This invention relates to adsorbents that are made of metal ion removing chelate adsorbent fibers and which may typically be used in the treatment of wastewater in the acidic region.
Ion adsorbents of a phosphoric and phosphonic acid type are good adsorbers of divalent ions such as Cu(II) and Pb(II) at near neutrality but their adsorption capacity and rate drop in the acidic region at pH 2 and below. They also have difficulty in adsorbing trivalent ions such as Fe(III) for two reasons, i.e., at near neutrality, ligand exchanging is slow and bulky binuclear hydroxide complex ions form. Information about these adsorption techniques is given in the following known prior art references:
Conventional commercial adsorbent resins have the problem that adsorption capacity and rate drop during use in the acidic region. In addition, they have been unable to adsorb metal ions such as Fe(III) in the neutral region because not only are they slow in ligand exchanging but they also form bulky binuclear hydroxide complex ions that tend to precipitate.
An object, therefore, of the present invention is to provide an adsorbent that allows for adsorption in the acidic region.
Another object of the present invention is to provide an adsorbent that facilitates adsorption in the neutral region at faster rate and which have higher adsorption capacity.
The present invention provides adsorbents that can adsorb and remove metal ions dissolved in acidic wastewater, particularly those metal ions of higher valency which have small solubility products with the hydroxide ion.
The chelate adsorbent fibers of the present invention can be produced by relying upon the graft polymerization technique for providing various shapes of material with the desired adsorbing capability. In the present invention, polypropylene, polyethylene or natural polymer fibers, polyester fibers or fibers of their composites are used as the substrate for preparing chelate adsorbent fibers of a phsophonic acid type, a sulfonic acid type, or a complex thereof. The chelate adsorbent fibers may assume various forms including short cut filaments, nonwoven fabrics, woven fabrics, and long filaments.
The chelate adsorbent fibers of the present invention are produced by a process comprising the steps of exposing a polymer substrate to an electron beam or other radiations and then performing a graft polymerization technique that enables a metal ion adsorbing capability to be incorporated in the presence of an added reactive monomer reagent.
In the present invention, polyethylene or otherwise made fibers are used as the polymer substrate, into which reactive monomers permitting the introduction of at least two functional groups such as a phosphonic acid group and a sulfonic acid group that contribute to the adsorption of metal ions are introduced by graft polymerization.
Thus, the present invention produces a bifunctional adsorbent by first exposing a polymer substrate to a radiation and then performing graft polymerization such that two reactive monomers, one having a phosphonic acid group and the other having a sulfonic acid group, are introduced into the substrate. Alternatively, the present invention produces a bifunctional adsorbent by first exposing a polymer substrate to a radiation, then performing graft polymerization such that two reactive monomers, one permitting the introduction of a phosphonic acid group and the other permitting the introduction of a sulfonic acid group, are introduced into the substrate and thereafter introducing phosphonic and sulfonic acid groups.
The chelate adsorbent fiber of the present invention was compared for performance (adsorption capacity) with a commercial chelate resin and a monofunctional fiber (an adsorbent fiber having a single type of functional group had been introduced) by measuring the concentration of Pb(II) ions in solution; the fiber of the present invention was more than twice in adsorption capacity at pH of 2 or less. The adsorbent fiber of the present invention was also compared with the monofunctional fiber for the flow rate dependency of Fe(III) adsorption; the fiber of the present invention showed a satisfactory adsorption behavior at more than 100 times faster flow rates.
The chelate adsorbent fiber as produced by radiation induced graft polymerization in accordance with the present invention exhibits better adsorption performance than the monofunctional fiber and the commercial chelate resin (DIAION CRP200 of Mitsubishi Chemical Co.) and hence is promising for use in the treatment of acidic wastewater.
Exposure to radiation is performed on a preliminarily nitrogen-purged polymer substrate as it is placed in a nitrogen atmosphere either at room temperature or under cooling with Dry Ice. The radiation to be used is either an electron beam or γ-rays and the dose of irradiation can appropriately be determined to satisfy the condition that it be sufficient to generate active points for the reaction; a typical value is between 5 and 200 kGy.
The present invention is described below in greater detail with reference to examples.
A nonwoven fabric as a polymer substrate was irradiated to generate reactive points for the reaction. To this end, an electron beam was applied in a nitrogen atmosphere to give a total dose of 200 kGy. Subsequently, two monomers having a vinyl group, i.e., chloromethylstyrene and styrene, were reacted at a weight ratio of 4:1 in DMSO (dimethyl sulfoxide) at 40° C. for 3-24 hours to give monomer concentrations of 10-50%, thereby introducing graft chains into the fiber yarns.
Conversions obtained by 2- and 3-hour reactions at 40° C. were 100% and 130%, respectively. After introducing triethyl phosphite/phosphonic acid complex groups, chlorosulfonic acid was used to sulfonate the substrate, thereby producing a grafted, bifunctional chelate adsorbent fiber having phosphonic and sulfonic acid groups introduced therein. When Pb(II) ions were fed into the fiber, the feed solution could be recovered up to a functionality concentration of 90% without any loss.
The bifunctional chelate adsorbent fiber having phosphonic and sulfonic acid groups introduced therein was conditioned by alternating hydrochloric acid and sodium hydroxide and subjected to an adsorption test. A Pb(II) ion solution as the feed was adjusted to 0.001 M before the adsorbent fiber was immersed in it, which was then agitated at 20° C. for 24 hours at various pH values between 0 and 3.0.
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The bifunctional chelate adsorbent fiber into which phosphonic and sulfonic acid groups had been introduced was packed into a column having an inside diameter of 7 mm and then conditioned by alternating hydrochloric acid and sodium hydroxide before it was subjected to an adsorption test. Two feeds, one being a Pb(II) ion solution and the other being a Fe(III) ion solution, were each adjusted to 0.01 M, provided that the Fe(III) ion solution was also adjusted to pH 1.8; the feeds were then passed through the column at space velocities (S.V.) in the range of 40 to 1000 h−1. As
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If the chelate adsorbent of the present invention is applied to acidic wastewater containing metal ions, the latter can be removed most satisfactorily in a strongly acidic range in terms of adsorption rate, adsorption capacity, and selectivity.
Number | Date | Country | Kind |
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324600/2005 | Nov 2005 | JP | national |