Analytical Chemistry Division, Bhabha Atomic Research Centre, Trombay Mumbai, India.
J Environ Sci Health A Tox Hazard Subst Environ Eng. 2013;48(4):422-8. doi: 10.1080/10934529.2013.728919.
Sorption of As(III) and As(V) on manganese dioxide was studied by batch equilibration method using (76)As radioactive tracer. Manganese dioxide was prepared by two different methods viz. reacting (a) KMnO(4) solution with MnSO(4) solution, and (b) KMnO(4) solution with concentrated hydrochloric acid. Manganese dioxide was characterized by zeta potential measurement, surface area measurement, thermogravimetry (TG), differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Point of zero charge (PZC) for manganese dioxide was between pH 3 and 4. Radioactive tracer ((76)As) was prepared by neutron irradiation of arsenious oxide in self serve facility of CIRUS reactor followed by conversion to As(III) and As(V), by appropriate chemical methods. Sorption of As(III) and As(V) were studied separately, between pH 1 to 11, using (i) freshly prepared, (ii) air-dried and (iii) aged manganese dioxide. Sorption of As(III) and As(V) on freshly prepared as well as aged manganese dioxide, from both the methods was greater than 98% between pH 1 to 9 and decreased above pH 9. Percentage sorption was comparable for manganese dioxide prepared by both the methods in different batches. Sorption capacity was ∼2 mg g(-1) for both As(III) and As(V). Arsenic was desorbed from the manganese dioxide by 0.1 M sodium hydroxide and oxidation state of desorbed arsenic was determined by solvent extraction method. It was found that the desorbed arsenic was present in As(V) oxidation state, independent of the initial oxidation states. This simple and direct chemical evidence, establishing that As(III) is converted to As(V) by manganese dioxide, is reported for the first time. Sorption of As(III) and As(V) on manganese dioxide did not cause an increase in manganese concentration above solubility limit confirming that Mn(2+), formed during oxidation of As(III) to As(V), was re-adsorbed.
采用放射性示踪剂（76）As 通过批量平衡法研究了二氧化锰对 As(III)和 As(V)的吸附。采用两种不同的方法制备了二氧化锰：（a）KMnO4 溶液与 MnSO4 溶液反应，（b）KMnO4 溶液与浓盐酸反应。通过 ζ 电位测量、表面积测量、热重分析（TG）、差热分析（DTA）和 X 射线衍射（XRD）技术对二氧化锰进行了表征。二氧化锰的等电点（PZC）在 pH 3 到 4 之间。放射性示踪剂（（76）As）是通过在 CIRUS 反应堆的自助设施中用中子辐照三氧化二砷，然后通过适当的化学方法转化为 As(III)和 As(V)制备的。单独研究了 pH 值为 1 到 11 之间的 As(III)和 As(V)的吸附，分别使用（i）新鲜制备的、（ii）风干的和（iii）老化的二氧化锰。从两种方法制备的新鲜和老化的二氧化锰中，在 pH 值为 1 到 9 之间，As(III)和 As(V)的吸附率均大于 98%，在 pH 值大于 9 时则降低。在不同批次中，两种方法制备的二氧化锰的吸附率相当。As(III)和 As(V)的吸附容量约为 2mg g(-1)。用 0.1M 氢氧化钠从二氧化锰中解吸砷，并用溶剂萃取法测定解吸砷的氧化态。结果发现，解吸的砷呈 As(V)氧化态，与初始氧化态无关。这是首次报道的关于二氧化锰将 As(III)转化为 As(V)的简单直接的化学证据。二氧化锰对 As(III)和 As(V)的吸附不会导致锰浓度超过溶解度极限，这证实了在将 As(III)氧化为 As(V)过程中形成的 Mn(2+)被重新吸附。
