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Wednesday, 03 August 2011 00:05

Alkaline Materials

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This article discusses ammonia, sodium, potassium, calcium and lithium, and their compounds. With the exception of ammonia, these are the most common alkali and alkaline earth metals.


Ammonia is an important source of various nitrogen-containing compounds. An enormous quantity of ammonia is used in the production of ammonium sulphate and ammonium nitrate, which are used as fertilizers. Ammonia is further used for oxidation into nitric acid, for the production of synthetic urea and soda, and for the preparation of water solutions used in chemical and pharmaceutical industries. It is employed in the explosives industry, in medicine and in agriculture. In refrigeration, ammonia is used to lower temperatures below the freezing point and for the manufacture of synthetic ice.

Ammonium hydroxide is employed in the textile, rubber, pharmaceutical, ceramics, photography, detergent and food industries. It is also used in extracting such metals as copper, nickel and molybdenum from their ores. Ammonium hydroxide is useful for removing stains and bleaching. It is a household cleansing agent as well as a solvent for casein in the pulp and paper industry. Diammonium phosphate is used for fireproofing textiles, paper and wood products. It is found in fertilizers and in flux for soldering metals. Ammonium chloride is used in flux for coating sheet iron with zinc, in safety explosives, medicine, and in cement for iron pipes. In addition, it is utilized in tinning, dyeing, electroplating and tanning.

Calcium is the fifth most abundant element and the third most abundant metal; it is widespread in nature as calcium carbonate (limestone and marble), calcium sulphate (gypsum), calcium fluoride (fluorspar) and calcium phosphate (apatite). Calcium minerals are quarried or mined; the metallic calcium is obtained by the electrolysis of molten calcium chloride or fluoride. Metallic calcium is used in the production of uranium and thorium and in the electronics industry. It serves as a deoxidizer for copper, beryllium and steel, and as a hardener for lead bearings. In addition, calcium is an industrial catalyst for polyester fibres.

Calcium chloride is obtained as a waste product in the Solvay ammonia-soda process. It is used as a pavement de-icer, a refrigerant, and as a drying agent in air-conditioning systems. Calcium chloride is utilized in the production of barium chloride, metallic calcium and various dyes. It is also used to prevent dust formation during road construction, to accelerate concrete curing times, and to inhibit spontaneous combustion of coal in coal mines. Calcium nitrate is used in agriculture as a fertilizer and in match manufacture as an oxidizing agent. It is also found in the explosives and pyrotechnics industries. Calcium sulphite is used as a reducing agent in the production of cellulose. Calcium carbide is used for the industrial production of acetylene and in the manufacture of calcium cyanamide. It is employed in the pyrotechnics industry and in acetylene generators for acetylene lamps. Calcium carbide is also used for oxyacetylene welding and cutting.

Lime is a general term for the products of calcined limestone—for example, calcium oxide and calcium hydroxide. Calcium oxide is used as a refractory material, as a flux in steelmaking, a binding agent in the building industry and as the raw material for chlorinated lime bleaching powder. It is employed in the pulp and paper, sugar refining, agriculture and leather tanning industries. Calcium hydroxide is used in building and civil engineering for mortars, plasters and cements. It is used for soil treatment, dehairing hides and fireproofing. Calcium hydroxide also finds use in lubricants and in the pulp and paper industry.

Lithium is used as a “getter” in vacuum tubes, a constituent of solder and brazing alloys, a coolant or heat exchanger in reactors, and as a catalyst in the manufacture of synthetic rubber and lubricants. It finds use in the manufacture of catalysts for polyolefin plastics and in the metal and ceramics industries. Lithium is also used in special glasses and in fuels for aircraft and missiles. Lithium chloride is used in the manufacture of mineral waters and for soldering aluminium. It is employed in the pyrotechnics industry and in medicine as an antidepressant. Lithium carbonate is utilized in the production of glazes on ceramic and electrical porcelain and for the coating of arc-welding electrodes. It is found in luminescent paints, varnishes and dyes. Lithium carbonate is also used in medicine as a mood-stabilizing drug and antidepressant. Lithium hydride is a source of hydrogen and a nuclear shielding material.

Potassium is used in the synthesis of inorganic potassium compounds. It is found in agriculture as a component of fertilizers. Potassium is also employed in sodium-potassium alloy for heat transfer in nuclear reactor systems and in high-reading thermometers.

Potassium hydroxide is used for the manufacture of liquid soap, for absorbing carbon dioxide, mercerizing cotton, and for the production of other potassium compounds. It finds use in electroplating, in lithography and as a mordant for wood. Potassium hydroxide is also used in paint and varnish removers and in printing inks.

Other potassium compounds include potassium bromate, potassium chlorate, potassium nitrate, potassium perchlorate and potassium permanganate. They are used in the pyrotechnics, food and explosives industries, and they serve as oxidizing agents. Potassium chlorate is a component of match tips, a bleaching agent and a dyeing agent for furs, cotton and wool. It is also used in the dye-stuffs and pulp and paper industries. Potassium chlorate is used in the manufacture of explosives, matches, pyrotechnics and dyes.

Potassium bromate is a dough conditioner, a food additive, an oxidizing agent and a permanent wave compound. Potassium nitrate is used in fireworks, fluxes, gunpowder and in the glass, match, tobacco and ceramics industries. It is also used for pickling meats and for impregnating candle wicks. Potassium nitrate acts as a fertilizer in agriculture and as an oxidizer in solid rocket propellants. Potassium perchlorate is used in the explosives, pyrotechnics and photography industries. It serves as an inflating agent in automobile safety air bags. Potassium permanganate is used as an oxidizing agent, a disinfectant and a bleaching agent in the leather, metal and textile industries. It is also employed in metal cleaning, separation and purification in mining. In addition, potassium permanganate is a tanning agent in the leather industry.

Sodium is used in the manufacture of sodium compounds and in organic syntheses. It serves as a reducing agent for metals and as a coolant in nuclear reactors. Sodium is also found in sodium lamps and in electric power cable. Sodium chlorate is an oxidizing agent in the dye-stuffs industry and an oxidizing and bleaching agent in the pulp and paper industry. It is used for dyeing and printing fabrics, tanning and finishing leather, and uranium processing. It is also employed as an herbicide and a rocket fuel oxidant. Sodium chlorate finds additional uses in the explosives, match and pharmaceutical industries.

Sodium hydroxide is used in the rayon, mercerized cotton, soap, paper, explosives, dye-stuffs and chemical industries. It is also used in metal cleaning, electrolytic extraction of zinc, tin plating, laundering and bleaching. Trisodium phosphate finds use in photographic developers, in detergent mixtures and in the paper industry. It it used for clarifying sugar, removing boiler scale, softening water, laundering, and for tanning leather. Trisodium phosphate is also a water-treatment agent and an emulsifier in processed cheese. Disodium phosphate is used in fertilizers, pharmaceuticals, ceramics and detergents. It is used for weighting silk, dyeing and printing in the textile industry, and for fireproofing wood and paper. Disodium phosphate is also a food additive and a tanning agent. Sodium hypochlorite is a household and laundry bleaching agent, and a bleaching agent in the paper, pulp and textile industries. It is employed as a disinfectant for glass, ceramics and water as well as a sanitizer in swimming pools. Sodium chloride is used for metalworking, curing hides, highway de-icing, and preserving food. It also finds use in the photography, chemical, ceramic and soap industries, and in nuclear reactors.

The salts of carbonic acid (H2CO3), or carbonates, are widespread in nature as minerals. They are used in the construction, glass, ceramics, agriculture and chemical industries. Ammonium bicarbonate is used in the plastics, ceramics, dye-stuffs and textile industries. It finds use as a blowing agent for foam rubber and as a leavening agent in the production of baked goods. Ammonium bicarbonate is also used in fertilizers and in fire extinguishers. Calcium carbonate is used primarily as a pigment and is employed in the paint, rubber, plastics, paper, cosmetics, match and pencil industries. Calcium carbonate also finds use in the manufacture of Portland cement, foods, polishes, ceramics, inks and insecticides. Sodium carbonate is widely used in the manufacture of glass, caustic soda, sodium bicarbonate, aluminium, detergents, salts and paints. It is utilized for the desulphurization of pig iron and for the purification of petroleum. Sodium bicarbonate is used in the confectionery, pharmaceutical, non-alcoholic beverage, leather and rubber industries, and for the manufacture of fire extinguishers and mineral waters. Potassium carbonate is widely used in potash fertilizers and in the textile industry for dyeing wool. It also finds use in the glass, soap and pharmaceutical industries.


Alkalis are caustic substances which dissolve in water to form a solution with a pH substantially higher than 7. These include ammonia; ammonium hydroxide; calcium hydroxide and oxide; potassium; potassium hydroxide and carbonate; sodium; sodium carbonate, hydroxide, peroxide and silicates; and trisodium phosphate.

Health hazards

In general, the alkalis, whether in solid form or concentrated liquid solution, are more destructive to tissues than most acids. The free caustic dusts, mists and sprays may cause irritation of the eyes and respiratory tract, and lesions of the nasal septum. Strong alkalis combine with tissue to form albuminates, and with natural fats to form soaps. They gelatinize tissue to form soluble compounds which may result in deep and painful destruction. Potassium and sodium hydroxide are the most active materials in this group. Even dilute solutions of the stronger alkalis tend to soften the epidermis and emulsify or dissolve the skin fats. First exposures to atmospheres slightly contaminated with alkalis may be irritating, but this irritation soon becomes less noticeable. Workers often work in such atmospheres without showing any effect, while this exposure will cause coughing and painful throat and nasal irritation in unaccustomed persons. The greatest hazard associated with these materials is the splashing or splattering of particles or solutions of the stronger alkalis into the eyes.

Potassium hydroxide and sodium hydroxide. These compounds are very dangerous to the eyes, both in liquid and solid form. As strong alkalis, they destroy tissues and cause severe chemical burns. Inhalation of dusts or mists of these materials can cause serious injury to the entire respiratory tract, and ingestion can severely injure the digestive system. Even though they are not flammable and will not support combustion, much heat is evolved when the solid material is dissolved in water. Therefore, cold water must be used for this purpose; otherwise the solution may boil and splatter corrosive liquid over a wide area.

Carbonates and bicarbonates. The principal carbonates are: calcium carbonate (CaCO3), magnesite (MgCO3), soda ash (NaCO3), sodium bicarbonate (NaHCO3) and potash (K2CO3). The normal carbonates (with the anion CO3) and the acid or bicarbonates (with the anion HCO3) are the most important compounds. All bicarbonates are water-soluble; of the normal carbonates only the salts of alkaline metals are soluble. Anhydrous carbonates decompose when being heated before reaching the melting point. Carbonate solutions give rise to alkaline reactions because of the considerable hydrolysis involved. The bicarbonates are converted to normal carbonates by heating:

2 NaHCO3 = Na2CO3 + H2O + CO2

The normal carbonates are decomposed by strong acids (H2SO4, HCl) and set free CO2.

The sodium carbonates occur in the following forms: soda ash—anhydrous sodium carbonate (Na2CO3); crystallized soda— sodium bicarbonate (NaHCO3); and sodium carbonate decahydrate (Na2CO3·10 H2O).

Alkaline carbonates may cause harmful irritation of the skin, the conjunctivae and the upper airways during various industrial operations (handling and storage, processing). Workers who load and unload bagged carbonates may present cherry-sized necrotic skin portions on their arms and shoulders. Rather deep ulcerated pitting is sometimes observed after the black-brown scabs have fallen off. Prolonged contact with soda solutions may cause eczema, dermatitis and ulceration.

Calcium and compounds. Calcium is a well-known essential constituent of the human body, and its metabolism, alone or in association with phosphorus, has been widely studied with special reference to the musculoskeletal system and cellular membranes. Several conditions may lead to calcium losses such as immobilization, gastrointestinal disturbances, low temperature, weightlessness in space flights and so on. The absorption of calcium from the work environment by inhalation of calcium compounds dust does not increase significantly the calcium daily intake from vegetables and other food (usually 0.5 g). On the other hand, metallic calcium has alkaline properties, and it reacts with moisture, causing eye and skin burns. Exposed to air it may present an explosion hazard.

Calcium carbide. Calcium carbide exerts a pronounced irritant effect due to the formation of calcium hydroxide upon reaction with moist air or sweat. Dry carbide in contact with skin may cause dermatitis. Contact with moist skin and mucous membranes leads to ulceration and scarring. Calcium carbide is particularly hazardous to the eyes. A peculiar type of melanoderma with strong hyperpigmentation and numerous telangiectases is often observed. Burns caused by hot calcium carbide are common. The tissues are generally damaged in depths of 1 to 5 mm; the burns evolve very slowly, are difficult to treat, and often require excision. Injured workers may resume work only after the burnt skin surface is completely scarred. Persons exposed to calcium carbide frequently suffer from cheilitis characterized by dryness, swelling and hyperaemia of the lips, intense desquamation, and deep radial fissures; erosive lesions with a tendency to suppuration can be observed in the mouth angles. Workers with a long professional history often suffer from nail lesions—that is, occupational onychia and paronychia. Eye lesions with pronounced hyperaemia of the lids and conjunctiva, often accompanied by mucopurulent secretions, are also observed. In heavy cases the sensitivity of the conjunctiva and cornea is strongly reduced. While the keratitis and keratoconjunctivitis evolve first without symptoms, they may later degenerate into corneal opacities.

In calcium carbide production, impurities may produce additional hazards. Calcium carbide contaminated with calcium phosphate or calcium arsenate may, when moistened, give off phosphine or arsine, both of which are extremely toxic. Calcium carbide itself, when exposed to damp air, gives off acetylene, which is a moderate anaesthetic and asphyxiant, and a considerable fire and explosion hazard.

Calcium chloride has a powerful irritant action on the skin and mucous membranes, and cases have been reported, amongst workers packing dry calcium chloride, of irritation accompanied by erythema and peeling of facial skin, lacrimation, eye discharge, burning sensation and pain in the nasal cavities, occasional nose bleeding and tickling in the throat. Cases of perforation of the nasal septum have also been reported.

Calcium nitrate has an irritating and cauterizing action on skin and mucous membranes. It is a powerful oxidizing agent and presents a dangerous fire and explosion hazard.

Calcium sulphite. Cases of occupational calcium sulphite poisoning do not appear to have been reported. Accidental ingestion of a few grams may produce repeated vomiting, violent diarrhoea, circulatory disorders and methaemoglobinaemia.


Ammonia is present in small amounts in the air, water, earth, and particularly in decomposing organic matter. It is the product of normal human, animal and plant metabolism. Muscular effort and excitement of the nervous system result in the formation of an increased amount of ammonia, an accumulation of which in the tissues would result in poisoning. Endogenous formation of ammonia increases also in the course of many diseases. Through vital processes it is combined and excreted from the organism, mainly via urine and sweat, in the form of ammonium sulphate and urea. Ammonia is also of primary importance in the nitrogen metabolism of plants.

Ammonia is lightly reactive, easily undergoing oxidation, substitution (of hydrogen atoms) and additional reactions. It burns in air or in hydrogen to form nitrogen. An example of substitution would be the formation of amides of alkaline and alkaline-earth metals. As a result of addition it forms ammoniates (e.g., CaCl2·8NH3, AgCl3NH3) and other compounds. When ammonia dissolves in water, it forms ammonium hydroxide (NH4OH), which is a weak base and dissociates as follows:

NH4OH → NH4+ + OH-

The radical NH4+ does not exist in free form since it decomposes into ammonia and hydrogen when an attempt is made to isolate it.

Ammonia poisoning may occur in the production of ammonia and in the manufacture of nitric acid, ammonium nitrate and sulphate, liquid fertilizers (ammoniates), urea and soda, in refrigeration, synthetic ice factories, cotton printing mills, fibre dyeing, electroplating processes, organic synthesis, heat treatment of metals (nitriding), chemical laboratories, and in a number of other processes. It is formed and emitted into the air during the processing of guano, in the purification of refuse, in sugar refineries and tanneries, and it is present in unpurified acetylene.

Industrial poisoning is usually acute, while chronic poisoning, although possible, is less common. The irritant effect of ammonia is felt especially in the upper respiratory tract, and in large concentrations it affects the central nervous system, causing spasms. Irritation of the upper respiratory tract occurs at concentrations of above 100 mg/m3, while the maximum tolerable concentration in 1 hour is between 210 and 350 mg/m3. Splashes of ammonia water into the eyes are particularly dangerous. The rapid penetration of ammonia into the ocular tissue may result in perforation of the cornea and even in death of the eyeball. Particular health hazards exist in each section of an ammonia plant. In the sections where the gas is generated, converted (oxidation of CO to CO2), compressed and purified, the main problem is the emission of carbon monoxide and hydrogen sulphide. Considerable quantities of ammonia may escape during its synthesis. Escaping ammonia in the atmosphere may reach explosive limits.

Chlorates and perchlorates

Chlorates and perchlorates are the salts of chloric acid (HClO3) and perchloric acid (HClO4 ). They are strong supporters of combustion, and their main hazard is associated with this property. The potassium and sodium salts are typical of the group and are those most commonly used in industry.

Fire and explosion hazards. Chlorates are powerful oxidizing agents, and the main dangers are those of fire and explosion. They are not themselves explosive but they form flammable or explosive mixtures with organic matter, sulphur, sulphides, powdered metals and ammonium compounds. Cloth, leather, wood and paper are extremely flammable when impregnated by these chlorates.

Perchlorates are also very strong oxidizing agents. Heavy metal salts of perchloric acid are explosive.

Health hazards. Chlorates are harmful if absorbed by ingestion or by inhalation of the dust, which can provoke sore throat, coughing, methaemoglobinaemia with bluish skin, dizziness and faintness, and anaemia. In case of large absorption of sodium chlorate an increased sodium content in the serum will be seen.

Perchlorates may enter the body either by inhalation as dust or by ingestion. They are irritant to skin, eyes and mucous membranes. They cause haemolytic anaemia with methaemoglobinaemia, Heinz bodies in the red cells, and liver and kidney injuries.

Alkaline materials tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Table 3 - Physical and chemical hazards.

Table 4 - Physical and chemical properties.



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