Hydrous Manganese Dioxide Research Articles

Atomic force microscopy study on the microtopography of natural organic matter and newly formed hydrous MnO2

To understand the water purification mechanism of potassium permanganate as a coagulation-aid during the preoxidation process, the microtopography of its reductive products, the newly formed hydrous manganese dioxide and the aged hydrous manganese dioxide, was investigated. The morphology of natural organic matter (NOM) adsorbed by the newly formed hydrous manganese dioxide was also compared with that of NOM alone. By using the tapping mode atomic force microscopy (AFM), the observation results show that the newly formed hydrous manganese dioxide possess a perforated sheet (with a thickness of 0–1.75 nm) as well as some spherical particle structures compared with the hydrous manganese dioxide with 2 h aging time, which demonstrated that the newly formed hydrous manganese dioxide had a large surface area and adsorption capacity. When 1 mmol/L newly formed hydrous manganese dioxide was added, the microtopography of NOM molecules shifted from a loosely dispersed pancake shape (with adsorption height of 5–8.5 nm) to a densely dispersed and uniform spherical structure. These results provide a valid proof that it is the perfect adsorption capability of the newly formed hydrous manganese dioxide that might result in the coagulation aid effect of potassium permanganate preoxidation.

Adsorptive behaviors of humic acid onto freshly prepared hydrous manganese dioxides

This study focused on the adsorptive behaviors of humic acid onto freshly prepared hydrous MnO2(s) (δMnO2), and investigated the feasibility of employing δMnO2 for humic acid removal from drinking water. Effects of such parameters as molecular mass of humic acid, kinds of divalent cations on adsorptive behaviors and possible mechanisms involved were investigated. This study indicated that humic acid with higher molecular mass exhibited more tendency of adsorbing onto δMnO2 than that with lower molecular mass. Ca2+ facilitated more humic acid adsorption than Mg2+; UV-Vis spectra analysis indicated higher capabilities of Ca2+ coordinating with acidic functional groups of humic acid than that of Mg2+. Additionally, ζ potential characterization indicated that Ca2+ showed higher potential of increasing gz potential of δMnO2 than Mg2+. Ca2+ of 1.0 mmol/L increased ζ potential of δMnO2 from −37 mV (pH 7.9) to +7 mV (pH 7.2), while 1.0 mmol/L Mg2+ increased to lower value as −9 mV (pH 6.5), correspondingly. Fourier transform infrared (FTIR) spectra demonstrated the adsorption of humic acid onto δMnO2, showing the important roles of-COO− functional groups and surface Mn-OH in the adsorption of humic acid onto δMnO2.

Adsorption of Cd 2+ on hydrous manganese dioxide from aqueous solutions

The adsorption of Cd 2+ onto amorphous hydrous manganese dioxide (δ-MnO 2) has been studied in (a) 0.5 M NaCl solution and (b) major ion seawater. The adsorption experiments were carried out in two methods: isotherms at constant pH in the presence of a buffer solution over a wide range of initial Cd 2+ concentrations (0.0089 to 0.5357 mM) and varied pH (2–7.5) in the absence of a buffer solution at 0.0911 mM Cd 2+ concentration. In order to describe the isotherm mathematically, the experimental data of the adsorption equilibrium were correlated by either the Langmuirian or Freundlich equations. Results indicated that the Langmuirian-type model gave a better fit to the experimental data than the Freundlich type in both electrolyte media. The proton stoichiometry derived from isotherms at two close pH values varies between 0.22 to 0.42 for the 0.5 M NaCl solution. The variation of fractional adsorption with pH can be modeled either with the formation of a SOCd+ complex or with a combination of SOCd+ and SOCdOH complex, depending upon the electrolyte medium. The equilibrium constants obtained from Kurbatov-type plots are found to be the most suitable for these model calculations.

Layered hydrous manganese dioxide saturated with alkaline-earth cations: Synthesis and sorption properties

Layered compounds based on hydrous manganese dioxides (hereafter, Mn-phases) saturated with alkaline-earth cations were synthesized at 3–6°C. These phases are analogues of manganese minerals from oceanic iron-manganese sediments (vernadite, birnessite, buserite-I, an asbolan-like phase, and a hybrid phase). All the Mn-phases, as a rule, had poorly ordered structures. The sorption properties of these phases were studied with respect to alkali-metal cations (Na+, K+), an s-metal cation (Ba2+), a p-metal cation (Pb2+), and d-metal cations (Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+). The exchange capacities of the Mn-phases were 0.45–1.06 mg-equiv/g for the alkali cations and 0.94–5.78 mg-equiv/g for the other cations. The phase composition of the Mn-phase did not affect the alkali cation sorption but affected the divalent cation sorption. The divalent cation exchange capacity increased from well-ordered birnessite to poorly ordered vernadite.

Determination of radium and uranium isotopes in natural waters by sorption on hydrous manganese dioxide followed by alpha-spectrometry

Water samples, spiked with 133 Ba and 232 U radiotracers, are scavenged for radium and uranium isotopes using hydrous manganese dioxide which is produced in-situ, by reacting manganese (+2) and permanganate ions at pH 8-9. The precipitate is solubilized with ascorbic and acetic acids and the resulting solution filtered through a glass fibre filter GF/F to remove particulate matter. The radium is co-precipitated with barium ions by the addition of a saturated Na 2 SO 4 solution where a small amount of BaSO 4 suspension is introduced to initiate crystallization. The micro precipitate containing the radium is collected on a 0.1 µm membrane filter and the filtrate saved for follow-up uranium analysis. The 226 Ra on the filter is determined by alpha-spectrometry and its recovery is assessed by measuring the 133 Ba on the same filter using gamma-spectrometry. The filtrate containing uranium is passed through a Dowex AG 1x4 ion-exchange resin in the SO 4 2- form which retains uranium while other ions are eluted by dilute (0.25M) sulphuric acid. Uranium is eluted from the column by distilled water, electrodeposited on a silver disc and the uranium isotopes and their recovery are determined by alpha-spectrometry. The method was tested on a variety of natural and spiked water samples with known concentrations of 226 Ra and 238 U and was found to yield accurate results within ±10p RSD of the target values.

Amorphous Manganese Dioxide as a Material for an Electrochemical Pseudocapacitor

The charge storage process of amorphous hydrated manganese dioxide (MnO2) as a pseudo-capacitor involves a fast redox reaction at the electrode surface. In order to understand the charge storage mechanism of MnO2 as a pseudo-capacitor in an aqueous KCl solution, we monitored the change of the capacitance by varying the pH of the solution, the cation of the electrolyte, the concentration of the KCl electrolyte, and the solvent. The charge storage mechanism of a metal oxide electrode such as MnO2 is concluded to involve a fast redox reaction through both the potassium ion exchange, MnO2 + δK+ + δe- ⇔ MnO2-δ(OK)δ and the proton exchange, MnO2 + δH+ + δe- ⇔ MnO2-δ(OH)δ dependent upon the availability of the cations in the electrolyte.

The role of cations of the electrolyte for the pseudocapacitive behavior of metal oxide electrodes, MnO 2 and RuO 2

The energy storage process for amorphous hydrated manganese dioxide (MnO 2) is suggested as fast faradaic reactions occurring at the solid electrode surface with the reduction from Mn 4+ to Mn 3+. In order to understand the role of cations of the electrolyte for the MnO 2 electrode as a pseudocapacitor in aqueous KCl solution, we monitored the change of the capacitance by varying the concentration of the KCl electrolyte, the cation of the electrolyte, the pH of the solution, and the solvent. The charge storage for the metal oxide electrode such as MnO 2 is concluded to involve a fast redox reaction through both potassium ion exchange, MnO 2 + δ K + + δ e − ⇔ MnO 2−δ(OK) δ and proton exchange, MnO 2 + δ H + + δ e − ⇔ MnO 2−δ(OH) δ dependent upon the availability of cations in the electrolyte. The contribution of proton to the pseudocapacitive process is not negligible in aqueous solution.

Synthesis and electrode performance of layered nickel dioxide containing alkaline ions

Several polymorphs of layered nickel dioxide were prepared by using the chemical insertion of alkaline ions into Li 0.10NiO 2. We used aqueous AOH (A = Li, Na, K) solutions as reducing agents. Sodium and potassium insertion resulted in hydrated layered compounds that can be classified as γ-NiOOH with high crystallinity, while lithium insertion occurred without hydration. We discuss the coordination environment around the A + ions for these inserted compounds. The thermal behavior, analyzed using high temperature (HT) X-ray diffraction (XRD) and thermogravimetric (TG) measurements, indicated that heating the hydrate at 150 °C yielded its dehydrate. The electrode performance of the nickelate was studied in lithium cells. We discuss the effect of interlayer water on cell rechargeability and the similarity between these nickelate and hydrated manganese dioxide (birnessite).

Self-diffusion of cesium ions in hydrous manganese dioxide from mixed solvent solutions

Self-diffusion coefficients ( D̄) of cesium ions in hydrous manganese dioxide have been determined radiochemically at different apparent capacities in aqueous and alcoholic solutions. The apparent capacity decreases in the order n-propanol>methanol and is determined by both ion–solvent and ion–ion interaction. Self-diffusion coefficients ( D̄) have been determined in all different media by using Paterson's approximation equation. Also, the effect of adding CsCl to the external aqueous or alcoholic hydroxide solution has been studied.

Adsorption of Co, Ni, Cu, and Zn on hydrous manganese dioxide from complex electrolyte solutions resembling sea water in major ion content

Adsorption of Co, Ni, Cu, and Zn onto a poorly crystalline hydrous manganese dioxide (δ-MnO2) has been studied in complex electrolyte solutions such as (a) 0.5 M NaCl+0.054 M MgCl2, (b) 0.5 M NaCl+0.028 M Na2SO4, and (c) artificial sea water prepared according to the standard literature method. These three solutions allow us to identify the specific effect of major cations, major anions, and the mixture of major cations and anions (including carbonate and bicarbonate) that is present in real sea water. The adsorption isotherm in major ion sea water at pH 7.25 indicates that while Co and Zn exhibit increases in adsorption with increase in concentration, Ni shows relatively poor adsorption, reaching a plateau at 0.075 mM concentration. The three trace metals (Co, Ni, and Zn) show Langmuirian behavior for adsorption at low concentration. It is generally observed that the fractional adsorption vs pH curve shifts to higher pH either in the presence of 0.054 M MgCl2 or in sea water. In the presence of 0.028 M Na2SO4 the fractional adsorption vs pH curve remains almost unchanged with respect to a 0.5 M NaCl solution. The competitive adsorption of one trace metal in the presence of other three in major ion sea water indicates that this phenomenon is more predominant with Ni and Zn than with Co and Cu.

Adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide from simple (1–1) electrolyte solutions

The adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide (δ-MnO2) has been studied using two methods, viz., isotherms at constant pH in the presence of buffer solution and pH variation in the absence of buffer solution from a fixed metal ion concentration. While the adsorption isotherm experiments were carried out in 0.5 M NaCl only, pH variation or batch titration experiments were carried out in 0.5 M NaCl, 0.01 M NaCl, and 0.01 M KNO3 solutions. The complex nature of adsorption isotherms at constant pH values indicates that adsorption of all the cations is non-Langmuirian (Freundlich) and takes place on the highly heterogeneous oxide surface with different binding energies. The proton stoichiometry derived from isotherms at two close pH values varies between 0.3 and 0.8. The variation of fractional adsorption with pH indicates that the background electrolyte solution influences the adsorption of cations through either metal-like or ligand-like complexes with Cl−, the former showing a low adsorption tendency. The proton stoichiometry values derived from the Kurbatov-type plot varies not only with the electrolyte solution but also with the adsorbate/adsorbent ratio. The variation of fractional adsorption with pH can be modeled either with the formation of the SOM+ type or with a combination of SOM+ and SOMOH type complexes, depending upon the cation and electrolyte medium. The equilibrium constants obtained from Kurbatov-type plots are found to be most suitable in these model calculations. Adsorption calculated on the basis of ternary surface metal–chlorocomplex formation exhibits very low values.

Purification of arsenic contaminated ground water using hydrated manganese dioxide

An analytical methodology has been developed for the separation of arsenic from ground water using inorganic material in neutral medium. The separation procedure involves the quantitative retention of arsenic on hydrated manganese dioxide, in neutral medium. The validity of the separation procedure has been checked by a standard addition method and radiotracer studies. Neutron activation analysis (NAA), a powerful measurement technique, has been used for the quantitative determination of arsenic.

Abiotic hydrolysis of the detergent builder tripolyphosphate by hydrous manganese dioxide

The hydrolysis of tripolyphosphate to orthophosphate is facilitated by suspensions of amorphous manganese dioxide. Pyrophosphate is observed as an intermediate. The rate enhancement decreases with increasing pH. The weak sorption of orthophosphate on the oxide also decreases with increasing pH, indicating that the orthophosphate product would be bioavailable. The presence of calcium ions in natural waters increases both the rate of hydrolysis of tripolyphosphate and the extent of sorption of orthophosphate. Under some circumstances this abiotic mechanism could play a significant role in the hydrolysis of tripolyphosphate in the aquatic environment.

Oxidative Transformations of Phenylacetylene on a Manganese(IV) Oxide Adsorbent-Catalyst

It is shown by IR spectroscopy and thermally programmed surface reactions that the complete oxidation of phenylacetylene on hydrated manganese dioxide in an adsorption catalytic regime occurs via dissociation of the C≡C bond (during chemisorption) with the formation of formate and benzoate on the surface.

Chemisorption and oxidative decomposition of pyridine on hydrated manganese dioxide

An experimental study using IR spectroscopy and TPSR techniques showed that the extensive oxidation of pyridine on the surface of hydrated manganese dioxide in a two-step adsorption-catalytic mode proceeds through the formation of complexes of the heterocycle with Lewis acid sites.

ESCA and Vibrational Spectroscopy of Alkali Cation Exchanged Manganic Acids with the 2×2 type Tunnel Structure Synthesized via Different Chemical Routes

ABSTRACTManganese dioxides have received much attention over the last two decades as ion exchangers. Actually these are typically mixed-valence compounds and the terminology of ‘dioxide’ is not appropriate. The mechanisms for their variety of chemical reactivities are still open for study. On the cation uptake mechanism there are strong claims that a redox process is involved in cation uptakes by manganic acids synthesized by substituting H+ for alkali cations incorporated in ‘hydrous manganese dioxides’. The present work was carried out to physically demonstrate the alkali cation exchange mechanism on tunnel-structured manganic acids and to study the ion exchange with lattice vibrational spectroscopy. Manganic acids were prepared through the redox process using KMnO4 and MnSO4, and thermal decomposition of (CH3)3COK and MnCO3 at 530°C. ESCA spectra of their alkali cation exchanged forms indicated no evidence of redox process and supported the ion exchange mechanism on these materials. Their infrared absorption spectra strongly depended on their preparation routes and are closely related to their ion-exchange selectivity of each material. Thus, the vibrational spectra of manganic acids take an important role as a synthesis index together with XRD patterns.

Sorption of cobalt on hydrated manganese dioxide

The sorption of cobalt from 7.7.10−6M solution of Co(NO3)2 onto two different MnO2.xH2O preparations was followed. Physico-chemical properties of exchangers were studied, and following empirical formulas determined: 4 MnO2.5 H2O (sample D), and 10 MnO2.3 H2O (sample I). Using 60Co radiotracer, the influence of pH value on the kinetics and on the distribution coefficients values KD (mL.g−1) was followed in static (batch) tests. Equilibration time needed was increasing with decreasing pH. KD values were increasing with pH from 1.24.103 mL.g−1 (sample D), and 28.3 mL.g−1 (sample I) at pH ≈1. Both exchangers exhibited about the same KD value 2.2.10−5 mL.g−1 at pH≈4, a slight decrease occurred above pH≈5. These results can be qualitatively explained anticipating, the absorbers perform as weakly acidic cation-exchangers in H+ cycle. Sorption isotherms determined at pH=5 complied with Langmuir isotherm giving sorption capacities of 0.682 mmol.g−1, and 0.210 mmol.g−1 for D and I sample, respectively. The sorption capacity of sample D was found to increase with pH up to 2.69 mmol.g−1 at pH=7.

Determination of U, Pu, Am and Cm in water coolant of nuclear power plants using membranes impregnated with hydrated manganese dioxide

Methods have been developed for the rapid determination of the total activity of α-emitting radionuclides in water coolant. The samples with a volume of 0.05–2.5 dm3 are filtered at a flow rate of 2–2.5 dm3/h through a system of membranes. The first membrane is a mechanical filter for the separation of suspensions, the second one is impregnated with manganese dioxide which is intended for the deposition of actinoids in an ionic state. The detection limit for a 2.5 l sample measured with a low-background alpha-radiometer is equal to 0.037 Bq. The measurement error does not exceed 30% at a confidence level of 0.95 over a determined concentration range from 0.037 to 3.7·105 Bq/l.

Ce3+ adsorption on hydrated MnO2

The adsorption of Ce3+ on hydrated manganese dioxide (HMD) was studied as a function of concentration, temperature and pH of the cerium solution labelled with141Ce. The steady state values of cerium adsorption at various concentrations fit well with the classical Freundlich isotherm. The effect of temperature on equilibrium adsorption values was utilized to determine the change in the standard enthalpy ΔHo of the cerium uptake process and its value (ΔHo=10.57) indicates that the uptake process proceeds via ion exchange.141Ce desorption studies, from HMD in water, HCl and unlabelled CeCl3 solution, confirmed the ion exchange nature of the cerium uptake process as well as its reversibility.

Removal of Manganese and Iron from Drinking Water Using Hydrous Manganese Dioxide

ABSTRACT This paper examines the use of synthetic manganese dioxide as a material for the removal of Mn++ and Fe++ from drinking water. Three different types of Mn02 were prepared. One involved the production of the dioxide from permanganate and hydrogen peroxide, the second involved the use of the permanganate and manganous ions and the third used a formulation the included all three reagents. Tests showed that the first type of dioxide was by far the best for both iron and manganese removal and that the mechanism for the process was by ion exchange. Other tests indicated that the dioxide exchanger could be regenerated partially by contact with chlorine gas or hypochlorite which is commonly available as a process chemical at water treatment works.