a slight trendgold
There was a slight trend in K HA with increasing HCl concentration (mean values were 6.2, 5.4 and 5.0 × 10 −59 at HCl concentrations of 0.70, 1.0 and 10.0 mmol/L, respectively), but no trend was observed at fixed acid concentration with solid-to-solution ratios varying from 0.2 to 2.0 g/100 mL.