Liquid purification or separation – Processes – Using magnetic force
Patent
1994-05-16
1995-08-15
McCarthy, Neil
Liquid purification or separation
Processes
Using magnetic force
210717, 210912, 210913, 210914, C02F 148, C02F 162
Patent
active
054416485
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the separation of heavy metals, especially toxic metals, from aqueous media containing the same, e.g. industrial effluents.
There is a need for simple and effective methods for removing heavy metals, especially toxic heavy metals such as cadmium, from industrial effluents and other aqueous media which contain them. Treatment to remove heavy metals is necessary before effluent can be sent to waste and there are increasingly stringent requirements for acceptably low levels of such metals.
In our European specification 0186445A we described a process for the separation of metals from aqueous media in which an aqueous medium containing a paramagnetic metal is contacted with cellular particles, e.g. bacteria, in the presence of a compound converted by the particles into a product which interacts with the metal and causes the metal to become bound to the particles which are then separated magnetically. In one embodiment of this process Desulphovibrio bacteria which reduce sulphate to sulphide are used. When the aqueous medium containing the paramagnetic metal is contacted with Desulphovibrio in the presence of dissolved sulphate, a water-insoluble sulphide of the metal is formed on the cell wall of the Desulphovibrio and is thereby removed from the aqueous medium.
The present invention provides an improved method for removing heavy metals, which need not be paramagnetic, from aqueous media containing them. The new method is simple to use, can be operated without the use of microorganisms and rapidly removes a very large proportion of the heavy metals present in the aqueous medium.
The process of the present invention for the separation of a heavy metal from an aqueous medium containing the same comprises contacting the said medium with finely divided iron oxide (Fe.sub.3 O.sub.4) and finely divided ferrous sulphide, preferably formed in situ and preferably physically attached to the iron oxide, maintaining said contact until at least a substantial proportion of said heavy metal has become bound to the said iron oxide and ferrous sulphide, and then separating the iron oxide and ferrous sulphide having the heavy metal bound thereto from the aqueous medium, preferably by magnetic means. The iron oxide used in the present invention is Fe.sub.3 O.sub.4, sometimes called magnetite, a term which however includes both mineral and synthetic Fe.sub.3 O.sub.4. Only synthetic Fe.sub.3 O.sub.4 is used in the present invention.
The iron oxide used in the present invention must be very finely divided and must in particular have a particle size less than about 1 micron. Iron oxide of this grade is produced by a precipitation process and is obtainable commercially.
According to a preferred embodiment of the present invention the ferrous sulphide is produced biologically by growing sulphate reducing bacteria, e.g. Desulphovibrio, in a nutrient medium in the presence of dissolved ferrous sulphate. The medium may be as described by Postgate, "The Sulphate Reducing Bacteria", Cambridge University Press, sec. ed, 1984. Iron sulphide is formed round the growing bacteria and clumps of bacteria having ferrous sulphide adherent thereto settle at the bottom of the culture vessel and can be removed as a slurry. For use in the present invention, this slurry at a concentration at 1 to 10% w/v, preferably about 3% w/v, ferrous sulphide in water is mixed with the iron oxide in a ratio of 50 to 500 parts by volume of the ferrous sulphide slurry to 1 part by weight of the iron oxide. The slurry obtained containing both ferrous sulphide and iron oxide may then be used to treat 100 to 1,000 times its volume of aqueous medium containing heavy metal.
In an alternative embodiment of the present invention, the ferrous sulphide is formed in situ in the presence of the iron oxide by mixing the iron oxide with an aqueous solution of ferrous sulphate, preferably containing 5 to 25% w/v of ferrous sulphate heptahydrate. The proportion of iron oxide may be preferably from 0.5 to 5% by weight of the solution. An aqueous solution of
REFERENCES:
patent: 3142638 (1964-07-01), Blaisdell et al.
patent: 3697420 (1972-10-01), Blaisdell et al.
patent: 3960723 (1976-06-01), Butler
patent: 3983033 (1976-09-01), de Latour
patent: 4294705 (1981-10-01), Hellestam
patent: 4502958 (1985-03-01), Sasaki
patent: 4701261 (1987-10-01), Gibbs et al.
patent: 4735725 (1988-04-01), Reischl et al.
patent: 4806264 (1989-02-01), Murphy
patent: 4839052 (1989-06-01), Maree
patent: 4861493 (1989-08-01), Jansen
patent: 4981593 (1991-01-01), Priestley et al.
patent: 5000853 (1991-03-01), Reischl et al.
patent: 5308500 (1994-05-01), Schwarzbach
Bio-Separation Limited
McCarthy Neil
LandOfFree
Separation of heavy metals from aqueous media does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Separation of heavy metals from aqueous media, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Separation of heavy metals from aqueous media will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2179542