Researchers at the Faculty of Chemistry, Brno University of Technology, have developed a patent which enables the efficient inhibition of toxic hydrogen sulphide in the production of non-shaped refractory and fire-proof materials from a phosphate binder.
The phosphorus bond consists in the addition either of phosphoric acid or a mixture of phosphoric acid and phosphates, or just phosphates, to sand mixtures, or to sand with a lower part of clays than usual in classical refractory materials. Phosphorus bonds are most often used with sands based on aluminium-silicates. Using phosphoric acid causes the production of mostly aluminium phosphates. These can be added as a bond directly, in particular to materials with high aluminium content.
Non-shaped refractory materials are mixtures of refractory sand and an inorganic binder, which reinforces the material and enables it to be fired without defects the first time the heat unit is put into operation. Phosphorus bonds are used, in addition to other types of inorganic chemical bond and hydraulic bond (e.g. bonds based on aluminate cement), for binding non-shaped refractory materials.
Hydrogen sulphide develops in the production of these materials in the course of the reaction between phosphoric acid in the phosphate binder with sulphides and disulphides (most often FeS2 in a form of a mineral pyrite of marcasite), which are natural admixtures of a range of natural raw materials, in particular bauxite, which is the most often used.
According to the submitted invention, the inhibition of hydrogen sulphide development in the production of non-shaped refractory materials bonded by phosphorus bond is produced “in situ” in the course of the reaction between sand and phosphoric acid, or brought about indirectly in a mixture of phosphoric acid and phosphate salts. The binder is supplemented with a soluble metal salt which precipitates hydrogen sulphide in an acidic environment (Cu, Ag, Bi, Sb etc.) in an amount of several tens of grams per ton of binder. Hydrogen sulphide produced in the reaction of the binder with the ferrous sulphides (pyrite, marcasite) in the sand is precipitated as a sulphide of the aforementioned metal and H2S does not develop.
This method developed by researchers at the Faculty of Chemistry for inhibiting the development of hydrogen sulphide, i.e. which limits the development of this toxic gas during the production of refractory materials and building materials bonded with a phosphorus bond, enables an increase in hygiene levels and thus improves the safety of the working environment not only at the production plant, but also during the installation of a monolithic lining directly at the manufacturers of these materials.
This aspect is essential when lining heat units directly at the manufacturers, since providing effective ventilation for such premises is difficult, especially for minor equipment and equipment with complex shapes.
Another important aspect of the invention’s usability is its reduction of the impact of production on the environment. Sales of licences can be expected in particular to major companies engaged in manufacturing phosphate binders and in building and maintaining furnaces and foundry equipment.
