This paper is devoted to the features of the synthesis and applications of suspension iron(III)-based sorbents in water treatment. The problems of toxic impurities of the drinking water, especially soluble arsenic compounds or different organic disinfection by-products, are very acute not only for Ukraine, but for many other countries too. So, it is very important to find simple and effective method to treat polluted natural waters to the required quality. The comparison of different treatment methods for removal of arsenic compounds and humates was made, as a result of which it was determined that the usage of adsorbents, especially fine particle iron-based sorbents, is very effective in natural organic matter removal and some other pollutants. Fine particle iron-based adsorbents are effective for arsenic removal due to its chemical structure. These materials removed arsenic compounds by chemisorption processes and immobilization of arsenate and arsenite ions in the insoluble form of ferric arsenate. Thus, the aim of the work was to develop the adsorbent for effective removal of arsenic compounds and humates from natural waters. We synthesized 7 suspension iron(III)-based sorbents by homogeneous precipitation from FeCl3 solution by thermal hydrolysis of urea. The efficiency of synthesized samples was checked by adsorption tests (humates and arsenite removal) and capillary suction time test. Iron(III) oxyhydroxide was the main phase of the most effective fine particle adsorbents. Applications on natural water showed that the synthesized iron(III) oxyhydroxide effectively removed arsenic compounds not only from model waters, but also from natural water with reaching of regulatory requirements.

Different factors often make the surface and ground water sources unfit for drinking purpose. Arsenic is often found in natural waters and makes it unsuitable for consumption without special treatment. Arsenic is released into water bodies as a result of human activity and natural processes. There are the following natural ways of arsenic release into ground water and atmosphere: volcanic activity, forest fires and leaching from arsenic rocks and minerals. The use of arsenic pesticides, processing of sulphide ore production, arsenic dyes and pigments production, producing of arsenic are encountered among anthropogenic sources. The terrible influence of long-acting arsenic compounds on the body (cancer, endocrine and neurological disorders, etc.) make dearsenication the necessary stage of the drinking water treatment. The problem of arsenic compoundspresence in natural waters is the challenge not only for underdeveloped countries where water treatment is performed using outdated methods, but also for many developed countries which require more economically and environmentally effective methods of water purification from arsenic compounds.

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Membrane technologies are very popular both in drinking water and wastewater treatment due to their significant advantages. However, colloidal fouling is one of the main disadvantages of low-pressure membranes. Fine particle ferric oxyhydroxide effectively protected membrane and adsorb humates, phosphates, arsenates, etc. Dividing of adsorption and microfiltration into two stages was the recommended regime. Mixing with adsorbent was the first one and separation on the membrane was the second stage. The adsorbent with immobilized impurities formed protective layer on the membrane surface. The non-adsorbed organic matter was left on this thickness. During backwash, water flow removed the adsorbent with immobilized pollutants. Afterwards, membrane was as clean as before filtration.

The paper is devoted to the development of a method for obtaining and using iron-containing sorption materials for the effective removal of arsenic compounds of different oxidation states from an aqueous medium. It is known that arsenic compounds have a harmful effect on biota due to high toxicity. The paper theoretically and experimentally substantiates the choice of iron-containing materials as the main sorbent material for arsenic compounds removal from the aqueous medium. A series of iron-containing adsorbents, including powder, activated carbon-based granular and suspension sorbents, was synthesized by different methods (heterogeneous and homogeneous precipitation). Experimental studies have confirmed that the adsorption of arsenate ions on iron-containing sorption materials corresponds to the pseudo-second order of the reaction (R2=0.999), which is inherent in adsorption processes. It was determined that oxyhydroxide sorption materials obtained by the homogeneous precipitation demonstrate higher sorption activity (up to 70 mg/g for As(III) and over 70 mg/g for As(V)). It was found that activated carbon-based iron-containing sorption materials showed approximately 2 times lower efficiency than powder iron(III) oxide, iron(III) oxyhydroxide and amorphous iron(III) hydroxide. It was shown that the use of microfiltration membranes is promising for the removal of spent suspension iron-containing sorption materials. Experimental studies have confirmed that the use of the combination “fine-particle iron(III) oxyhydroxide/membrane” allows removing arsenic compounds from contaminated water to the sanitary requirements level (less than 10 μg As/l) and separating effectively the spent fine-particle sorbent from water