Transformations of Synthetic Birnessite as Affected by pH and Manganese Concentration

Abstract

AImtract--The amount of Mn 2+ adsorbed or removed from solution by birnessite is several times greater than its reported cation exchange capacity. Extractability of the sorbed Mn 2+ decreases with aging. It is uncertain whether the sorbed Mn 2+ is oxidized on the surface or incorporated into the structure of birnessite. Using X-ray powder diffractometry and transmission electron microscopy, a study was conducted to examine the mineralogical alteration of birnessite after treatment with various concentrations of MnSO4 and solution pH.The sorbed Mn 2+ was not directly oxidized and remained on the birnessite surface. The sorption of Mn 2+ was followed by alteration ofbirnessite with the formation of new Mn minerals. The specific Mn minerals formed were governed by the pH of the reaction, and the rate of the transformation was determined by Mn 2+ concentration and pH. Nsutite and ramsdellite were identified at pH 2.4, cryptomelane at pH 4, groutite at pH 6, and mangarfite at pH 8. Other Mn minerals formed at these and other pH levels could not be identified. As the concentration of Mn in the solution decreased, the time required to form new minerals from the birnessite increased. The newly formed phases were the result of structural conversion since dissolution of birnessite and reprecipitation of new phases were not observed.

Structure of heavy-metal sorbed birnessite: Part 1. Results from X-ray diffraction

“…Partial dehydration of buserite leads to the formation of 7 Å birnessite with a single layer of H 2 O molecules and various interlayer cations Burns 1977, 1978;Chukhrov et al 1978Chukhrov et al , 1989Cornell and Giovanoli 1988). Buserite and birnessite have remarkable cation exchange (Healy et al 1966;Murray 1974;Balistrieri and Murray 1982;Stumm 1992;Le Goff et al 1996), sorption (Gray and Malati 1979;Catts and Langmuir 1986;Paterson et al 1994;Tu et al 1994;Appelo and Postma 1999), and redox properties (Oscarson et al 1983;Stone and Morgan 1984;Stone and Ulrich 1989;Manceau and Charlet 1992;Bidoglio et al 1993;Silvester et al 1995;Manceau et al 1997;Pizzigallo et al 1998;Daus et al 2000;Nico and Zasoski 2000;Chorover and Amistadi 2001).…”

Pb2+ adsorption on birnessite affected by Zn2+ and Mn2+ pretreatments

“…The remaining unoxidized Co 2+ is adsorbed above or below the vacant sites . As Mn 2+ is easily oxidized by birnessite (Tu et al 1994) and as the radius of Mn 3+ (0.066 nm) is close to that of Co 3+ (0.063 nm; Pauling 1960), it is reasonable to suggest that the oxidation of Mn 2+ to Mn 3+ on birnessite is similar to the oxidation of Co 2+ adsorbed on buserite. Therefore, the first and third mechanisms are both possible.…”

“…Mn 2+ can be oxidized to Mn 3+ by birnessite (Tu et al 1994), and the radius of Mn 3+ (0.066 nm) is close to that of Co 3+ (0.063 nm; Pauling 1960), suggesting that the oxidation of Mn 2+ to Mn 3+ on birnessite is similar to that of Co 2+ oxidation to Co 3+ on buserite, leading to a decrease in vacant Mn sites in birnessite.…”

“…The interlayer water molecules and cations that compensate the charges created by defects in the Mn octahedral layers have a profound influence on the resulting structure (Webb et al 2005). Many Mn oxides can be synthesized by direct or indirect transformation of birnessite (Golden et al 1987;Tu et al 1994). Birnessite synthesis can be achieved by the reduction of potassium permanganate in a strong acidic medium (McKenzie 1971), which is termed "acid-birnessite" (Villalobos et al 2003).…”

Shape‐controlled Synthesis of Nanostructure Ramsdellite‐type Manganese Oxide at Atmospheric Pressure

“…R-MnO 2 was formed with transformation of birnessite after adsorbing Mn 2＋ at pH 2.4, but XRD results identified that the product was a mixture of nsutite and ramsdellite. 17 Rietveld refinement technique and oriented single-crystal IR absorption spectra were used to characterize the ramsdellite, which was found to be easily distorted to groutite, α-MnOOH. 18,19 Rossouw et al prepared pure R-MnO 2 with digestion of spinel LiMn 2 O 4 or Li 2 Mn 4 O 9 in moderately concentrated sulfuric acid solution at 95 ℃ for 24 h. However, the preparation process was multistep, complicated and timeconsuming.…”