KR100197300B1 - Biological absorbents prepared with colloidal silica gel and absorption and recovery of heavy metal by the same - Google Patents

Abstract

The present invention relates to a method for producing a spherical silica bead in which microbial cells or chemically modified microbial cells by introducing oxime groups or phosphoric acid groups are mixed with colloidal silica sol and the mixture is put into a thermostatic chamber to form a spherical silica bead carrying microbial cells, The present invention relates to a biocompatible material capable of adsorbing heavy metals and the like produced by aging a silica bead and extracting it with a solvent. The present invention also includes a method for desorbing and recovering a heavy metal adsorbed on the bioabsorbent. The present invention also relates to a method and apparatus for preparing silica beads carrying microbial cells by adding a mixture of a chemically modified microorganism and a colloidal silica sol to a thermostatic chamber, And a method and an apparatus for producing silica beads composed of a plurality of glass tubes for dropping the mixture in a droplet state.

Description

Bioabsorbent composition prepared by colloidal silica gel and method for adsorbing and recovering heavy metals using the same

FIG. 1 is a graph showing the effect of hydrogen ion concentration on the stability of silica sol (sol) in a colloidal silica-water system.

FIG. 2 is a schematic illustration of an apparatus for producing spherical bioadhesives according to the present invention using colloidal silica. FIG.

FIG. 3 is a graph showing curves of copper adsorption and the like of a bioabsorbent having a oxime group introduced therein according to an embodiment of the present invention. FIG.

FIG. 4 is a graph showing the removal amount of lead ions contained in the wastewater by passing the wastewater through the filler-type contactor after filling the bioabsorbent according to another embodiment of the present invention.

FIG. 5 is a graph showing the results of recovering heavy metals adsorbed with 0.5 N hydrochloric acid solution after adsorbing heavy metals using a bioabsorbent according to another embodiment of the present invention. FIG.

[0001]

The present invention relates to a bioabsorbent for adsorbing heavy metals or recovering heavy metals adsorbed thereon. More particularly, the present invention relates to a bioabsorbent prepared by supporting microbial cells on colloidal silica sol in order to adsorb and recover heavy metals or rare metals contained in wastewater and the like.

The present invention also includes an apparatus for producing a bioabsorbent according to the present invention and a method for separating or recovering heavy metals and the like using the bioabsorbent of the present invention.

BACKGROUND OF THE INVENTION [

It has long been known in the field that living microbial cells such as bacteria, fungi, algae, or dead microbial cells can remove heavy metal ions present in aqueous solutions. In other words, it has been known that biological cells can remove heavy metals, and many studies have been conducted to develop an adsorbent for removing heavy metals by using biological cells. In particular, biological cells are characterized by the removal of heavy metal ions from various metal ions present in aqueous solution, rather than light metal ions such as calcium and magnesium.

In addition, conventionally used ion exchange resins have a property of removing light metal ions such as calcium and magnesium as well, so that it is not easy to efficiently remove only heavy metals in the case of an aqueous solution containing a large amount of light metal ions. The excellent affinity of these biological cells for heavy metals is advantageous in that heavy metals can be removed in an aqueous solution containing various light metals compared to conventional ion exchange resins. In particular, when the groundwater or soil is contaminated with heavy metals such as lead or cadmium, the bioabsorbent produced using the biological cell can efficiently and economically remove heavy metals.

Therefore, many researches have been conducted to apply the present invention to a wastewater treatment process for adsorbing and recovering heavy metals by using a bioabsorbent. The bioabsorbent was immobilized because its strength was weak. Although the organic polymer is generally used as the immobilization method, the bioabsorbent by this method has a weak mechanical strength and is frequently expanded by water, which makes it difficult to apply it to actual processes.

The inventors of the present invention have developed a new method for recovering heavy metals adsorbed on a bioabsorbent and a bioabsorbent capable of adsorbing heavy metals present in an aqueous solution using the excellent affinity for heavy metals of biological cells .

[Object of the invention]

An object of the present invention is to provide a bioabsorbent having good immobilization, that is, having good mechanical strength, because microorganisms are supported on silica as a biosorbent in which colloidal silica gel is supported on a microorganism.

Another object of the present invention is to provide a bioabsorbent which can be applied to an actual wastewater treatment process by preventing a phenomenon such as a pressure drop and a channeling of a packing layer due to expansion phenomenon caused by water.

Another object of the present invention is to provide a bioabsorbent resistant to acid or base.

Another object of the present invention is to provide a bioabsorbent which can be prevented from being damaged by abrasion when applied to wastewater treatment because it is produced in a spherical shape.

Yet another object of the present invention is to provide a bioabsorbent which efficiently removes heavy metals and has increased adsorption to heavy metals.

Another object of the present invention is to provide a bioabsorbent which does not deteriorate the adsorption ability even when the adsorption and desorption processes are repeated.

The above and other objects of the present invention can be clearly understood by the following specific embodiments.

[Summary of the Invention]

The present invention relates to a method for producing a silica bead in which microbial cells or chemically modified microbial cells by introducing oxime groups or phosphate groups are mixed with colloidal silica sol and the mixture is placed in a thermostatic chamber to prepare silica beads carrying microbial cells, To a bioabsorbent capable of adsorbing heavy metals and the like produced by aging silica beads and extracting oil components permeated into beads by using a solvent.

The present invention also includes a method for desorbing and recovering a heavy metal adsorbed on the bioabsorbent.

The present invention also relates to a method and apparatus for preparing silica beads carrying microbial cells by adding a mixture of a chemically modified microorganism and a colloidal silica sol to a thermostatic chamber, And a method and an apparatus for producing silica beads composed of a plurality of glass tubes for dropping the mixture in a droplet state.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

The bioabsorbent of the present invention can be obtained by mixing microbial cells with colloidal silica sol and dropping the mixture into an oil thermostat to prepare silica beads carrying the microbial cells, aging the silica beads produced, The beads are produced by extraction and removal.

The affinity of the bioabsorbent for heavy metals is caused by the chelating groups such as carboxyl group, phosphoric group, and sulfur group present on the surface of the microbial cells. Despite these advantages, microbial cells have a disadvantage in that the number of functional groups present on their surface is less than that of ion exchange resins and that the number or types thereof can not be artificially altered. It is possible to remove various heavy metals at the same time by introducing functional groups capable of forming complexes to various kinds of heavy metals while maintaining selective adsorption to heavy metals, which is a unique property of biological hop complexes.

In the present invention, oxime group or phosphate group is introduced on the surface of microbial cells through a chemical synthesis method to greatly increase the adsorption capacity of microbial cells and to produce a biosorbent having affinity for various heavy metals. That is, microbial cells are chemically modified and the modified microorganisms are mixed with colloidal silica sol to prepare spherical silica beads carrying microbial cells.

Examples of the microbial cells used in the present invention include algae such as Undaria, Sargassum, yeast, bacteria, fungi and the like, which are a kind of sea brown algae. Algae contain a large amount of alginic acid, a kind of polysaccharide, in the cell wall. Alginic acid has a carboxyl group in its chemical structure, and this carboxyl group forms a constant tertiary structure to form a complex with heavy metals. These alginates are identified as having one carboxyl group and two hydroxyl groups per constituent. In addition, microbial cells contain amine groups on their cell surface. In order to increase the heavy metal adsorption capacity of microbial cells, a chemical modification is made by bonding an oxime group or a phosphate group to a group existing on the surface of microbial cells.

The reaction of introducing an oxime group into microbial cells consists of two steps. The first reaction is to enhance the structure of the cell wall by cross-linking epichlorohydrin to the microbial cells. In the second reaction, the glutaraldehyde solution is used to activate the amine groups on the microbial cell surface, Followed by stirring to introduce an oxime group. Microbial cells are added to the sodium hydroxide solution, mixed and epichlorohydrin is added to form cross-linking. After cooling, filter using Whatman filter paper and wash with distilled water. The washed microbial cells are put into phosphate buffer and the glutaraldehyde solution is added to activate the amine groups on the microbial cell surface. Here, when the oxime solution is added again and reacted with stirring, a microbial cell agent into which a oxime group is introduced is produced. At this time, the oxime group is bonded to the amine group on the microbial cell surface.

The reaction for introducing phosphoric acid groups into the microbial cells is carried out by dissolving urea and orosoic acid in a dimethylformamide solution and mixing the microbial cells. The phosphate group is bonded to the hydroxyl group of the alginic acid on the surface of the microbial cell. The phosphoric acid content of the microbial cells into which the phosphate group is introduced according to the present invention varies depending on the kind of phosphoric acid used, but H ₃ PO ₄ , Na ₂ HPO ₄ and NaH ₂ PO ₄ or a mixture thereof can be used.

As described above, the microorganism cells chemically modified by introduction of the oxime group or the phosphoric acid group have an increased adsorption ability to heavy metals.

The chemically modified microbial cells or unmodified microbial cells are mixed with colloidal silica sol. FIG. 1 is a graph showing the effect of hydrogen ion concentration on the stability of silica sol in a colloidal silica-water system. As shown in FIG. 1, the silica surface can maintain a stable colloid state because the SiO ₂ is dissolved and has an anion form at a pH of 10 or more. In the present invention, since it is necessary to accelerate the gelation reaction of the colloidal silica carrying the microbial cells, it is necessary to add an acid to the colloidal silica solution so that the colloidal silica quickly gels. That is, since the gelation reaction proceeds most rapidly at a pH of about 6, an acid is added to accelerate the gelation reaction. However, once the pH drops below 6, the colloidal silica will stabilize again, so the acid should be used in an appropriate amount without excessive use.

The microbial cell-supported colloidal silica solution having the pH reduced by the addition of the acid as described above is made into a spherical silica bead by using the silica bead apparatus of the present invention. FIG. 2 is a schematic illustration of an apparatus for producing spherical bioadhesives using colloidal silica. FIG. A colloidal silica solution (hereinafter referred to as "colloidal silica solution") mixed with an acid solution is introduced into the apparatus of FIG. 2 to prepare silica beads (hereinafter referred to as "silica beads") carrying microbial cells.

2 shows a cylindrical oil thermostat 1 in which a plurality of glass tubes 3 are installed and filled with oil 8, a thermostat 2 for maintaining the oil thermostat 1 at a constant temperature, A plurality of glass tubes 3 for dropping and passing the colloidal silica solution in a droplet state, a dropping device 4 for dropping the colloidal silica solution in a droplet state, a temperature controller 5 for adjusting the temperature of the thermostatic chamber 1 And an oil discharge port 6 for discharging the oil 8 inside the oil chamber 1 for collecting the silica beads 7.

A plurality of glass tubes 3 for allowing the colloidal silica solution to be dropped in a droplet state are provided in the oil thermostatic chamber 1 and the inside of the oil thermostatic chamber 1 and the glass tube 3 is filled with oil. Of course, even if the glass tube is one, the silica bead according to the present invention can be manufactured when the length of the glass tube is long. A constant temperature device 2 is provided outside the oil chamber 1 to keep the temperature of the oil chamber 1 constant and the temperature at that time is controlled by the temperature controller 5. The oil used in the present invention is preferably water-reactive or insoluble so long as it has a high boiling point. In the examples of the present invention, soybean oil was used.

In the second drawing device of the present invention, the dropping device 4 for dropping the colloidal silica solution into the glass tube 3 in a droplet state can use an apparatus such as a syringe pump, And can be easily carried out.

In order to prepare the colloidal silica solution according to the present invention with the spherical silica beads 7, the time required for the drop passage in the glass tube 3 is about 30 seconds. That is, while passing through the glass tube 3, the colloidal silica solution undergoes a complete gelation reaction, resulting in a spherical silica bead 7. In order to form the above-mentioned discharge passage time of about 30 seconds, when the diameter of the silica beads 7 is 2 to 3 mm, the height of the glass tube 3 is about 120 cm and the inside diameter is about 0.7 to 1.0 cm . This is to provide the drag by the glass tube wall to drop at a low rate when the droplets of the colloidal silica solution pass through the glass tube 3. [

When a certain amount of silica beads 7 are accumulated in the lower portion of the oil chamber 1, the oil outlet 6 is opened to discharge the oil 3, and then the accumulated silica beads 7 are collected.

The collected silica beads 7 are aged in a sterilizer at about 120 ° C. The mechanical strength of the silica beads 7 after the aging process is increased. The silica beads that have undergone the aging process are washed with a solvent and then dried. Examples of the solvent used herein include toluene, methanol, and water. The silica bead bioabsorbent thus prepared has a porous structure, and its size can be variously produced.

The prepared silica bead bioabsorbent is used for treating wastewater for adsorbing and recovering heavy metals or adsorbing and recovering rare metals.

The silica bead bioabsorbent of the present invention has excellent adsorption power against heavy metals. FIG. 3 is a graph showing a copper absorption adsorption temperature curve of a bioabsorbent having a oxime group introduced therein according to an embodiment of the present invention. FIG. As shown in FIG. 3, the biosorbent incorporating the oxime group exhibits a high adsorption amount of copper, showing an adsorption amount of about 4 times or more at pH 4.5 than the original undisturbed (unlandia) cells which are not chemically modified. However, at low pH (pH 2.5), the adsorption of copper is lower than pH (pH 4.5), but also chemically high. This fact also indicates that once adsorbed copper ions can be easily recovered using an acid solution. This is presumably because the oxime group bonds with the chelating structure.

The silica bead bioabsorbent according to the present invention can effectively adsorb heavy metals such as copper, cadmium, lead, nickel, zinc and cobalt even in the presence of a light metal such as calcium or magnesium. That is, the bioabsorbent of the present invention has a low adsorption power against a light metal such as calcium or magnesium.

The heavy metal adsorbed on the silica bead bioabsorbent of the present invention can be recovered by using various desorbents. The desorption efficiency of heavy metals at the time of recovery can be changed depending on the type of desorbent and the concentration of hydrogen ions upon desorption, but NH ₃ , NTA (Nituilrotriacetic acid), EDTA (ethylene diamine tetraacetic acid) and the like are used as desorbents. In the case of desorbing the adsorbed lead (Pb), EDTA is most preferable.

The bioabsorbent of the present invention, prepared by supporting microbial cells on silica gel, shows an excellent effect in adsorbing heavy metals. FIG. 4 is a graph showing the removal amount of lead ions existing in the wastewater after filling the bioabsorbent according to one embodiment of the present invention with the filler-type contactor. The bioabsorbent of the present invention has a sufficient strength that can be used for treatment of heavy metal-containing wastewater in the form of silica beads. As shown in FIG. 4, the bioabsorbent of the present invention removes lead ions having a bed volume of 400 or more, so that the amount of lead ions in the effluent has a high adsorption power so that the amount of lead ions can hardly be measured.

The bioabsorbent of the present invention in which the microbial cells are supported on silica gel shows excellent results in recovering the adsorbed heavy metals. FIG. 5 is a graph showing the results of recovering heavy metals adsorbed with a 0.5 N hydrochloric acid solution after adsorbing heavy metals using a bioabsorbent according to one embodiment of the present invention. FIG. In Fig. 5, the amount of lead contained in the wastewater was about 10 ppm. However, as a result of treating the biosorbent adsorbed with heavy metals using the desorbing agent, the pewter ion concentration reached 1200 ppm in the desorption solution. It can be seen that lead ions concentrated more than 100 times by biosorbent have been desorbed.

The bioabsorbent according to the present invention can withstand repeated adsorption / desorption processes because it can maintain strong mechanical and chemical strength. Table 1 shows that the bioabsorbent prepared according to one embodiment of the present invention exhibits excellent adsorbability without changing the adsorption capacity when the adsorption / desorption process is repeated. This shows that the bioabsorbent can be repeatedly used in a similar manner as the ion exchange resin, which is advantageous from the economical point of view.

The following examples are intended to illustrate specific embodiments of the invention and are not intended to limit or limit the scope of protection of the invention. The present invention will be further illustrated by the following examples.

[Example]

[Example 1]

[Preparation of microbial cells into which a oxime group was introduced]

10 g of the powdered wakame was added to 600 ml of a 0.07 molar sodium hydroxide solution and mixed for 30 minutes. 18 ml of epichlorohydrin was added to the mixture and crosslinked at 40 占 폚 for 5 hours. After cooling the solution, the reaction solution was filtered using Watman filter paper and washed with distilled water. The washed microbial cells are placed in 0.1 M phosphate buffer (pH 7.8) and 25% glutaraldehyde solution is added. The oxime solution was added to the solution, and the mixture was reacted at room temperature while stirring for 10 hours. After filtration to remove unreacted material, it was washed with ethanol and dried at room temperature. The degree of cross - linking reaction of microbial cells was indirectly measured using the degree of puffing. The degree of puffing was reduced to more than 50%. The oxime content of the prepared microbial cells was measured by the Pycrcic acid determination method. The result showed that the content of the oxime group (1 g) per cell weight was about 0.2 mol.

Adsorption isotherm curves were obtained using a bioabsorbant in which microbial cells having a oxime group introduced thereto were supported on colloidal silica sol.

FIG. 3 is a graph showing a copper adsorption isotherm curve of a bioabsorbent having oxime groups introduced according to one embodiment of the present invention. FIG. As shown in FIG. 3, the biosorbent incorporating the oxime group exhibits a high adsorption amount of copper, showing an adsorption amount of about 4 times or more at pH 4.5 than the original undisturbed (unlandia) cells which are not chemically modified. However, at lower pH (pH 2.5), the copper adsorption is lower than at higher pH (pH 4.5), but even higher than conventional seaweed cells, which are not chemically modified.

[Example 2]

[Preparation of microbial cells into which phosphoric acid groups are introduced]

100 g of urea and 5 g of phosphoric acid were dissolved in 100 ml of dimethylformamide solution, and then 10 g of seaweed was mixed at 100 ° C for 5 hours to introduce phosphate groups onto the microbial cell surface. After the reactor was terminated, the microorganism cells into which the phosphate group had been introduced were recovered by using a filtration method. The total yield of phosphoric acid was measured by the molybdophosphoric acid production method. The phosphoric acid content varies depending on the type of phosphoric acid used and the results are shown in Table 2. The amount of lead adsorbed by the microbial cells was 900 mg per g of microbial cells. This shows a high adsorption amount of about 2.5 times as compared with the amount of lead adsorption of 350 mg per 1 g of the seaweed to which the phosphate group is not introduced.

The lead adsorbed by the microbial cells into which the phosphate group was introduced was recovered using various desorbents. The desorption efficiency was different depending on the type of desorbent and hydrogen ion concentration. The results are shown in Table 3. It can be seen that when EDTA is used, the most effectively adsorbed lead ions can be recovered.

[Example 3]

[Manufacture of spherical silica beads]

The chemically unmodified microbial cells were mixed with a colloidal silica solution to prepare spherical silica beads. The temperature of the oil chamber was maintained at 80 ° C, and soybean oil was used inside the chamber. 14 ml of acid solution (2.5% sulfuric acid + 20% saline), 100 ml of colloidal silica solution. After a certain amount of powdered microbial cells were mixed, they were put into a droplet state through a dropping device installed at the upper end of the oil chamber. The dropping time was 30 seconds to produce the silica beads that had completed the gelling reaction. The silica beads were collected from the bottom of the thermostat and then aged in a sterilizer at 121 ° C to increase the mechanical strength. After the aging process, the silica beads were extracted with toluene, washed and dried. The silica beads thus produced have a diameter of 2-3 mm.

[Measurement of adsorption capacity]

Using the bioabsorbent prepared in Example 3, lead ions were adsorbed in a solution containing lead ions. The wastewater containing 10 ppm of lead ion was passed through and the results are shown in FIG.

[Recovery experiment]

The adsorbed lead was recovered by adding a 0.5 N hydrochloric acid solution to the bioadhesive adsorbing the lead ion, and the results of the experiment are shown in FIG. The amount of lead contained in the waste water was 10 PPm, but the lead ion concentration in the desorption solution was more than 1200 ppm as a result of desorbing the lead ion adsorbed on the bioabsorbent. This means that the lead ion is concentrated about 100 times or more by the bioabsorbent, and as a result, it can be applied to the concentration and recovery of useful rare metals.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (10)

Characterized in that microbial cells selected from the group consisting of algae, yeast, bacteria, and molds are carried on a colloidal silica sol in the form of spherical silica beads. The biosorbent composition for adsorbing heavy metals according to claim 1, which is chemically modified by introducing a reactor into the microbial cells. The biosorbent composition according to claim 3, wherein the reactor is an oxidizing agent or a phosphate. Mixing microbial cells selected from the group consisting of algae, yeast, bacteria, and fungi with colloidal silica sol; Dropping the mixture into a liquid crystal state through a glass tube installed in an oil thermostat to produce a silica bead carrying microbial cells; Aging the silica beads; Extracting the aged silica beads using a solvent; And drying the silica beads from which the solvent has been extracted; The method of claim 1, wherein the bioabsorbent composition is adsorbed on a support. 5. The method of manufacturing a bioabsorbent composition according to claim 4, wherein the oil filled in the oil chamber is soybean oil. 5. The method of claim 4, wherein the solvent is selected from the group consisting of toluene, methanol and water. 5. The method of claim 4, further comprising the step of adding the mixture to the acid. 5. The method of claim 4, wherein the microorganism cells are chemically modified by introducing a reactor into the microbial cells. A cylindrical oil chamber (1) in which a plurality of glass tubes (3) are installed and filled with oil (8); A thermostat device (2) for maintaining the oil thermostat (1) at a constant temperature; A plurality of glass tubes (3) through which a mixture solution of microbial cells and a colloidal silica gel is dropped and passed through in a droplet state; A dropping device (4) for dropping the colloidal silica gel mixed solution into the glass tube (3) in a droplet state; A temperature regulator 5 for regulating the temperature of the thermostatic chamber 1; And an oil outlet (6) for discharging the oil (8) in the oil thermostat (1) for repairing the silica bead (7). The apparatus for manufacturing silica beads carrying microbial cells . The apparatus of claim 9, wherein the glass tube has a height of about 120 cm and an inner diameter of 0.7 to 1.0 cm.