CATION EXCHANGER AND METHOD OF REMOVING HEAVY METAL
IONS IN WASTEWATER
Background of the Invention
1. Field of the Invention
The present invention relates to a cation exchanger prepared from plant biomass as a raw material and a method of removing heavy metal ions from heavy metal ion-containing wastewater by using the cation exchanger.
2. Description of the Related Art
Prevention of water pollution by heavy metal ions is a big technical challenge for environmental protection. Increased recognition of toxicity of heavy metal ions lead to gradual increase in strictness about the regulations on discharge of heavy metal ions. To comply with these discharge regulations, there exists a need for an ion removing method capable of removing heavy metal ions from wastewater containing heavy metal ions effectively and as easily as possible at low cost.
There have been proposed many methods of removing heavy metal ions for example from factory wastewater, such as aggregation and sedimentation, ion-exchange, adsorption for example on activated carbon, electrical adsorption, and magnetic adsorption.
For example, Japanese Patent Application Laid-open No. Hei 9-117776 (claim 1, p. 2-4) (hereinafter,
referred to as Patent Document 1) proposes, as the aggregation and sedimentation method, a method of first insolubilizing most of heavy metal ions by adding a base to heavy metal ion-containing wastewater for forming a hydroxide and then removing the aggregate by filtration with a cellulosic filter.
It is not possible, by the method of insolubilizing heavy metal ions by making the wastewater basic, to remove residual ions such as ions remaining soluble in aqueous solution even in basic condition and ions that become soluble by forming complex ions under basic condition. As a result, it is often difficult only by the aggregation and sedimentation method to reduce the concentration of heavy metal ions in wastewater to a concentration satisfying the discharge regulations. For that reason, the aqueous solution after aggregation precipitation treatment is additionally treated by an ion exchange or adsorption method, to reduce the concentration of heavy metal ions in wastewater to a regulated value or lower.
For example, Japanese Patent Application Laid-open No. 8-168798 (claim 1, p. 2-5, Fig. 1) (hereinafter, referred to as Patent Document 2) described below proposes a method of removing heavy metal ions in heavy metal-containing wastewater, by aggregating heavy metals in the heavy metal-containing wastewater as hydroxides by adding alkali thereto, separating the
aggregate by solid-liquid separation, and removing heavy metal ions in the basic wastewater by adsorption on a chelating resin or a weakly acidic cation exchange resin, characterized in that the pH of the basic wastewater after solid-liquid separation is adjusted to 5 or less and then, the heavy metal ions in wastewater are removed by adsorption on the chelating resin or the weakly acidic cation exchange resin in which 60 to 100 equivalence % of the exchange groups are in the form of an alkali metal form or alkali-earth metal form and 0 to 40 equivalence % thereof are in the H form.
Patent Document 2 describes that it is possible to make heavy metal elements reliably adsorbed, by acidifying the basic wastewater after solid-liquid separation to pH 5 or less for solubilization of the heavy metal elements that are contained as fine hydroxides and carbonate salts in wastewater as ions and treating the ions with a cation exchange resin.
The weakly acidic cation exchange resin for use is for example a carboxy group-containing resin, such as a copolymer of styrene, divinylbenzene and acrylic acid or methacrylic acid. These ion exchange resins, which are normally synthetic products produced from oil or natural gas, become higher in cost and result in waste of resources and generate environmental pollutants, when disposed of after use. Thus, these ion exchange resins are used repeatedly, as the ion exchange resins

after use are regenerated to the original state by regeneration treatment.
Summary of the Invention As described above, it is often difficult to reduce the concentration of heavy metal ions in wastewater sufficiently, only by the aggregation and sedimentation method proposed, for example, in Patent Document 1. The method of using ion-exchange method in combination, as proposed for example in Patent Document 2, demands additional steps for pretreatment and regeneration treatments of ion exchange resin and also for disposal treatment of the treated solution, leading to increase in the number of steps and thus making the system more complicated. Consequently, it leads to increase in equipment and running costs.
In view of the above-mentioned circumstances, there is a need for providing a disposable cation exchanger prepared from plant biomass as raw material and a simple and highly efficient method of removing heavy metal ions in wastewater by using the same.
According to an embodiment of the present invention, there is provoded a cation exchanger, including at least one leaf vegetable selected from a group including molokheiya (Corchorus olitorius), komatsuna (Brassica rapa var. peruviridis), Japanese honeywort (Cryptotaenia japonica), potherb mustard
(Brassica rapa var. nipposinica), and spinach (Spinacia oleracea).
According to another embodiment of the present invention, there is provoded a method of removing heavy metal ions in wastewater, at least including an adsorption step of bringing wastewater including the heavy metal ions into contact with a cation exchanger including at least one leaf vegetable selected from a group including molokheiya, komatsuna, Japanese honeywort, potherb mustard, and spinach, to thereby cause part of the heavy metal ions to be adsorbed on the cation exchanger.
The cation exchanger according to the embodiment of the present invention is a cation exchanger prepared from a plant biomass selected from the leaf vegetable group consisting of molokheiya, komatsuna, Japanese honeywort, potherb mustard, and spinach as raw material and thus, it is disposable and may not become a practical carbon dioxide emission source, even if incinerated after use. As will be described below in Examples, it also has a cation exchange performance equivalent to or more than that of artificially-synthesized cation exchange resins.
Since the method of removing heavy metal ions in wastewater according to the embodiment of the present invention has an adsorption step of bringing the wastewater containing dissolved heavy metal ions into
contact with the cation exchanger and making part of the heavy metal ions adsorbed on the ion exchanger, it is possible to remove the heavy metal ions in the wastewater effectively. In addition since the ion exchanger is disposable, it is possible to eliminate the step for regeneration treatment of the ion exchanger and to construct a simplified, high treatment efficiency wastewater treatment system. Since the cation exchanger has a high cation exchange performance, it is also possible to reduce the amount of the cation exchanger used and the cation exchanger can also be treated easily after use.
Brief Description of Drawings Fig. 1 is a flow chart showing the step of removing heavy metal ions from heavy metal ion-containing wastewater according to an embodiment of the present invention; and
Fig. 2 is a graph showing the titration curve of untreated aqueous sodium carbonate solution and the titration curves obtained in Examples 1-1 and 1-2 according to Examples of the present invention.
Description of Preferred Embodiments The cation exchanger according to an embodiment of the present invention preferably contains molokheiya. The cation exchanger preferably contains a dried leaf,

a dried stalk, or a dried root of the leaf vegetable.
In the method of removing heavy metal ions in wastewater according to another embodiment of the present invention, the cation exchanger for use is preferably a molokheiya-containing cation exchanger. The cation exchanger for use is preferably a cation exchanger containing the dried leaf, the dried stalk, or the dried root of the leaf vegetable.
The adsorption step is preferably carried out by feeding the wastewater through an adsorption layer containing the cation exchanger.
In such a case, the adsorption step is preferably carried out after a step of adding a base to the wastewater containing dissolved heavy metal ions to make the wastewater basic, thus insolubilizing at least part of the heavy metal ions and generating suspended solid matter, and a step of adding an inorganic coagulant to the wastewater for aggregation and sedimentation of the suspended solid matter.
In this case, for example, a step of separating and removing the suspended solid matter from the wastewater by solid-liquid separation is preferably carried out before the adsorption step. In such a case, a step of adding a polymer coagulant to the wastewater for promoting the aggregation and sedimentation of the suspended solid matter and thus separating and removing the suspended solid matter and the polymer coagulant
from the wastewater is preferably carried out before the adsorption step.
Alternatively, it is preferable to feed the suspended solid matter-containing wastewater through the adsorption layer described above for solid-liquid separation of the suspended solid matter in the adsorption layer and thus separate and remove it from the wastewater. Then, it is preferable to add a polymer coagulant to the wastewater for promoting the aggregation and sedimentation of the suspended solid matter, before the adsorption step, and separate and remove the suspended solid matter and the polymer coagulant from the wastewater in the adsorption layer by solid-liquid separation. It is also preferable to previously mix a polymer coagulant into the adsorption layer, feed the suspended solid matter-containing wastewater through the adsorption layer, and separate and remove the suspended solid matter from the wastewater by solid-liquid separation in the adsorption layer.
The polymer coagulant for use in the step is preferably a nonionic polymer coagulant and/or an anionic polymer coagulant. For example, the polymer coagulant for use is polyacrylamide and/or a hydrolysate product thereof.
Hereinafter, the cation exchanger and the method of removing heavy metal ions in wastewater according to
an embodiment of the present invention will be described in detail with reference to embodiments of the present invention. However, it should be understood that the present invention is not limited to these embodiments.
[Cation exchanger]
After intensive studies, the inventors have found that a group of leaf vegetables, consisting of molokheiya, komatsuna, Japanese honeywort, potherb mustard, and spinach, has a cation exchange performance equivalent to or higher than that of artificially-synthesized cation exchange resins, as will be described below in Examples. It is presumably because carboxy and hydroxy groups of pectin, folic acid, acidic polysaccharides (in particular, D-glucuronic acid and D-galacturonic acid) and others constituting the leaf vegetable function effectively for cation exchange action.
The leaf vegetable used as the cation exchanger may be any portion, i.e., leave, stalk or root, of the leaf vegetable, but use of the stalk and root portions, which are less used in food, would be more favorable, from the viewpoint of efficient use of resources. In addition, the leaf vegetable may be used in any state, i.e., as it is, after dried, or after extracted with various solvents or aqueous solutions, but it is preferably used as it is or after dried, because of

simplicity and easiness of handling. Further, the shape thereof may be as it is, but pulverized products such as dry powder, which have larger surface area, can have a larger ion exchange performance.
Since the leaf vegetable is a high-water content product having a water content of as high as 90 to 95% of the weight, the dried product of the leaf vegetable is highly compatible with water. For the properties above, water-insoluble pectin is considered to have a large area in contact with water per unit dry mass, and thus to have an effective ion exchange performance.
Examples of the leaf vegetables for use include molokheiya, komatsuna, Japanese honeywort, potherb mustard, and spinach, and among the leaf vegetables above, molokheiya has high ion exchange performance. It is probably because molokheiya contains much mucin, in contrast to other leaf vegetables.
The molokheiya is not different, if it is produced in Japan (e.g., Gunma, Mie, Saga, or Okinawa Prefecture) or abroad (e.g., Egypt, Philippines, Malaysia, or China). However, the production site closer to the utilization site is more advantageous from the viewpoints of environmental load and transportation cost. The method of drying molokheiya may be any one of solar drying, hot air drying, freeze drying, frozen drying, vacuum drying, and the like, but overheating may lead to decrease of molecular weight
and intramolecular crosslinking of the acidic polysaccharides forming the molokheiya, generation of carbonization reaction, and deterioration of metal ion-adsorbing effect, and thus, it is desired to make the drying temperature 200°C or lower.
[Method of removing heavy metal ions in wastewater]
Examples of the heavy metal ions present in wastewater include ions of copper (Cu), nickel (Ni), chromium (Cr), lead (Pb), cadmium (Cd), cobalt (Co), zinc (Zn) . These heavy metals are present in wastewater as suspended solid matter such as of hydroxides or in the state of metal ions and complex ions. The concentration of the heavy metal ions in wastewater is about 1 to 1000 ppm.
The adsorption step of bringing the wastewater containing dissolved heavy metal ions into contact with the cation exchanger containing a leaf vegetable selected from a group consisting of molokheiya, komatsuna, Japanese honeywort, potherb mustard, and spinach and making part of the heavy metal ions adsorbed on the cation exchanger may be carried out generally at any timing. For example, the heavy metal ion-containing wastewater may be brought into direct contact with the cation exchanger. However, the adsorption step is preferably carried out after the step of adding a base to the wastewater containing
dissolved heavy metal ions to make wastewater basic for insolubilization of at least part of the heavy metal ions and generation of suspended solid matter and the step of adding an inorganic coagulant to the wastewater for aggregation of the suspended solid matter, because the residual ions that were not precipitated as the suspended solid matter can be removed effectively by adsorption. The form of the contact of the wastewater with the cation exchanger is also not particularly limited, but the contact is normally made by feeding the wastewater through a cation exchanger-containing adsorption layer that is filled for example in an adsorption tower. Hereinafter, such an example will be described.
Fig. 1 is a flow chart showing the step of removing heavy metal ions from wastewater containing dissolved heavy metal ions according to an embodiment of the present invention. A case where the heavy metal ion used is copper (II) ion and the inorganic coagulant used is iron (III) chloride will be described in Fig. 1 as an example.
First, a base is added to the heavy metal ion-containing wastewater, to make the wastewater basic. It is then preferable to add a hydroxide such as calcium hydroxide Ca(0H)2 or sodium hydroxide NaOH as a base and to adjust the pH of the wastewater PH normally to 7 to 14, preferably 8 to 12, although the desired pH

depends on the kind of the wastewater. Excessively smaller addition amount leads to deterioration in removing effect of heavy metal ions, while excessively large addition amount to economical disadvantage.
In this way, most of respective heavy metal ions are insolubilized as hydroxides and oxides, generating suspended solid matter. For example, most of copper
(II) ions are converted to copper (II) hydroxide,
Cu(OH)2 in the following reaction:
Cu2+ + 20H- → Cu(OH)2
However, part of the metal ions remains dissolved in the aqueous solution as ions even under basic condition or as they form complex ions under basic condition. Then, an inorganic coagulant, for example iron
(III) chloride, is added to the wastewater. Iron (III)
ion added in the step is converted to iron (III)
hydroxide Fe(OF)3 in the following reaction:
Fe3+ + 30H- → Fe (0H)3
Copper (II) hydroxide previously generated aggregates with the iron (III) hydroxide.
Then, a polymer coagulant is added. The polymer coagulant further aggregates the suspended solid matter previously formed by aggregation for example with the
inorganic coagulant into macroflocs, thus making solid-liquid separation easier. The polymer coagulant for use is preferably a nonionic polymer coagulant and/or an anionic polymer coagulant, such as polyacrylamide and/or the hydrolysate product thereof or sodium polyacrylate. The amount of the polymer coagulant added is normally 0.01 to 1000 ppm, preferably 0.1 to 100 ppm, more preferably 0.5 to 10 ppm, although it depends on the kind of the wastewater and the molecular weight of the polymer coagulant. Addition of the polymer coagulant may be eliminated, if necessary.
Then, the aggregated suspended solid matter and polymer coagulant are separated from wastewater by solid-liquid separation, to obtain primary treated water. The method of solid-liquid separation is not particularly limited and, for example, sedimentation treatment or filtration can be used favorably.
In the case of the method of insolubilizing heavy metal ions by making the wastewater basic, it is not possible to remove residual ions, such as ions remaining dissolved in aqueous solution even under basic condition and ions remaining dissolved as they form complexes under basic condition, and thus, there is limitation on metal ion-removing effect.
Thus in this embodiment, an adsorption step of feeding the primary treated water through an adsorption layer containing an cation exchanger containing a leaf
vegetable such as molokheiya is carried out then. It is possible in this way to remove part of the remaining heavy metal ions effectively by adsorption on the ion exchanger and to obtain high-quality secondary treated water lower in metal ion concentration. Since the cation exchanger made of a plant biomass material such as molokheiya is disposable, it is also possible to eliminate the cation exchanger-regeneration treatment step and construct a simplified, high treatment efficiency wastewater treatment system. Since the cation exchange performance of the cation exchanger is high, it is also possible to reduce the amount of the cation exchanger used, and the cation exchanger after use can be treated easily.
Although examples of removing suspended solid matter (and polymer coagulant) from wastewater by solid-liquid separation before the adsorption step have been described above, it is also possible to feed the wastewater containing suspended solid matter (and polymer coagulant) through an adsorption layer and separate and remove the suspended solid matter from the wastewater in the adsorption layer by solid-liquid separation. It is possible in this way to eliminate the solid-liquid separation step. In such a case, it is also possible, by previously mixing a polymer coagulant in the cation exchanger layer, to eliminate the step of adding a polymer coagulant.
Since the leaf vegetable for use in the present invention is a plant biomass material, cation exchangers made of the leaf vegetable or the dried product thereof are safer to human body and environment, compared to conventional ion exchange resins, and can be prepared from a renewable resource without consumption of fossil resource. For that reason, the invention can contribute to protection of global environment, from the viewpoints of resource conservation, reduction of hazardous substance and efficient use of waste.
Hereinafter, the present invention will be described in more detail.

The basic pH adjuster for use in the present invention is, for example, one or more of calcium hydroxide Ca(0H)2, sodium hydroxide NaOH, magnesium hydroxide Mg(0H)2, sodium carbonate Na2CO3, sodium silicate Na2SiO3, bentonite, and coal ash (flyash) . It is possible, by adding such a basic pH adjuster, to precipitate the heavy metal ions contained in wastewater as suspended solid matter by hydroxylation.

The inorganic coagulants are, for example, at least one of iron (III) chloride (ferric chloride), aluminum sulfate, polyaluminum chloride (PAC), iron (II) sulfate (ferrous sulfate), ferric polysulfate
(polyiron), sodium aluminate, chlorinated copperas, and modified basic aluminum sulfate. It becomes possible to aggregate the suspended solid matter (such as metal hydroxides) in wastewater by addition of these inorganic coagulants. In addition, it becomes possible, by combined use of molokheiya and the inorganic coagulant, to adsorb not only the suspended solid matter in wastewater but also the soluble metal ions simultaneously and thus to remove the metal ions contained in the wastewater effectively. The amount of the inorganic coagulant added to wastewater is normally 1 to 50000 ppm, preferably 5 to 5000 ppm, although it depends on the kind of the wastewater. Excessively small addition amount leads to low metal ion-removing effect, while excessively large addition amount is not advantageous economically.
A commercially available organic coagulant may be used in combination. The organic coagulant is, for example, at least one coagulant of dimethyldiallylammonium chloride, epichlorohydrin condensates, polyethyleneimine, condensates from an alkylene dichloride and a polyalkylene polyamine, dicyandiamide-formalin condensates, aniline-formaldehyde polycomplex hydrochloride salt, polyhexamethylene thiourea acetate salt, and polyvinylbenzyltrimethylammonium chloride. The amount of the organic coagulant added is normally 1 to 10000
ppm, preferably 5 to 1000 ppm.

The polymer coagulants for use in the present invention include nonionic polymer coagulants, anionic polymer coagulants, cationic polymer coagulants and ampholytic polymer coagulants.
(Nonionic polymer coagulants)
- Polyacrylamide, polymethacrylamide, starch, guar
gum, gelatin, polyoxyethylene, and polyoxypropylene
(Anionic polymer coagulants)
- (Meth)acrylic polymers such as partial hydrolysates of polyacrylamide and polymethacrylamide, copolymers of acrylic or methacrylic acid and acrylamide or methacrylamide and the salts thereof, ternary copolymers of acrylic or methacrylic acid, acrylamide or methacrylamide and 2-acrylamido-methylpropanesulfonic acid, vinylsulfone acid or vinylmethylsulfonic acid and the salts thereof, sulfomethylated compounds of polyacrylamide and polymethacrylamide and the salts thereof; sodium alginate, guar gum sodium salt, carboxymethylcellulose sodium salt, starch sodium salt
- As the other polymers, exemplified are the sulfonated compounds of the following polymer compounds and the salts thereof: polystyrene, polyphenylene ether, polycarbonate, polyphenylene sulfide, and polyethylene terephthalate; preferably polyphenylene ether and
polycarbonate.
(Cationic polymer coagulants)
- Quaternary compounds of dialkylaminoalkyl
(meth)aerylate (the quaternarizing agent is for example
methyl chloride, or benzyl chloride) and the acid salts thereof (the acid salt is for example an inorganic salt such as hydrochloride salt or sulfate salt or an organic salt such as acetate salt), or polymer or copolymers of these quaternary compounds with (meth)acrylamide; such as quaternary compound from dimethylaminoethyl acrylate and methyl chloride or the polymers or copolymers of the compound and acrylamide;
- Quaternary compounds from dialkylaminoalkyl
(meth)acrylamide or the acid salt thereof, or the
polymer or copolymers from the quaternary compounds with (meth)acrylamide, such as copolymers of a quaternary compound from dimethylaminopropylacrylamide and methyl chloride with acrylamide
- Cationically modified polyacrylamide, such as Mannich modification products and Hofmann degradation products of polyacrylamide;
- Epihalohydrin-amine condensates, such as polycondensates from epihalohydrin and an alkylenediamine having 2 to 8 carbon atoms;
- Polydimethyldiallylammonium chloride
- Polyvinylimidazoline and the salts thereof
- Polyvinyl amidine and the salts thereof
- Chitosan and the salts thereof
- Polyvinylpyridine and the salts thereof
- Polythiourea
- Water-soluble aniline resins
- Chloromethylated polystyrene ammonium salts or amine quaternary salt
- Polyvinylimidazole and the salts thereof
(Ampholytic polymer coagulants)
- Acrylamide-acrylic acid (or the salts thereof)-
dialkylaminoalkyl(meth)acrylate (or the salts and
quaternary compounds thereof)
- Polyglutamic acid and the salts thereof

In addition to the coagulants above, secondary treatment agents such as ion exchange resins, ion-exchange membranes, and other secondary treatment agents may be mixed or used in combination.
(Ion-exchange resin)
The ion exchange resin for use in the present invention is for example an anionic or cationic ion exchange resin. The anion exchange resin is typically a strongly basic anion exchange resin obtained by halomethylating a crosslinked styrene-divinylbenzene copolymer and then reacting the halomethyl group with a tertiary amine, or an anion exchange resin in the structure having a spacer group. On the other hand, as for the strongly acidic cation exchange resin, a
sulfonated compound of a crosslinked styrene-divinylbenzene copolymer is typically used as an ion exchange resin for production of ultrapure water. Among these ion exchange resins, cation exchange resins are suitable for applications of heavy metal ion removal. The addition amount thereof is 0.01 to 100 times, preferably, 0.1 to 10 times more by weight than the addition amount of the molokheiya, although it depends on the kind of the wastewater.
(Other chemicals used in combination) The cation exchanger according to the embodiment of the present invention can be mixed in or used in combination with secondary treatment agents such as chelating resins, chelating agents, activated carbon, ozone water, water-absorbing resins, hydrogen peroxide solution, chlorine and liquid chlorine, sodium hypochlorite, chlorine dioxide, bleaching powder, isocyanuric chloride, diatomaceous earth, photocatalysts such as titanium oxide or biological treatment agents.
When molokheiya is used, a normal dehydrator can be used in the method of adsorbing and separating the metal ion-containing insoluble component contained in the wastewater. For example, filter press, vacuum dehydrator, belt press dehydrator, centrifugal dehydrator, or screw press is usable. The dehydrate
(cake) can be reclaimed by a known method. It can also be converted into fuel or compost extremely easily.
[EXAMPLES]
Hereinafter, Examples and Comparative Examples of the present invention will be described. However, it should be understood that the present invention is not limited to the following Examples.
[Example 1]
In Example 1, it was confirmed experimentally that dry molokheiya powder has action as cation exchanger.
[Example 1-1]
First, 0.05 mol/L aqueous sodium carbonate solution was prepared by using sodium carbonate Na2 CO3 (manufactured by Wako Pure Chemical Industries, Ltd.) and ion-exchange water. The aqueous solution contains sodium ion Na+ at a concentration of 0.1 mol/L.
Then, dry leaf, stalk, and root powder of molokheiya (produced by K.Kobayashi & Co., Ltd.) was added to the aqueous sodium carbonate solution as cation exchanger and the mixture was stirred overnight. The dry molokheiya powder of molokheiya was then added in an amount of 1% with respect to the mass of the aqueous sodium carbonate solution. The solid matter was then filtered, to obtain a filtrate (1) .
If the dry molokheiya powder has action as cation
exchanger, by the treatment above, part of the hydrogen atoms of the acidic groups in the cation exchanger is released as hydrogen ions into the aqueous solution and sodium ions in the aqueous solution are incorporated into the cation exchanger instead. The hydrogen ions released into the aqueous solution bind to carbonate ions CO32", forming hydrogen carbonate ions HCO3-. The reaction formula (and ion reaction formula) is shown below (where, R represents the base group of the cation exchanger and the carboxyl group represents an acidic group).
R-COOH + Na2CO3 → R-COONa + NaHCO3 (reaction 1) (R-COOH + Na+ + CO32- → R-COO-Na+ + HCO3-)
Subsequently, the filtrate (1) was neutralization-titrated with 0.1 mol/L hydrochloric acid, and the titration amount of the acid necessary to the first neutralization point was determined. Hydrogen ions in hydrochloric acid bind then to carbonate ion C032-, forming hydrogen carbonate ion HC03-. The reaction formula (and ion reaction formula) is shown below.
HC1 + Na2CO3 → NaCl + NaHCO3 (reaction 2) (H+ + CO32- → HCO3-)
[Example 1-2]
Dry molokheiya powder was added to the aqueous sodium carbonate solution as cation exchanger in an amount of 5 % with respect to the mass of the aqueous sodium carbonate solution. The aqueous sodium carbonate solution was treated similarly to Example 1-1, except the change above, to obtain a filtrate (2). The filtrate (2) was neutralization-titrated, and the titration amount to the first neutralization point was determined.
In addition, the untreated aqueous sodium carbonate solution was also neutralization-titrated with 0.1 mol/L hydrochloric acid, and the titration amount to the first neutralization point was determined.
Since there is no consumption of carbonate ion in (reaction 1) in the case of the untreated aqueous sodium carbonate solution, the titration amount of hydrochloric acid necessary for (reaction 2) is largest in the three titrations. In contrast in Examples 1-1 and 1-2, if the dry molokheiya powder has cation exchange action, the titration amount of hydrochloric acid necessary for (reaction 2) will become smaller, because there is consumption of carbonate ion in (reaction 1). Accordingly, it is possible to estimate the ion exchange amount in (reaction 1), based on the difference between the titration amount of hydrochloric acid to the untreated aqueous sodium carbonate solution and the titration amount of determined in Example 1-1
or 1-2.
Fig. 2 is a graph showing the titration curve of the untreated aqueous sodium carbonate solution and also those obtained in Examples 1-1 and 1-2. Among the three titrations, the titration amount of hydrochloric acid necessary for (reaction 2) was largest in titration of the untreated aqueous sodium carbonate solution, as expected. The difference between the titration amount for untreated aqueous sodium carbonate solution 29.1 mL and the titration amount for filtrate (1) 25.2 mL or filtrate (2) 12.9 mL was 3.9 mL or 16.2 mL. The ratio of ion exchange amount of Example 1-1 to Example 1-2, as determined from the values above, is 3.9:16.2 = about 1:4.2, and it agrees well with the ratio 1:5 of additive amounts of the dry molokheiya powder in Examples 1-1 and 1-2. The results above demonstrated that the dry molokheiya powder shows ion exchange action reproducibly.
[Example 2]
It was experimentally confirmed in Example 2 that dry powders of molokheiya, komatsuna, Japanese honeywort, potherb mustard, and spinach have action as cation exchanger and action to remove copper (II) ion being, a heavy metal ion from wastewater.
[Example 2-1]
First, an aqueous copper acetate solution
containing copper (II) ion Cu2+ at a concentration of 3 mass ppm was prepared by using copper acetate (II) (produced by Kanto Chemicals Co., Inc. ) and ion-exchange water.
Subsequently, dry powder of a leaf, a stalk, and a root of molokheiya (produced by K.Kobayashi & Co., Ltd.) was added to the aqueous copper acetate solution as cation exchanger, and the mixture was stirred for 1 hour. The dry molokheiya powder was added then in an amount of 5 ppm with respect to the mass of the aqueous copper acetate solution. Then, the solid matter was removed by filtration and the concentration of copper (II) ion in the filtrate obtained was measured. The concentration of copper ion in the aqueous solution was measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) by using ICPE9000 (trade name; manufactured by Shimadzu Corporation). The aqueous copper acetate solution remaining unused was used then as the standard solution for copper (II) ion concentration (hereinafter, the same shall apply).
Part of the hydrogen atoms of the acidic groups in the cation exchanger is released as hydrogen ions into the aqueous solution and copper (II) ions Cu2+ in the aqueous solution are incorporated into the cation exchanger instead in the treatment, and thus, the concentration of copper (II) ions in the aqueous solution declines. Thus, the reduction in
concentration of copper (II) ions corresponds to the ion exchange amount in (reaction 3) and shows the performance of the cation exchanger as a heavy metal ion scavenger.
[Example 2-2]
Dry komatsuna powder was added, instead of dry molokheiya powder, to the aqueous copper acetate solution as cation exchanger in an amount of 5 ppm with respect to the mass of the aqueous copper acetate solution. The dry komatsuna powder was prepared in house by drying purchased raw komatsuna in a drier and pulverizing the dried komatsuna. The aqueous copper acetate solution was treated similarly to Example 2-1, except the change above, and the concentration of copper (II) ion in the filtrate obtained was measured.
[Example 2-3]
Dry Japanese honeywort powder was added, instead of the dry molokheiya powder, to the aqueous copper acetate solution as cation exchanger in an amount of 5 ppm with respect to the mass of aqueous copper acetate solution. The dry Japanese honeywort powder was prepared in house by drying purchased raw Japanese honeywort in a drier and pulverizing the dried Japanese honeywort similarly to Example 2-2. The aqueous copper acetate solution was treated similarly to Example 2-1, except the change above, and the concentration of copper (II) ion in the filtrate obtained was measured.
[Example 2-4]
Dry potherb mustard powder was added, instead of dry molokheiya powder, to the aqueous copper acetate solution as cation exchanger in an amount of 5 ppm with respect to the mass of aqueous copper acetate solution. The dry potherb mustard powder was prepared in house by drying purchased raw potherb mustard in a drier and pulverizing the dried potherb mustard similarly to Example 2-2. The aqueous copper acetate solution was treated similarly to Example 2-1, except the change above, and the concentration of copper (II) ion in the filtrate obtained was measured.
[Example 2-5]
Dry spinach powder was added, instead of the dry molokheiya powder, to the aqueous copper acetate solution as cation exchanger in an amount of 5 ppm with respect to the mass of aqueous copper acetate solution. The dry spinach powder was prepared in house by drying purchased raw spinach in a drier and pulverizing the dried spinach similarly to Example 2-2. The aqueous copper acetate solution was treated similarly to Example 2-1, except the change above, and the concentration of copper (II) ion in the filtrate obtained was measured.
[Comparative Example 2-2]
Amberlite IR124 (trade name; produced by Rohm and Haas Japan Co., Ltd. and distributed by Organo
Corporation), a strongly acidic cation exchange resin, was added at 5 ppm to the aqueous copper acetate solution, instead of the cation exchanger. The aqueous copper acetate solution was treated similarly to Example 2, except the change above, and the concentration of copper (II) ion in the filtrate obtained was measured.
[Comparative Example 2-1]
A polymer coagulant Sanfloc NOP (trade name; produced by Sanyo Chemical Industries, Ltd.) was added at 5 ppm to the aqueous copper acetate solution instead of the cation exchanger. The aqueous copper acetate solution was treated similarly to Example 2, except the change above, and the concentration of copper (II) ion in the filtrate obtained was measured.
Table 1 is a table showing the measured values of the concentrations of copper (II) ion in Examples 2-1 to 2-5 and Comparative Examples 2-1 and 2-2. The concentration of copper (II) ion in the Table is expressed by percentage, as compared to the standard (100%) of the concentration of copper (II) ion in the untreated aqueous copper acetate solution.
[Table 1]
[Table1] (Table Removed)

Table 1 shows the followings. The concentration of copper (II) ion declined in all Examples 2-1 to 2-5, in which dry leaf vegetable powder was added, indicating that the dry leaf vegetable powder added had ion exchange action and heavy metal removal performance. The effectiveness is in the order of molokheiya, komatsuna, Japanese honeywort, potherb mustard, spinach from the highest. Comparison with Comparative Examples shows that the leaf vegetables have heavy metal removal performance equivalent to or thrice higher than that of strongly acidic ion exchange resins and polymer coagulants used in wastewater treatment.
The present invention has been described with reference to the embodiments and Examples, but the present invention is not limited to these embodiments and examples, and it is needless to say that the present invention can be modified appropriately without departing from the gist of the invention.
The present application contains subject matter related to that disclosed in Japanese Priority Patent
Application JP 2010-067376 filed in the Japan Patent Office on March 24, 2010, the entire content of which is hereby incorporated by reference.
It should be understood by those skilled in the art that various modifications, combinations, subcombinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.

What is claimed is:
1. A cation exchanger, comprising at least one leaf
vegetable selected from a group including molokheiya
(Corchorus olitorius), komatsuna (Brassica rapa var. peruviridis), Japanese honeywort (Cryptotaenia japonica), potherb mustard (Brassica rapa var. nipposinica), and spinach (Spinacia oleracea).
2. The cation exchanger according to claim 1, further comprising molokheiya.
3. The cation exchanger according to claim 1, further comprising a dried leaf, a dried stalk, or a dried root of the leaf vegetable.
4. A method of removing heavy metal ions in wastewater, at least comprising an adsorption step of bringing wastewater including the heavy metal ions into contact with a cation exchanger including at least one leaf vegetable selected from a group .including molokheiya, komatsuna, Japanese honeywort, potherb mustard, and spinach, to thereby cause part of the heavy metal ions to be adsorbed on the cation exchanger.
5. The method of removing heavy metal ions in wastewater according to claim 4, wherein a cation exchanger including molokheiya is used as the cation exchanger.
6. The method of removing heavy metal ions in wastewater according to claim 4, wherein a cation exchanger containing a dried leaf, a dried stalk, or a
dried root of the leaf vegetable is used as the cation exchanger.
7. The method of removing heavy metal ions in wastewater according to claim 4, wherein the adsorption step is carried out in such a manner that the wastewater is fed through an adsorption layer including the cation exchanger.
8. The method of removing heavy metal.ions in wastewater according to claim 7, further comprising, before the adsorption step:
adding a base to the wastewater including the heavy metal ions to make the wastewater basic and insolubilize at least part of the heavy metal ions, to thereby form a suspended solid matter; and
adding an inorganic coagulant to the wastewater, to thereby aggregate and sediment the suspended solid matter.
9. The method of removing heavy metal ions in wastewater according to claim 8, further comprising separating and removing the suspended solid matter from the wastewater by solid-liquid separation before the adsorption step.
10. The method of removing heavy metal ions in wastewater according to claim 9, further comprising promoting the aggregation and sedimentation of the suspended solid matter by addition of a polymer coagulant to the wastewater and separating and removing
the suspended solid matter and the polymer coagulant from the wastewater before the adsorption step.
11. The method of removing heavy metal ions in wastewater according to claim 8, further comprising feeding the wastewater including the suspended solid matter through the adsorption layer, and subjecting the suspended solid matter to the solid-liquid separation in the adsorption layer, to thereby be removed and separated from the wastewater.
12. The method of removing heavy metal ions in wastewater according to claim 11, further comprising, before the adsorption step, adding a polymer coagulant to the wastewater, to thereby promote the aggregation and sedimentation of the suspended solid matter, and subjecting the suspended solid matter and polymer coagulant to the solid-liquid separation in the adsorption layer, to thereby be removed and separated from the wastewater.
13. The method of removing heavy metal ions in wastewater according to claim 11, further comprising previously mixing a polymer coagulant in the adsorption layer, feeding the wastewater including the suspended solid matter through the adsorption layer, and subjecting the suspended solid matter to the solid-liquid separation in the adsorption layer, to thereby be removed and separated from the wastewater.
14. The method of removing heavy metal ions in
wastewater according to any one of claims 10, 12, and 13, wherein a nonionic polymer coagulant and/or an anionic polymer coagulant is used as the polymer coagulant.
15. The method of removing heavy metal ions in wastewater according to claim 14, wherein polyacrylamide and/or a hydrolysate product thereof is used as the polymer coagulant.