IONTOVÁ VÝMĚNA V POČÁTEČNÍCH STÁDIÍCH INTERAKCE ŽIVEC–VODA

Abstract

The sample of perthitic alkali feldspar (62.5 wt. % of KAlSi3O8 and 37.5 wt. % of albite, Na0,996Ca0,004Al1,004Si2,996O8) was dissolved in a special stirred batch reactor (polyethylene vessel of 5 liter volume situated horizontally and rotating at few rotations per hour). The reactor was opened to atmosphere (log PCO2 ~ -3.5) through the mouth at the vessel axis. During the experiment, pH was monitored by pH-meter with combined glass electrode. Solutions were analyzed for Si, Al (spectrophotometry), K, Na (flame AAS), and Ca (ICP-OES). The results showed a fast preferential leaching of alkaline cations with respect to both Al and Si during the early stages of experiment that was diminishing during more advanced stages of the experiment. The released cations exceeded the consumed H+ ions by the range of two up to four magnitudes. The preponderance of cations over H+ ions was especially apparent during few initial days, when the buffering by atmospheric CO2 was insufficient. Simulation of the process by the PHREEQC code covering the CO2 buffering indicated that system feldspar–water–CO2(g) was evolving near the equilibrium in open system during the period after 5th day of the experiment. The results suggested that the mechanism of feldspar dissolution during the initial stages of the process does not correspond to a simple ion exchange and that it is more complicated.