Classifying – separating – and assorting solids – Fluid suspension – Liquid
Patent
1995-01-18
1997-05-27
Jones, Deborah
Classifying, separating, and assorting solids
Fluid suspension
Liquid
2091725, 252 60, 252 61, B03B 560
Patent
active
056323824
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the field of heavy liquids, and in particular, heavy liquids having application in the fields of mineral and other material separations.
Many mineral and mining companies have a need to determine how much of their ore or mineral product is a "heavy" mineral, since the heavy minerals often are the valuable component of the ore. This requires a separation of the heavy components from the light components such as silica, which have a density usually less than 2.7 g/cc.
Current practice is to use either bromoform, or 1,1,2,2-tetrabromoethane (commonly known as and hereinafter referred to as TBE) to effect the mineral separation. Bromoform has a density of 2.87 g/cc and TBE has a density of 2.95 g/cc. However, both of these compounds have been shown to have adverse effects on the health of humans exposed to them, and there is pressure both from within the mineral industry and externally to replace these toxic substances with a safer heavy liquid.
Most mineral companies using either TBE or bromoform require a heavy liquid with a density in excess of 2.80 g/cc at room temperature. Another requirement is that the heavy liquid be not significantly more viscous than TBE. Bromoform (2 cP) (centipoise) is twice as viscous as water, and TBE (10 cP) has about ten times the viscosity of water. The time to achieve an effective mineral separation in the liquid increases in direct proportion to viscosity, because the movement of particles in the liquid is slowed down.
A low-toxicity substitute for bromoform and TBE is already available, and is known as SPT (actually sodium metatungstate, but commonly known as sodium polytungstate). This is an inorganic compound, having the chemical formula Na.sub.6 [H.sub.2 W.sub.12 O.sub.40 ] in anhydrous form, which is dissolved in water to form very dense solutions. SPT has not been readily accepted by those users who need a heavy liquid with a density of 2.8 g/cc or more, because its solutions at these densities are too viscous at >28 cP, or more than 28 times the viscosity of water. Another disadvantage of SPT is its lack of thermal stability above 60 degrees Celsius.
Sodium metatungstate is a salt of metatungstic acid. Metatungstic acid is a metatungstate ([H.sub.2 W.sub.12 O.sub.40 ].sup.6-) and is one of a family of compounds known as the isopolytungstates. Isopolytungstates also include paratungstate-A ([W.sub.7 O.sub.24 ].sup.6-), and paratungstate-B ([W.sub.12 O.sub.41 ].sup.10-).
Isopolytungstates are themselves, from one group of tungsten polyacids. The number of different types of tungsten polyacids is large. They are conveniently divided into heteropoly and isopoly acids, where the isopoly acids are those containing only tungsten, oxygen and hydrogen, and the heteropoly acids are those containing one or two other elements in addition to tungsten, oxygen and hydrogen.
Heteropolytungstic acids are more numerous, and include species such as [X.sup.n+ W.sub.12 O.sub.40 ].sup.(8-n)-, [X.sup.n+ W.sub.11 O.sub.39 ].sup.(12-n)-, [X.sub.2.sup.n+ W.sub.18 O.sub.62 ].sup.(16-2n)-, and [X.sup.n+ W.sub.6 O.sub.24 ].sup.(12-n)-.
For each of these species, X.sup.n+ represents a positively charged hetero element. For the species [X.sup.n+ W.sub.12 O.sub.40 ].sup.(8-n)-, it is known that X may represent phosphorus, arsenic, boron, silicon, germanium, zirconium, titanium, iron, zinc, cobalt, nickel, copper, other transition metal elements, and rare earth elements.
It is also possible to prepare mixed isopoly or heteropoly acids, where another element may substitute for a tungsten atom. An example of this is [SiMoW.sub.11 O.sub.40 ].sup.4-, in which a single tungsten is replaced by a molybdenum atom.
Even for tungsten heteropolyanions which have a single formula, e.g. [SiW.sub.12 O.sub.40 ].sup.4-, there can be several isomers in which the spatial configuration of the tungsten atoms differ. Tungstosilicic acid has two relatively stable and well characterised forms, the alpha- and the beta- forms.
The alpha- form is the more common and is the only form available comm
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patent: 3857929 (1974-12-01), Quatrini et al.
patent: 4272400 (1981-06-01), Silbernagel et al.
patent: 4557718 (1985-12-01), Kamps et al.
patent: 4612180 (1986-09-01), Kim et al.
patent: 4916101 (1990-04-01), Lyons et al.
Derwent Abstract Accession No. 89-332691/46, 8703660 (Jielin Prov Inst ME) 30 Nov. 1988.
Derwent Abstract Accession No. 87-324418/46, 2230619 (polytronics KK) 09 Oct. 1987.
Patrick Jennifer M.
Patrick Vincent A.
Harding Amy M.
Jones Deborah
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