Surface charge of MnCO sub 3 and FeCO sub 3

Journal Article · Wed Aug 01 00:00:00 EDT 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90059-T· OSTI ID:5982138

Charlet, L ^[1]; Wersin, P; Stumm, W ^[2]

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1. Univ. of Bern (Switzerland)
2. Swiss Federal Institute of Technology, Duebendorf (Switzerland)

The surface charge of two carbonate minerals (rhodochrosite, and siderite) was investigated as a function of pH (4 to 8) and ionic strength (0.03, 0.1, and 1.0 mol dm{sup {minus}3} NaCl) under two different partial pressures of CO{sub 2} (0.5 and 0.005 atm). The acid/base titrations were performed with a flow-through reactor. This technique minimizes the contribution of dissolution and precipitation and thus allows the measurement of the surface charge to be performed. The point of zero charge (PZC) at the mineral surface is found to be equal to the point of zero salt effect and to the pH at which, in solution, the free metal ion concentration is equal in charge to the bicarbonate concentration. At lower pH values, the positive charge of the carbonate mineral surface increases as pH decreases. Above PZC, the surface of carbonate minerals is negatively charged. Whatever partial pressure of CO{sub 2} and ionic strength, this negative charge was found to be a unique function of the variable {l brace}HCO{sup {minus}}{sub 3}{r brace}/{l brace}HCO{sup {minus}}{sub 3}{r brace}{sub PZC}. This variable appears to control the sorption of bivalent trace metals onto carbonate surfaces. This is shown by taking into account previous studies such as sorption of Mn(II) onto siderite or sorption of Zn(II) onto calcite. Finally, a control of weathering of carbonate minerals by their surface charge is suggested.

• OSTI ID: 5982138
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:8; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
DISSOLUTION
GEOCHEMISTRY
IRON CARBONATES
IRON COMPOUNDS
IRON ORES
MANGANESE CARBONATES
MANGANESE COMPOUNDS
MINERALS
ORES
OXYGEN COMPOUNDS
PH VALUE
PRECIPITATION
SEPARATION PROCESSES
SIDERITE
SORPTIVE PROPERTIES
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
VALENCE