Effect Of Ni Doping And Exchange On Transformation Of Birnessite To Todorokite

Todorokite is common manganese oxide mineral in soils, sediments environment with tunnel structure. it can be transformed by layered birnessite. Ni, Co and other transition metals be occurrenced with todorokite, which can impact their geochemical behaviors. Previous studies show that todorokite is transformed by alkaline birnessite. Different transition metal ions doped, co-doped layered structre manganeses and the same transition metal ion doped different average Mn oxidation state(AOS) layered manganeses will changes structure and physical and chemical properties of layered manganeseshave have been reported. However, the occurrence pattern and structure of transition metals in Earth surface environments and the effect on transformtion of todorokite are not clear, and the related experimental geochemical studies are also rarely reported. In this papper, different AOS alkaline birnessites doped with Ni were synthesized through the method of oxidation of Mn SO4 by Na Mn O4 in alkaline conditions, then birnessite in Ni SO4/Mg Cl2 solution with ion exchange transformed to buserite and finally buserite under hydrothermal conditions transformed to todorokite. XRD, TEM/ED, BET were ultilized to investigated the effect on the buserite precursor interlayer cation species and quantity, degree of crystallization and AOSs, Ni ion doping transformed to todorokite and the crystal chemistry of Ni in todorokite. The main results are as follows:1. The amount of Ni ion in the interlayer of birnessite can affect the transformed of its to todorokite.The concentration of Ni ion exchange solution is too low or too high will hinder the birnessite transformed to todorokite,when Ni ion exchange solution concentration is about 0.1 mol/L, birnessite transformed to todorokite is the most complete.2. Buserite interlayer ion type and its AOS affect it transformed to todorokite. When buserite has high AOS, Mg2+ which has weak binding force with buserite octahedral layer is conducive to the formation of todorokite; when buserite AOS is low,Ni2+ which has strong binding force with buserite octahedral layer is conducive to the formation of todorokite.Buserite with high AOS is more easy to the transformed of todorokite than buserite with low AOS.3. The structure and properties of birnessite is affected by the content of Ni doping. With the increase of Ni doping content, the AOS of high and low AOSs birnessites increased, the specific surface area increased, the crystallinity decreased, and crystallinity of high AOS birnessite decreased more obvious.birnessite unit cell parameters change, unit cell parameter of high AOS birnessite is changed, a increases first and then decreases, b has been reduced, c decreases first and then increases, while in low AOS birnessite, both cell parameters a and b were decreased, unit cell volume of both birnessites were decreased.4. Different Ni doping content in birnessite has an effect on it transformed to todorokite. With the increase of Ni doping content, different AOS and different interlayer ions buserites were more likely to transformed to todorokite. The AOS of all series todorokites are rised, the specific surface area are also increased, and the parameters of the unit cell parameters of todorokites ore are changed as different transformation condition.5. Todorokite which transformed by high AOS has fibrous crystals morphology, and when low AOS buserite as precursor, todorokite which transformed by Mg2+-buserite has fibrous morphology, Todorokite which transformed by low AOS has fibrous crystals morphology, and when high AOS buserite as precursor, todorokite which transformed by Mg2+-buserite has fibrous morphology, when Ni2+-buserite as precursor,the morphology of todorokite is strip of the plate.