Forsterite Dissolution From Indian Olivine in Saline Water

The rate and mechanism of forsterite dissolution was studied using naturally weathered olivine FO₇₉ (Mg_1.591Fe_0.182)SiO₄ from an Indian source, that also contains serpentine mineral lizardite. A series of batch dissolution experiments were carried out to check the influence of temperature (25– 75 ^oC), initial olivine concentration (0.5 and 20 g/L) and salinity (0– 35,000 mg/L NaCl) under fixed headspace CO₂ pressure (P_CO2= 1 bar) on forsterite dissolution.  Dissolved Mg, Si and Fe concentrations were determined by inductively coupled plasma atomic emission spectroscopy. End-product solids were characterized by scanning electron microscopy and X-ray diffraction. Initially, rates of dissolution of Si and Mg were observed to be in stoichiometric proportion. After 8 h the dissolution rate was observed to decline. At the end of the experiment (504 h) an amorphous silica-rich layer was observed on the forsterite surface. This results in decay of the dissolution rate. A comparison was made between experimentally obtained dissolution rates and corresponding theoretical estimates from a batch dissolution model.