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

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.