| Heavy metals are extensively used in industrial production in the last few decades. With their mining, processing and application, heavy metals were released to aquatic environment, causing serious pollution of received water bodies and consequently, posing threat to the ecosystem and human health. Therefore, the removal of heavy metals from water is attracting more and more attention.Arsenic, a well-known highly toxic and carcinogenic element, is ubiquitous in the environment. In natural environments, arsenic exists in two predominant species, arsenate [As(V)] and arsenite [As(III)]. As(III) is much more toxic, more soluble, more mobile and therefore more difficult to be removed than As(V). Lead, another highly toxic and extensively used element, has seviously adverse effect on human health. Ingestion of lead may result in many diseases and particlully influence children’s mental development. Lead mainly exists in bivalent cation form in natural water. These two kinds of heavy metals are typically representative and their removal gets increasing attentions.Compared with other traditional treatment technologies for arsenic and lead removal, adsorption technique is considered one of the most popular and practical methods for arsenic and lead removal due to its high efficiency, low cost and reusable characteristics. However, now existing adsorption material is often difficult to remove arsenic and lead wastewater at the same time, namely, it is hard to purify sewage containing anionic and cationic heavy metal pollutants simultaneously. Therefore, it is necessary to develop new, cost-effective, efficient heavy metal removing materials to reduce the cost of water treatment.A multifunctional absorbent material —— Ti-Mn binary oxide which combined the high adsorption features to As(V) of titanium oxides, the high adsorption features to Pb(II) of manganese dioxide and its oxidation property to As(III), were developed aiming at simultaneously effectively removing both As and Pb from drinking water. A systematic investigation including optimization of preparation, characterization of adsorbent, evaluation of adsorption performance, and arsenic, lead removal mechanisms was conducted in present paper.The following results were obtained.1. A novel Ti-Mn binary oxide adsorbent has been synthesized by a one-step simultaneous oxidation and coprecipitation method. The synthetic Ti-Mn binary oxide with a high BET surface area(349.5 m2/g), a huge pore volume and an abundant surface hydroxyl groups was amorphous structure.2. Ti-Mn binary oxide has high adsorption capacities of As(V) and As(III), especially As(III). At p H 7.0, the maximum adsorption capacities of As(III) and As(V) on Ti-Mn binary oxide adsorbent are 107.0 mg/g and 87.2 mg/g, respectively. This adsorbent could effectively oxidize As(III) to As(V), and also could be effective in removing As in a wide p H range. Moreover, the adsorbent could be readily regenerated and repeatedly used.3. As(V) was removed by forming an inner-sphere complex on surface of the adsorbent. The removal mechanism of As(III) is an oxidation coupled with sorption approach. During As(III) oxidation, fresh adsorption sites for arsenic adsorption were created at the solid surface, due to the reductive dissolution of manganese dioxide. This was responsible for the higher As(III) uptake.4. Ti-Mn binary oxide has a high Pb adsorption capacity, especially at low concentrations. At p H 5.0, the maximum Pb adsorption capacity is 186.3 mg/g. This adsorbent could be effective in removing Pb in a wide p H range, and also could be readily regenerated and repeatedly used.5. The adsorption process may be chemisorption between Pb and Ti-Mn binary oxide, and Pb form monodentate mononuclear or bidentate mononuclear inner sphere complexes with the Ti-Mn binary oxide surface, respectively. |
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