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WO2018127679A1 - Procédé de régénération d'un matériau échangeur d'ions - Google Patents

Procédé de régénération d'un matériau échangeur d'ions Download PDF

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Publication number
WO2018127679A1
WO2018127679A1 PCT/GB2017/053740 GB2017053740W WO2018127679A1 WO 2018127679 A1 WO2018127679 A1 WO 2018127679A1 GB 2017053740 W GB2017053740 W GB 2017053740W WO 2018127679 A1 WO2018127679 A1 WO 2018127679A1
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Prior art keywords
ion exchange
regenerant
hydroxide
salt solution
bed
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Ceased
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PCT/GB2017/053740
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English (en)
Inventor
Michael Waite
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IONEX SG Ltd
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IONEX SG Ltd
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Publication of WO2018127679A1 publication Critical patent/WO2018127679A1/fr
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J41/00—Anion exchange; Use of material as anion exchangers; Treatment of material for improving the anion exchange properties
    • B01J41/04—Processes using organic exchangers
    • B01J41/05—Processes using organic exchangers in the strongly basic form
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
    • B01D15/08—Selective adsorption, e.g. chromatography
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/34—Regenerating or reactivating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J49/00—Regeneration or reactivation of ion-exchangers; Apparatus therefor
    • B01J49/05—Regeneration or reactivation of ion-exchangers; Apparatus therefor of fixed beds
    • B01J49/07—Regeneration or reactivation of ion-exchangers; Apparatus therefor of fixed beds containing anionic exchangers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J49/00—Regeneration or reactivation of ion-exchangers; Apparatus therefor
    • B01J49/50—Regeneration or reactivation of ion-exchangers; Apparatus therefor characterised by the regeneration reagents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J49/00—Regeneration or reactivation of ion-exchangers; Apparatus therefor
    • B01J49/50—Regeneration or reactivation of ion-exchangers; Apparatus therefor characterised by the regeneration reagents
    • B01J49/57—Regeneration or reactivation of ion-exchangers; Apparatus therefor characterised by the regeneration reagents for anionic exchangers
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/42—Treatment of water, waste water, or sewage by ion-exchange
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/42—Treatment of water, waste water, or sewage by ion-exchange
    • C02F2001/422—Treatment of water, waste water, or sewage by ion-exchange using anionic exchangers
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • C02F2101/22—Chromium or chromium compounds, e.g. chromates
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2201/00—Apparatus for treatment of water, waste water or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/16—Regeneration of sorbents, filters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S210/00—Liquid purification or separation

Definitions

  • the present invention relates to a method of regenerating an ion exchange material for an ion exchange column, particularly but not necessarily for the regeneration of a strong base anion exchange resin for use in the removal of hexavalent chromium from potable water.
  • Chromium ions are a common contaminant arising most frequently from leaching of the underlying bedrock or from industrial sources, and there are strict requirements as to the safe level of various chromium ions which can be present in water. It is therefore useful to remove as much chromium from water as is possible, and ideally to treat the waste fraction in such a manner as to permit safe disposal thereof.
  • the removal of contaminants is commonly achieved by running the water through an ion exchange column containing an ion-exchange material such as a strong base anion (SBA) exchange resin, particularly for the treatment of drinking water.
  • ion exchange columns may operate on a proportion of the total water flow or on the total water flow in order to improve the quality of the water so as to meet the relevant potable standard.
  • SBA exchange resins operate by binding contaminants contained within the water at functional sites within the resin. Contaminant ions will be captured at the functional sites, allowing decontaminated water to pass through the ion exchange column.
  • Regeneration of the SBA exchange resin is typically achieved by passing a strong brine solution through the ion exchange column, with ions from the brine solution displacing the captured contaminant anions, reforming the active SBA exchange resin functional sites.
  • Hexavalent chromium maybe present in groundwater as chromate or dichromate ions, having a valence of six. Chromium in a lower valence state, such as trivalent chromium, is insoluble at pH values greater than 3, whereas most groundwaters have a pH in the range of 6.5 to 8, at which chromium is only soluble in the hexavalent form.
  • Traditional treatment methods have used weak base anion resins for its removal; however, this method also uses significant quantities of acid to reduce the pH of the feed water and removes a large amount of other anions from the water, resulting in very high operational costs and significant waste volumes.
  • SBA exchange resins are used in the removal of hexavalent chromium contaminants from water, such as Cr04 2" anions. It has, however, been found that the regeneration of the SBA exchange resin becomes less efficient over time, resulting in a reduced hexavalent chromium capture by the SBA resin, and therefore a higher incidence of hexavalent chromium in the treated water. This could lead to dangerous levels of hexavalent chromium being present in the potable water despite treated.
  • the present invention seeks to provide an improved regeneration process for an SBA exchange resin which overcomes the blinding of the SBA exchange resin by trivalent chromium hydroxide over time.
  • a method of regenerating an ion exchange material for an ion exchange bed such as an ion exchange column, the method comprising the steps of: a] preparing a regenerant which comprises a salt solution; b] modifying the regenerant by increasing the pH and/or increasing the oxidation potential thereof to promote conversion of trivalent chromium hydroxide to soluble hexavalent chromium ions; and c] passing the regenerant through the ion exchange bed to at least partially remove hexavalent chromium ions from the ion exchange material.
  • the present inventors have found that either increasing the pH or oxidation potential (Eh) of the salt solution promotes the conversion of trivalent chromium hydroxide to hexavalent chromate ions within the ion exchange material, effectively solubilising the trivalent chromium hydroxide to permit its removal as hexavalent chromium. It is thought that the pH of raw water which is processed is around 7 to 8, with the Eh being in the range 400 to 500 mV, typically. This is very close to the equilibrium change between trivalent chromium hydroxide and hexavalent chromate ions.
  • Eh oxidation potential
  • the increase in the pH or the increase in the oxidation potential moves the position of the equilibrium towards the hexavalent chromate during the regeneration, and thus the insoluble trivalent chromium converted back to hexavalent chromium can be extracted from the ion exchange material.
  • the salt solution may comprise sodium chloride or potassium chloride.
  • Said salt solution may comprise from 7.4 to 12.0 % w/v of sodium chloride or potassium chloride.
  • regenerant having such a concentration has been shown to have excellent regeneration properties for SBA exchange resin materials under normal circumstances, notwithstanding the issue of blinding by trivalent chromium hydroxide.
  • the regenerant may be modified to increase the pH of the salt solution.
  • the alteration of the pH of the salt solution is one mechanism by which the efficiency of the regenerant can be improved.
  • Data for chromium ions in water suggests that the equilibrium boundary between hexavalent chromium and trivalent chromium hydroxide exists in a region for oxidation potential of between 0.2V and 0.5V and for pH of between 6.5 and 10.5, which may be depicted on a Pourbaix diagram.
  • the pH of the raw water passed through the ion exchange material is typically between 7 and 8, whilst having an oxidation potential of around 400 to 500mV.
  • the pH may be increased by adding a metal hydroxide, and said metal hydroxide added may be an alkali metal hydroxide or an alkali earth metal hydroxide.
  • the metal hydroxide added may be any one of: sodium hydroxide; potassium hydroxide; lithium hydroxide; magnesium hydroxide; and/or calcium hydroxide; or a mixture thereof.
  • Addition of a hydroxide into the regenerant solution can significantly increase the pH without significantly altering the oxidation potential thereof. This allows a user to redress the balance between trivalent and hexavalent chromium easily.
  • the pH may be increased to between 9.1 and 9.3.
  • a pH of approximately 9.2 has been found to render the regenerant near to 100% efficient, in that repeated regeneration of an SBA exchange resin with the regenerant at a pH of 9.2 maintains the effective capacity of the resin for hexavalent chromium.
  • the regenerant may be modified by addition of an oxidising agent to increase the oxidation potential of the regenerant.
  • an oxidising agent to increase the oxidation potential of the regenerant.
  • the oxidation potential can be increased; this is most readily achieved by introducing an oxidising agent into the regenerant solution.
  • the boundary between trivalent and hexavalent chromium for aqueous chromium favours trivalent chromium hydroxide at lower oxidation potentials.
  • an oxidising agent should shift the balance back to soluble hexavalent chromium.
  • the oxidising agent added may be hydrogen peroxide, ozone, or hypochlorite, for example, in the form of hypochlorous acid or a salt thereof.
  • Hydrogen peroxide, ozone and hypochlorite are mild oxidising agents which, in small concentrations will readily alter the oxidation potential of the regenerant by a sufficient degree to render the equilibrium balance to favour hexavalent chromium instead of the insoluble trivalent chromium hydroxide.
  • the ion exchange material may be a strong base anion (SBA) exchange resin.
  • SBA exchange resins are effective ion exchange materials for chromium removal. Traditional techniques which have relied on weak base anion exchange for removal require significant volumes of acid to reduce the pH of the water prior to treatment and have a tendency to remove a large amount of other anions from the processed water, and therefore the process produces a significant volume of waste, and therefore cost. SBA exchange resins do not require pH adjustment of the water prior to treatment, which significantly reduces the operational costs of the process.
  • the salt solution of the regenerant may have a concentration of at least 2M.
  • at least 2.5 bed-volumes (BV) of the regenerant may be passed through the ion exchange bed, and more preferably, at least 3 to 3.5 bed volumes of the regenerant may be passed through the ion exchange bed.
  • one bed volume is the volume of ion exchange resin contained within the ion exchange vessel.
  • a fractionated set-up may be provided in which only a proportion of the regenerant is provided so as to be pH-treated. It is preferable to introduce such a volume of regenerant following the removal of the majority of the hexavalent chromium using untreated brine solution.
  • the regenerant may comprise at least one first fraction of an untreated salt solution and at least one second fraction of the said salt solution, and wherein, during step c], the at least one first and second fractions of the regenerant are passed through the ion exchange bed sequentially.
  • a second, modified fraction of salt solution can be passed through the ion exchange bed subsequent to one or more initial fractions specifically so as to target the trivalent chromium hydroxide which blinds some of the binding sites of the SBA exchange resin.
  • the at least one second fraction may be passed through the ion exchange bed either before or after the or each first fraction has been passed through the ion exchange bed.
  • the at least one second fraction may comprise no more than 1 bed volume of regenerant.
  • the proportion of the second fraction may be between 1 bed volume and the total volume of regenerant.
  • the entire volume of regenerant may comprise the said salt solution which is treated.
  • salt solution to remove trivalent chromium hydroxide from an ion exchange material loaded with chromate ions, wherein the salt solution has a pH of between 9.1 and 9.3.
  • a salt solution to remove trivalent chromium hydroxide ions from an ion exchange material loaded with chromate ions, wherein the salt solution has a pH of between 9.1 and 9.3.
  • the term loaded is intended to refer to an ion exchange material in which at least some of the functional sites thereof are bound to chromate ions, and does not necessarily reflect whether a predetermined percentage of the functional sites are bound.
  • the ion exchange material may be a strong base anion exchange resin.
  • the salt solution may comprise sodium chloride or potassium chloride, in which case, the salt solution may comprise from 7.4 to 12.0 % w/v of sodium chloride or potassium chloride.
  • the pH may be increased by adding a metal hydroxide.
  • Said metal hydroxide added may be an alkali metal hydroxide or an alkali earth metal hydroxide.
  • the metal hydroxide may be any one of: sodium hydroxide; potassium hydroxide; lithium hydroxide; magnesium hydroxide; and/or calcium hydroxide; or a mixture thereof.
  • the present invention relates to a method for regenerating an ion exchange material used in the removal of chromate ions from a water supply.
  • chromate ions includes any hexavalent chromium species present in aqueous solution. These include hydrated and non-hydrated forms of CrC"4 2" , HCrCV, Cr 2 C"7 2" , HCr 2 07 “ , and mixtures of two or more thereof.
  • the method comprises the regeneration of an ion exchange material.
  • An "ion exchange material” or “ion exchange resin” is an insoluble material or support structure normally in the form of small beads, typically having a diameter of around 0.5 to 1.0mm, fabricated from a, preferably organic polymer, substrate. The beads may typically be porous, providing a high surface area.
  • the process of ion exchange involves passing a solution through a resin, such that the ions present in the solution displace ions that initially form part of the resin.
  • the order of selectivity of an SBA exchange resin is CI " , HCO3 " , NO3 " , and SO4 2" .
  • Nitrate selective resins are also known, in which the selectivity of sulphate and nitrate is reversed.
  • Both SBA exchange resins and nitrate selective resins may be regenerated by elution with, for example, brine (concentrated sodium chloride or potassium chloride solution), as the chloride ions are able to displace HCO3 " , NO3 " , and SC"4 2" ions adsorbed on the resin.
  • brine concentrated sodium chloride or potassium chloride solution
  • ion exchange material refers to an ion exchange material contained within an ion exchange bed, such as an ion exchange column.
  • the ion exchange material may be present preferably in a fixed bed, but may alternatively be in a moving bed or fluidized bed.
  • the ion exchange resin may be an SBA exchange resin.
  • SBA exchange resins are Purolite A600E/4149 supplied by Purolite International Limited, Amberlite (TM) PWA7 supplied by Rohm & Haas Limited, Resintech SGB1 and Resintech SGB2 both supplied by Resintech, Inc., and Lewatit ASB 1 supplied by Lanxess Deutschland GmbH.
  • ion exchange effluent refers to the waste solution obtained from an ion exchange column outlet upon elution of the ion exchange material with a regenerant.
  • the ion exchange effluent comprises sodium chloride or potassium chloride.
  • chloride ions are able to displace ions adsorbed onto an ion exchange resin, thus regenerating the resin and providing an effluent containing ions that were previously adsorbed onto the resin.
  • ICPMS Inductively Coupled Plasma Mass Spectrometry
  • absorption spectroscopy For determining chelated chromium or the hexavalent or trivalent form only, such methods as gas chromatography (with various detection techniques), liquid chromatography (LC), polarography, and spectrophotometry can be used.
  • LC-ICPMS liquid chromatography
  • polarography polarography
  • spectrophotometry Preferably, hexavalent chromium is determined by LC-ICPMS.
  • Environmental Protection Agency method 218.6 may be used ("Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography").
  • Figure 1 shows a graph indicating the chromate concentration in water treated by an ion exchange column versus a cumulative flow of regenerant passed through the ion exchange column in mega-gallons, indicating the chromate concentration both before and after pH adjustment of a regenerant
  • Figure 2 shows an ion exchange bed regeneration system comprising a plurality of regeneration tanks so as to provide a sequential regeneration process
  • Figure 3 shows a graph indicating the chromate concentration in the ion exchange effluent with respect to the bed volume of regenerant passed through the ion exchange material, both with and without pH adjustment;
  • Figure 4 shows an enlarged section of the graph of Figure 3 centred around 2.6 bed volumes indicating the second chromate elution peak.
  • An ion exchange column or similar ion exchange bed is loaded with a strong base anion resin for hexavalent chromium removal.
  • Regeneration of the strong base anion resin uses approximately 3 bed volumes of a strong salt solution, typically 7.4 to 12% solution by weight of sodium chloride or potassium chloride. It will, however, be appreciated that stronger or weaker salt solution could be used.
  • the strong base anion resin exhibited a significantly decreased capacity for hexavalent chromium, leading to higher hexavalent chromium leakage from the ion exchange column, eventually up to a level which was above the desired compliance level.
  • the regenerant may be supplied from a tank or reservoir which is in fluid communication with the ion exchange bed. If a single tank is provided, then the entire regenerant would be provided as an adjusted or modified regenerant.
  • a regenerant which comprises a salt solution having a modified pH prior to performing the regeneration.
  • the pH of the salt solution is increased by the addition of an alkali metal hydroxide or alkali earth metal hydroxide, such as any of sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), magnesium hydroxide (Mg(OH)2), and calcium hydroxide (Ca(OH)2), or a mixture of the above.
  • alkaline substances could alternatively be introduced to increase the pH, such as a buffer solution.
  • the pH is modified so as to be in a range of 9.1 to 9.3, although higher pHs may also achieve a similar result. Use of modified pH to be greater than 10 is not recommended since this will likely lead to degradation of the SB A exchange resin over time.
  • pH adjustment is achieved by dosing in a solution of a metal hydroxide to achieve the desired pH.
  • a metal hydroxide For example, if a 3M solution of sodium hydroxide is used, around 200mL of 3M sodium hydroxide solution would be added to 1000L of 2M brine solution.
  • the exact amount will, of course, be dependent upon the water quality due to the buffering effect, for example, based on the concentration of bicarbonate ions present in the water used to produce the 2M brine solution.
  • a typical ion exchange resin used is A600/5149, supplied by Purolite Ltd. Flow rates during the regeneration with the modified pH brine solution would typically be of the order of lBV/hour, to allow the relatively slow reaction kinetics to occur.
  • the pH of raw water typically ranges from 7 to 8, with the oxidation potential (Eh) being around 400 to 500mV relative to the standard hydrogen electrode.
  • Eh oxidation potential
  • Local conditions around functional groups on the ion exchange resin will likely result in a proportion of the hexavalent chromium being converted to trivalent chromium hydroxide.
  • the trivalent chromium hydroxide is insoluble, blinding the strong base anion resin to the hexavalent chromium, thereby reducing the efficiency of the regeneration process.
  • the modification of the pH of the salt solution solubilises the trivalent hexavalent chromium hydroxide which is blocking the functional groups of the ion exchange column, converting it back to hexavalent chromium which can be extracted in the ion exchange effluent during the regeneration process.
  • This effect can be seen in Figure 1.
  • the chromium concentration in the treated water is illustrated with respect to a total cumulative flow across an ion exchange column, in mega-gallons, across many regeneration cycles.
  • Example 2 An ion exchange column is loaded with a strong base anion exchange resin for hexavalent chromium removal. Regeneration of the strong base anion exchange resin uses approximately 3 bed volumes of a strong salt solution, typically 7.4 to 12% solution by weight of sodium chloride or potassium chloride.
  • the regenerant is divided into at least two fractions: a first fraction or a plurality of first fractions which comprise a strong salt solution which is not pH-treated; and at least one second fraction which comprises a strong salt solution which is pH- treated, preferably so as to be in the range 9.1 to 9.3, and most preferably 9.2.
  • the ion exchange bed regeneration system 100 comprises an ion exchange bed 102, here formed as an ion exchange column, within which is contained the strong base anion exchange resin.
  • the ion exchange bed 102 is fed by a plurality of regenerant tanks 104 which are in fluid communication with the ion exchange column 102.
  • the ion exchange column 102 is then connected to one or more outlet tanks 106, into which effluent solution can drain.
  • Each regenerant tank 104 may preferably, but not necessarily exclusively, be arranged so as to contain half a bed volume of a regenerant solution, and each regenerant tank 104 may be activatable in sequence. Regenerant tanks 104 having said volume are used in this embodiment, but it will evidently be possible to provide tanks of different volumes.
  • Six regenerant tanks 104 are shown, but any number of regenerant tanks 104 may be provided in fluid communication with the ion exchange column 102.
  • the six regenerant tanks 104 may be provided with a regenerant which is suitable for chromium elution, but more regenerant tanks may be provided for other tasks, such as regenerant tanks comprising weak brine solution for the removal of, for example, sulphate and bicarbonate ions from the ion exchange column 102.
  • regenerant tanks 104 contains a pH- modified or otherwise modified regenerant solution.
  • first fractions of regenerant may be passed through the ion exchange column 102; each first fraction is here an untreated brine solution.
  • second fraction of regenerant which comprises pH-treated brine solution may be passed through the ion exchange column 102.
  • Figure 3 shows a graph of the concentration of chromium in the ion exchange effluent against the bed volume passed through for a standard brine solution, shown using triangular points and the dashed line, and for a regenerant comprising the passage of two first unmodified fractions of brine solution, one bed volume each, followed by one bed volume of a second brine solution comprising pH-modified salt solution having a pH of 9.3, indicated by the circular points.
  • the chromium removed in the initial bed volumes is as would be expected for an untreated brine solution, since this will be what passes through the ion exchange column 102 in the first instance.
  • there is a secondary chromium elution peak centred on or around 2.6 bed volumes which is only present for the pH adjusted salt solution which is passed through in the second fraction. This strongly implies that the unmodified regenerant is not capable of eluting all of the chromium in the ion exchange material, which is leading to the drop in ion exchange efficiency over time.
  • the approximately 3 to 3.5 bed volumes of regenerant which is passed through the ion exchange column is formed from the or each first fraction and the or each second fraction. At least one first fraction is applied to the ion exchange column prior to the application of the or each second fraction, and is designed to elute the majority of the hexavalent chromium which is present and bound as hexavalent chromium in the strong base anion exchange resin. Once a majority of the hexavalent chromium, and preferably at least 90% of the hexavalent chromium, has been removed from the ion exchange resin, then a second fraction can be applied to the ion exchange material.
  • a standard maintenance regeneration might comprise a plurality of bed volumes of untreated brine solution to be passed through the ion exchange column 102, with a single bed volume or less of pH- modified brine solution being passed through the ion exchange column 102, preferably as a final step so as to remove the trivalent chromium hydroxide by conversion to soluble hexavalent chromium ions. This might be the more common regeneration process. It may also be preferable to provide a mechanism of fully recovering the ion exchange material by increasing the proportion of the regenerant which comprises the second fraction, that is, comprising the pH-modified brine solution. The proportion of pH- modified solution may be increased from anywhere between one bed volume to the total volume of regenerant passed through the ion exchange column 102. This could be considered to be a full recovery stage of regeneration, and may be performed less frequently than the maintenance regeneration.
  • first and second fraction are used to refer to the untreated and treated strong brine solutions respectively, it may be relatively common for the sequential regeneration to utilise other fractions of regenerant for the removal of other contaminants in the water.
  • One or more third fractions could therefore be provided, typically comprising a weaker brine solution than that used for chromium elution, for the removal of other ions in the water.
  • the or each third fraction would be passed through the ion exchange column 102 before the first and second fractions used for chromium elution.
  • An ion exchange column is loaded with a strong base anion exchange resin for hexavalent chromium removal.
  • Regeneration of the strong base anion exchange resin uses approximately 3 bed volumes of a strong salt solution, typically 7.4 to 12% solution by weight of sodium chloride or potassium chloride.
  • the regenerant comprises at least one fraction which includes a strong salt solution which is treated with an oxidising agent so as to increase the oxidation potential (Eh) of the regenerant.
  • the modification of the Eh of the salt solution solubilises the trivalent hexavalent chromium hydroxide which is blocking the functional groups of the ion exchange column, converting it back to hexavalent chromium which can be extracted in the ion exchange effluent during the regeneration process.
  • an ion exchange material such as a strong base anion ion exchange resin
  • the mechanism of regeneration is such that the efficiency of the ion exchange material does not depreciate over time. This is achieved by modifying the characteristics of the regenerant applied, preferably by altering a pH, but possibly by altering a oxidation potential of the regenerant so as to shift a balance between trivalent and hexavalent chromium in the ion exchange material in favour of the hexavalent chromium, which is soluble in brine.
  • the method is theorised to effectively solubilise trapped trivalent chromium present on the ion exchange material which is otherwise blocking functional sites of the ion exchange material.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Analytical Chemistry (AREA)
  • Treatment Of Water By Ion Exchange (AREA)

Abstract

Un procédé de régénération d'un matériau d'échange d'ions pour une colonne d'échange d'ions, le procédé comprenant les étapes consistant à : a] préparer un régénérant qui comprend une solution de sel; b] modifier le régénérant en augmentant le pH et/ou en augmentant le potentiel d'oxydation de celui-ci pour favoriser la conversion d'hydroxyde de chrome trivalent en ions de chrome hexavalent solubles; et c] faire passer le régénérant à travers le lit d'échange d'ions (102) pour convertir l'hydroxyde de chrome trivalent en ions de chrome hexavalent et éliminer les ions de chrome hexavalent du matériau échangeur d'ions.
PCT/GB2017/053740 2017-01-03 2017-12-14 Procédé de régénération d'un matériau échangeur d'ions Ceased WO2018127679A1 (fr)

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GB1700039.9A GB2558552A (en) 2017-01-03 2017-01-03 Method for regenerating ion exchange material

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GB2583528A (en) * 2019-05-03 2020-11-04 Agua Db Ltd Water treatment method to generate fertilization or fertigation product

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CN112403533A (zh) * 2020-11-06 2021-02-26 安徽皖东树脂科技有限公司 一种阴离子交换树脂的提纯工艺及提纯设备

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GB201700039D0 (en) 2017-02-15

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