Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Patent
1996-03-04
1998-07-14
Langel, Wayne
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
423340, C01B 3312
Patent
active
057800057
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a method for manufacturing silica in the form of spherical particles with a low content of iron and impurities, by leaching natural silicates with the use of hydrochloric acid or other mineral acids in a reactor, and then separating, washing, drying and possibly grinding up the silica. The raw material used is mineral, preferably monovalent mineral olivine with the highest possible degree of purity, that the raw material is reduced to a particle diameter between 0.05 and 5 mm, preferably 0.1 and 0.5 mm.
BACKGROUND OF THE INVENTION
Silica is generally employed as a filling material over a wide range of products and over an extensive range of applications. In order to achieve the best possible effect as a filling material it is therefore important for it not only to have adequate purity and whiteness, but that it should be possible to surface and pore volume. Substances regarded as impurities in this context are mineralogical particles, ionic deposits and the like. This is of vital importance for the filler's adsorption properties, viscosity-regulating properties, abrasion and refraction properties. It is also important to be able to control the particle size and surface characteristics, thus enabling control to be retained over the introduction of fillers into a product and their effect. In this connection it will be advantageous to be able to manufacture silica in spherical form and with a defined size.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method for the manufacture of the silica with satisfies the above-mentioned requirements, i.e. a spherical silica with a controlled particle size and surface characteristics. This silica has characteristics corresponding to precipitated silica which has a number filler. These products are manufactured from potassium silicate and sulphuric acid. The object of the invention is to develop an alternative process with olivine as a raw material which provides corresponding products.
This object is achieved with a method which is characterized by the features in the patent claims presented.
By means of the invention the surprising discovery has been made that silica prepared from olivine can be formed in the shape of spherical primary particles with a diameter of 30-70 nanometres (10.sup.-9 m). The particles which are extracted by the method according to the invention will be an agglomerate of primary particles which easily disperse in liquids. By means of the invention it has further been discovered that the silica's primary particle size, its specific surface and pore volume, measured according to the BET method, can be adjusted depending on the leaching time, the temperature and acid concentration used in the process. This fact makes it possible by means of the method according to the invention to give the spherical silica particles the desired properties, which are adapted to suit the respective purposes.
For the basic material use is preferably made of crushed olivine, (Mg.sub.1.85, Fe.sub.0.15) SiO.sub.4 from the most monovalent possible natural mineral deposits. By the admixture of a mineral acid, e.g. HCl, H.sub.2 SO.sub.4, HNO.sub.3, the olivine dissolves and forms a green liquid consisting of the acid's anions and cations which are released from the olivine (Mg.sup.2+, Fe.sup.2+, Ni.sup.2+). In addition a residue of solid material is obtained which is a colloidal amorphous silica (SiO.sub.2) in the form of a gel. The silica is separated from the liquid by pressure filters, washed clean of acid remains, dried and ground. A white powder is thus obtained which consists of amorphous silica in the form of primary particles which form larger particle agglomerates. The primary particles will have obtained a spherical shape and a diameter of 30-70 nanometres. The material has a large specific surface (100-450 m.sup.2 /g), a large pore volume (0.7-1.7 cm.sup.3 /g) and thus a high degree of porosity. The process can be controlled in such a manner that the desired surface and/or pore volume can
REFERENCES:
patent: 4367215 (1983-01-01), Gjelsvik et al.
patent: 4405588 (1983-09-01), Caballero et al.
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