Silicified modified zero-valent iron and its preparation method and application

Abstract

A silicified modified zero-valent iron, whose surface layer is a silicon-containing oxide layer formed by silicate, which is obtained by the following method: dissolved silicate and micron iron powder are used as raw materials and mixed in proportion, and ball milling under an inert gas atmosphere to obtain the silicified modified zero-valent iron. The invention also discloses the application of silicified modified zero-valent iron in repairing polluted water bodies. The invention uses green silicate as silicon source to carry out surface silicification modification of micron zero-valent iron, which has simple operation, low cost and is convenient for large-scale production. Moreover, the prepared silicified zero-valent iron has good dispersibility, high reduction activity and strong recycling performance, and can be used for the treatment of various polluted water bodies and soil.

Claims

1. A method for preparing a silicified zero-valent iron, comprising: mixing a silicate and micron-sized iron powder in proportion to form a mixture; and ball milling the mixture under an inert gas atmosphere to obtain the silicified zero-valent iron comprising a surface layer of a silicon containing oxide; wherein the silicate comprises one of sodium silicate, potassium metasilicate, a layered crystalline sodium disilicate, a layered crystalline potassium disilicate, or a mixture of two or more thereof, and wherein a ratio of the silicate to the micron-sized iron powder is from 0.02 to 20% based on a molar ratio of silicon to iron.

2. The method of claim 1, wherein the micron-sized iron powder is one of reduced iron powder, pig iron powder, foamed iron powder, or a mixture of two or more thereof, and wherein a particle size of the micron-sized iron powder is from 100 to 800 mesh.

3. The method of claim 1, wherein the ball milling is performed at a speed from 300 to 900 r/min for a duration from 2 to 20 hours.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 is the Fourier transform infrared spectrum characteristics of the silicified modified zero-valent iron of the present invention and the ordinary unsilicified zero-valent iron;

(2) FIG. 2 is the SEM-EDS Mapping of the silicified modified zero-valent iron of the present invention and the ordinary unsilicified zero-valent iron;

(3) FIG. 3 is the Tafel diagram of the silicified modified zero-valent iron of the present invention and the ordinary unsilicified zero-valent iron;

(4) FIG. 4 is the effect diagram of treating hexavalent chromium polluted water body with silicified modified zero-valent iron according to the present invention;

(5) FIG. 5 is the effect diagram of treating hexavalent chromium polluted water with zero-valent iron with different degrees of silicidation modification in Embodiment 2 of the present invention.

(6) FIG. 6 shows the performance comparison of sulfamethazine treated by the silicified micron zero-valent iron in Embodiment 3 of the present invention and the ordinary unsilicified ball milled iron.

(7) FIG. 7 compares the performance of treating dichlorophenol with persulfate activated by different silicified micron zero-valent iron in Embodiment 4 of the present invention.

DETAILED DESCRIPTION

(8) The technical principle of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Embodiment 1

(9) Micron zero-valent iron has low activity to remove heavy metals, and it is easy to form a hydroxyl-rich surface passivation layer, which is not conducive to the adsorption of heavy metals and sustained electron release, resulting in serious loss of activity during repair. The present invention selects environment-friendly soluble silicate (an inorganic component in the background of natural water) as the surface modification regulator of zero-valent iron. Through repeated grinding in the ball milling process, the zero-valent iron oxide layer is broken to form a new silicified oxide layer, and in this process, the particle size of the zero-valent iron is reduced and the specific surface area is increased, and the reduction activity of the zero-valent iron is improved. According to the Fourier transform infrared spectrum characteristics (FIG. 1), compared with the unsilicified ball-milled zero-valent iron (mZVI.sup.BM), the silicified modified zero-valent iron (Si-mZVI.sup.BM) appears an asymmetric stretching peak representing SiO, and a SiOSi in-plane stretching vibration peak, indicating that the silicate reacts with the hydroxyl on the surface of the iron, and the silicate coordinates with the zero-valent iron surface to form a silicified oxide layer, which is further confirmed that Si-mZVI.sup.BM sample has significant abundance of silicon based on the element distribution energy spectrum (FIG. 2). The silicified layer on the surface of the zero-valent iron after silicidation can inhibit the agglomeration of the sample, strengthen the selective adsorption of heavy metal ions, and promote the electron-supply ability of the zero-valent iron (FIG. 3).

(10) Take 5 grams of reduced micron iron powder and 0.16 grams of layered sodium disilicate, mix them and place them in a ball mill tank, ball mill for 4 hours in an argon atmosphere, the ball mill speed is 500 rpm/min, wash and dry.

(11) Take 100 mL of simulated hexavalent chromium polluted water with a concentration of 2.5 g/L as the model pollutant, add 0.2 g of above-prepared iron silicide sample (Si-mZVI.sup.BM) to it, under constant temperature conditions, rotating at 200 rpm/min shaker reaction, after regular sampling. Cr(VI) were determined via the 1,10-phenanthroline colorimetric and 1,5-diphenylcarbazide methods using an UV-visible spectrophotometer.

(12) At the same time, the unsilicified ball milled iron (mZVI.sup.BM) in the same ball milling method was used as a control, the results are shown in FIG. 4. After 100 minutes of reaction, the removal rate of hexavalent chromium in the silicified modified zero-valent iron system treated by silicidation ball milling reached 100%, while the removal rate of hexavalent chromium in the unsilicified iron system was less than 10%.

Embodiment 2

(13) Take 10 grams of reduced micron iron powder, add 0, 0.165, 0.33, 0.66, 1, 1.3 grams of sodium silicate respectively and mix them in a ball mill tank, and ball mill under argon atmosphere for 5 hours, the ball mill speed is 550 rpm/min, wash and dry, marked as mZVI.sup.BM, 1 #mZVI.sup.BM, 2 #mZVI.sup.BM, 3 #mZVI.sup.BM, 4 #mZVI.sup.BM and 5 #mZVI.sup.BM respectively.

(14) Take 100 mL of simulated hexavalent chromium polluted water with a concentration of 2 g/L as the restoration object, add 0.2 g of above-prepared iron silicide sample (Si-mZVI.sup.BM) to it, under constant temperature conditions, rotating at 200 rpm/min shaker reaction, after regular sampling, use a spectrophotometer to determine the content of hexavalent chromium, the results are shown in FIG. 5. After 60 minutes of reaction, the removal rate of hexavalent chromium by 3 #mZVI.sup.BM reached 97%, followed by the removal rate of hexavalent chromium by 4 #mZVI.sup.BM reached 72%, the removal rate of hexavalent chromium by all silicified zero-valent iron was stronger than that of unsilicified mZVI.sup.BM.

Embodiment 3

(15) In this embodiment, silicified modified zero-valent iron is used as a catalytic activator, and persulfate is used as an oxidant to treat organic wastewater. The key feature of silicified modified zero-valent iron is that its surface and interface are rich in silanol groups.

(16) Take 10 grams of reduced micron iron powder and 0.64 grams of layered sodium disilicate, mix them and place them in a ball mill tank, ball mill for 4 hours in an argon atmosphere, the ball mill speed is 550 rpm/min, at the same time, use the same ball milling method to prepare unsilicified ball milled iron (mZVI.sup.BM) as a control, wash and dry. X-ray photoelectron spectroscopy and infrared spectroscopy were performed on the chemical composition of the two surfaces (see FIG. 6 and FIG. 7), the Si-mZVI.sup.BM surface interface has a significant content of silicon.

(17) Taking 100 mL of the water contaminated by a simulated antibiotic (sulfamethazine) with a concentration of 10 mg/L as the restoration object, add 0.02 grams of the ball milled iron prepared above and 1.5 mM sodium persulfate to it. Under the constant temperature condition, and shaker reaction with rotating speed of 200 rpm/min, after regular sampling, the content of sulfamethazine is determined by high performance liquid chromatography, and the result is shown in FIG. 6. After 32 minutes of reaction, the removal rate of sulfamethazine in the zero-valent iron system treated by silicified ball milling reached 100%, and the removal rate of hexavalent chromium in the unsilicified ball milled iron system was less than 20%, while the removal of single persulfate and iron silicate is very small.

Embodiment 4

(18) Take 10 g of reduced micron iron powder, add 0, 0.16, 0.33, 0.66, 1, 2.6 g of sodium silicate respectively, mix them and place in a ball mill tank, ball mill in a vacuum environment for 5 hours, the ball mill speed is 550 rpm/min, wash and dry, marked as mZVI.sup.BM, 1 #Si-mZVI.sup.BM, 2 #Si-mZVI.sup.BM, 3 #Si-mZVI.sup.BM, 4 #Si-mZVI.sup.BM and 5 #Si-mZVI.sup.BM respectively.

(19) Taking 100 mL of simulated dichlorophenol-contaminated water with a concentration of 10 mg/L as the restoration object, add 0.03 g of the ball milled iron sample prepared above and 2 mM potassium persulfate to it, under constant temperature conditions, and shaker reaction with rotating speed of 200 rpm/min, after regular sampling, the high-performance liquid chromatography was used to determine the content of dichlorophenol, the results are shown in FIG. 7. After 60 minutes of reaction, the removal rate of dichlorophenol by 4 #Si-mZVI.sup.BM and 5 #Si-mZVI.sup.BM reached 95%, and the removal efficiency of dichlorophenol by 2 #Si-MZVI.sup.BM and 3 #Si-MZVI.sup.BM activated persulfate was lower than 5 #Si-mZVI.sup.BM, and the removal of dichlorophenol by all activated persulfate systems with silicified zero-valent iron was stronger than that by mZVI.sup.BM with unsilicified ball-milled iron.

(20) The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.

(21) These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.