Dissolved Manganese Concentrations Research Articles

The influence of environmental factors on the rate and extent of stainless steel ennoblement mediated by manganese‐oxidizing biofilms

The increase in the open circuit potential of passive metals in natural waters due to biofilm formation at the metal surface, termed ennoblement, has been reported for nearly 30 years. Although its occurrence is undoubtedly associated with microbial colonization, the underlying mechanism of ennoblement remains controversial. Recent work produced in the authors’ laboratory has provided convincing experimental evidence that ennoblement can be caused by deposition of biomineralized manganese produced by manganese‐oxidizing biofilms. The purpose of this study was to determine the effects of environmental factors on the rate and extent of ennoblement of 316L stainless steel exposed to natural waters. This was accomplished by exposing corrosion coupons to four freshwater systems over a 4‐yearperiod. The rate and extent of ennoblement observed in these locations was correlated with dissolved manganese concentrations, the mass of accumulated manganese oxides, organic carbon concentration, dissolved oxygen concentration, flow, conditions, temperature, and pH in these environments.

Kinetic study of manganese behavior in the Scheldt estuary

Combination of radiochemistry with simultaneous determination of corresponding stable isotope concentration allows the study of the biogeochemical behavior of manganese in an estuarine system which is not at equilibrium. A bacterial uptake in the dark of 0.40 μM in 50 hours at 6 °C, corresponding to an uptake rate of 8 nM·h−1, was measured for the sample collected in winter. However, this biological uptake represents only 60% of the decrease in stable dissolved manganese concentration after 50 hours. Other abiotic processes inducing the precipitation of dissolved manganese are thus occurring in this low salinity region of the Scheldt estuary (Belgium).

Disappearance of Reduced Manganese in Reservoir Tailwaters

Results of field studies conducted downstream of five reservoirs are used to develop an improved understanding of the disappearance of reduced manganese in tailwaters. A first-order removal formulation accurately describes the removal of dissolved manganese versus travel time downstream. Results support the theory that adsorption to the stream bottom is the primary removal mechanism. The first-order removal rate, which varied by an order of magnitude from 0.30 to 4.45 day −1 , is found to be highly correlated to the stream slope, which affects shear velocity. Using observed removal rates, a formulation based on the ratio of the stream-bottom mass-transfer velocity, which depends on bottom-shear velocity, and stream depth is developed for computing the removal-rate coefficient. The formulation also depends on substrate type (i.e., cobble or fine-grain sediments). Dissolved manganese concentrations computed with the developed mathematical model show good agreement with observations. Some questions still rem...

Spectrophotometric determination of dissolved manganese in natural waters with 1-(2-pyridylazo)-2-naphthol: application to analysis in situ in hydrothermal plumes

A spectrophotometric method using the complexing reagent 1-(2-pyridylazo)-2-naphthol (PAN) was developed for the determination of dissolved manganese in seawater. A detection limit of approximately 22 nM was obtained when the analyses were performed in situ with a submersible chemical analyzer (Scanner). Color formation was rapid (less than 1 s), which permitted the technique to be used in flow injection and continuous flow systems. An investigation of possible interferences revealed that the only significant interferent to manganese determinations in seawater (hydrothermal plumes) was iron. The iron-specific chelating agent desferrioxamine B was used to mask this interference. Temperature and pressure did not adversely affect the sensitivity of the technique, which made it amenable to applications in situ to depths of 3000 m. This method was tested by measuring dissolved manganese concentrations in situ in submarine hydrothermal plumes using a Scanner. Scanner deployments over the Juan de Fuca Ridge produced the first near real time analyses of manganese from a hydrothermal plume environment. Estuarine samples have also been successfully analyzed in the laboratory and the results confirmed by an independent method.

Treatment of Manganese from Mining Seep Using Packed Columns

A manganese‐laden seep from a reclaimed strip‐mined area in north Alabama was successfully treated on a small‐scale basis using packed column technology. Manganese concentrations were reduced from about 10 mg/L to below 2 mg/L to meet Alabama discharge standards. The process looks very promising as a new manganese treatment method. The three columns developed during this research used chert, sandstone, and glass marbles as packing material. The olumns were either four or six feet tall and hydraulically loaded at about 5.4m3/secper100,000M2. The mass loading with a dissolved manganese concentration of 9 mg/L was about 0.24 mg/min. The pH of the seep water ranged from 5.8 to 6.3. The columns were operated in a submerged, upflowing manner at temperatures between 20° and 30 °C. The acclimation of the columns required eight weeks using seed from a river having manganese oxidizing slimes on the stream‐bed stones.

Manganese oxide deposition in a hot spring microbial mat

Abstract The vertical distribution of manganese in a hot spring microbial mat has been analyzed chemically and structurally. Dissolved manganese concentrations were highest near the surface of the mat but decreased rapidly with depth. At the same time, an increase was observed in the amount of a solid manganese phase with an O/Mn ratio of 1.7 to 1.9. Electron microscopy and energy‐dispersive x‐ray spectroscopy of thin‐sectioned material revealed a variety of manganese oxide‐encrusted microbial forms. A 10‐A tunnel structure prominent in the manganese precipitates and a 2.44‐A d‐spacing in the corresponding electron diffraction patterns indicated that todorokite was the predominant manganese oxide polymorph formed within the microbial mat.

Oxidation of Mn(II): Initial mineralogy, oxidation state and ageing

The initial solid phase oxidation products formed during the oxidation of aqueous Mn(II) at 25°C were studied as a function of time. The analyses included morphology (TEM), mineralogy (x-ray diffraction), O Mn ratio (iodometric method), oxidation state of manganese (XPS), and dissolved manganese. The initial solid formed under our conditions was Mn 3O 4 (hausmannite) which converted completely to γMnOOH (manganite) after eight months. βMnOOH (feitknechtite) appeared to be an intermediate in this transformation. The O Mn ratio was initially 1.37 and increased to 1.49 over the same time span. Throughout the course of this study the XPS analyses showed that the surface of the solids (<50 Å) was dominated by Mn(III). The solution pH and dissolved manganese concentrations were consistent with disproportionation and oxidation reactions that favor the transformation of Mn 3O 4 to γMnOOH but not to γMnO 2.

Reduction and dissolution of manganese(III) and manganese(IV) oxides by organics. 1. Reaction with hydroquinone

The chemical processes by which manganese oxides are solubilized by reduction in anoxic waters are poorly understood. A study of the reduction and dissolution of manganese oxide suspensions by hydroquinone was undertaken to determine the rate and mechanism of the solubilization reaction. Dissolution of the manganese (III,IV) oxide suspension by hydroquinone in the pH range 6.5 , pH < 8.5 is initially described by the following empirical rate law: d(Mn/sup 2 +/)/dt = k/sub 1/(H/sup +/)sup 0.46(QH/sub 2/)/sup 1.0/((MnO/sub x/)/sub 0/ - (Mn/sup 2 +/)) where (Mn/sup 2 +/) is the dissolved manganese concentration, (QH/sub 2/) is the hydroquinone concentration, and (MnO/sub x/)/sub 0/ is the amount of manganese oxide added. The apparent activation energy was found to be at +37 kJ/mol. Calcium and phosphate inhibited the reaction, by adsorbing on the oxide surface. A model is proposed for the observed rate dependence, according to which complex formation between hydroquinone and manganese oxide surface sites occurs prior to electron transfer.

The distribution of manganese in the strait of Georgia, British Columbia

Abstract The distribution of dissolved manganese in surface waters of the Strait of Georgia is determined by the dilution of Fraser River water. Bottom waters have enhanced dissolved manganese concentrations due to reductive remobilization of manganese from the sediments. Concentrations of dissolved manganese at mid‐depths are determined by seasonal variations in the stability of the water column. Depth profiles of suspended particulate manganese indicate increasing concentrations with depth. This may result from the oxidative precipitation of manganese and/or the resuspension of bottom sediments.

Manganese recycling in coastal waters

Abstract Both water and suspended particulate matter in the deep water of the Gulf of St. Lawrence are greatly enriched in manganese. Maximum dissolved manganese concentrations are encountered close to the sediment-water interface whereas the particulate matter with highest manganese content occurs 30–100 m above the bottom. The elevated concentrations are attributed to the diagenetic release of dissolved manganese from the underlying fine-grained sediments and its subsequent precipitation in the water column. The rate of manganese precipitation is rapid compared to the rates of diffusion and mixing in the bottom water. Part of the manganese-enriched particulate matter becomes mixed throughout the water column by advection and diffusion. Thus, particles enriched in manganese can ultimately be carried into the open ocean by prevailing currents. This process, which appears to be widespread in eastern Canadian coastal waters, enables manganese originally associated with rapidly settling terrigenous particles to be transferred to slowly settling fine-grained suspended particles entering the ocean from coastal environments. In this way, riverborne manganese of terrigenous origin may well account for a major proportion of the excess manganese in pelagic sediments.