuum (negative pressure) air lines literally pulls the dust from given points in the loading system. The air in the vacuum lines is cleaned and filtered through bag houses. A 1,400 ton ….Read more

Ferrocyanide Methods of Analysis & Assay Procedure

QUALITATIVE DETECTION

Because of the distinctive colors of the precipitates formed, various cations have been proposed for the qualitative detection of the ferrocyanide ion. Since interference frequently occurs, some care is usually necessary. As an illustration, the following condensed procedure serves for the detection of the ferrocyanide ion in the presence of ferricyanide and thiocyanate:

A dilute solution of the alkali salts of the anions is acidified with a slight excess of hydrochloric acid and is treated with an excess of ammonium molybdate solution. Brown molybdenum ferrocyanide precipitates. The liquid is shaken with a little fine asbestos and filtered. The residue is washed with cold, dilute acid, and then dissolved in ammonium hydroxide. The solution is saturated with hydrogen sulfide and then acidified with sulfuric acid. After removal of the precipitated sulfide by filtration, the filtrate is boiled to drive off the hydrogen sulfide. A ferric chloride solution is added; the formation of Prussian Blue indicates ferrocyanide.

ferrocyanide-methods-of-analysis

A simple test in which most anions do not interfere may be carried out by the addition of one drop of a 0.5 percent solution of N-chlorosuccinimide in 95 percent ethanol to a neutral or slightly acid ferrocyanide ….Read more

Ferrocyanide Toxicity

ferrocyanide-toxicity

It is generally agreed that the ferrocyanide ion is of a low order of oral toxicity, even in relatively large dosage. Kobert states that potassium ferrocyanide in alkaline solution is nontoxic. In Precis de Toxicologie it likewise is asserted that this salt is nonpoisonous and that it is useful as a diuretic. There is recorded a case of ingestion of a rather sizable dose (30 grams) of potassium ferrocyanide by a man aged 52 which caused serious, but apparently not critical illness. The patient suffered damage to the kidney tubules with marked albuminuria, appearance of casts, and prolonged disturbances of concentration ability. The poisoning was said to be due to the ferrocyanide ion and not to any liberated hydrogen cyanide.

The slow intravenous injection of 5 percent sodium ferrocyanide solution administered to children and adults in clinical tests was without toxic effect. Glomerular function was studied in 45 normal children and adults and in 70 cases with glomerulonephritis, hypertension, and tonsillitis. The results indicate that the quantity excreted by the kidneys is independent of the volume of the urine and is greater than 25 percent in the first thirty minutes.

No case of contact ….Read more

Ferrocyanides Usage & Applications

ferrocyanides-applications

Alkali metal ferrocyanides and their easily obtainable derivatives such as ferricyanides, nitroprussides, and hydroferrocyanic acid have found application in a wide variety of fields during the two centuries that they have been known. Through continued research new uses are being uncovered with increasing frequency.

Most of these applications depend upon oxidation-reduction potentials, sequestering and precipitating ability, color formation, or the high nitrogen content of the prussiates. In the following sections, the applicability of these properties to a number of specific uses will be discussed.

ANALYTICAL CHEMISTRY

Since ferrocyanides and their derivatives have found so many and such diverse applications in analytical chemistry, a complete coverage of the field is beyond the scope of this review. The following, however, will indicate some of the potential uses of these compounds as analytical reagents.

Potassium ferrocyanide has been found useful for the qualitative detection of certain sugars, the nitrite ion in urine, thiourea, a number of alkaloids, and various metals such as cadmium, iron, uranium, and zinc.

The quantitative determination of zinc, cadmium, cerous ion, uranyl ion, and lead also may be accomplished through the use of potassium ferrocyanide. The same salt has been reported in a new analytical method ….Read more

Hydroferrocyanic Acid

hydroferrocyanic-acid

PHYSICAL PROPERTIES of Hydroferrocyanic Acid

ferrocyanide-physical-properties

Hydroferrocyanic acid is most conveniently prepared by the treatment of an alkali metal ferrocyanide with a strong mineral acid. A typical preparation would involve the treatment of a saturated aqueous solution of potassium ferrocyanide with concentrated hydrochloric acid. The acid separates as a crystalline solid that may be purified further by solution in ethanol and reprecipitation by the addition of ether.

Hydroferrocyanic Acid CHEMICAL PROPERTIES

Outside of neutralization and esterification, the chemical reactions of hydroferrocyanic acid are limited chiefly to the formation of addition compounds. These are formed with sulfuric acid, alcohols, ethers, aldehydes, ketones, and certain hydrocarbons. A brief description of the formation of these adducts and other reactions involving essentially nonionized hydroferrocyanic acid is given in the following paragraphs. Reactions of the acid in aqueous solution are included in the chapter dealing with the chemical properties of the ferrocyanide ion.

Reaction with Sulfuric Acid

The addition of small amounts of water to a saturated solution of hydroferrocyanic acid in concentrated sulfuric acid leads to the formation of a series of addition products that are said to have ….Read more

Cyanide Destruction Hypochlorite / Chlorine

In the Cyanide Destruction by Hypochlorite reaction, the pH has a strong inverse effect on the ORP. Thus, wastewater treatment facilities must closely control the pH to achieve consistent ORP control, especially if they use hypochlorite as the oxidizing agent. Adding hypochlorite raises the pH, which, if unchecked, lowers the ORP. calling for additional hypochlorite. Controlling the pH at a setting above the pH level where hypochlorite has an influence and separating the ORP…

Alkaline Chlorine-Hypochlorite Oxidation: Chlorine was used for cyanide destruction in the early days of cyanidation in the late 1800s, because chlorine and its derivatives were readily available in the industry at that time. The method has been applied ever since in a variety of forms.

The active reagent for chlorine oxidation of free and complexed cyanide is the hypochlorite ion, produced when chlorine dissolves in water, as described. Alternatively, hypochlorite ions can be produced by dissolving suitable salts, such as sodium or calcium hypochlorite, in water.

Free cyanide reacts rapidly with hypochlorite (OCl) in aqueous solution to form cyanogen chloride, otherwise known as tear gas.

Cyanide also reacts rapidly with free chlorine.

However, at high pH, cyanogen chloride is readily hydrolyzed to cyanate and chloride ions.

In ….Read more

Rotary Kiln Maintenance

Rotary Kiln Alignment

The continuity of operation of a lime sludge kiln requires strict maintenance control. The rotary kiln is among the largest type of moving machines made and is subjected to extreme temperatures, power failures, atmospheric conditions, varying loads, and other operating conditions which affect its wear and alignment. It should be erected under the supervision of an experienced erecting engineer.

Even though great care has been taken in the design and the construction of the concrete piers, in some cases settling or tipping of the foundation can occur, throwing the carrying mechanisms, bases, and rollers out of alignment. If this condition is not corrected, it will lead to continual trouble with the kiln shell and the riding rings and rollers. It is advisable when making the original installation of the kiln to establish bench marks away from the kiln foundation. The kiln alignment should then be checked from the bench marks within six months after initial installation, and annually thereafter.

rotary_lime_kiln_maintenanceCarrying Roller Adjustment of the Lime Kiln

Heavy localized loadings leading to adverse wear can be encountered if the rollers and riding rings do not make contact across the full width of face, ….Read more

Rotary Lime Kiln Operation

Precipitated calcium carbonate, commonly called lime sludge or lime mud, is produced when sulphate green liquor is causticized with lime. For many years this lime sludge was considered a waste product and was dumped into rivers or waste ponds, or used for fill around the plants. Large quantities of new lime were purchased from commercial producers to replace that lost in the sludge waste.

A number of paper manufacturers soon became aware of the savings that could be achieved by recovering the lime. Beginning in the ’20’s, efforts were directed toward lime recovery installations. Today, a proper Rotary Lime Kiln Operation is an integral part of all modern pulp mills.

How a Rotary Lime Kiln Works

Kiln Feed and Feeders

High quality lime can be produced at a uniform rate only if the kiln is fed at a constant rate with lime sludge of constant composition. In some cases the feed to the kiln consists of a pumpable sludge containing 55 to 65% water. However, in most installations a drum filter or a centrifuge is installed just ahead of the kiln to reduce the moisture content to 35 to 50%. This cake is fed to the kiln through a screw conveyor, which ….Read more

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