Separation of Arsenic from Liquid Media

33

As

Water/Wastewater

Arsenate, As5+, forms anionic complexes so it can be removed from solutions with a strong base anion exchange resin like DOWEX™ 21K XLT Resin. For streams that have a high organic content and are prone to surface fouling DOWEX MARATHON™ MSA Resin is recommended. Unfortunately, arsenate is very weakly ionic so it is not selectively removed and resin capacity will be limited in the presence of the other anions. Arsenate can also be removed with reverse osmosis (RO) membranes.

At pH 6.5 to 8.5, arsenite, As3+, is present as uncharged arsenious acid, H3AsO3, under reducing conditions. Therefore, it needs to be further oxidized to arsenate for removal as described above. Oxidation can be accomplished by air stripping the water stream, by addition of an oxidizing agent such as peroxide, or by ozonolysis.



Selective Removal

Arsenic removal is reported with immobilized metals on a variety of ion exchange supports.

Chanda1 reports using the ferric ion form of DOWEX™ M4195 Chelating Resin to remove arsenic from solution.

Chanda2 similarly reports the use of an iminodiacetic acid chelating/selective resin such as AMBERLITE™ IRC748i Resin in the ferric ion form for this same purpose.

Ramana3 reports using DOWEX M4195 in the copper form.


Drinking Water

In drinking water applications, selective removal of arsenate (As5+) can be achieved with ADSORBSIA™ As600 Titanium-based Adsorbent Media. Designed to be non-regenerable, ADSORBSIA As600 can be disposed in compliance with the EPA TCLP tests for disposal.

DOW™ Ultrafiltration Modules have also been used to remove coagulated iron-arsenate complexes from drinking water.

Note: Arsenate is weakly held by anion exchange resins and is easily displaced by sulfate. This may result in effluents having extremely high arsenate levels as arsenate is displaced by these competing anions. Currently there are no sensors that can measure the arsenate breakthrough and switch a system into regeneration mode to prevent high concentrations of arsenic from potentially ending up in the produced drinking water. Therefore, care must be taken when employing anion exchange resin as the primary method of removing arsenate from drinking water.

These products may be subject to drinking water application restrictions in some countries. Please check the application status before use and sale. For more information see our regulatory information.

1 "Ligand Exchange Sorption of Arsenate and Arsenite anions by chelating resins in ferric ion form. I. Weak-base chelating resin DOWEX XFS-4195." Chanda, M.; O'Driscoll, K.F.; Rempel, G.L., Reactive Polymers, 7, 251-61 (1998).

2 "Ligand Exchange Sorption of Arsenate and Arsenite anions by chelating resins in ferric ion form. II. Iminodiacetic chelating resin CHELEX 100." Chanda, M.; O'Driscoll, K.F.; Rempel, G.L., Reactive Polymers, 8, 85-95 (1998).

3 "Removing selenium(IV) and arsenic(V) oxyanions with tailored chelating polymers. " Ramana, Anuradha; Sengupta, Arup K.. ERM Inc., Exton, PA, USA. J. Environ. Eng. (N. Y.) (1992), 118(5), 755-75.

Arsenic is commonly found as the oxidized species of arsenate (As5+) and arsenite (As3+). The current US EPA standard for drinking water is 10 ppb.