Hydrous Manganese Dioxide Research Articles

Kinetics of isotopic exchange of sodium ions in hydrous manganese dioxide from mixed solvent solutions

The Na + capacity of cryptomelane type-hydrous manganese dioxide in aqueous, methanolic and propan-1-olic solutions was determined using two different methods. The Na + capacity decreases reprogressively with alcohol. This pointed to an imbibition of alcohols by the solid. Self-diffusion coefficients (D¯) of sodium ions in manganese dioxide have been determined in aqueous and alcoholic (methanolic and propan-1-olic) solutions by using Paterson's approximation equation. These coefficients (D¯) generally increase with alcohol concentration. The effect of alcohol addition on ion-solvent interactions is counteracted by the effect of ion-ion interactions in the exchanger, leading to an increase of (D¯). Also, adding NaCl to the external aqueous or alcoholic hydroxide solution enhances Na + diffusivity due to a weaker interaction with Cl − coions inside the oxide pores, or it may be that the addition of NaCl decreases the imbibition of alcohol by the oxide.

Preliminary Investigation of Manganese-Catalyzed Ozonation for the Destruction of Atrazine

A preliminary experimental study conducted with a conventional bubble ozonation contactor column has shown that small amounts of Mn(II) greatly enhanced the destruction of atrazine by ozone. There is an inversely linear relationship between the dosed Mn(II) concentration and the residual ozone concentration at a specific reaction time. The ozone transfer efficiency into water is greater with the increase of Mn(II) dosage. Hydrous manganese dioxide prepared by reacting permanganate with manganese sulfate, also was shown to be effective in catalyzing the destruction of atrazine by ozone. The efficiency of catalytic activity for the destruction of atrazine caused by preformed hydrous Mn(IV) is slightly lower than the case of Mn(II). A lower residual ozone value using manganese dioxide compared to the case of ozone alone suggests that ozone also may be decomposed by hydrous Mn(IV). However, a commercial MnO2 did not show any catalytic activity for atrazine destruction. The very much greater degree of atrazine oxidation by manganese-catalyzed ozonation compared to ozone alone is speculated to be the result of the generation of highly oxidative intermediate species such as hydroxyl radicals during the reaction between ozone and manganese species.

Determination of antimony in impure zinc sulphate solution by coprecipitation followed by differential pulse anodic stripping voltammetry

A simple coprecipitation technique for the quantitative separation of the antimony present in impure zinc sulphate electrolyte followed by its voltammetric determination is described. Antimony in microgram levels is separated from the matrix zinc sulphate solution, which contains higher levels of copper, lead and cadmium, and is subsequently determined by differential pulse anodic stripping voltammetry (DPASV) in 3 M hydrochloric acid. Hydrous manganese dioxide is employed as the collector. This procedure, which effects considerable saving in time, is of comparable accuracy to the conventional spectrophotometric method using the antimony-rhodamine B complex. A series of synthetic zinc sulphate solutions spiked with known amounts of antimony as well as plant solutions gave near theoretical values.

Separation of uranium from thorium on cryptomelane-type hydrous manganese dioxide

The distribution of UO 2 2+ and Th4+ in nitric acid media on crypomelane-type hydrous manganese dioxide (CRYMO) has been investigated by batch equilibrations and column break-through techniques. The parameters studied involve the media composition and concentrations of HNO3, NaNO3, UO 2 2+ and Th4+. It is found that Th4+ is more strongly adsorbed on CRYMO than UO 2 2+ with sufficient differences for chromatographic separation from each other. Uranium was quantitatively eluted from a CRYMO column with 0.1M HNO3. Th4+ has been recovered by using ≥ 1M HNO3 as eluent.

Separation of Co(II) from dilute aqueous solutions by precipitate and adsorbing colloid flotation

Ion, precipitate and adsorbing colloid flotation of cobalt(II) have been investigated at different pH values, using N-dodecylpyridinium chloride (DPCl), A strong cationic surfactant, and sodium lauryl sulfate (NaLS), a strong anionic surfactant, as collectors. In case of adsorbing colloid flotation, hydrous manganese dioxide was used as an adsorbent. The precipitate flotation curves experimentally obtained with the two tested collectors were compared with the corresponding theoretical one calculated from the data published for Co(II) hydrolysis. The effects of the collector concentration, ageing of the water-MnO2−Co(II) system, bubbling time period, cobalt(II) concentration and foreign salts on the percent removal of Co(II) by adsorbing colloid flotation using DPCl as collector were determined. Removals approaching 100% could be achieved under the optimum conditions.

Technology for Removing Potassium Ion from Concentrated Seawater by Electrodialysis and Solar Salt Dissolved in Brine

Abstract Cryptomelane-type hydrous manganese dioxide (CRYMO) has a high adsorption selectivity toward potassium ions (K+). The distribution coefficients of the highly selective adsorption are evaluated by the theoretically proven calculation method, that adsorption isotherm data and Kielland plot data are taken for granted. The calculated results and the experimental results of the adsorption isotherm show fairly good agreement for a whole range of conditions. CRYMO has been successfully applied to the caustic soda manufacturing process. The concentration of K+ in brine for the process was lowered to less than 1 ppb. This purity is sufficient for the high quality caustic soda manufacturing process. Another advantage of CRYMO is its acidification ability for solutions. The brine is acidified with hydrochloric acid before being introduced to the electrolytic bath in the present process.

SORPTION BEHAVIOUR OF URANIUM AND THORIUM ON CRYPTOMELANE-TYPE HYDROUS MANGANESE DIOXIDE FROM AQUEOUS SOLUTION

Abstract The kinetics of sorption of uranium and thorium from aqueous nitrate solutions on cryptomelane-type hydrous manganese dioxide (CRYMO) was studied. The exchange of uranium is particle diffusion controlled while that of thorium is chemical reaction at the exchange sites. Sorption of uranium and thorium by CRYMO has been also studied as a function of metal concentrations and temperature. The sorption of both cations is found to be an endothermic process and increases markedly with temperature between 30 and 60°C. The sorption results have been analysed by the langmuir adsorption isotherm over the entire range of uranium and thorium concentrations investigated.

ION-EXCHANGE SELECTIVITY FOR ALKALI METAL IONS ON A CRYPTOMELANE-TYPE HYDROUS MANGANESE DIOXIDE

ABSTRACT A cryptomelane-type hydrous manganese dioxide in the H+ form has been studied for its ion-exchange selectivity for Li+, Na+, K+, Rb+ and Cs+/H+ exchange at 30*C. The distribution coefficients for each alkali cation were calculated as a function of the initial concentration of exchanging cations in the presence of a constant total normality of 0.1 N. The separation factor for the Na+ - K+ pair attained 1.3 x 10 at Xx→0 This extremely high selectivity can be attributed to the rigid tunnel structure with an opening which is only accessible to less hydrated cations, those that shed their hydration shell easily and those with crystal ionic radius of approximately 1.4A.

Adsorptive characteristics of iron(III) onto hydrous manganese dioxide in model lake water under acidic conditions

The adsorption of iron(III) onto hydrous manganese dioxide was studied in the model water of Lake Tjeukemeer, The Netherlands, as a function of pH under the condition where no precipitation of iron(III) hydroxide occurs.

Synthesis of a manganese dioxide-silica hydrous composite and its properties as a sorption material for strontium

This paper reports on hydrous manganese dioxide prepared by precipitation of MnO{sub 2} from potassium permanganate with H{sub 2}O{sub 2}. The reaction was carried out in the presence of SiO{sub 2} as sodium silicate. Afterward the precipitate was dewatered, washed, and dried. The resultant materials were tested for strontium sorption as a function of MnO{sub 2}:SiO{sub 2} content and as a function of drying temperature. A product containing 17% SiO{sub 2} in the initial solution was shown to be the best for Sr adsorption. The mechanical strength, density, capacity, and water stability of the exchangers were determined. Their properties were compared with a grade of MnO{sub 2} available commercially. Addition of SiO{sub 2} had several advantages.

Interfacial properties of some hydrous manganese dioxides in 1-1 electrolyte solution

Interfacial properties of four synthetic hydrous manganese dioxide samples, two belonging to birnessite (7 Å manganite) and two to amorphous δ-MnO 2 varieties, in aqueous 1:1 electrolyte solutions have been studied. Chemical analysis shows that the samples are only partially oxidized and have high water contents. Electron micrographs indicate that the samples occur in aggregates, consisting of finely divided spherical or plate-shaped particles, though the porosities of some of them are low and these, therefore, exhibit low surface area. Both salt and potentiometric titrations reveal that the pH pzc of the samples varies from 2.25 to 3.0 depending upon the preparation method. However, the IEP values of the samples as determined from the electrophoretic mobility measurements tend to shift to higher pH values with respect to pH pzc. All the samples have very high surface charge, due to which specific adsorption of some counterions also takes place. Calculation of the concentrations of surface species shows that at pH near pzc surface complexation is negligibly small and the point of zero charge is possibly characterized by the presence of equal amounts of positive and negative charges.

A 99mTc generator based on the adsorption of [ 99Mo]molybdophosphate on hydrous manganese dioxide

The adsorption behaviour on hydrous manganese dioxide of 99Mo in the form of molybdate and molybdophosphate and of 99mTc in the form of pertechnetate was investigated at different solution acidities. The adsorption capacity of molybdenum is much higher for the molybdophosphate form. A 99mTc-generator is suggested. This generator is based on the adsorption of [ 99Mo]molybdophosphate on MnO 2, at an acidity of 0.5 N. 99mTc is then eluted either by 0.9% NaCl or by methyl ethyl ketone. Radionuclidic, radiochemical and chemical purity tests of the eluates were performed and the present generator seems to offer some advantages over the traditional alumina generator.

Radiochemical neutron activation analysis for thirteen trace metals in human blood serum by using inorganic ion-exchangers

Thirteen trace elements in blood serum are determined by using a radiochemical group separation procedure based on acid aluminium oxide, hydrated antimony pentoxide and hydrated manganese dioxide. The method allows the determination of Ag, Co, Cr, Cs, Fe, Hg, Rb, Sb, Sc, Se, Sn, Sr and Zn, which occur in concentrations at the μg g −1 to pg g −1 level. The procedure separates the elements into four groups with matched γ-ray energies and intensities, ensuring reliable and efficient γ-ray measurements. The k 0 method, adapted for the specific sample composition and sizes, was applied. Where possible, results are compared with published data. The results obtained by the relative method are in good agreement with those from the k 0 method, with 95Zr 97Zr, 198Au and 59Fe 54Mn as neutron flux monitors. The values for the human blood serum reference material agree with the certified values available for most of these elements.

The use of neutron activation in dietary reference material analysis

Results for a number of trace elements in a total human diet material (USDIET-1), obtained by the application of both INAA and RNAA are presented. Several dietary reference materials such as NBS SRM 1577A, and BCR CRM Single Cell Protein were also analyzed, and these results are also given. Combining measurements on short and long lived radionuclides, the INAA approach is useful for the determination of about 20 elements. In order to expand the elemental coverage or improve detection limits, RNAA was also explored in two modes: separation of radionuclides using organic ion exchange resins and the use of hydrated manganese dioxide. This combination is applicable to 15 trace elements. For example, using RNAA, the following results were obtained for USDIET-1: Cd=31.8, Mo=280, Cr=71, Ag=4, As=117 and Sb=9.4 μg/kg. In the INAA mode, special attention was given to Al, F and Se. The F content of USDIET-1 was found to be 840 mg/kg, a rather high value, resulting from handling USDIET-1 by Teflon tools. By applying INAA and RNAA under two different laboratory conditions, it has been demonstrated that, even for the so-called difficult to determine elements like Cr, As or Mo, consistent results can be obtained. Thus, NAA promises to be a strong tool for human nutritional studies.

Investigation of silica gel supported inorganic ion exchangers

Microcrystalline zirconium phosphate (α-ZrP), hydrous manganese dioxide (HMnO), ammonium molybdophosphate (AMP) and silica gel supported forms of these materials as well as silica gel (SG) itself were investigated by thermoanalytical, electron microscopic, X-ray diffraction and infrared spectrometric methods. Chemical composition, structure and some related properties of the inorganic ion exchangers mentioned above are reported.

Permanganate peroxidation of cyclohexene. III. Hydroxide ion and salt effect studies

Good yields of cis-1,2-cyclohexanediol were formed by the reaction of cyclohexene and aqueous potassium permanganate under turbulent stirring conditions only in the presence of low concentrations of sodium hydroxide. Larger amounts had no further benefit or were deleterious. The lack of sensitivity to low concentrations of hydroxide ion indicated that its benefit is to inhibit acid promoted oxidations. There was no indication of its participation in the mechanism of glycol formation. The addition of the neutral salts, sodium sulfate or sodium nitrate, caused a decrease in glycol yields presumably due to a positive salt effect on a secondary negative ion – negative ion reaction, which formed other oxidation products. Stoichiometric amounts of hydroxide and potassium ions were not isolated as reaction products due to interaction with the hydrated manganese dioxide in a 1:2 ratio. The mechanisms in acidic and basic solutions appear to be quite different. A mechanism for basic solutions is suggested.

Co, Cu, Ni, and Ca Sorption by a Mixed Suspension of Smectite and Hydrous Manganese Dioxide

AbstractThe sorption properties of Co, Cu, Ni, and Ca were studied in a mixed mineral suspension of synthetic MnO2 and Wyoming montmorillonite. The distribution of the sorbed cations between the two solid phases was measured by indirect chemical fractionation with acidified NH2OH-HCl and by direct X-ray spectroscopic analysis of mineral particles using electron microscopy. Electron microscope and NH2OH-HCl measurements of the quantity of Co sorbed on MnO2 agreed within 6%. Seventy-seven, 67, and 69% of the total Co, Cu, and Ni sorbed by the mixed mineral suspension was found on the manganese oxide. The opposite distribution was found for sorbed Ca with 28% on the manganese oxide and 72% on the montmorillonite particles. The observed differences in metal sorption by these minerals are related to the cation-sorption mechanisms of manganese oxide and montmorillonite.

Heavy Metal Induced Releases of Manganese (II) From a Hydrous Manganese Dioxide

The sorption of Co(II), and Cu(II), and Mn(II) by the manganese oxide birnessite, was studied at pH 3.3 to 8.9 to ascertain the mechanisms responsible for heavy metal induced releases of Mn from MnO2. Cobalt sorption resulted in a release of Mn to solution and the presence of Mn(II) on the oxide surface. Manganese releases during Cu addition only occurred if Mn(II) was present on the oxide prior to Cu sorption. The simultaneous sorption of Co + Cu resulted in greater releases of Mn than were observed during Co sorption alone. In all cases, Mn release was found to increase with decreased pH. It is suggested that Mn releases during Co(II) sorption result not only from the oxidation of Co(II) to Co(III), but also from a direct exchange of Co(II) for Mn(II) produced during the redox reaction.

Statistical analysis of estuarine profiles: II application to arsenic in the Tamar estuary (S.W. England)

By combining field observations with a statistical approach and a simple but effective estuarine analogue, the main features of the cycling of arsenic in the Tamar estuary have been elucidated. As(III) and As(V) enrichment in the water column is due to a combination of localized inputs and effective recycling of sediment interstitial waters. The profiles of As(V) are similar to those of NH 4 + and are dominated by an estuarine maximum resulting from an input from the sediments. As(III) profiles are correlated with those of dissolved manganese and exhibit both fresh water and estuarine maxima. As(III) appears to be effectively removed at the freshwater/brackish water interface by a combination of heterogenous oxidation, catalysed by hydrous manganese dioxide, and adsorption on to iron oxyhydroxide. The estuarine distribution of As(III) within the water column is consistent with the published rates of oxidation of As(III) to As(V) by both inorganic and microbiological processes. The reduction of As(V) to As(III) in the sediments is incomplete. On the basis of our observations a tentative estuarine arsenic cycle is presented.

SYNTHETIC INORGANIC ION-EXCHANGE MATERIALS XXXVI. SYNTHESIS OF CRYPTOMELANE-TYPE HYDROUS MANGANESE DIOXIDE AS AN ION-EXCHANGE MATERIAL AND THEIR ION-EXCHANGE SELECTIVITIES TOWARDS ALKALI AND ALKALINE EARTH METAL IONS

Abstract Hydrous manganese dioxide in a cryptomelane-type showed an excellent ion-exchange selectivity for K+, Rb+and Ba2+ ions having the effective ionic radii of about 1.4 Å. Log-log plots of distribution coefficients for alkali and alkaline earth metal ions vs. [HNO3] yielded a straight line with a slope of −1 and −2, respectively, indicating the “ideal” ion-exchange mechanism. The stoichiometry of ion-exchange reactions was also established for the uptake of macro-amounts of alkali metal ions in nitrate media.