the ck guy

The rare earth elements (REE) were analysed in the interstitial fluids, in the basalts and in the alteration products (clays and zeolites) of Mururoa atoll volcanic rocks (French Polynesia) in order to investigate REE behaviour during seawater/basalt interactions at low temperature. The REE distribution coefficients between fluids and secondary products were calculated using the EQ3/6 geochemical code. The reversible/irreversible character

Steady-state dissolution rates of a synthetic basaltic glass were measured in an open-system mixed flow reactor as a function of solution composition at a temperature of 90°C and over the pH range 7.8 to 8.3. The dissolution is a two-step process. The first of these steps involves the release of the cation modifier elements leading to the formation of a hydrated surface gel (HBG) of which the solubility controls the overall dissolution reaction. The glass steady-state dissolution rates were found to be independent of aqueous aluminium and silicium concentration but to depend on the chemical affinity for the overall hydrolysis reaction. The glass is a rapidly reacting solid, whose dissolution induces a dramatic change in solution concentration, which results readily in small chemical affinities for the dissolution reaction. Consequently, conditions of great undersaturation have not been investigated (affinity max. 9.8 kJ/mol). However, our results strongly suggest that the dissolution rates are controlled by the decomposition of a stoichiometric silico-aluminous surface precursor. The variation of the steady-state dissolution rates can be described using a simple expression based on the concept that the precursor is formed by the simple absorption of reactants: R (mol cm−2s−1) = 3 × 10−10 (OH−)0.39 (1−Q/8.2 × 10−5), where Q, the ion activity quotient is equal to: Q = (H4SiO4) (Al(OH)4−)0.36 (Fe(OH)3)0.18 (OH−)−0.36.