Ammonium Sulfate (NH4)2SO4
CAS No. 7783-20-2, Diazanium sulfate, ammonium sulfate, ammonium sulfate, diammonium sulfate, sulfuric acid diammonium salt, mascagnite, Actamaster, Dolamin
Ammonium sulfate, also spelled ammonium sulphate, (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen as ammonium cations and 24% sulfur as sulfate anions. In fertilizer the purpose of the sulfate is to reduce the soil pH.
Ammonium sulfate is used largely as an artificial fertilizer for alkaline soils. In the soil the ammonium ion is released and forms a small amount of acid, lowering the pH balance of the soil , while contributing essential nitrogen for plant growth.
Ammonium sulfate is also used as an agricultural spray adjuvant for water soluble insecticides, herbicides, and fungicides. There it functions to bind iron and calcium cations that are present in both well water and plant cells. It is particularly effective as an adjuvant for 2,4-D (amine), glyphosate, and glufosinate herbicides.
Ammonium sulfate is also used in the preparation of other ammonium salts.
In biochemistry, ammonium sulfate precipitation is a common method for purifying proteins by precipitation. As such, ammonium sulfate is also listed as an ingredient for many United States vaccines per the Center for Disease Control.
Ammonium sulfate is also a food additive. It has also been used in flame retardant compositions acting much like Diammonium phosphate. As a flame retardant, it lowers the combustion temperature of the material, decreases maximum weight loss rates, and causes an increase in the production of residue or char.
In November 2009, a ban on ammonium sulfate, ammonium nitrate and calcium ammonium nitrate fertilizers was imposed in the former Malakand Division - comprising the Upper Dir, Lower Dir, Swat, Chitral and Malakand districts of the North West Frontier Province (NWFP) of Pakistan, by the NWFP government, following reports that those chemicals were used by militants to make explosives. In January 2010, these substances were also banned in Afghanistan for the same reason.
Ammonium sulfate is made by reacting synthetic ammonia (or by-product ammonia from coke-ovens) with sulfuric acid. A mixture of ammonia gas and water vapor is introduced into a reactor that contains a saturated solution of ammonium sulfate and about 2 to 4% of free sulfuric acid at 60°C. Concentrated sulfuric acid is added to keep the solution acidic, and to retain its level of free acid. The heat of reaction keeps reactor temperature at 60°C.
Dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The heat of reaction evaporates all water present in the system, forming a powdery salt.
Ammonium sulfate also is manufactured from gypsum (CaSO4-2H2O). Finely divided gypsum is added to an ammonium carbonate solution. Calcium carbonate precipitates out, leaving ammonium sulfate in the solution.
Ammonium sulfate decomposes upon heating above 250°C, firstly forming ammonium bisulfate. Heating at higher temperatures will result in full decomposition into ammonia, nitrogen, sulfur dioxide and water. As a salt of a strong acid (i.e. H2SO4) and weak base (i.e. NH3), its solution is acidic; pH of 0.1M solution is 5.5.
In aqueous solution the reactions are those of NH4+ and SO4-2 ions. For example, addition of barium chloride, precipitates out barium sulfate. The filtrate on evaporation yields ammonium chloride.
Ammonium sulfate forms many double salts (ammonium metal sulfates) when its solution is mixed with equimolar solutions of metal sulfates and the solution is slowly evaporated. Such double metal sulfates include ammonium cobaltous sulfate, ferric ammonium sulfate, ammonium nickel sulfate and ammonium cerous sulfate.
