The incorporation of Ni and Co in aragonite was experimentally investigated as a function of mineral growth rate using the constant addition technique at 25 °C and 1 bar pCO2. The distribution coefficients of Ni and Co (i.e., DMe=[Formula presented]) exhibit a linear correlation with mineral growth rate in the range −9.1 ≤ Log rp ≤ −7.5 mol/m2/s. The obtained results suggest a stronger dependency of DNi to growth rate compared to that observed for DCo. These dependencies can be described as: Log DNi = 1.247 (±0.152) Log rp + 7.448 (±1.212); R2 = 0.82 Log DCo = 0.312 (±0.047) Log rp + 1.664 (±0.383); R2 = 0.81 The DMe-aragonite values for both Ni and Co are systematically lower than unity and their increase with increasing growth rate is in agreement with the incorporation of elements incompatible with the host mineral structure. Using the dependency of DNi and DCo to the saturation indices (SI) of the reactive solution with respect to aragonite, the DMe under equilibrium were estimated. These estimates yield equilibrium Log DMe values of −3.9 and − 1.0 for Ni and Co, respectively. These experimentally defined Deq values are 1.3 to 4.3 orders of magnitude lower compared to theoretical estimates that were earlier published in the literature. Similar to other incompatible elements, the observed increase of DNi and DCo values with degree of saturation, points towards incorporation related to the density of defect sites on the mineral surface. Finally, the dependencies recorded in this study suggest that DNi and DCo have the potential to be used as a proxy for saturation degree of the reactive solution.
|Publication status||Published - 30 Jun 2022|
- Distribution coefficient
- Growth rate
ASJC Scopus subject areas
- Geochemistry and Petrology