“…As Table 3 shows, most often HCl solutions are applied for the recovery of metal ions, however the concentrations recommended vary within a wide range, from 1 mmol dm À 3 to 1 mol dm À 3 (Geay et al, 2000;Liu et al, 2001Liu et al, , 2002Güc -lü et al, 2003;Zhou et al, 2004). Othman et al (2009) used concentrations up to 5 mol dm À 3 , however, at high concentrations hydrolysis of cellulose must be considered.…”