Copperas process

Traditionally caput mortuum is associated with a synthetic reddish purple or violet pigment derived from iron(III) oxide. Harley (1982) and sources therein consider the material to be formed as a by-product of sulphuric acid manufacture during the seventeenth and eighteenth centuries. This was probably an early form of the copperas process used for the manufacture of Venetian red and copperas red qq.v.). The synthetic origin of the pigment... 

The most important synthetic routes to iron oxide pigments involve either thermal decomposition or aqueous precipitation processes. A method of major importance for the manufacture of a-Fe203, for example, involves the thermal decomposition in air of FeS04-7H20 (copperas) at temperatures between 500 °C and 750 °C. The principal method of manufacture of the yellow a-FeO(OH) involves the oxidative hydrolysis of Fe(n) solutions, for example in the process represented by reaction (1). 

It will be observed from the preceding table that the copperas prepared at Paris and Honfleur is absolntely free from copper and alum, and is, therefore, of very great purity. This arises from the fact that in these localities it is prepared by the direct process, Instead of obtaining it from the pyritous Bhales in connection with the manufacture of alum. 

High-quality pigments called copperas reds are obtained by the thermal decomposition of FeS047 H20 in a multistage process (Fig. 22). If an alkaline-earth oxide or carbonate is included during calcination, the sulfate can be reduced with coal or carbon-containing compounds to produce sulfur dioxide, which is oxidized with air... 

Galvanizing. The process of galvanizing consists of placing a protective coating of zinc upon the surface of iron. Before application of the zinc, the iron must be cleaned of rust or scale by treatment with dilute sulfuric acid, a process known as pickling, which incidentally produces important quantities of copperas, hydrated ferrous sulfate (FeS04-7H20), as a by-product. 

The sulfate process has traditionally used batch ore digestion, in which concentrated sulfuric acid is reacted with ilmenite. This reaction is very violent and causes the entrainment of sulfur oxides (SOA) and sulfuric acid in large amounts of water vapor. In an effort to reduce the particulate emissions, scrubbers have been installed at most plants, but these, in turn, have necessitated the treatment of large quantities of scrubbing liquid before discharge. Other waste-disposal problem products are spent sulfuric acid and copperas (FeS04-7H20). 

About 70% of all iron oxide pigments are produced synthetically. Copperas or ferrous sulfate heptahydrate (FeS04-7H20) is the primary source of iron. It is a byproduct of the sulfate process for the manufacture of titanium dioxide as well as a by-product of pickling operations in the steel industry. Other sources of iron include ferric sulfate, ferrous chloride, ferric chloride, and the iron oxide slurry from the production of aniline by nitrobenzene reduction. 

There is still another economically attractive use for this material. It can be moved into the more lucrative and larger potable water treating markets as a replacement for either alum or copperas (FeSOi,). Heretofore, this has not been possible because of hydrocarbon contaminants. This paper describes a process that has been developed to upgrade the AICI3 solution into a product that is suitable for this use. The quality of the purified Aids and the results obtained when it was used as a coagulant in a commercial clarifier are presented. 

One of the earlier processes for reducing Indigo, based on the use of chemicals instead of micro-organisms, was with copperas , the colloquial name for ferrous sulphate. The ferrous sulphate was dissolved in water and lime water added ferrous hydroxide was then precipitated which rapidly reacted with the oxygen with the formation of ferric hydroxide, accompanied by the liberation of hydrogen. 

Soaps are colored by adding to them small amounts of copperas, ultra-marine, or other pigment. Transparent soaps are made by dissolving a common soap in alcohol and distilling off the latter from the decanted solution until the residue is obtained as a clear transparent jelly, which is finally carefully dried in moulds. The addition of glycerol and alcohol or a solution of cane sugar to cold-process soaps, renders them more or less transparent. 

Ecological Aspects of Modern Production Processes. Sulfate Process. The conventional sulfate process is characterized by a linear flow of sulfuric acid through the process. Some H2SO4 ends up in the copperas by-product, but the main part remains separate from the pigment end product, as a used reagent with deteriorated quality in terms of concentration and purity. Formerly, this large stream was discarded as waste (see Fig. 80). Now, the spent acid is recovered, and complex acid concentration and filter salt treatment plants are added to recycle the acid entirely. Hence, the modern sulfate process plant for titanium dioxide pigment manufacture is characterized by a closed sulfuric acid cycle that completely withholds spent acid from the environment (see Fig. 81). 

Goethite process. Precipitation of goethite, FeOOH, is performed by adding a solution of ferrous sulfate to zinc calcine along with oxygen or air to ensure the oxidation of ferrous iron at a pH of about 3. Ferrous sulfate comes from copperas (FeSO 7H2O) or from the leaching of zinc ore concentrates ... 

Fuller (1973a) describes a number of processes that result in synthetic iron oxides and hydroxides. For red iron oxides he details calcination of iron(II) sulfate hydrate (copperas reds), calcination of synthetic yellow iron oxides (ferrite reds), aqueous precipitation from iron(III) hydroxide nucleation in solutions of iron(II) salts and calcination of magnetite at about 370°C. For... 

---