Aluminum Compounds, Inorganic1 Aluminum Compounds, Inorganic Otto Helmboldt, Giulini Chemie GmbH, Ludwigshafen, Germany (Chap. 1 and 2) L. Keith Hudson, Aluminum Company of America, Alcoa Center, Pennsylvania, USA (Chap. 2.1) Chanakya Misra, Aluminum Company of America, Alcoa Center, Pennsylvania, USA (Chap. 2.1) Karl Wefers, Aluminum Company of America, Alcoa Center, Pennsylvania, USA (Chap. 2.1) Wolfgang Heck, BASF Aktiengesellschaft, Ludwigshafen, Germany (Chap. 3) Hans Stark, BASF Aktiengesellschaft, Ludwigshafen, Germany (Chap. 4.1 and 5) Max Danner, Hoechst Aktiengesellschaft, Werk Gersthofen, Augsburg, Germany (Chap. 4.2, 4.3 and 5) ¨ Norbert Rosch, Clariant Produkte (Deutschland) GmbH, Gersthofen, Germany Related Articles → Aluminum Oxide is a separate keyword. Aluminum fluoride and cryolite → Fluorine Compounds, Organic 1. 1.1. 1.1.1. 1.1.2. 1.1.3. 1.2. 1.2.1. 1.2.2. 1.2.3. 2. 2.1. 2.2. Aluminum Sulfate and Alums Aluminum Sulfate . . . . . . . Properties . . . . . . . . . . . . . . Production . . . . . . . . . . . . . Uses . . . . . . . . . . . . . . . . . Alums . . . . . . . . . . . . . . . . Potassium Aluminum Sulfate . Ammonium Aluminum Sulfate Sodium Aluminum Sulfate . . . Aluminates . . . . . . . . . . . . Sodium Aluminate . . . . . . . Barium Aluminates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1 2 4 5 6 7 8 8 8 9 1. Aluminum Sulfate and Alums 1.1. Aluminum Sulfate Aluminum sulfate is the second most important industrial compound of aluminum, after aluminum oxide. Aluminum sulfate was first used in Paris in 1844 to replace potassium alum. Today, it has taken over almost all areas of application that potassium alum originally had. 1.1.1. Properties Aluminum sulfate is almost insoluble in anhydrous alcohol but readily soluble in water; aqueous solutions are acidic. Literature data on solubility and the structure of the precipitate in water differ markedly and should be used with caution (see Table 1). Previously, Al2 (SO4 )3 · 18 H2 O c 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002/14356007.a01 527.pub2 3. 4. 4.1. 4.1.1. 4.1.2. 4.1.3. 4.1.4. 4.1.5. 4.2. 4.3. 5. 6. Aluminum Alkoxides . . . . . . . . . . Aluminum Chloride . . . . . . . . . . Anhydrous Aluminum Chloride . . Properties . . . . . . . . . . . . . . . . . . Production . . . . . . . . . . . . . . . . . Quality Specifications and Analysis . Handling, Storage, and Transportation Uses . . . . . . . . . . . . . . . . . . . . . Aluminum Chloride Hexahydrate . Basic Aluminum Chlorides . . . . . . Toxicology . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . 10 10 10 10 11 11 12 12 13 13 15 15 was thought to crystallize from aqueous solution under normal conditions (20 ◦ C, 1 bar). This is now doubted, because such factors as hydrolysis, oversaturation, shifts in equilibrium, and, particularly, poor crystal formation make definitive characterization difficult [5]. The common form of aluminum sulfate, generally considered to be Al2 (SO4 )3 · 18 H2 O [7784-31-8], occurs in nature as alunogen (hair salt) and can be crystallized from hydrochloric acid solution as microscopically small, white needles. However, some researchers ascribe a hydrate water content of 17 mol to this form of aluminum sulfate [6]. A hydrate containing 27 mol of water can be prepared readily and in high purity [1]. Other well-defined aluminum sulfates contain 16, 10, and 6 mol of water. A total of 39 basic and 3 acidic aluminum sulfates, as well as 13 different hydrates of the neutral salt, are described in the literature [7]. The existence of aluminum 1 %) is still important in some countries. the melt is sucked into a wellisolated vacuum tank (c). The Fe2 O3 component in bauxite is disregarded because the Al2 O3 is only 97 – 98 % digested and therefore sufficient sulfuric acid is available for production of aluminum sulfate containing 17. Generally. A pressure-resistant. For details. is precipitated with calcium hexacyanoferrate (II) as Berlin blue (iron hexacyanoferrate (II)). Production In Germany and most European countries. At a temperature above 340 ◦ C. stirred vessel (a) is filled with aluminum hydroxide (moist or dry). The calculated quantity of warm sulfuric acid is added from a preheater. a white powder. the hydrate water content is unimportant because “crystalline” aluminum sulfate is a ground. Production from Bauxite. all process steps involving the introduction or the removal of water must be accounted for.g.6 g/cm3 is used. and 1 mol of water can be concluded from the vapor-pressure curves and the dehydration curves of the Al2 (SO4 )3 – H2 O and Al2 (SO4 )3 – Al(OH)3 – H2 O systems [8. 8 % to avoid crystallization during transport. acid of density 1. The purity depends on the process and starting materials. This vacuum cooling avoids incrustation of the heat exchanger surfaces. 32 % H2 O) also can be used as starting material. The clear solution is de- . Fe2 O3 ca. 170 ◦ C.71 g/cm3 . 1. 1.. digestion of the aluminum hydroxide is almost complete. 2. which is obtained from a melt.5 % Al2 O3 . The reaction starts after 60 – 300 s and is complete after 10 – 12 min. Giulini Process [10]. The desired Al2 O3 content is adjusted within certain limits by heating. see [11]. 3. Finely ground bauxite (for example. 1. 9. 0.5 % Fe2 O3 . or by hydrolysis as basic iron sulfate. 13. Aluminum sulfate with 17. The pulplike product reaches the “crystallization belt.5 % Fe2 O3 and ca. bauxite with SiO2 > 5 %. The mixture must not be stirred for more than 1 h because otherwise the aluminum sulfate can hydrolyze to give insoluble basic aluminum sulfate and strongly acidic sulfate melt. The melt falls from the vacuum container into the mixer.6 % TiO2 . after which it is ground (h) and sieved (i). The heat of reaction causes the temperature to rise to ca. 50 t of aluminum sulfate in a 10-h shift. trough-form rubber conveyor belt (e). In this process. 1 % below stoichiometric.0 % SiO2 . The goods are filled (j) into paper or jute sacks or transported loose in silo cars. 12. From the evaporator. The Giulini method for producing various grades of aluminum sulfate. is shown schematically in Figure 1. 7.2 % Al2 O3 produced in this way contains only 0. heat-resistant. containing between 8 and 23 % Al2 O3 . 2. aluminum sulfate is produced on a large scale only from aluminum hydroxide and sulfuric acid by the Giulini process.01 % insoluble material. Acid digestion of predominately siliconrich raw materials gives a solution of aluminum sulfate. while the pressure rises to 5 – 6 bar. Production from Less Pure Starting Materials.” a smooth. 3 mol H2 SO4 are charged onto 1 mol Al2 O3 . Production by the action of sulfuric acid on aluminum-containing ores (clays and bauxite with high silicon and low iron content. where it is seeded at 85 ◦ C with 1 – 2 % aluminum sulfate powder. which is evacuated to the vapor pressure of the aluminum sulfate melt. microcrystalline solid with variable water content. An auto- clave unit allowing batches of 2. 2. 60 % Al2 O3 . Iron. For transportation as a solution the Al2 O3 content is adjusted to ca.5 t can produce ca. In this case. therefore. and the mixture is stirred. The aluminum sulfate obtained by digestion of bauxite contains ca. Inorganic sulfates with 14.2. e. anhydrous aluminum sulfate [10043-01-3] is formed. 30 min. aluminum sulfate is obtained relatively easily with high purity. 90 ◦ C and cannot be broken to fine size in one step (f).1. which strongly interferes. and crystallizes there in ca. with calcium sulfide as iron sulfide.2 % insoluble residue. Because of the high heat of crystallization. that decomposes above 770 ◦ C to aluminum oxide [9]. the material has a temperature of ca. It passes over air-cooled conveyor belts until it has cooled to 40 ◦ C. In industrial practice. 9]. The melt is led into a copper container where it is concentrated by flash evaporation (b). 4. In calculating the sulfuric acid concentration required to obtain an SO3 content of ca.2 Aluminum Compounds. 6 25.4 70 66.5 ◦ B´e.5 % Fe2 O3 and 0. which contains ca.2 29. large crystals of Al2 (SO4 )3 · 18 H2 O (15.85 47.0 38. The formation of colloids is avoided by using vacuum apparatus. The final product. and milled.6 41. 2 – 4 % Fe2 O3 ) with sulfuric acid.8 31.0 Reference [1] [2] [3] [4] Figure 1.5 23.73 46.10 59.4 28.0 20 36.5 33. Production of aluminum sulfate by the Giulini process [10] canted and sold as a liquid or concentrated to 61. 0.0 40 45. there is an iron-free grade having an Fe2 O3 content of ca.Aluminum Compounds. Solubility of aluminum sulfate as a function of temperature (grams of anhydrous salt per 100 g water) t.5 50 52.1 % insoluble material. 40 – 43 % Al2 O3 .3 % Al2 O3 ) can be separated easily from the impure mother liquor by . iron-free aluminum sulfate by diges- tion of clay (for example.0 36. Inorganic 3 Table 1.3 31.36 40.23 66. The Kretzschmar process is used to produce very pure. is the technical grade. 53 – 56 % SiO2 .2 27.2 31.0 46.15 36.1 28.83 80. In addition.7 90 80. Pure.8 80 73.005 %. allowed to solidify.4 26. ◦ C 0 31.9 30 40.74 100 89. The greater part of the impurities is removed and crystals are separated from the solution by stirring.9 60 59.9 10 33.0 36.11 89.14 73.13 52. 0.1 32.5 27. 1 – 1 %.30. Generally.1 – 1 %. Aluminum sulfate with more than 0. such as calcium sulfate. 246].e.. In a process developed by the U. Commercial Grades. Disadvantages are the formation of free carbon dioxide.25 mmol/L of carbonate hardness (based on alkaline-earth ions) is consumed. the aluminum sulfate containing 17 – 18 % Al2 O3 (water-soluble aluminum content. such as low arsenic or low iron content. After filtration and removal of the sulfur dioxide in vacuo to give a pH of 4. some carbonate hardness is consumed: 2− Al2 (SO4 )3 +6 HCO− 3 →2 Al (OH)3 +6 CO2 +3 SO4 For 50 mg/L of the 17 – 18 % Al2 O3 grade 0. the increase of non-carbonate hardness. Water Purification. Whereas Al2 (SO4 )3 · 18 H2 O theoretically contains 15. 18 %. An advantage of using aluminum sulfate is the lack of postflocculation. The calculated hydrate water content of this aluminum sulfate is 13 mol. Uses About two thirds of the total aluminum sulfate production is used for treating water. and the pH remaining between 5 and 7. wetstrength agents. and basic dyes. 2. and finally settles as sludge after 15 – 150 min. Olin Mathieson Chemical Corp. commercial grades of aluminum sulfate contain 14 – 15 %. for improving retention. Occasionally. the Al2 O3 content exceeds the stoichiometric amount by 0. This weakly basic aluminum sulfate has the advantage that it is less hygroscopic and therefore hardly affects either the metal parts of the apparatus during use or paper sacks during transport. developed an economical process for producing highquality aluminum sulfate from the clay or waste shale of coal mines.3 % Al2 O3 . alcohol is used to reduce the viscosity of the oversaturated aluminum sulfate mother liquor [13].35. Large crystals (1. 5 – 50 g aluminum sulfate is sufficient to purify 1 m3 of water. or 22 – 23 % Al2 O3 (Table 2). A process for producing aluminum sulfate from alum-containing ores is given in [15]. this ratio is ca. The mechanism is as follows: Positively charged aluminum ions.S.3. Aluminum sulfate is an important flocculating agent for purifying water [19]. About one half of the total production goes into the paper industry (paper sizing. the term “basicity” is defined as the ratio % SO3 to % Al2 O3 . The basicity of the product is defined as the excess in Al2 O3 over the stoichiometric SO3 : Al2 O3 ratio. The 17 – 18 % Al2 O3 grade has a basicity of 0. as the starting material of a high-quality slip for coating glossy paper (satin white). Bureau of Mines. i. which increases the hardness of and also plasticizes lime mortar. and for the production of lake dyes and wallpaper. calculated as Al2 O3 ) is used most frequently. Al(OH)SO3 and SiO2 · n H2 O precipitate. For commercial aluminum sulfate. for dispersing resin particles that stick together and block sieves. free acid damages cellulose fibers in the paper industry. see [18]. neutralize the negative charge on the colloidal material in the water. see [5]. whereby aluminum sulfate dissolves. for a detailed discussion on the importance of aluminum sulfate in paper production. To neutralize the hydrogen atoms formed on hydrolysis of aluminum sulfate.4 Aluminum Compounds. Aluminum sulfate is used for precipitating and fixing sizing agents. 15 – 16 %. [16].5 – 3 mm) with iron contents of less than 0. pH adjustment. sediments at various rates.1.03 % are produced in a patented crystallizer [14]. Inorganic centrifuging [12]. The residue from the digestion process (SiO2 ) can be converted with lime to calcium hydrosilicate.5 – 5. If no natural bicarbonate hardness is . Paper Industry. The precipitate is filtered and treated with sulfuric acid. p. provided the correct amount is added. For an overview of uses in newspaper factories.0. the material flocculates. wastewater purification) [17. which are hydrated or hydroxylated with water via numerous intermediate stages. 17 – 18 %. Generally. Also. As a result of mutual adsorption. whereas the theoretical value is 2. The commercial grade containing 17 – 18 % Al2 O3 is delivered also with various special qualities. 1.2 % Fe2 O3 gives paper a yellow tinge and cannot be used for good-quality white paper. Aluminum sulfate is produced from waste “red mud” (from the aluminum oxide industry) by suspending the mud in water and passing sulfur dioxide through the suspension until pH 2 is reached. 22.0 0. as a filler for synthetic rubber.2. Alumen. vanadium. tawing. Finally. interest. Commercial grades of aluminum sulfate Grade 8 % (solution) 14 – 15 % 15 – 16 % 17 – 18 % 18 % 22 – 23 % Al2 O3 . % 1 0. Alum was employed in processing skins.01 < 0. M+ Al3+ (SO2− 4 )2 · 12 H2 O. Other Uses. alkylammonium. 17. The main U. which is obtained by the Bayer process from bauxite (→ Aluminum Oxide). The raw material of the ancient alum industry was alum stone (alunite) or alum shale.03 Basicity * .S.1 – 1. Further uses are for pickling of seeds. 1. for example. manganese. The most useful alums are those with trivalent aluminum cations and sulfate anions.8 Fe2 O3 . was known to the ancient Greeks and Romans as an astringent and also as a mordant in dyeing wool.04 0. The main Japanese producers are Nikkei Kako Co.006 – 0. The alum industry played an important role during the whole of the Middle Ages. particularly bauxite. and Scintoma Aluminum Smelting Co.Aluminum Compounds. Aluminum sulfate.1 – 16.0 ca.004 0. arylammonium.1 – 1. wt % – 0.02 Insoluble material. Alums Historical Aspects. Alum stone contains all components of the alum in the correct ratios and is processed by roasting and leaching. from which the word alum is derived. Alums with the following trivalent metals are known: iron. a higher iron content is unacceptable because this leads to color changes. partly only historical. The individual components of the alum can be replaced. alums are produced only from aluminum hydroxide. Production and Capacity Data.0 0. Paracelsus was the first to distinguish true alum from iron vitriol. wt % 8 14 – 15 15. Alums are crystalline double salts of the general formula (cation 1)+ (cation 2)3+ (anion2− )2 · 12 H2 O. were used as raw materials and were digested using alkali or acid.01 %) is used as a mordant in dyeing. and for fireproofing wood.0 ca.03 ca. scandium. rhodium. retaining both the regular crystalline form and the hydrate water.0 0. deodorizing of mineral oils. and iridium. because only the aluminum content is of practical importance. Aluminum sulfate with a very low iron content (below 0. Roasting. or it can be ammonium.006 – 0.03 < 0. it is the starting material for almost all other aluminum compounds. Most of the alum production methods now have only limited. However. an alkaline substance that also has a dispersing effect.8 * Defined in text present. and producing aluminum hydroxide gel employed.8 – 1. Today. aging for several years. Clay and other alkali-containing silicates. 18. In the years 1776 – 1798.04 0. Chaptal and Vauquelin established that alum was a double salt of potassium and aluminum sulfates and that the potassium ions could be replaced by ammonium ions. indium. for embalming animal and human corpses.008 < 0. titanium. The industrial production of the alums ceased to have particular importance when it became possible to produce aluminum sulfate economically in high purity. must be added. chromium.01 < 0.008 0. or thallium.0 – 1. used in combination with calcined leached clay.5 1. The monovalent component can be an alkali metal. for example. Aluminum sulfate has some importance also as a catalyst support.2 ca. and leaching of alum shale gave an aluminum solution from which the alum was precipitated with alkali. General Properties. in sea water [20]. 0. wt % 0. cobalt. that in Japan was 757 000 t in 1980 [22].1 – 1. gallium. such as lime or sodium aluminate. The existence of a lithium alum is uncer- . what was known at first as alum was not a defined substance but referred to both alum-containing minerals and mixtures of alum with iron vitriol. Inorganic 5 Table 2. producer of aluminum sulfate is Allied Corp. Aluminum sulfate production in the USA was 1 168 000 t in 1980 and 1 075 000 t in 1982 [21]. is suitable for binding mercury ions. a stoichiometric quantity of potassium sulfate (as chloride-free as possible) is added. The solution is heated to ca. and freezing-point lowering. The octahedra absorb long-wavelength IR radiation almost completely. 40 ◦ C by air bubbles. potassium alum can be purified more easily than other aluminum salts by recrystallization and. into a copper container. carbamides. where it is cooled to ca. the alum melt is brought into a stirred crystallization bath.016 – 0. also metals and organic dyes) promote the formation of basic aluminum sulfate by binding free sulfuric acid in the mother liquor. Another basic potassium aluminum sulfate. the alum melt is left in crystallization boxes for 10 days. the cubic form is favored (cubic or Roman alum). K[Al3 (OH)6 (SO4 )2 ] [1302-91-6]. 0. borates. the alums lose their water of crystallization either partially or completely.023 %.6 Aluminum Compounds. When heated above its melting point.004 % chloride. The hardness of the crystals on the Mohs scale is 2. H2 O 42. and < 0. cesium–aluminum. provided the solutions are very dilute. Fe2 O3 0. carbonates. Basic potassium aluminum sulfate. For the production of alum crystals. After filtration from insoluble material. The solubilities of the alums in water decrease from sodium to cesium (see Table 3). SO3 is released.001 – 0. amorphous powder by heating aluminum sulfate. are formed. The mother liquor is collected and returned to the copper container.040 g/L) react in a stirred.75 g/cm3 .001 % Fe2 O3 . K[Al(OH)2 ]3 (SO4 )2 · 3/2 H2 O. α-Al2 O3 . Potassium alum is stable in air of normal humidity. and an excess of potassium sulfate or by heating potassium alum with water in the ratio 1 : 4 to 200 ◦ C [24]. Fe2 O3 0. such as color. are the sum of the properties of the components.1.5 ◦ C in their own water of crystallization. but are transparent to visible light. and ammonium aluminum sulfate are the aluminum compounds known longest. whereas K2 SO4 . Production. and methyl acetate. forming calcined alum (alum ustum). with release of pressure. which melt at 92. According to these results. Al2 O3 ca. potassium–chromium. acetone. The potassium alum is dried at 50 – tain. On heating. known as potassium alum. KAl(SO4 )2 · 12 H2 O. Physical properties. In aqueous solution. 57 %. such as [Al(SO4 )2 · (H2 O)2 ]− . All alums crystallize in strongly refracting octahedra or cubes [1]. Potassium alum occurs in nature as efflorescence on alum shale and in volcanic areas on trachyte and lava as feather alum. . Under these conditions. A selenate alum also is known: KAl(SeO4 )2 · 12 H2 O. can be freed from iron sulfate. Potassium Aluminum Sulfate K2 SO4 . protein-precipitating properties.2.6 g/cm3 .5 %) and sulfuric acid ( ≈1. in particular. However. Because of the marked increase in solubility in water with temperature. The aluminum sulfate melt is then led. Inorganic 1. KAl (SO4 )2 [10043-67-1]. containing less water. Literature data on the dehydration are contradictory.01 % insoluble material. Mixed crystals form readily with ammonium sulfate. At higher concentrations. Dehydration does not begin below 30 ◦ C. potassium alum dehydrates. Aluminum hydroxide (wet hydrate. The product obtained in this way contains < 0. and 3 K2 SO4 · Al2 (SO4 )3 form at 780 ◦ C. is the alum stone (alunite) occurring in nature. Known combinations include potassium– aluminum. Investigations on thermal decomposition are given in [23]. 1. colorless. after which the alum is removed in blocks.020 – 0. Potassium aluminum sulfate [7784-24-9]. alums show all the chemical properties that their components show separately. The pulp is then separated from the mother liquor by centrifuging and washed. complexes. electrical conductivity. The compound is made synthetically as a rather insoluble. occurs in nature as l¨owigite. Certain substances (hydroxides. Potassium alum crystallizes in large. and hydroxyammonium–aluminum. and K2 O · 12 Al2 O3 are produced at 1400 ◦ C. γ-Al2 O3 . water. transparent octahedra.4. part of the water is taken up again at normal temperature and humidity. 100 ◦ C for 2 – 3 h and adjusted to 40 – 44 ◦ B´e with mother liquor. Potassium alum is soluble in dilute acid but almost insoluble in anhydrous alcohol. Here. corrosion-resistant pressure boiler at 5 – 6 bar to form aluminum sulfate as shown in Figure 1. M r 474. At red heat. but at 65 ◦ C nine moles of water are lost. They have an astringent taste and rot-proofing. as is required for production of synthetic gems. Gel’Perin and Chebotkevich [26] 22. In the United States.9 6. and the production of basic potassium and sodium alums from synthetic alum is described in [25]. Inorganic 7 Table 3. ammonium alum is neutral. so that it is in fact more correct to formulate ammonium alum with 24 mol water.5 ◦ C. Ammonium alum occurs as an intermediate in the “aloton” process. 1. then to that with 3 mol water.9 9. In Europe.2 Potassium 3. Solubility of some aluminum alums as a function of temperature (grams of anhydrous salt per 100 g water) t. normal quality ca. NH4 Al(SO4 )2 · 12 H2 O. As already mentioned.9 71 35. A process for obtaining potassium alum from alum-containing ores is given in [15]. The most important application today is in the gypsum industry. Because of its astringent and protein-precipitating properties. and. 1.8 12.2.8 60 ◦ C. and finally to the anhydrous product. for purifying water and sizing paper. M r 453. The procedure is analogous to the potassium alum process. although incorrectly.2 21. Production. loose aluminum oxide of high purity that is required for synthesizing corundum gems. decomposition with the release of ammonia begins. In the paper industry.09 0.6 5. and as a coagulating agent for latex.05 10 60. The salt. ◦ C 0 Sodium 56.0 4. ammonium alum is important as an additive in baking powder.7 12.2 Thallium 3. which employs potassium alum as hardening agent and setting accelerator for the production of marble cement and alabaster plaster. However. mp 93. as a mordant in dyeing. potassium alum has been replaced completely by aluminum sulfate. because of its blood-stanching property. leaving an aluminum oxide residue. such as rubies and sapphires.0 have reported that water of crystallization is released in three stages: first to give the hydrate with 21 mol water.64 g/cm3 . as a disinfectant. The solubility of ammonium alum in water is similar to that of potassium alum.6 1. is very widespread and popular. To obtain a quality particularly low in iron oxide or other metal oxides (< 0.8 26.98 1. also called ammonium alum.3 154 70.0 40 50 60 70 80 90 100 11.6 17 15.1 40 26. Uses.6 Rubidium 0.Aluminum Compounds. Crystals doped with other alums show birefringence. The use of potassium alum as a styptic pencil.4 3. On glowing above 1000 ◦ C.9 4.24 25 21.2. Ammonium Aluminum Sulfate Ammonium aluminum sulfate [7784-26-1]. Above 193 ◦ C. ammonium alum is not used in large quantities. which operates in a sulfuric acid medium.001 % Fe2 O3 ). sulfur trioxide is lost. This quality . 0. potassium alum is used in the pharmaceutical and cosmetics industries. in some countries outside Europe.3 109 50. as an alum.5 5. the industrial importance of potassium alum has declined considerably. with which it forms a continuous series of mixed crystals. This process had some importance prior to 1945 in Germany and the United States for aluminum hydroxide and aluminum oxide production (→ Aluminum Oxide) Uses.4 20 61.2 30 66. ca.0001 % Fe2 O3 . is sieved and packed in paper bags that are lined with polyethylene. More recently.0 Ammonia 2. Applications include those in dressing furs in tanning. occurs in nature as shermigite. aluminum sulfate is designated traditionally.5 4. in the production of very fine aluminum oxide particles for polishing metallographic surfaces.3 4. it is still employed in tawing skins. 500 t/a are produced for this purpose.5 1. Ammonium alum is slightly soluble in dilute acids and glycerol but insoluble in absolute alcohol. However.40 0.71 Cesium 0.4 6.33. Data on loss of water on heating are in disagreement. which forms lustrous crystals. In aqueous solution. very pure starting materials must be used. Ammonium alum is made mainly by dissolving aluminum hydroxide in sulfuric acid and adding ammonium sulfate but sometimes by the reaction of ammonia gas with aluminum sulfate and sulfuric acid. ammonium alum has gained considerable importance as starting material for the production of the finely powdered.7 7.1 0. 3000 t/a) in baking powder. melts at 61 ◦ C in its water of crystallization. 2. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAlO2 . In Europe. After being crushed. Alternatively. always contain more than the stoichiometric amount of Na2 O. Aluminates occur also in cement and in spinels.1. and the aluminum hydroxide is boiled with ca.3. Sodium Aluminum Sulfate Sodium aluminum sulfate [7784-28-3]. The sodium aluminate solution obtained from the digestion process is separated from any impurities and then concentrated to the commercial liquid grade by evaporation. a sludge of potassium sulfate. The chief commercial process for the manufacture of sodium aluminate is the dissolution of aluminum hydroxides in sodium hydroxide solution. Because of this and also because of its strong tendency to age. Inorganic of aluminum oxide is made by heating ammonium alum (or ammonium aluminum selenate alum) to 1000 ◦ C. sodium alum is produced by adding a clear solution of sodium sulfate to aluminum sulfate. sodium alum. 90 % NaAlO2 and 1 % water. Commercial grades.8 Aluminum Compounds. it softens above 1700 ◦ C when sodium begins to evaporate slowly. however.50 times the formula requirement. Sodium alum is insoluble in absolute alcohol but is much more soluble in water than all other alums. together with 1 % free NaOH. its use has been abandoned. Commercial grades of sodium aluminate are available in solid and liquid forms. In nature. the ratio of aluminum sulfate to sodium sulfate is adjusted to the stoichiometric amount. NaAl(SO4 )2 · 12 H2 O. and caustic soda is added to improve the purity of the product. . sodium alum has never gained the same importance as the other alums. These two facts make it difficult to obtain sodium alum free from iron. the data on thermal dehydration disagree. Aluminates Only the aluminates of barium and sodium have importance in industry. In the United States. where it is mixed for several hours.2. Aluminum trihydroxide (gibbsite) from the Bayer process (→ Aluminum Oxide) can be dissolved in 10 – 30 % aqueous NaOH solution at a temperature near the boiling point. 250]. it occurs as the mineral mendozite. The resulting product contains ca. The mixture is pumped into a stirred vessel. The use of more concentrated NaOH solutions leads to a semisolid product. This sodium alum cake is then heated and finally ground to the desired size (99 % through a sieve of 100 mesh) [17. whereas boehmite containing bauxite requires higher temperatures (230 ◦ C) and pressures. Sodium Aluminate Sodium aluminate [1302-42-7] is an important commercial inorganic chemical. a solid mass containing about 70 % NaAlO2 is formed. sodium silicate. The solubility of the salt produced in this way depends strongly on how much excess sodium hydroxide is used. 2. 1. The process is carried out in steam-heated vessels of nickel or steel. bauxite can be used directly as the alumina source. Bauxites containing gibbsite are extracted at 150 ◦ C and 5 bar. Sodium aluminate has no defined melting point. however. It func- tions as an effective source of aluminum hydroxide for many industrial and technical applications. Again. Production. the excess being on the order of 1. 50 % aqueous sodium hydroxide until a pulp forms. In the United States. leaving aluminum oxide. The solid product is obtained by drying the liquid. or Na2 Al2 O4 . this product is dehydrated in a rotary oven heated either directly or indirectly by burning hydrogen. the melt is pumped into an evaporator and concentrated to such an extent that it solidifies to a hard cake on pouring into a cooling tank. After dilution to 30 ◦ B´e and subsequent heating. Hydrated forms of sodium aluminate are crystallized from concentrated solutions. Production. sodium alum is still utilized in relatively large quantities (ca. Alum powder (very fine crystalline form) is not available commercially. During this stage. p.05 to 1. Afterwards. Na2 O · Al2 O3 . After this is poured into a tank and cooled. mp 1915 ◦ C. Compared to calcium chloride.Aluminum Compounds. alkali. Because it does not attack the reinforcing metals. Sodium aluminate is used as an adjunct to water softening systems. Sodium aluminate increases the resistance of mortar to water. Uses. The major use of sodium aluminate is for water treatment. or Na2 SO4 [31] the final strength increases without affecting the setting rate significantly. up to 5 % (relative to the total dry mass) sodium aluminate is added. in the production of waterinsoluble floor waxes [47]. and for removing dissolved silica. When sintering bauxite. In the enamel industry. Also. and 3 BaO · Al2 O3 [12004-05-6]. aluminum [43]. used as catalyst supports or as catalysts [33 – 36] and as adsorbents. which does not affect the metallic luster. from . This effect is based on the formation of a thin. mp 1425 ◦ C [50]. and antistatic properties of polyester synthetic fibers. improving dyeing. protection of steel surface during galvanizing. mp 1815 ◦ C. in the detergent and varnish industries. it stabilizes the pH value of the water circulation [40] and increases the dispersion stability of titanium dioxide [41]. among others). and the paper strength [39]. sugar. of aluminum oxide on the surface. By adding substances such as oxoacids [29]. The aluminum hydroxide that precipitates from this solution has excellent flocculation properties and coagulates other impurities present in the water. as a dispersion agent for production of high-purity asbestos [48]. and as a binder in the ceramics industry. very firmly adhering layer of aluminum hydroxide or. For the production of expanded concrete. In construction technology. mainly when working during frost. retention of fibers and filling materials [38].2. Another application of sodium aluminate is as a pickle to protect metallic surfaces (copper [42]. By sintering sodium carbonate directly with Bayer aluminum trihydroxide in rotary sintering kilns at 1000 ◦ C. sodium aluminate is being used for the production of synthetic zeolites. sodium aluminate increases the opacity [37]. as a coagulant aid to improve flocculation. under water. 2. Further applications of sodium aluminate are in lithography for the production of printing inks [45] and print forms [46]. To stabilize foam formation in the production of light refractory bricks. and in the textile industry as a mordant in dyeing and in printing cloth. and in humid soil (see Table 4). The first two crystallize hexagonally. naphthene [30]. These include inhibition of glass etching by alkaline solutions. as an additive to drilling fluids [49]. Barium Aluminates The industrially important barium aluminates are BaO · 6 Al2 O3 [12254-17-0]. and 1 part water % NaAlO2 in concreteSetting started 0 4 h 30 min 1 30 min 1. sodium aluminate has the advantage of greater setting acceleration at low water-to-cement ratios [28]. which acts in a similar manner. after heat treatment. Many other uses of sodium aluminate have been reported. Barium aluminates are produced by melting bauxite with coal and barite. Sodium aluminate dissolves in water to give a solution that has a pH value of 8. sodium aluminate is added to enamel mixtures to achieve low-melting covers [44]. 9 Table 4. Depending on the impurities. it can be used for work with steel-reinforced concrete. sodium aluminate serves to activate nitrogen-releasing substances [32]. including both potable and industrial waters. 2 parts concrete. K2 CO3 . an essentially anhydrous product can be obtained. Leaching the melt gives a solution of barium aluminate. Inorganic The sinter method also has been used to produce sodium aluminate. Acceleration of setting by sodium aluminate in a mixture of 6 parts sand. antipiling. sodium aluminate is employed to accelerate the solidification of concrete. Increasingly. Too rapid setting can cause cracks in the concrete. affecting the final strength of the building. and acid. BaO · Al2 O3 [12004-04-5]. as an additive to foundry sand molds and cores. it is essential to leach the sinter mass with water and separate the impurities. the conditions of precipitation can be improved by adding aluminum sulfate [27]. Sodium aluminate is one of the principal sources of alumina of the preparation of alumina adsorbents and catalysts.5 15 min 2 10 min 10 instantly Setting completed 6h 1 h 40 min 30 min 15 min In the paper industry. including such hydrated compounds as BaO · Al2 O3 · 4 H2 O. and 7 BaO · 6 Al2 O3 · 36 H2 O.44 g/cm3 181. and relatively soluble barium hydroxide.1.5 ◦ C –705.1. Al(OC4 H9 )3 . as binding agent for the production of high-temperature refractories. no catalyst was required and nearly quantitative conversion was obtained. Hydrolysis with water occurs readily.1 kJ/mol . Dissociation of the dimer progresses with rising temperature and is quantitative above 800 ◦ C. 4. It is usually produced by direct reaction of aluminum and isopropyl alcohol in the presence of mercury(II) chloride catalyst. Aluminum Chloride 4. flash point 26 C. Anhydrous Aluminum Chloride Oerstedt first prepared anhydrous aluminum chloride [7446-70-0] in 1825 by the reaction of chlorine gas with a mixture of alumina and carbon. and perfumery chemicals. for example. mp 118 ◦ C. but sparingly soluble in alcohols. to impregnate textiles.2 ◦ C 192. Al(OH)3 .34 2. see [1] and [54]. bp ◦ 180 ◦ C at 533 Pa.30 kJ/mol 35. A further use of barium aluminates is as a special cement. as intermediates in the production of pharmaceuticals. Al2 Cl6 . Aluminum isopropoxide [555-31-7]. Solid aluminum chloride crystallizes to form a monoclinic layer lattice. 2 BaO · Al2 O3 · 5 H2 O. In the industrial production of ketones and aldehydes. d20 4 0.73 ± 2. only the isopropoxide (isopropylate) and sec-butoxide (sec-butylate) are important. Physical properties of anhydrous aluminum chloride [55]: Mr at 25 ◦ C Sublimation temperature at 101. is a colorless liquid. whereas the aluminate ions form insoluble calcium aluminate. M r 246. and is produced in a manner similar to aluminum isopropoxide. ◦ d20 4 1. Al(OCH(CH3 )2 )3 . Industrially. Pure aluminum chloride is white. 4. For general literature. They are readily soluble in hydrocarbons. Aluminum Alkoxides Aluminum alkoxides (alcoholates) are solid or liquid compounds of covalent character. For a general review of aluminum alkoxides. In a later version of the process [53].84 kJ/mol –325. M r 204. is a white solid.84 kJ/mol 115. and in the production of radiation shields [51]. particularly for Friedel-Crafts syntheses and allied reactions for the production of alkylated aromatics. bp 125 – 130 ◦ C at 533 Pa. Inorganic which the salt is obtained by evaporation.9671. excess isopropyl alcohol is added to a solution of aluminum chloride in benzene. BaO · Al2 O3 · 7 H2 O. see [52]. Barium aluminate is used for purifying water because the Ba2+ ion precipitates both the sulfates and the carbonates. the hydrogen chloride formed is removed by introducing dry ammonia into the reactor and filtering off the ammonium chloride that precipitates. 3. flash point 26 C. and as antitranspirants in cosmetics.25. but the commercial product usually has a yellowish or grayish tinge because of small amounts of iron chloride or aluminum impurities. dyestuffs. forming hydrargillite (gibbsite). These compounds are used to adjust the viscosity of varnishes. In an alternative production method.0346. The alkoxide can be purified by distillation. This compound has acquired great significance in organic chemistry as a catalyst.10 Aluminum Compounds. Aluminum sec-butoxide [2269-22-9].35 ± 0. the alcohol was heated under reflux in a column filled with aluminum chips.3. hydrolyze in water. at 233 kPa Heat of formation at 25 ◦ C Heat of sublimation of dimer at 25 ◦ C Heat of fusion Heat of solution at 20 ◦ C 133. aluminum alkoxides are employed as reducing agents (Meerwein-Ponndorf reaction). aluminum chloride is present as the dimer. pharmaceuticals.1. All barium aluminates.63 ± 0. Very pure barium aluminates can be produced by sintering mixtures of aluminum oxide with barium carbonate. giving aluminum hydroxide and the corresponding alcohol. In the solid and gas phases at temperatures up to 400 ◦ C. Properties Physical Properties.3 kPa Triple point. and the low reaction temperature insures that the brick lining has a long life. The off-gas contains chlorine. In aqueous solution. The gaseous reaction mixture enters a brick-lined. Chlorination of alumina is advantageous over the formerly widely used bauxite process (less reactor corrosion and higher-purity product). is formed. For this reason. Bauxite now has no economic significance as a raw material because of the iron chloride always present in the product. volatile aluminum monochloride [13595-81-8]. The reaction is exothermic enough (ca. ground (insuring exclusion of moisture). condensed. such as CaCl2 . evolving hydrogen chloride.2. Extremely pure aluminum chloride is obtained by resublimation from molten sodium aluminum chloride. Aluminum is . ethers. The reaction is highly exothermic: 2 Al (s) +3 Cl2 (g) →Al2 Cl6 (s) ∆H 11 ◦ = −1411 kJ/mol The temperature in the reactor is maintained at 670 – 850 ◦ C by controlling the admission rates of chlorine and aluminum and by cooling the reactor walls with water. Quality Specifications and Analysis Anhydrous aluminum chloride is ground and marketed as powder or granules. The hexahydrate [7784-13-6]. AlClO. such as hydrogen chloride. Reaction between aluminum chloride and other metal halides. for example. Anhydrous aluminum chloride dissolves readily in polar organic solvents. Today.44. 300 kJ/mol.1. As a Lewis acid it forms addition compounds with numerous electron donors. sulfur tetrachloride. amines. esters. and large amounts of carbon dioxide. Inorganic Chemical Properties. The aluminum chloride vapor is filtered through a bed of coarse pumice chips. and the phosgene is hydrolyzed with water. tube-shaped reactors. Chlorine is passed through molten aluminum in ceramic-lined. The aluminum chloride vapor leaving the reactors is passed through ceramic-lined tubes into large.Aluminum Compounds. Carbon monoxide and chlorine are partially converted to phosgene over an activated charcoal catalyst. CrCl3 . The chlorine is removed by scrubbing. and alcohols. but this reaction goes in the reverse direction at temperatures above 700 ◦ C: AlCl3 +Al2 O3 3 AlClO If aluminum chloride vapor is passed at 1000 ◦ C under reduced pressure over molten aluminum. forms. AlCl3 · 6 H2 O. aluminum oxychloride. M r 241. Production The starting materials are either aluminum or pure aluminum oxide. 4. Chlorine in the off-gas is removed by conventional methods. The difficulty of controlling the large heat of reaction can be overcome also by dividing the process into a number of small units. The aluminum usually is replenished in the form of lumps. AlCl. anhydrous aluminum chloride cannot be obtained by concentrating the solution and calcining the hydrate. Eutectic melts with other metal chlorides are of industrial significance. that with sodium chloride is used as a solvent in chlorination reactions. hydrogen sulfide. gives mixed halides. where it reacts with finely divided γ-alumina to yield aluminum chloride. Consequently. This method has been adopted for purifying aluminum. 4. the process permits large units.3. phosphorus trichloride. and further processed as described above. phosgene.1. air-cooled iron chambers. aluminum chloride is partially hydrolyzed to hydrochloric acid and aluminum oxychloride. sulfur dioxide. and classified by sieving. fluidized-bed reactor. Chlorination of Pure Aluminum Oxide. When aluminum chloride is heated with γ-alumina. and at the same time it avoids the high raw material costs involved in metal chlorination [57]. such as absorption in caustic soda solution. most anhydrous aluminum chloride is made by chlorinating aluminum. but this decomposes immediately into the elements in cooler zones of the reactor. Solid aluminum chloride is withdrawn from the condenser walls at regular intervals. is formed in this reaction. AlClO [13596-11-7]. Chlorination of Aluminum [56]. based on AlCl3 ) to maintain the temperature at 500 – 600 ◦ C without external heat. Anhydrous aluminum chloride reacts extremely violently with water. and FeCl3 . U. Data on the consumption of anhydrous aluminum chloride in the USA are given in Table 5. 2801. or 0. which are in this way protected from oxidation by an oxide layer.1. A principal application is the alkylation of benzene by alkyl halides to form alkylbenzenes that are consumed in the production of synthetic detergents. It is still employed in reforming hydrocarbons. International marine transportation is governed by the IMDG code.12 Aluminum Compounds. anhydrous aluminum chloride consumption in 1993 (not including the amounts consumed in the production of aluminum) [61] Alkylate detergents Ethylbenzene Hydrocarbon resins Pharmaceuticals Titanium dioxide Miscellaneous Total 2200 t 4000 t 3900 t 4000 t 2200 t 4900 t 21200 t . Aluminum chloride is dispatched in vented steel drums or in tank trucks or rail tankcars that can be emptied pneumatically with dry air or nitrogen (dew point below − 40 ◦ C). aluminum chloride is widely used as catalyst in the production of anthraquinone and its derivatives and of pigments. such as aromatic aldehydes. UN no. class 8. no. EG no. ADR. UK: Blue Book. Handling.101. 6801. such as phthalocyanine green. Rn 801. The assay is 98 – 99 % AlCl3 . Aluminum chloride also catalyzes the liquid-phase ethylation of benzene with ethylene to yield ethylbenzene. A further application of aluminum chloride is as a finish for titanium dioxide pigments. It is a catalyst also in the production of compounds. 59]. lithium aluminum hydride. 172. Table 5. Corrosives & IMDG code E 8031. packaging. and Transportation Because of its corrosive and irritant action. and labeling of dangerous substances. corrosive solid. Inorganic usually determined by atomic spectrometry. residual amounts can be washed away with plenty of water. Other applications for anhydrous aluminum chloride include the production of aluminum borohydride. aluminum chloride was used extensively in petroleum refining for cracking and isomerization. Ethyl chloride is produced mainly by the reaction of hydrochloric acid and ethylene in the presence of aluminum chloride. National and international regulations must be observed.1. Uses Anhydrous aluminum chloride is an important Friedel-Crafts catalyst in the chemical and petrochemical industries [58. Handling. and for the production of butyl rubber. the consumption has significantly decreased because of the declining demand for tetraethyl lead as an antiknock additive. anhydrous aluminum chloride is classified as a dangerous substance. most of which is used in the production of styrene. used in fragrances. Until 1960. it should not be stored for more than six months. 013−003−00−7.5. Sodium bicarbonate or slaked lime should be used for neutralization. 11b. Storage. ADNR: Class 8. gloves. respectively.01 wt % for resublimed product). and only small. 4. such as 67/548/EEC. Most of these reactions with aluminum chloride produce a solution that is often used as a flocculating agent in the treatment of waste water.S. A fume cupboard or a respirator with filter type B/St against acid gases should be used. any spills must be taken up dry. the chloride by argentometry. ketones. The main impurity is iron (0. EEC: Yellow Book 78/79. USA: DOT regulations. as a polymerization catalyst in the production of hydrocarbon resins. Because the product tends to cake. RID. 4.05 wt % max. such as alkylbenzenesulfonates. as well as compounds of phosphorus and sulfur. Goggles. Sampling and analysis of anhydrous aluminum chloride must be carried out in an atmosphere of dry air or nitrogen. CFR 49. Aluminum chloride also is an intermediate in the production of aluminum by the Alcoa smelting process [60] (→ Aluminum). the key European Economic Community directive dealing with the classification. and protective clothing must be worn when handling aluminum chloride. In the dyestuffs industry. Because hydrogen chloride is evolved when aluminum chloride is exposed to water.4. and 2-phenyl-ethanol. Storage and Transportation. but it has now been replaced by zeolite catalysts. 1726. ) prepared directly from AlCl3 · 6 H2 O Aqueous solutions of basic aluminum chlorides are acidic because the compounds hydrolyze (see Table 6). 67]. crystallizes hexagonally and dissolves exothermally in water (133 g hexahydrate per 100 g water at 20 ◦ C) [62]. the compounds are unstable. in %) w 60 30 15 10 5 3 pH 3. and all are white. 0. The electrical conductivities of the aqueous solutions.Aluminum Compounds. Aluminum chloride hexahydrate has only minor importance as such.3 4. can be removed [62]. compounds with the approximate composition Al2 (OH)5 Cl · 2 – 3 H2 O [12042-91-0] are so stable at concentrations > 50 % that no decomposition occurs. Electrical conductivity of freshly prepared basic aluminum chloride solutions: ◦) from Locron L (ca.4 4.3.43. but readily soluble in water. 65].5 %) and 20 ◦ C.5 H2 O) and hydrochloric acid at constant aluminum oxide concentration (11. In this way. The solubility increases only slightly with temperature.5 H2 O at 20 ◦ C (mass fractions. Aluminum Chloride Hexahydrate Properties. Figure 2. For example. decompose to give insoluble basic aluminum chloride at a rate that depends on the temperature and concentration of the solution [68]. Hydrogen chloride is evolved on heating concentrated solutions. have the general formula Al2 (OH)6−n Cln · x H2 O. For example. Basic aluminum chlorides [1327-41-9]. corresponding to basicities of ca. compounds of basicity greater than 75 % are very stable in aqueous solution. The stability of the solutions depends on the basicity: compounds with aluminum to chloride molar ratios of ca. All basic aluminum chlorides with n = 1 – 5 can be isolated. aluminum hydroxychlorides. they decompose to aluminum hydroxide and aluminum oxide on heating to above 80 ◦ C.6 : 1. impurities.2 4. 30 – 75 %. The aqueous solutions are strongly acidic because the salt hydrolyzes. However. M r 241. w. pH values of aqueous solutions of Al2 (OH)5 Cl · 2. but form . 170 g of the compound Al2 (OH)5 Cl · 2. Below a minimum water content. in some cases crystalline substances. Basic Aluminum Chlorides Properties. Table 6. shown in Figure 2. are characteristic of the basic aluminum chlorides. The structure of aqueous solutions of AlCl3 · 6 H2 O is discussed in [63]. Production and Uses. The individual compounds are best defined either by the molar ratio of aluminum to chloride (2/n) or by their basicity. defined as (1 – n/6) · 100 %.2. even on boiling for days. partially soluble in the lower alcohols [66. for example.5 H2 O dissolves in 100 g water at 20 ◦ C. poly(aluminum hydroxychlorides).5 : 1 to about 1. particularly iron (III) chloride. the viscosity of the solution prevents further amounts from dissolving. it is of industrial importance as an intermediate in the production of aluminum oxide [64. the compounds of high basicity (above 65 %) do not crystallize from their aqueous solutions.4 In contrast to the aluminum chlorides of low basicity (below 65 %).0 4. which depends on n. 4. However. Inorganic 13 4. Aqueous solutions of AlCl3 · 6 H2 O can be obtained by dissolving aluminum hydroxide in hydrochloric acid: the hexahydrate crystallizes when hydrogen chloride passes into cold (about 20 ◦ C) saturated solution. aluminum chloride hydroxides. 50 % aqueous solution of Al2 (OH)5 Cl · 2. The white hydrate AlCl3 · 6 H2 O [7784-13-6]. it is used for hardening photographic layers.4 4. On the other hand. releasing water and hydrogen chloride. and indicator (dithizone in ethanol) are added. 80 ◦ C. One milliliter of 0. the solution is backtitrated with 0. Various qualities are available with aluminum contents between 7.9 at 60 – 70 ◦ C. Inorganic glassy masses. the compound Al2 (OH)3. Basic aluminum chlorides are made by dissolving either aluminum hydroxide or metallic aluminum in hydrochloric acid. p. At the same time the cell voltage falls. ammonium acetate). Analysis. large quantities of aluminum sulfate had to be substituted by PAC. Hydrochloric acid converts all basic aluminum chlorides to the hexahydrate: Al2 (OH)5 Cl+5 HCl+7 H2 O→2 AlCl3 ·6 H2 O Chemical Structure. On addition of alkali to basic aluminum chlorides.7 Cl2. Production.14 Aluminum Compounds. The most important basic aluminum chloride with regard to consumed quantities are the polyaluminum chlorides (PAC) with basicities in the range of 35 – 60 %.5. SO4 500 ppm.1 M disodium ethylenediaminetetraacetate is equivalent to 2. The pH is adjusted to 4. PAC is widely used as a flocculating agent for purifying water. In water treatment PAC can be used for purifying surface water. The formation of explosive gas mixtures must be avoided throughout the reaction by diluting the hydrogen with air or nitrogen to below the explosion limit.1 M zinc sulfate. The corresponding bromides as well as iodides are obtained by the same method. Basic aluminum chlorides have been known for a long time [1.698 mg of aluminum. corresponding to a basicity of 83 %. Hydrochloric acid ( 1. 20 % sodium hydroxide. calculated as aluminum oxide. freshly precipitated aluminum hydroxide [77] must be used. When solutions in the basicity range 30 – 65 % are evaporated. 170 A/m2 . aluminum hydroxide precipitates. and the pH value to about 3.7 – 4. 205]. Basic aluminum chlorides are mixtures of complex compounds of various degrees of polymerization. The solid halides are obtained from the solutions by careful evaporation or by spray drying [79]. A second important application for PAC is as fixing sizing agent in the paper industry. Basic aluminum chlorides are so stable that the aluminum content can be determined only after decomposition of the complex ion [75. The maximum levels permitted are Fe 100 ppm. Recently another method may be of interest: Controlled thermic decomposition of AlCl3 × 6 H2 O [86]. followed by ca.5 and 18.2 – 1. Another important basic aluminium chloride has the composition Al2 (OH)5 Cl · 2 – 3 H2 O and is known in the literature as aluminum chlorohydrate. After all the hydrochloric acid has been added. After the solution is cooled to about 25 ◦ C and buffer solution (acetic acid. but only recently have investigations given significant insight into their chemical structures [70 – 73]. . the preferred method is to dissolve aluminum in hydrochloric acid either thermally or electrochemically: 2 Al+HCl+5 H2 O→Al2 (OH)5 Cl+3 H2 This method is exemplified by the following process [78]: Aluminum electrodes are set up at distances of 40 mm in a corrosion-resistant electrolysis cell. the voltage between the first and last electrodes is set so that an average voltage of 0. The usual procedure is to mix the solution containing aluminum with 60 % sulfuric acid and 0. Aged aluminum hydroxide leads only to compounds of basicity up to 65 % [68]. Spectroscopic and kinetic investigations of the basic aluminum chlorides and of their solutions [70 – 73] lead to the conclusion that the complex ion [Al13 O4 (OH)24 (H2 O)12 ]7+ is present and is in equilibrium with its polymeric forms.3 · 6.04 g/cm3 ) is poured into the cell at a rate such that the reaction temperature remains at ca. Uses and Quality.6 V per electrode pair is obtained at a current density of ca. Variations observed in the properties of these aqueous solutions such as viscosity and pH are caused by polymerization and depolymerization [74]. acetone. Because of the change from acidic to neutral or alkaline sizing.0 %. and wastewater from industry and municipalities and for water treatment in swimming pools. sewage.05 H2 O (basicity 62 %) always crystallizes [69]. However. The electrolyte then consists of a solution containing aluminum and chloride in the molar ratio 2 : 1. After about 70 h. 76]. Very stringent purity specifications apply to this substance. the density of the electrolyte increases to about 1.1 M disodium ethylenediaminetetraacetate.3 g/cm3 . To obtain aluminum chlorides of high basicity. Papazian. Chebotkevich. G. 8. J. 16 (1972) no. W. Metall. F. Prikl. Eng. USA) and Locron (Clariant). vol. G. as a binding agent for fire-resistant ceramic products as a hardening agent for rapid fixing baths in the photographic industry and as a flucculant for purifying swimming-pool water. 260 (1965) 2823. Kovarskaya. Trav. 425. vol. 1960 (J. Walsh. as a hydrophobic agent for impregnation of cotton textiles. Soc. 3. 20. Heindl. Papier (Darmstadt) 17 (1963) 14. Toxicology Aluminum sulfate is classified as nontoxic. Akad. Kretschmar. Alum solutions are known for their astringent (tissue-contracting) effects. 15 ed. Kaltenbach. Orrell. Chem. 19. R. Fiz. N. SSR 15 (1970) 110. 25. 626 – 672.Aluminum Compounds. as a retention agent in paper production. 24. As 3 ppm. Thermochim. Kommunal Khoz. Khim. Linke: Solubilities of Inorganic and Metal Organic Compounds. H. 18. 3rd ed. R. Zh.” in Handbuch der Lebensmittelchemie. Chemfacts Japan. 17. Inst. Ullmann. N. Gee. Chem. 3 (1967) 77 – 87. 10. Chem. Barret. R. F. US 2951743. McGraw-Hill. 10th ed. . SE 341381.. Khim. M. Acta 4 (1972) 97. Molodykh Uch. Liants Hydrauliques. p. F¨aßle). Berlin 1969. Can. News 61 (1983) 32. H. Aluminium (D¨usseldorf) 39 (1963) 624. Oehler: “Technologie des Wassers. namely. Prakt. King. Seidell. M. The extensive use of the basic aluminum chloride Al2 (OH)5 Cl · 2 – 3 H2 O in the cosmetic industry worldwide over more than 30 years has shown that this compound is not irritating to the skin in the concentrations used commercially. Chem. Tr. Springer Verlag. O. 394 – 446. Princeton.. 3.. Akad. Am. Boliden. 35 “Aluminium. 74 (1971) 101 183. Mater. M. Hebd. 4th 26. System No. 15. A TLV of 2 mg/m3 was established for water-soluble aluminum salts [83]. 83 (1861) 477. 27. Lange: Handbook of Chemistry. J. 23. 3rd ed. The toxic effect is caused by the evolution of hydrochloric acid when the product is exposed to moist air. R¨uter. Van Nostrand. E. Akad. 2. Pulp Pap. New York 1961. Cunningham. vol. Nauk Az. Publics 1967. B.. Pizzolato. L. G. 72 (1950) 1282. 22. part 1: Wasser und Luft. Henry. P. 14. 1967. Berlin 1967. 76 (1954) 2054. Inorganic Pb 20 ppm. trade names are Chlorhydrol (Reheis. Khalilov. Mater. Chemical Data Series. 10. Issled. Abstr. 12.. Khim. 2. 11. that in the cosmetics industry as the effective component of antiperspirants [80. Chem. 16. SSR 1968.. These are required for one of its major applications. 1. C. 3rd. Abstr. Inst. R. (Leningrad) 44 (1971) 420.” part B. 1. 84].. J. 39 (1947) 1178. Nauk Kaz. Other important areas of application for this aluminum chloride are in the production of catalysts and highly temperature-resistant fibers based on Al2 O3 . H. vol. for tanning leather. Jui-Hsiung Tsai. IPC Industrial Press. Giulini. Gmelin. R. J. N. Kh. Paris. I. R. 6. 71 (1970) 23. N. 1971. Although intermittent application of 150 mg Al2 (OH)5 Cl · 2 – 3 H2 O over a period of 3 days was found to cause mild skin irritation in humans. Gel’Perin. Khim. D’Ans-Lax: Taschenbuch f¨ur Chemiker und Physiker. G. Venuat. and eyes. 77 (1972) 50847. a dose of only 7.J. 2. P. Kirk-Othmer. A. N. Akhmetora et al. Springer Verlag. V. B. L. respiratory tract.Y. Thiard. J. 1960 (J. Lebel. P. Neorg. A. 28. Eng. Cherdron). 5. Zh. DE 1125894. Smith. N. 21. A. DE 1146042. 13. Chem. References 1. ed. Ind. an LD50 value of 6207 mg/kg ( mouse. 4. Konf. 5. 1957. The resulting respiratory difficulties vary from mild irritation to coughing. 1958. Kazakov et al. 34. Sci. A. The MAK value (1995) and TLV (1983) for hydrochloric acid are both 7 mg/m3 [83. vol. no. A. Uzb. US 3574537. A.) 68 (1961) 36. K.5 mg of AlCl3 · 6 H2 O caused the same degree of irritation [85]. Anhydrous aluminum chloride has a corrosive and irritant effect on the skin. 6. 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