Name: removal of arsenic using a cationic polymer gel impregnated with iron hydroxide
Uploaded: 2019-06-28T14:00:00
Description: Watch this Scientific Journal Video about Removal of Arsenic Using a Cationic Polymer Gel Impregnated with Iron Hydroxide at JoVE.com

This research was supported by the JSPS KAKENHI Grant Number (26420764, JP17K06892). The contribution of Ministry of Land, Insfrastructure, Transport and Tourism (MLIT), Government of Japan under &#8216;Construction Technology Research and Development Subsidy Program&#8217; to this research is also recognized. &#160;We also acknowledge the contribution of Mr. Kiyotaka Senmoto to this research. Ms. Adele Pitkeathly, Senior Writing Advisor Fellow from Writing Center of Hiroshima University is also acknowledged for English corrections and suggestions. This research was selected for oral presentation in 7th IWA-Aspire Conference, 2017 and Water and Environment Technology Conference, 2018.

CAUTION: Arsenic is extremely toxic. Please use gloves, long sleeve clothing, and experimental goggles at all times during the experiment to prevent any contact of arsenic solution with the skin and eyes. If arsenic comes into contact with any part of your body, wash it immediately with soap. Additionally, please clean up the experimental surroundings regularly so that you and others do not come into contact with arsenic, even when the experiment is not being performed. The symptoms of arsenic exposure may appear after a...

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The main advancement of our developed method is the unique design strategy of the gel composite. The purpose of our gel preparation method was to maximize the amount of iron content in the gel. During the preparation, we added FeCl3 and NaOH to the &#8220;initiator solution&#8221; and the &#8220;monomer solution,&#8221; respectively. Once the monomer solution was mixed with the initiator solution, there was a reaction between FeCl3 and NaOH, producing FeOOH inside the gel. This phenomenon ensured ma...

Water pollution is a great environmental concern, motivating researchers to develop methods for removing contaminants such as arsenic from wastewaster1. Among all the reported methods, adsorption processes are a relatively low cost approach for heavy metal removal2,3,4,5,6,7. Iron oxyhydroxide powders are considered to be one of the most efficient adsorbents for extracting arsenic from aqueous solutions8,9. Still, these materials suffer from a number of drawbacks, including early saturation times and toxic synthetic precursors. Additionally, there is a severe adverse effect in the water quality when these adsorbents are used for a long period of time10. An additional separation process, such as sedimentation or filtration, is then needed to purify the contaminated water, which increases the cost of the production further8,11.
Recently, researchers have developed polymer gels such as cationic hydrogels, microgels, and cryogels that have demonstrated efficient adsorption properties. For example, an arsenic removal rate of 96% was achieved by the cationic cryogel, poly(3-acrylamidopropyl) trimethyl ammonium chloride [p(APTMACl)]12. Additionally, at pH 9, approximately 99.7% removal efficiency was achieved by this cationic hydrogel13. At pH 4, 98.72 mg/g of maximum arsenic adsorption capacity was achieved by the microgel, based on tris(2-aminoethyl) amine (TAEA) and glyceroldiglycidyl ether (GDE), p(TAEA-co-GDE)14. Although these gels demonstrated good adsorption performances, they failed to effectively remove arsenic from water at neutral pH levels, and their selectivities in all studied environments were not reported15. A maximum adsorption capacity of 227 &#956;g/g of was measured when Fe(III)-Sn(IV) mixed binary oxide-coated sand was used at a temperature of 313 K and a pH of 716. Alternatively, Fe-Zr binary oxide-coated sand (IZBOCS) has also been used to remove arsenic and achieved a maximum adsorption capacity of 84.75 mg/g at 318 K and a pH of 717. Other reported adsorbents suffer from low adsorption performances, lack of recyclability, low stability, high operational and maintenance costs, and the use of hazardous chemicals in the synthesis process4.
We sought to address the above limitations by developing a material with improved arsenic adsorption performance, high selectivity in complex environments, recycling capability, and efficient activity at neutral pH levels. Therefore, we developed a cationic gel composite of N,N-dimethylamino propylacrylamide methyl chloride quaternary (DMAPAAQ) gel and iron(III) hydroxide (FeOOH) particles as an adsorbent for arsenic removal. We chose to combine FeOOH with our gel because FeOOH increases the adsorption of both forms of arsenic18. In this study, our gel composite was designed to be non-porous and was impregnated with FeOOH during preparation. In the next section, the details of the gel preparation method, including our strategy for maximizing the content of FeOOH is discussed further.

<table>
	<tbody>
		<tr>
			<td>N,N&#8217;-dimethylamino propylacrylamide, methyl chloride quaternary (DMAPAAQ) (75% in H2O)</td>
			<td>KJ Chemicals Corporation, Japan</td>
			<td>150707</td>
			<td></td>
		</tr>
		<tr>
			<td>N,N&#8217;-Methylene bisacrylamide (MBAA)</td>
			<td>Sigma-Aldrich, USA</td>
			<td>1002040622</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium sulfite (Na2SO3)</td>
			<td>Nacalai Tesque, Inc., Japan</td>
			<td>31922-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium sulfate (Na2SO4)</td>
			<td>Nacalai Tesque, Inc., Japan</td>
			<td>31916-15</td>
			<td></td>
		</tr>
		<tr>
			<td>Di-sodium hydrogenarsenate heptahydrate(Na2HAsO4.7H20)</td>
			<td>Nacalai Tesque, Inc., Japan</td>
			<td>10048-95-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Ferric chloride(FeCl3)</td>
			<td>Nacalai Tesque, Inc., Japan</td>
			<td>19432-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide(NaOH)</td>
			<td>Kishida Chemicals Corporation, Japan</td>
			<td>000-75165</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium peroxodisulfate (APS)</td>
			<td>Kanto Chemical Co. Inc., Japan</td>
			<td>907W2052</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid (HCl)</td>
			<td>Kanto Chemical Co. Inc., Japan</td>
			<td>18078-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride (NaCl)</td>
			<td>Nacalai Tesque, Inc., Japan</td>
			<td>31320-05</td>
			<td></td>
		</tr>
	</tbody>
</table>

removal of arsenic using a cationic polymer gel impregnated with iron hydroxide

In this work, we prepared an adsorbent composed of a cationic polymer gel containing iron hydroxide in its structure designed to adsorb arsenic from groundwater. The gel we selected was the N,N-dimethylamino propylacrylamide methyl chloride quaternary (DMAPAAQ) gel. The objective of our preparation method was to ensure the maximum content of iron hydroxide in the structure of the gel. This design approach enabled simultaneous adsorption by both the polymer structure of the gel and the iron hydroxide component, thus, enhancing the adsorption capacity of the material. To examine the performance of the gel, we measured reaction kinetics, carried out pH sensitivity and selectivity analyses, monitored arsenic adsorption performance, and conducted regeneration experiments. We determined that the gel undergoes a chemisorption process and reaches equilibrium at 10 h. Moreover, the gel adsorbed arsenic effectively at neutral pH levels and selectively in complex ion environments, achieving a maximum adsorption volume of 1.63 mM/g. The gel could be regenerated with 87.6% efficiency and NaCl could be used for desorption instead of harmful NaOH. Taken together, the presented gel-based design method is an effective approach for constructing high-performance arsenic adsorbents.

Figure 1 describes the experimental setup for the preparation of the DMAPAAQ+FeOOH gel. Table 1 illustrates the compositions of the materials involved in the preparation of the gel.
Figure 2 shows the relation of contact time with the adsorption of arsenic by the DMAPAAQ+FeOOH gel. In the figure, the amount of adsorption of arsenic was examined at 0.5, ...

Watch this Scientific Journal Video about Removal of Arsenic Using a Cationic Polymer Gel Impregnated with Iron Hydroxide at JoVE.com

Removal of Arsenic Using a Cationic Polymer Gel Impregnated with Iron Hydroxide

In this work, we prepared an adsorbent composed of the cationic N,N-dimethylamino propylacrylamide methyl chloride quaternary (DMAPAAQ) polymer gel and iron hydroxide for adsorbing arsenic from groundwater. The gel was prepared via a novel method designed to ensure the maximum content of iron particles in its structure.

In this work, we prepared an adsorbent composed of a cationic polymer gel containing iron hydroxide in its structure designed to adsorb arsenic from ...

The main advantages of this procedure are that the gel selectively adsorbs arsenic from groundwater at higher arsenic concentrations than the other techniques and the gel can be regenerated. Demonstration of this method is critical because the preparation of the gel and the absorption experiments need to be visualized to replicate the experiments. Arsenic is found in the groundwater of more than 20 countries.The implication of this technique can be extended toward the challenge of removing arsenic from contaminated water. This method can also be applied to the treatment of industrial effluent contaminated with arsenic. When trying this technique for the first time, follow the precautions strictly at all times.The formation of the gel block may be challenging if the solutions are not mixed properly and proportionately. Dry two 20 milliliter measuring flasks and two 20 milliliter beakers equipped with magnetic stir bars. Transfer 4.13 grams of DMAPAAQ, 0.31 grams of N, N'prime methylenebisacrylamide, 0.5 grams of sodium sulfite, and 3.36 grams of sodium hydroxide to one 20 milliliter beaker.Dissolve the solution wholly in distilled water as solvent, stirring it for 30 minutes with the magnetic stir bar. Transfer the mixture from the beaker to one 20 milliliter measuring flask, and add distilled water to generate a 20 milliliter solution. Label the solution as the monomer solution.Similarly, take 0.54 grams of ammonium peroxodisulfate and 7.57 grams of iron chloride in another 20 milliliter beaker. Dissolve the solution completely in distilled water, stirring it for 30 minutes with a magnetic stir bar. Transfer the mixture from the beaker to another 20 milliliter measuring flask.And add distilled water to compose a 20 milliliter solution. Label the solution as the initiator solution. After preparing the experimental setup as diagrammed in the text protocol, transfer the solutions into the respective 20 milliliter separating funnels.Purge the solutions with nitrogen gas for 30 minutes. Mix the solutions together, and stir them in a 50 milliliter test tube with an electric stirrer. Then, place the mixture into a chiller maintained at 10 degrees Celsius for four hours.Take out the gel block from the test tube and place it on a flat cutting board. Get the gel block into a cubic shape five millimeters in length. Soak the gel slices with deionized water for 24 hours to remove the impurities.The next day, spread the gel slices onto a Petri dish and dry them at room temperature for 24 hours. Place the Petri dish with the gel slices in the oven at 50 degrees Celsius for 24 hours. Dry five 40 milliliter plastic containers.Then, measure and place 20 milligrams of dried gel in each 40 milliliter plastic container. Add 40 milliliters of disodium hydrogen arsenate heptahydrate solution to each container at a different concentration. Keep the containers in the stirrer at 20 degrees Celsius and 120 RPM for 24 hours.Collect a five milliliter sample from each container and place in a plastic tube using a micro pipette. Measure the equilibrium arsenic levels in the solutions using high performance liquid chromatography, or HPLC. Use a four by 200 millimeter analytical column, a four by 50 millimeter guard column, and a four millimeter suppressor.For adsorption analysis, add 20 milligrams of dried gel to a dried 40 milliliter plastic container. Then, add 40 milliliters of a 0.2 millimolar disodium hydrogen arsenate heptahydrate solution to the container. Keep the container in the stirrer at 20 degrees Celsius and 120 RPM for 24 hours.Then, collect a five milliliter sample in a plastic tube using a micro pipette. Evaluate the equilibrium arsenic level in the solution using HPLC as before. To clean the gel, first obtain a mesh sieve.Carefully collect the fragile gel pieces, one at a time so that they do not break, and place them in the mesh sieve. Wash the gel for a minimum of five times, using deionized water, so that any remaining arsenic on the surface of the gel is washed away. For desorption analyses, carefully transfer the fragile gel pieces into a dried 40 milliliter plastic container.Add 40 milliliters of a 0.5 molar sodium chloride solution to the container. Keep the container in the stirrer at 20 degrees Celsius and 120 RPM for 24 hours. Collect a five milliliter sample in a plastic tube using a micro pipette, and evaluate the equilibrium arsenic level in the solution using HPLC as before.Repeat the process for eight complete cycles, with each cycle including two rounds of the absorption and desorption analyses steps, separated by gel cleaning steps. The arsenic absorption amount by the cationic polymer gel containing iron hydroxide was plotted at different concentrations of arsenic. The results show that the maximum arsenic adsorption capacity of the gel was 1.36 millimoles per gram.The data are fit with the Langmuir isotherm model. The selective adsorption of arsenic was examined with coexisting sulfate anion. The results show that even if sulfate anion was present in the solution of gel, DMAPAAQ plus iron oxide adsorbed arsenic selectively because of the iron oxide components in the gel structure.The re-usability of the gel was examined for eight continuous days using arsenic solutions for adsorption and sodium chloride for desorption processes. A regeneration efficiency of 87.6%was calculated from the regeneration efficiency from the adsorption data on day one and day seven. Arsenic is extremely hazardous.Please use gloves, long-sleeved clothing, and experimental goggles at all times during the experiment to prevent any contact of arsenic solution with the skin and eyes.

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