Chatacterization And Properties Of Ni-and Fe-doped Alkaline Birnessites With Different Mn Average Oxidatrion State

Both different Mn average oxide states (AOS) and transition metal(TM) doping can make certain changes in the structures and physicochemical propertied of birnessite, and the diverse kinds of TMs have various effects. Acid birnessite and alkaline birnessite are not same in crystal structure and physicochemical properties, what changes in alkaline birnessite’s strcture and physicochemical property will happen by incorporating different TMs into alkaline birnessites and doping one kind of TM birnessites with different AOSs, it’s yet unclear. In this papper, different AOS alkaline birnessites doped with Ni and Fe-rich high AOS alkaline birnessites were synthesized through the method of oxidation of MnSO4by KMnO4in alkaline conditions.. XRD, BET, TGA, XPS, FTIR, FE-SEM and experiments of Pb2+/Zn2+adsorption, As(III) oxidation were ultilized to investigated the changes in crystal substructure and physicochemical properties of alkaline birnessite driving from Ni incorporation into different AOS alkaline birnessite and Fe doping with high AOS alkaline birnessite. The main results are as follows:1. The differernce in AOS and doping with Ni didn’t change the layer structure and flake morphology of alkaline birnessite. The crystallinity of Ni-rich highAOS alkaline birnessite obviously decreased while the low AOS grounp only had a little weaker crystallinity with Ni content increasing. In Ni-rich alkaline birnessites, the rise of Ni content made the thichness of high AOS birnessites plate thinner, specific surface area bigger, but the thickness of the plates of the low AOS firstly became thinner and then a slight increase, specific surface areas were increased initially and later decreased. Rietveld structure refinement implied that the unit cell parameters a and c of high AOS alkaline birnessites decreased, but a and b decreased in low AOS alkaline birnessites.2. The analysis of XPS and TGA indicated that Ni existed in a calence of+2in Ni-rich high and low AOS birnessites, part of Ni inserted into layer and mainly substituted for Mn3+in high AOS birnessites, but for Mn2+in low AOS birnessites which increased the Manganese AOS. The introduction of Ni made the hydroxyl contents gradually decreased in high AOS alkaline birnessite and firstly decreased and then increased in low AOS alkaline birnessites. The increase in Ni content led thermostability of high AOS birnessites lower while more stable in low AOS birnesites.3. The introduction of Ni made the removal capacity of heavy metals lower than the free sample. When the initial molar ratios of Ni/Mn were same, the adsorption capacities of Pb2+, Zn2+and oxide removal capacity of As(Ⅲ) by high AOS birnessites were stronger than those of low AOS birnessites. The analysis of relase of Ni2+and Mn2+during the process of Pb2+uptake implied that Ni tended to exist on the surface of Ni-rich high AOS alkaline birnessites, but Mn had a high content on the surface of Ni-rich low AOS alkaline birnessites.4. In Fe-rich high alkaline birnessites, the iron accounted for3.72%,3.95%, and11.72%in weight respectively. The introduction of Fe didn’t change the layer structure of alkaline birnessite as well as flake morphology. With the increase of Fe content in the samples, the crytallinity obviously decreased, and the number of MnO6layers stacked coherently along the c axis became fewer, while the surface area gradually increased and the AOS increased gradually. The parameter c tended to decrease. The introduction of Fe make the high AOS birnessite more stable, but the increase of Fe content then made thermostability weaker. The XPS data showed that Fe exits as Fe+3in the Fe-rich samples and part of Fe3+came into the layer and replaced Mn3+, resulting in the increase of Manganese AOS.After Fe3+doping, the contents of hydroxyl groups on the birnessite surfaces decreased firstly and then increased along with the increase of Fe content. These Fe-doped high AOS alkaline birnessites had reduced adsoption capacities of Pb2+and Zn2+, and increased total removal rate of As; but when the molar ratio of Fe with Mn was11.72%, the As depletion decreased.5. The introduction of TM didn’t change the position of virbration peak of alkaline birnessite in FTIR. With the increase of TM content, the intensity of band at418-424cm-1basically unchanged, while weakened at band479-483cm-1and510-512cm-1, the intensity of the later may implies crystallinity of alkaline birnessite. In the same sample, the relative intensity of band at418-424cm-1and band at479-483cm-1,510-512cm-1varied, the band at418-424cm-1may be related to the virbration of Mn4+,while the later may be belong to the virbration of Mn3+. In addation, the introduction of Ni and Fe which enhanced the intensity at band441cm-1and460cm-1、536cm-1respectively maybe one of reasons.