The effect of CO_(2(aq)), Al_((aq)) and temperature on feldspar dissolution

摘要

We measured labradorite (Ca_(0.6)Na_(0.4)Al_(1.6)Si_(2.4)O_8) dissolution rates using a mixed flow reactor from 30 to 130°C as a function of CO_2 (3 x 10~(-3) and 0.6 M), and Al (10~(-6) to 10~(-3)M) at pH 3.2. The net activation energy, E_a = 42.1 (kJ mol~(-1)); H~+-Al~(3+) exchange coefficient, n = 0.31; and silica-rich surface complex formation constant, K_T = 4.5 to 5.6 from 30 to 130°C. The effect of CO_(2(aq)) on mineral dissolution is accounted for by changes in solution pH. At temperatures below 60°C, labradorite dissolves incongruently with preferential dissolution of Na, Ca and Al over Si. Geologic sequestration of CO_2 in sedimentary basins or in saline aquifers appears to be a promising method for disposal, because the reaction of CO_2, water, and primary silicate minerals produces more stable secondary silicates, hydroxides, and carbonates. Measurement of mineral dissolution and precipitation rates is fundamental to the successful disposal of greenhouse CO_2-rich gases in aquifers, because reservoir storage capacity is related to the conversion of CO_(2(g)) to carbonate minerals, and because secondary mineral precipitation will alter reservoir porosity and permeability.