Preparation and uses of polyferric sulphate

Details Preparation and uses of polyferric sulphate Preparation and uses of polyferric sulphate

1996-09-18

1998-07-28

Straub, Gary P.

Liquid purification or separation

Processes

Making an insoluble substance or accreting suspended...

423558, 423138, C01G 4914, C02F 152

Patent

active

057858624

DESCRIPTION:

BRIEF SUMMARY
Chemical coagulants for drinking water, to purify and/or decolourise municipal water supplies for human consumption are known and include iron and aluminium-based inorganic coagulants.
Polyferric sulphate, PFS, is one known form of coagulant which has also been used to treat municipal and industrial waste waters to help remove, by flocculation, suspended organic waste matter. There is currently considerable interest in the more widespread application of PFS as coagulants. Because of its relative efficiency, PFS may need less chemical addition, it can have a greater removal capacity and may reduce the volumes of waste concentrates that require disposal or further treatments.
PFS is a known chemical and there are several patents describing methods for its preparation.
The present invention is concerned with methods for preparing polymeric forms of ferric sulphate, of which PFS is an example.
Essentially, the chemical can be prepared according to this invention by oxidising ferrous sulphate to ferric sulphate, and then carrying out a controlled, partial hydrolysis of the ferric sulphate to produce a !.sup.(3-x)+, and polynuclear complexes of iron (III), (Fe.sub.m (OH).sub.x !.sub.n.sup.(3m-x)n+. The functions of these species are to provide both colloid charge neutralization and polymer bridging between floc particles, leading in practice to a greater coagulating (and therefore, treatment) performance.
According to this invention there is provided a process for preparing a polymeric form of ferric sulphate wherein an acidic aqueous solution comprising ferrous sulphate is oxidised to form ferric sulphate in said solution in an oxidation stage at ambient pressure and in the absence of oxidation catalyst preferably using at least one oxidising agent from the following: ozone, nitric acid, peroxide, perchlorate and persulphate,
said ferric sulphate subsequently being at least partially hydrolysed by addition to said solution of at least one base, the ferric sulphate being kept in contact with said base at the temperature selected for a time sufficient for polymerisation of the at least partially hydrolysed ferric sulphate.
The ferrous sulphate solution may be rendered acidic by addition of e.g. sulphuric acid. This may usefully increase the level of sulphate ions in solution, without adding unwanted ionic species. The pH of the starting solution is preferably less than 2.0, more preferably in the range 0.8 to 1.5.
Preferably the oxidation stage is a one-step oxidation stage. Preferred oxidising agents include peroxide and nitric acid. It is possible to use strong concentrated or even fuming nitric acid.
Accordingly the concentration of the nitric acid used in the oxidation stage is preferably at least 50% by volume, more preferably at least 70% by volume although nitric acid as concentrated as 90% by volume can be used.
It is also preferred to use peroxide as an oxidising agent and more preferably hydrogen peroxide. The strength of the hydrogen peroxide used, as with the option of nitric acid mentioned above, may be dictated by the economics of the cost of raw materials, oxidation temperature and oxidation time.
Thus a stronger oxidising agent will most likely allow a shorter oxidation time and/or a lower oxidation reaction temperature. With hydrogen peroxide at very strong concentration, perhaps of the order 30 volumes, it may even be possible to effect the oxidation stage at ambient temperatures, for example at a temperature in the range of 15.degree. to 25.degree. C. Oxidation temperatures when using hydrogen peroxide may be 70.degree. C. or lower, such as 60.degree. C. or lower, preferably no higher than 50.degree. C.
Oxidation temperatures when using nitric acid as the oxidising agent, may be 110.degree. C. or lower, such as 90.degree. C. or lower, preferably no higher than 70.degree. C. (which temperature may be possible when using the very concentrated, fuming nitric acid having a strength of at least 90%).
The oxidation time for a preferred one-step oxidation stage may be up to 3 hours, for example up to

REFERENCES:
patent: 2905533 (1959-09-01), Webb

Affiliated with

Also associated with

Rating

Preparation and uses of polyferric sulphate does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Preparation and uses of polyferric sulphate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation and uses of polyferric sulphate will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-20166