CHLORITE AND BIOTITE WEATHERING BY FULVIC ACID SOLUTIONS IN CLOSED AND OPEN SYSTEMS

Publisher Website
Google Scholar
Abstract
The dissolution by dilute fulvic acid (FA) solutions of elements constituting two chlorites and biotite was investigated in closed and open systems. In closed systems, dilute FA solution rapidly dissolved substantial amounts of Si, Al, Fe, Mg, and K (in the case of biotite only) from chamosite and biotite during the first 100 h of contact. Thereafter, the rate of dissolution decreased exponentially with increasing time. Maximal concentrations of elements dissolved were approximately proportional to FA concentrations when these were 0.1% (wt/vol) and lower. In the open systems, relatively fast dissolution rates of Fe-clinochlore and biotite were observed initially (up to 30≈35 days). Following this, the rates slowed to near constancy. If the dissolutions had continued at the constant rates, it would have taken a 0.025% FA solution about 22 yr to dissolve 1 g of Fe-clinochlore and 7.2 yr to dissolve 1 g of biotite. Increases in flow rate from 1 to 3 mL/h increased the rates of dissolution of the elements by 2.5–3 times. Ratios of elements dissolved by FA in both systems differed from the elemental ratios of the minerals in being enriched in Fe and Mg, which indicates the preferential dissolution of elements in octahedral coordination. Key words: Fe-clinochlore, Mn-Mg-chamosite, dissolution rate