GB2350356A

GB2350356A - Removal of organometallic material from liquids

Info

Publication number: GB2350356A
Application number: GB9825179A
Authority: GB
Inventors: John Newham; David Harwood; Paul William Lomax
Original assignee: A & P Tyne Ltd; Northumbria University
Current assignee: A & P Tyne Ltd; Northumbria University
Priority date: 1998-11-18
Filing date: 1998-11-18
Publication date: 2000-11-29
Also published as: GB9825179D0

Abstract

A process for removing organometallic material from a liquid comprising contacting the liquid with a plant material derived from a natural flora product. The plant material may be in the form of a filter bed and consist of peat, seaweed, straw or cellulose waste. The organometallic material may comprise an organolead material from a petroleum source, an organotin material from anti-fouling coatings or an organomercuric material from an agricultural source. The liquid may be pre-filtered through a bed comprising sand, gravel, anthracite and may further be contacted with granular carbonaceous material comprising active charcoal, bone charcoal or gilsonite.

Description

2350356 PROCESS FOR THE REMOVAL OF ORGANOMETALLIC MATERIALS The present

invention concerns the removal of organometallic materials from liquids and is a process for that purpose.

Organometallic materials of various types are widely used for a variety of purposes. For example, organotin compounds are extensively used for application to the hulls of ocean-going vessels to prevent fouling of the hull surface. Alkyl lead compounds are used extensively as anti-knock additives to petrol. Organomercury compounds are widely used in various agricultural applications.

Inevitably, this extensive use of organometallic materials gives rise to the presence of such materials in the environment. For example, organotin compounds occur in the sea and in waterways, harbours and docks as a result of loss from the surface of a ships hull by damage or by leaching.

Because the presence of organometallic materials in the environment is highly undesirable, a process is required for the removal of such materials from water and other liquids containing them. Many of these materials exhibit elevated toxicity, so their removal is of particular importance.

It is an object of the present invention to provide a process for the foregoing purpose.

The process according to the present invention, for the removal of organometallic materials from liquids, comprises contacting the liquid with a plant material comprising or derived from a natural flora product. It has surprisingly been found that, by contacting the liquid in this way, a major part of any organometallic material present in the liquid, particularly in colloidal and/or soluble form, may successfully be removed.

A range of different plant materials may be used in the process according to the present invention. Among such materials may be mentioned various peat and seaweed products and straw. The cellulose waste residue which arises during the manufacture of paper is also suitable for this purpose. These various plant materials may be used as such or in a form in which they have been subjected to an activation step by which their capacity for absorbing the organometallic material and/or for retaining the latter material on their surface has been enhanced. By way of example, the plant material may have been subjected to a drying treatment by which its moisture content has been reduced. In this way, a natural ly- occurring peat product which may contain up to 50 per cent of moisture may be subjected to a drying treatment as a result of which its moisture content may be reduced to, say, of the order of 7 per cent, before it is used in the process according to the present invention.

Contacting a liquid with a plant material by the process of the invention is a very effective method of removing from the liquid organometallic materials which are in colloidal or soluble form. while solid such materials may be removed by the same treatment, it is much preferred to remove at least a major proportion of such solid material by subjecting the liquid to a separate filtration step before carrying out the contacting with the plant material. By way of example, the liquid may first be filtered by passing it through a bed of sand and/or anthracite.

While the process according to the present invention may be very effective in removing organometallic materials in colloidal or soluble form from a liquid, in some situations it may be desired to reduce even further the quantity of soluble such material remaining in the liquid after that treatment.

To that end, the liquid arising from that treatment may be contacted with a further material, for example a granular carbonaceous material such as charcoal. This contacting may entail passing the liquid through a bed of such material, for example a bed of active charcoal, bone charcoal or gilsonite.

The process of the invention may be applied to the removal of a range of organometallic materials, in particular organotin compounds, alkyl lead compounds and organomercury compounds.

By means of this process, concentrations of such components as low as 0.1 micrograms of organometallic material per litre of liquid may be achieved. The process is of particular merit as applied to the removal of organotin compounds from waste materials arising from the use of such compounds in antifouling coatings for the shipping industry.

It is a very common practice to apply antifouling coatings based on organotin compounds to the hulls of ocean-going vessels. During exposure to sea water when the vessel is in motion, tributyl tin residues are released into the water at a controlled rate and form highly effective biocides. However such coatings must be renewed at intervals of the order of 3 or 4 years, at which time the old paint material must be removed from the vessel hull, for example using abrasive water jets, and a new coating applied. Thus a waste material in the form of old paint containing tributyl residues arises. It is essential that such material be removed from the liquid effluents arising, for example in a dry dock, as a result of the removal of the coating from the vessel hull. The process of the present invention'is of value for that purpose.

The process of this invention will now be further described and illustrated, by way of example only, with reference to the removal of such organotin compounds from an aqueous effluent which has been produced as a result of the removal of an antifouling paint coating from an ocean- going vessel.

Example

The aqueous effluent treated comprised scrap paint material with a range of solid material particles having diameters extending down to 1 micron. The effluent contained organotin compounds in a concentration of approximately 900 micrograms/litre.

The effluent was first filtered by passing it through a fixed bed comprising anthracite, course sand and fine sand in the proportions 1:4:5 by volume. The aqueous material emerging from this first filter bed had an organotin compound concentration of 351 micrograms/litre.

This aqueous ef fluent was next passed through a peat filter bed comprising a peat derived from sphagnum moss, which peat had been screened to remove inert materials and then dried in a gas turbine dryer to remove water down to a concentration of about 8 per cent. As a result of this filter bed treatment, a major proportion of the organotin compounds were taken up by the peat, leaving a concentration of 3.0 microgram/litre of the compounds in the resulting aqueous effluent.

In order further to reduce the organotin concentration, the effluent from the activated peat bed was now passed through a third bed in the form of particles of bone charcoal packed at a density of 0.79 gram/millilitre. The concentration of organotin compounds in the aqueous effluent emerging from the charcoal bed amounted to just 0.34 microgram/litre.

Thus the overall effect of the passage of the original aqueous effluent through the three filter beds in turn was to remove over 99 per cent of the organotin compounds in the effluent.

Claims

CLAIMS:

1. A process for removing organometallic material from a liquid, said process comprising: contacting the liquid with a plant material comprising or derived from a natural flora product.

2. A process as claimed in claim 1, wherein said plant material is in the form of a filter bed.

3. A process as claimed in either of claims 1 or 2 wherein said plant material is selected from the group consisting of peat products, seaweed products and straw.

4. A process as claimed in claim 1, wherein said G- plant material is peat.

5. A process as claimed in claim 4, wherein said peat is derived from sphagnum moss.

6. A process as claimed in claim 1, wherein said 1 1 plant material is a cellulose waste residue obtainable from the manufacture of paper.

7. A process as claimed in any preceding claim, wherein said plant material is subjected to an activation step in which the capacity for absorbing the organometallic material is increased.

8. A process as claimed in any of claims 1 to 6, wherein said plant material is subjected to an activation step in which the capacity for retaining organometallic material is increased.

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9. A process as claimed in either of claims 7 or 8 in which the plant material is subjected to a drying step in which the moisture content is reduced.

10. A process as claimed in any of claims 7, 8 or 9 wherein said plant material is naturally occurring peat containing up to 50% moisture which is subjected to a drying step which reduces the moisture level to about 7 wt%.

11. A process as claimed in any preceding claim wherein said organometallic material is in colloidal, pArticulate or soluble form.

12. A process as claimed in claim 11, wherein said organometallic material is in colloidal or soluble form.

13. A process as claimed in any preceding claim, wherein said liquid is subjected to a pre-filtering step.

14. A process as claimed in claim 13, wherein said pre-filtering step is effected in a pre-filter bed.

15. A process as claimed in claim 14, wherein said pre-filter bed comprises material selected from the group consisting of coarse sand, fine sand, gravel and anthracite.

16. A process as claimed in any preceding claim, wherein said liquid is subjected to the further step of contacting with granular carbonaceous material.

17. A process as claimed in claim 16, wherein said granular carbonaceous material is present in a filter bed.

18. A process as claimed in claim 16 or 17, wherein said carbonaceous material is selected from the group consisting of active charcoal, bone charcoal or gilsonite.

19. A process as claimed in any preceding claim, wherein said organometallic material is an organotin compound, one or more alkyl lead compounds or one or more organomercuric compounds.

20. A process as claimed in any preceding claim for obtaining a liquid containing less than 0.1pg per litre of organometallic material.

21. A process as claimed in any preceding claim wherein the source of said organometallic material is anti fouling coatings used on ships and the like.

22. A Process as claimed in claim 21, wherein said organometallic material is an organotin compound.

23. A process as claimed in claim 22, wherein said organotin compound is tributyl tin.

24. A process as claimed in any of claims 1 to 20 wherein the source of said organometallic material is petrol.

25. A process as claimed in claim 24, wherein said organometallic material is an alkyl lead compound used as an antiknock additive.

26. A process as claimed in any of claims 1 to 20 wherein the source of said organometallic material is agricultural material.

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27. A process as claimed in claim 26, wherein said organometallic material is an organomercuric compound.