The influence of pH on biotite dissolution and alteration kinetics at low temperature

Biotite dissolution rates in acidic solutions were determined in fluidized-bed reactors and flowthrough columns. Biotite dissolution rates increased inversely as a linear function of pH in the pH range 3–7, where the rate order n = −0.34. Biotite dissolved incongruently over this pH range, with preferential release of magnesium and iron from the octahedral layer. Release of tetrahedral silicon was much greater at pH 3 than at higher pH. Iron release was significantly enhanced by low pH conditions.

Solution compositions from a continuous exposure flow-through column of biotite indicated biotite dissolves incongruently at pH 4, consistent with alteration to a vermiculite-type product. Solution compositions from a second intermittent-flow column exhibited elevated cation release rates upon the initiation of each exposure to solution.

The presence of strong oxidizing agents, the mineral surface area, and sample preparation methodology also influenced the dissolution or alteration kinetics of biotite.