Reusable porous Na(Si2Al)O6.xH2O/NiFe2O4 structure for selective removal of heavy metals from waste waters

Abstract

The 3-Glycidoxypropyltrimethoxysilane (GPTMS) decorated magnetic more-aluminosilicate shell Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 structures were hydrothermally prepared and were well characterized by different analysis methods. The XRD patterns were truly proved the formation of the aluminosilicate layer on the surface of the magnetic cores. In addition to the TGA curve which implied on the presence of the GPTMS organic segment, nitrogen adsorption-desorption isotherms demonstrated that the final sample has high specific surface area. The products were incredibly able to remove the toxic lead and cadmium ions from the wastewaters. Furthermore, the mechanism of the sorption and the role of GPTMS in enhancing the sorption capacity of the structures were comprehensively discussed.

Claims

1- A method of making a high capacity reusable magnetic core-aluminosilicate shell sorbent for selective purification of wastewaters containing heavy metal ions, comprising the steps of: a) preparing 50 ml transparent solution containing Ni(NO.sub.3).sub.2 and FeCl.sub.3 (corresponding to Ni.sup.2+/Fe.sup.3+ molar ratio of 1:2); b) adding said transparent solution to NaOH solution 2 M drop by drop under vigorous stirring; c) adding a mixture containing sufficient amount of EG and TMAOH the solution of step b, above suspension drop wise; d) Stirring the above combined mixture in step c for 2 hrs, then immediately transferring it into an autoclave and keeping it at 200 C. for 8 hrs; e) Collecting black solid particles by an external magnet, repeatedly washing said particles with de-ionized water, and drying them at 80 C. for 6 hrs.

2- The method of claim 1, further comprising the steps of preparing Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 particles as follows: f) dissolving Al(NO.sub.3).sub.3.9H.sub.2O in 30 mL of NaOH 2 M containing 0.9 g of cetyl trimethylammonium bromide (CTAB) and 5.05 mL of tetraethyl orthosilicate (TEOS); g) then magnetically stirring it for 90 min; h) Dispersing Magnetic particles (1.0 g) of the above mixture in 35 mL of water, ultrasonicating it for 20 min; i) Combining said magnetic particles to said earlier suspension, and stirring them for 24 hrs; j) Then immediately transferring the above reluctant mixture to a 200 mL autoclave and maintaining it in a preheated oven at 423 K for 48 hrs, in order to complete all the necessary reactions; k) after completion of said reaction, then magnetically separating product in step J, washing it with double distilled water, and drying it at 353 K overnight, creating a powder; wherein said powder is then calcined at 773 K for 3 hrs.

3- The method of claim 2, further comprising the following steps: l) Outer shell of said Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 particles were then modified with 3-glycidoxypropyltrimethoxysilane (GPTMS) in a basic medium; m) the as-prepared samples is dispersed in NaOH solution 0.1 M and ultrasonicated for 10 min; n) said suspension is then transferred into a flask bottle placed in 20 C., and said GPTMS is slowly added while vigorously being stirred and treated at 65 C. for another 2 hrs; o) Finally, the resulting product is separated with a permanent magnet, washed thoroughly with distilled water, and dried at 80 C.; therefore successfully growing Porous aluminosilicate shell layer on a surface of nickel ferrite particles by hydrothermal crystallization.

4- The method of claim 3, wherein SEM analysis shows a homogeneous formation of spherical aluminosilicate shell on said surface of nickel ferrite cores.

5- The method of claim 4, wherein an Inner surface of channels of said inorganic porous shell are successfully decorated with GPMTS organic agent.

6- The method of claim 5, wherein said final decorated Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 product shows great capacity toward selective removal of heavy metal ions from said wastewaters.

7- The method of claim 6, wherein said final product comprises higher tendency and efficiency, for removal of cadmium ions than the lead ones.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is the results of the TGA analysis for the final product and was very helpful to be sure of the organic decoration process;

[0020] FIG. 2 is the XRD pattern of the final product which showed the crystalline phase of the core-shell segments;

[0021] FIG. 3 is the SEM images of the final spherical product;

[0022] FIG. 4 is the results of the VSM analysis method and shows that the magnetic saturation has decreased significantly by surface modification and layer growth;

[0023] FIG. 5A is the removal of cadmium and lead ions from the wastewater over the final products;

[0024] FIG. 5B is the removal of cadmium and lead ions from the wastewater over the unmodified Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 structure;

[0025] FIG. 6 is the likely routes for removal of heavy metal ions over the final product;

[0026] FIG. 7 is the representative effect of epoxy cycle opening on the removal efficiency.

DETAILED DESCRIPTION OF THE INVENTION

[0027] NiFe.sub.2O.sub.4 particles were prepared by a simple coprecipitation-hydrothermal method in a 200 ml stainless steel autoclave with a Teflon liner under autogenous pressure as following: a 50 ml transparent solution containing Ni(NO.sub.3).sub.2 and FeCl.sub.3 (corresponding to Ni.sup.2+/Fe.sup.3+ molar ratio of 1:2) was prepared and added to NaOH solution 2 M drop by drop under vigorous stirring. Afterward, a mixture contained suitable amount of EG and TMAOH was added to the above suspension drop wise. After 2 h of stirring, the mixture was immediately transferred into the autoclave and kept at 200 C. for 8 h and then the black solid particles were collected by an external magnet, repeatedly washed with de-ionized water, and dried 80 C. for 6 hrs.

[0028] The Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 particles were also prepared as following: Al(NO.sub.3).sub.3.9H.sub.2O was dissolved in 30 mL of NaOH 2 M contained 0.9 g of cetyl trimethylammonium bromide (CTAB) and 5.05 mL of tetraethyl orthosilicate (TEOS) and then magnetically stirred for 90 min. Magnetic particles (1.0 g) was dispersed in 35 mL of water, ultrasonicated for 20 min, and then added to the earlier suspension. After 24 h of stirring, the reluctant mixture was immediately transferred to a 200 mL autoclave and maintained in a preheated oven at 423 K for 48 h. after the completion of the reaction, the product were magnetically separated, washed with double distilled water, and dried at 353 K overnight. Finally, the powder calcined at 773 K for 3 h.

[0029] Outer shell of the Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 particles were then modified with 3-glycidoxypropyltrimethoxysilane (GPTMS) in the basic medium. The as-prepared samples were dispersed in NaOH solution 0.1 M and ultrasonicated for 10 min. The suspension was transferred into a flask bottle placed in 20 C., and GPTMS was slowly added while vigorously being stirred and treated at 65 C. for another 2 h. Finally, the resulting product was separated with the help of the permanent magnet, washed thoroughly with distilled water, and dried at 80 C.

[0030] The removal tests were carried out in a 1 L batch reactor with the initial X(II) concentration (XPb and Cd) of 20 mg/L at the initial pH value 5. The sorbent mass was fixed at 0.1 g. The reactor was stirred with a magnetic stirrer operated at 300 rpm. At predetermined time intervals, 3 mL samples were taken from the reactor, centrifuged and residual X(II) concentration was measured with an atomic absorption spectrophotometer (AAS). By performing appropriate material balance, the quantity of X(II) adsorbed at the selected time intervals was determined and used for kinetic analysis.

[0031] The TGA curve of the final product depicts a significant weight loss from room temperature up to around 250 C. which can be attributed to the removal of GPTMS agents intercalated in the aluminosilicate pores (FIG. 1). We also observed two insignificant losses which probably are due to release strongly bonded extra organic components into the core-shell structure.

[0032] The XRD pattern of the final sample is shown in FIG. 2. These patterns were recorded on Bruker D8 advance X-ray diffractometer with CuK irradiation (=0.15406). The sharp peaks at 2=30.2, 35.1, 44.2, 90.6 and all the others remarked with red-like color are attributed to the crystal phase of the nickel ferrite magnetic particles. Hydrated aluminosilicate characteristic peaks can be observed at 2=16.7, 26.2, 30.9, 41, and all other remarked with green color. And there was no observed any extra peak in the XRD patters after surface modification process with GPTMS, as we also didn't expect to see any change after doing this section.

[0033] Braun Emmett Teller (BET)-Barrett-Joyner-Halenda (BJH) analysis was carried out to find the specific surface area and the pore size distribution of the final spherical core-shell particles which its SEM images are shown in FIG. 3. According to the SEM micrographs, the prepared samples have unique and spherical shape and the particles size are between 5-10 m. The results of BET analysis showed that the specific surface area and the pore size were 230.1 m.sup.2 g.sup.1 and 0.32 nm, respectively. The observed hysteresis loop from the N.sub.2 adsorption-desorption curve was also proved that the sample is highly porous.

[0034] The magnetic properties of the structures were measured by Vibrating Sample Magnetometer (VSM) and the results are indicated in FIG. 4. According to the obtained results, magnetic particles and final sample have the magnetic saturation values of 48.5 and 10.8 emu/g, respectively, which verify that the final products have still high magnetization and they are easy to separate after reusing. This is so important for reusing the sorbent during the subsequent treatment of the wastewater contained heavy metals.

[0035] The sorption curves of Pb.sup.2+ and Cd.sup.2+ over the prepared products are shown in FIG. 5. While the removal efficiency is less over unmodified Na(Si.sub.2Al)O.sub.6.xH.sub.2O/NiFe.sub.2O.sub.4 sample, the results demonstrated that the decoration of the porous shell with GPTMS increased it significantly even though this modification with organic agent reduced the specific surface area smoothly. The metal ions of the hydrated aluminosilicate channels (Na.sup.+) could be exchanged with the present ions in the wastewater.

[0036] As the final product is used as sorbent, in addition to the mentioned case, the heavy metal ions could be chemically trapped into the GPTMS-decorated pores of the surface via chemical sorption. It can be observed in all cases, the removal efficiency of Cd.sup.2+ is higher than Pb.sup.2+ ions. The radius size of Cd.sup.2+ (95 pm) is less than Pb.sup.2+ (119 pm) which makes it more suitable for effective ion exchange and also more effective bonding with organic groups on the surface. Even though, the presence of the GPTMS organic layer on the surface can block some channels and causes to reduce the surface area insignifacntly, the chemical sorption of the first layer and the physical sorption of the next layers on the surface would be likely. Thus, the highest removal is achieved with the modified structure. FIG. 6 explained schematically the overall route of the heavy metal ions removal over the products.

[0037] As an extra study, we found that the removal efficiency enhanced when the initial pH of the medium was increased. The pH of the aqueous solution is an important operational parameter in the adsorption process because it affects the solubility of the metal ions, concentration of the counter ions on the functional groups of the adsorbent and the degree of ionization of the adsorbate during reaction. The active sites on an adsorbent can either be protonated or deprotonated depending on the pH while at the same time the adsorbate speciation in a solution depends on the pH too. Lead for example, exists as Pb.sup.2+, PbOH.sup.+ and Pb(OH).sup..sub.3 depending on pH. Hydrated aluminosilicates are highly selective for H.sub.3O.sup.+ ions when they are predominant in the solution. Thus, at lower pH values the H.sub.3O.sup.+ ions compete with the metal ions for exchanging in the channels. Moreover, the ethylene oxide functional group of GPTMS on the surface affected in high pH and increases the chemical sorption via the below mechanism (FIG. 7):

[0038] The materials easily separated from the medium by an external magnetic field after the first treatment time, washed with a NaCl solution, dried, and reused repeatedly. This study showed that the sorption capacity under the same conditions for the next times decreased smoothly. If one takes the maximum sorption capacity of the final product 100% during the first time, it reduces to 93, 89, 78, 78, and 73% during the next usages. This decease can attribute to the detachment of GPTMS agents during the repeated using which fades out the chemical sorption route of the heavy metal ions over the sorbent.

[0039] Sorption activity of the sample is greatly dependent of the media acidity and should be optimized to get the best efficiency. The effect of the epoxy cycle of GPTMS segment on increasing the removal efficiency was mechanistically discussed. The final product indicated promising capacity during the recycling experiments of the purification of the heavy metal-contained wastewaters.