GB2433217A

GB2433217A - A filter medium

Info

Publication number: GB2433217A
Application number: GB0525390A
Authority: GB
Inventors: Timothy Maurice Shakesby
Original assignee: Shakesby & Sons Ltd
Current assignee: Shakesby & Sons Ltd
Priority date: 2005-12-14
Filing date: 2005-12-14
Publication date: 2007-06-20
Also published as: GB0525390D0

Abstract

A filter medium for removing undesired materials from liquids is made by contacting an ion exchange material with a solution of dissolved manganese ions. The filter medium may comprise a particulate material such as sulphonated cross-linked polystyrene particles, coated with manganese dioxide. The filter medium may be prepared by batch or continuous processing during which the ion exchange material is allowed to contact a solution of potassium permanganate thus causing a layer of manganese dioxide to deposit on the surface of the ion exchange material. Preferably the filter medium is used to remove substances such as iron, manganese, radioactive species or arsenic from water in an industrial or domestic environment.

Description

1059/S Title: Filter Medium for Water Treatment and the Like

Field of the Invention

The invention relates to a filter medium, a method of making the filter medium, a filter unit comprising the filter medium, and a method of treating a liquid using the filter medium.

Background of the Invention

Conventional water softeners employ a cation exchange resin to remove metallic cations from influent water. Metallic cations removed include dissolved calcium (Ca2+), Iron (Fe2+), and magnesium (Mg2+) ions. These resins are frequently used in domestic water softeners.

Another method of removing dissolved iron and manganese (and some other substances) from water is to use a filter medium comprising manganese dioxide. There is some disagreement as to precisely how manganese dioxide-based filters operate.

Examples of manganese dioxide based filter media include pyrolosite (manganese dioxide ore), such as PyroloxTM (which refers to a particular grade of manganese ore), "manganese greensand" and BirmRTM.

Manganese greensand is available from, for example, the Inversand Company of New Jersey. and consists of glauonitic greensand coated with a layer of manganese dioxide.

It is believed that manganese greensand removes iron and/or other materials from water supplies in three ways: (i) mechanical filtration (filters out particulates above 30 micron diameter); (ii) the manganese dioxide coating oxidises dissolved Fe2+ (ferrous) ions to insoluble Fe (ferric) ions which precipitate out of solution; and (iii) the medium acts as a catalyst and/or an adsorbant which attracts and retains ferric iron until the filter medium is cleaned by backwashing.

A major problem with these manganese dioxide-containing or coated filter media is that they require a flow rate to backwash them which is considerably higher than their forward "sepjice" flow rates. Typically at least two filters must be installed in parallel, so that one filter can be backwashed at a time, using all available water to provide a sufficiently high backwash flow rate.

The densest materials such as PyroloxRTM require backwash flow rates of 70m3/hr per square metre, or higher, which is about 6 times higher than its maximum service flow rate.

Even the most favourable materials have backwash: service flow rate ratios of about 2:1.

Another disadvantage of conventional manganese dioxide containing filter media is their high density (from about 72OgmsIL to about 2Kg/L) which means that transport costs are high.

The present invention aims to reduce or overcome one or both of these problems.

Summary of the Invention

In a first aspect the invention provides a filter medium for removing undesired materials from liquids, the medium comprising a particulate ion exchange material, the particles being at least partially coated with manganese dioxide.

In a second aspect, the invention provides a filter unit, the filter unit having a housing supplied with at least one inlet and at least one outlet with a liquid flow path therebetween, which flow path encompasses the filter medium of the first aspect of the invention.

The filter medium and corresponding filter unit are typically useful for removing certain undesired substances from aqueous liquids such as water supplies, which may be domestic, commercial, industrial or municipal water supplies. Alternatively, the filter medium can be used to reduce the concentration of pollutants in waste water output from industrial processes.

The filter medium and corresponding filter unit are preferably capable of removing iron and/or manganese from liquids, and optionally capable of removing other cationic species.

The medium may also prove useful for the removal of arsenic and other species such as radioactive entities.

In a preferred embodiment the particulate ion exchange material is a synthetic ion exchange resin. The synthetic ion exchange resin may be any suitable conventional resin, and such materials are readily available commercially. Examples incude: AmberliteTM and IMACTM resins available from Rohm & Haas, and DiaionTM resins available from Mitsubishi and ReliteTM resins available from Garix Associates, Woking, Surrey. These resins typically comprise suiphonated cross-linked polystyrene particles. The resins have low densities and so are cheap to transport. In addition the backwash flow rates required to clean the filters are much lower than for conventional manganese greensand or manganese dioxide ore-based filters.

Preferably, the particulate ion exchange material comprises particles having a surface-volume diameter (d3,2) of from 0.3 to 1.2mm.

The manganese dioxide coating on the particles can readily be prepared by contacting the particles with an aqueous solution of manganese ions under suitable conditions. Preferably the solution is relatively saturated with manganese ions but contains relatively low concentrations of other cations, especially divalent metallic cations, as these may compete with the manganese ions for binding to the resin. Conditions are selected such that the manganese ions form manganese dioxide, which has low solubility and is adsorbed onto the surface of the resin and possibly also within the pores and interstices thereof. A convenient method of achieving the coating is to contact the resin with a solution of potassium permanganate, KMnO4.

Accordingly, in a third aspect, the invention provides a method of making a filter medium for removing undesired materials from liquids, the method comprising contacting an ion exchange material with a solution comprising dissolved manganese ions. Preferably the solution used comprises manganese ions at a concentration of at least lOmg/L, more preferably at least lOOmg/L and most preferably at least lg/L. Preferably other metallic cations are not present above a concentration of lg/L, more preferably not above lOOmg/L, and most preferably not above lOmg/L.

The solution preferably comprises a solution of aqueous potassium permanganate.

Preparation of the filter medium may be performed in a batch-wise manner (i.e. mixing a batch of resin with a fixed amount of solution) or continuously (i.e. by allowing a solution of potassium permanganate or the like to flow through a resin bed). Conveniently the method can be performed at ambient temperature.

Thus, the ion exchange material of the first aspect preferably comprises manganese dioxide at a concentration that would be achieved by contacting the material when fresh with a solution of manganese ions at a concentration of at least lOmg/L, preferably at least lOOmg/L, more preferably at least lg/L, under standard conditions until steady state is achieved.

In a fourth aspect the invention provides a method of removing undesired substances, such as iron and manganese, from a liquid (especially water), the method comprising the step of contacting the liquid with a filter medium in accordance with the first aspect of the invention. The liquid may be passed over the surface of the filter medium or, more preferably, caused to pass through a filter bed comprising the filter medium.

The various aspects of the invention will now be further described by way of illustrative

example.

Description of an Embodiment

A filter medium in accordance with the invention is prepared as follows. A suitably sized vessel is charged with the desired volume of gel copolymer styrene -DVB, a particulate synthetic ion exchange resin.

A supply of 0.5 % w/v potassium permanganate solution is contacted with the resin in the vessel for at least 30 minutes at room temperature. This causes the deposition of a layer of manganese dioxide on at least part of the surface of the resin particles. After an appropriate time interval, the solution of potassium permanganate is removed, and the resin washed with distilled water to remove any excess potassium permanganate. The filter medium is now ready for use.

Claims

1059/S Claims 1. A filter medium for removing undesired materials from

liquids, the medium comprising a particulate ion exchange material, the particles being at least partially coated with manganese dioxide.

2. A filter medium according to claim 1, which comprises a synthetic ion exchange resin.

3. A filter medium according to claim 1 or claim 2, comprising particles having a surface-volume diameter (d3 2) of from 0.3 to 1.2 mm.

4. A filter medium according to any preceding claim, wherein the manganese dioxide is at a concentration that would be achieved by contacting the material when fresh with a solution of manganese ions at a concentration of at least 10 mg/L, preferably at least 100 mgIL, more preferably at least lg/L, under standard conditions until steady state is achieved.

5. A filter unit comprising a filter medium in accordance with any preceding claim.

6. A method of making a filter medium for removing undesired materials from liquids, the method comprising contacting an ion exchange material with a solution comprising dissolved manganese ions.

7. A method according to claim 6, wherein the solution comprises potassium permanganate.

8. A method according to claim 6 or claim 7, wherein the manganese ions are at a concentration of at least 10 mg/L, preferably at least 100 mgIL, more preferably at least 1 gIL.

9. A method according to any one of claims 6 to 8, wherein the concentration of non-manganese cations is not above 1 g/L, preferably not above 100 mg/L, more preferably not above 10 mgIL.

10. A method of removing undesired substances, such as iron and manganese, from a liquid (especially water), the method comprising the step of contacting the liquid with a filter medium in accordance with any one of claims 1 to 4.